IndexIndex Tech Notes - · PDF fileIndexIndex Tech Notes Tech Note # ... #9 Plastic Injection...

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Index Tech NotesIndex

Tech Note #

#30 Vibrating Objects

#31 What is Emissivity?

#32 Where is the Emissivity Adjustment?

#33 Calibrating with the D-Series

#34 Ambient Temperature

#35 Air Purge/Cooling Requirements

#36 Reflective Cup for Silicon Wafer

#37 Selecting Temperature Controllers

#38 Reliability

#39 Self-test for IRt/c

#40 Monitoring Plastic Extrusion

#41 IRt/c.5

#42 Hazardous Materials

#43 Dough Mixing

#44 Induction Heating

#45 Printing/Ink Drying

#46 Discrete Parts Monitoring

#47 Electric Power Distribution

#48 Glass Monitoring

#49 Temperature Selection Guide

#50 Improving Maching Tolerance

#51 Asphalt Temperature Monitoring

#52 Speed of Response

#53 Quick Selection Guide

#54 How to Use Infrared Effectively

#55 Understanding Field-of-View

#56 Calibrating with Simulators

#57 Measuring Small Objects

#58 Measuring High Temperatures

#1 Quick Installation Guide

#2 Auto-Tune Controllers

#3 Extension Wire Length

#4 Paint Curing

#5 Medical Diagnostic Equipment

#6 Furnace Electrical Isolation

#7 Steaming Environments

#8 Spinning Rotor in Vacuum

#9 Plastic Injection Mold

#10 Intrinsically Safe

#11 Reduces Air Purge

#12 Monitor Mechanical Drive

#13 Monitors Tire Temperatures

#14 Multiplexed Datalogging

#15 Air Purging/Water Cooling

#16 Offsets Leakage Currents

#17 Disposable Infrared Sensor

#18 Hot Melt Adhesives

#19 Pit Viper

#20 Relative Humidity Measurement

#21 Cotrolling Web Roller Temperature

#22 Vacuum & Thermoforming

#23 Printed Circuit Board

#24 Drying Paper, Wood, Textiles, Film

#25 Cooling Jacket Kit

#26 Long Term Accuracy

#27 Air Pump Accessory

#28 Trouble Shooting Guide

#29 Oblique Measuring

C O R P O R A T I O N57

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IndexTech Notes

Tech Note #

#59 Lo E Filter Reduces Errors

#60 Adjustable Models/Set-up & Calibration

#61 Adjustable Models

#62 Color Does Not Affect Readings

#63 Ambient Temperature Effects

#64 Reflective Errors

#65 Painting Metal Surfaces/Emissivity

#66 Sight Windows & Lo E Filter Models

#67 Dry-out Point in Web Production

#68 Fail-Safe Control Installation Models

#69 Selecting Hi E or Lo E Emissivity Table

#70 Calibrating Wide Linear Range

#71 Printing Press Applications

#72 OEM Low Cost Interface

#73 Flame Detection

#74 Calibrating Testing Procedures

#75 Calibration with Boiling Water

#76 Aperture Kit Usage

#77 IRt/c Tested at 5000psig Pressure

#78 IRt/c Tested for Vacuum & MicrowaveCompatibility

#79 IRt/c’s Withstand 1000G Shock

#80 Unique “Slot Spot”

#81 Monitoring Web Processes

#82 Grounding & Shielding

#83 Monitoring in Dirty/Vapor FilledEnvironments

#84 Usage in High Electrical Noise Area

#85 Selection/Application for OEM’s

#86 Infrared Scanning Arrays with IRt/c.01

#87 Two-Color Pyrometry

#88 Measuring Tire Tread InternalTemperature

#89 Real World Performance Accuracy

#90 More Accurate than Conventional IR

#91 Disposable Window

#92 Drying Paper Webs with IRt/c’s

#93 Pre-Calibrated Transmitter for EasyInstallation

#94 Easy Upgrade with IRt/c & t/c.XMTR

#95 Precalibrated Hi E & Lo E Models forOEM Applications

#96 Non-Contact Heat SealingTemperature Control/Packaging Machinery

#97 Web Drying for Transparent &Reflective Films, Paper & Textiles

#98 Heated Metal Rollers / Web ProcessesTo Increase Production

#99 IRt/c Heat Balance Series for MedicalApplications


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Index

Exergen’s library of IRt/c Tech Notes is always growing. If you do not see the topic which interests you,please call. To be notified of updates to the IRt/c Catalog and Book of Tech Notes, please fax or mail thereply card in the back of this book. If the card is missing, contact Exergen.

Tech Notes by Application

Adhesives

Air Purge Cooling Requirements

Asphalt

Automotive

Cure Monitoring/Control

Destructive Testing

Dirty or Vapor-Filled Environments

Disposable Windows

Drying

Electrical Noise Areas

Electrical Power

Electronics

Extrusions

Film

Food

Glass

Humidity

In-Process Testing

Induction Heating

Injection Molding

Ink

Machining

Medical

Metal Surfaces

Tech Note

18

34

51

13, 88

4, 86, 97

17

83

92

24, 45, 67, 93, 97

84

47

23

40

24, 97

43

48

20

8, 12, 13, 21, 42, 46, 73, 88

44

9

45

50

5, 99

65



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Tech Notes by Application Index

Tech Note

Multiplexed Datalogging

Paint

Packaging

Paper

Parts Monitoring

Plastics

Printed Circuit Boards

Printing

Radiant Heaters

Rollers

Scanning Arrays

Sight Windows

Small Objects

Software Self-Testing

Steam Heating

Textiles

Thermocouple Simulators, Calibration with

Thermoforming

Thermowells

Transmitters

Two-Color Pyrometry

Vacuum Forming

Vacuum Furnace

Vibrating Objects

Web Processes

Wood

14

4, 86

81, 86, 97, 98

24, 93, 97

46

9, 40

23

45, 67, 71, 81, 86

4, 22

21, 98

86

66

57

39

7

24, 97

56

22

58

94, 95

87

22

6

30

21, 67, 81, 86, 93, 98

24


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IRt/c Setup With A uto-Tune TemperatureControllers

Quick Installation GuidePre-Calibrated Models

Tech Note

1

Tech Note

2

All infrared-based sensing systems must becalibrated for specific material surface properties(for example, the amount of heat radiated from thetarget surface, environmental heat reflections, etc.).This calibration is performed by measuring thetarget surface temperature with a reliable indepen-dent surface temperature probe. The easiest andfastest method of accurately calibrating out theseeffects is to use an Exergen Microscanner D-Serieshand-held Infrared Thermometer with a patentedAutomatic Emissivity Compensation System, whichgives a true reading regardless of emissivity. YourAuthorized IRt/c Distributor will be pleased to makea D-Series available for your installation. Tocalibrate Adjustable models (IRt/c.xxA) see TechNote No. 60.

The following procedure is recommended:

1. Install the IRt/c as close as practical to view thetarget material to be measured.

2. Wire the IRt/c to the controller, PLC, transmitter,etc. in standard fashion (including ground shieldas in Tech Note #82). As with conventionalthermocouples, red wire is always (-).

In many applications, heating elements are em-ployed to heat a product in an oven, furnace, or withjets of hot air. Conventional control devices usingcontact thermocouples measure and control theoven air temperature, IR heating element tempera-ture, or air jet temperature in an effort to maintainproduct temperature and therefore, quality; oftenwith less than satisfactory results.

Replacing the contact thermocouple (for example,measuring oven temperature) with a non-contactIRt/c measuring product temperature directly willinsure that product temperature is maintained.Some readjustment of the controller parameters isrequired because of differences in sensor responsetimes (an IRt/c is much faster) and time required toheat the product compared to the original sensor(slower). After installing the IRt/c and calibrating thecontroller reading using a Microscanner D-Series(see Tech Note #1), initiate the self-tuning cycle of

the controller and check to see that the control isstable and accurate. If it will not self tune properly,manually adjust the control coefficients to achievestable control. Because the product temperature islikely to change temperature more slowly than theoriginal sensor, start with slowly increasing the “D”of the PID coefficients.

3. Bring the process up to normal operating tempera-ture and measure the actual temperature of thetarget material with the Microscanner D-SeriesInfrared Thermometer.

4. Adjust “input offset,” “zero,” “low cal,”on thereadout device to match the Microscanner reading.

Installation Complete. (For OEM installationspreset the same adjustments. Individual calibra-tion is not required.)

+

-

1

2

3 4

Time

Product Temperature

Heat Input



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IRt/c can be used with up to 1,000 feet (300 m)of Thermocouple Extension Wire

IRt/c Controls Paint Curing With RadiantHeaters

Tech Note

3

With twisted shielded pair thermocouple extensionwire, an IRt/c can be mounted as far as 1,000 ft (300meters) from the readout device, even in a veryfierce electrical noise environment. The extraordi-nary noise suppression characteristics designedinto the IRt/c make this possible, without using atransmitter. The IRt/c housing is electrically isolatedfrom the signal leads and is connected to theshielded ground of the extension cable. For longdistances, the twisted shielded extension cableshould be used, and the shield connected to a goodelectrical ground.

A demonstration test was performed with a 1000 ft(300 m) coil of twisted shielded pair of extensionwire, with 100 ft (30 m) unwound, connecting anIRt/c to a fast (100 msec response) A/D conversionmodule to a computer. As a noise generator, a 60

Hz 10,000 volt transformer and spark generator wasset up to spark within 6 inches (15 cm) of the wire.The test results showed less than 0.1°C of noise atany relative position of the wire, spark, and trans-former.

A rather logical combination of heating method andcontrol is radiant heat with an IRt/c for control. Theywork extraordinarily well together, since both theheating and measuring occur right at the surface,where the paint is located. The IRt/c reading isunaffected by reflections from the heater, since thespectral response of the 6-14 micron IRt/c lensfilters out the shorter wavelengths of the radiantheater energy.

The IRt/c may be mounted in the shroud or reflectorof the radiant heater, such that it can see throughthe elements. Select any of the IRt/c models,depending on the field-of-view required to see pastthe elements to the painted surface. Test thelocation by turning on the heater with no targetpresent. The change in reading should be small.Care should be taken in mounting the IRt/c in such away as to keep its temperature below 200°F (93°C)and to keep the lens clean. The IRt/c.3x, .5, and .10are the preferred models for this application be-cause of their built-in air purge. They can be used in

environments with temperatures up to 250°F(121°C) or higher when the air purge system isused. The narrow fields-of-view allow more leewayin positioning, and thus more flexibility in installation.

Tech Note

4

10,000 V60 Hz

FastMeter

IRt/c

1000 ft (300 m)

Twisted Shielded Pair t/c Wire


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IRt/c Solves Vacuum Furnace ElectricalIsolation Problem

IRt/c for Medical Diagnostic Equipment:IRt/c.2G-J-37

Tech Note

5

Tech Note

6

The IRt/c is an excellent solution to the problem. Itssmall size, low cost, and easy interface with stan-dard thermocouple closed-loop control circuitry areideal. The IRt/c.2G J-37 is designed and calibratedto be highly accurate at 37°C. The J-type is offeredbecause the leads are easily soldered to circuitboards with standard materials, and off-the-shelfcold junction compensation amplifiers are available.It is equipped with a hard pure germanium crystallens that withstands repeated cleanings, and a fail-safe xenon gas fill system. Its hermetically sealedstainless steel construction permits it to be gassterilized.

remaining completely isolated electrically by the gapbetween the part and IRt/c. Since the part is heatedto 1000°F (538°C), an aluminum clamp is employedas a heat sink to keep the IRt/c itself below 200°F(93°C). Since the part emissivity is low (shiny metal)the test part has a small area painted withRustoleum® Barbecue Black Paint, rated to 1300°F(704°C), to raise the emissivity.

A vacuum furnace manufacturer employs a heattreating process in which the metal parts experiencean electrical potential of 1000 volts. To control theheating process to produce the correct metallurgicalproperties, a conventional thermocouple embeddedin one of the parts produces the temperature signalfor the controller. However, since the parts are at1000 volts, an elaborate electrical isolation systemhas to be employed to permit the thermocouple towork safely, at a cost of well over $2,000.

Replacing the contact thermocouple with a non-contact IRt/c, the manufacturer effectively replaced$2,000 worth of equipment with about 1 inch (2.5cm) of vacuum separation between the IRt/c andtest part - which is free. Unlike a contact thermo-couple, the IRt/c can easily see the part through thevacuum, measure its temperature without touching,

Many processes in clinical diagnostics and thera-pies involve blood samples and other fluids thatmust be heated to 98.6°F (37°C) for optimumperformance. Since sterility and absolute preventionof contamination are paramount, measuring andcontrolling fluid temperatures is not a trivial task.Using accurate thermistors or thermocouples in thedisposable fluid handling components is generallymuch too expensive, and use of contact devicescreates the risk contamination and inaccuracies.

1000 Volts

Vacuum Connection

IRt/c

.500 (12,7) Dia..67 (17)

0.090 (2,3)

.300 (7,6)

1.75 (44,5)



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Rotor Disk Tests in Vacuum

Temperature Measurements in SteamingEnvironments

Tech Note

7

Large steam and gas turbine rotor disks require spintesting to assure mechanical reliability at the highforces experienced during full speed operation. Thistesting is usually conducted in a large vacuumchamber to minimize the required power to drive therotor. However, the vacuum is not perfect and rotorheating does occur during the test. To properlyassess performance, the disk temperature must beknown. Standard methods of measuring tempera-ture. such as disk-mounted sensors, using slip ringsor telemetry to transmit the data, are clumsy andexpensive.

The IRt/c can directly measure the temperature ofthe rotor under full speed conditions. With itshermetically sealed construction, the IRt/c operatesin a vacuum without any requirement for protection.Its thermocouple leads can be connected to astandard thermocouple vacuum connector.

Test installation design considerations shouldinclude IRt/c body temperature and target emissivi-ty. To assure that the IRt/c will remain below 200°F(95°C) even with very hot targets, use a solid metalmounting arrangement to heat sink the IRt/c body,

A common problem in processing of paper and othermaterial is measuring temperature in an area inwhich steam (water) is used to heat and cool thematerial. The resulting steam vapor makes it verydifficult to use non-contact infrared devices becausesteam vapor is opaque to infrared wavelengthscommonly used, i.e. the sensor cannot see throughthe vapor fog very well, and thus would reporttemperatures that were too low. In addition, con-densing steam vapor on the sensor lens wouldrender the IRt/c completely blind to infrared wave-lengths.

The IRt/c air purge models solve the problems in asimple and inexpensive fashion. The air jet from thebuilt-in air purge clears a path to the target materialby “blowing away” the steam vapor in the optical

path, replacing it with dry air. Care is required in theset-up of distance to the target and air pressureemployed, to prevent cooling of the target area bythe air jet.

Tech Note

8

since the internal construction is designed to readilyconduct away the radiated heat. For emissivityconsiderations, a shiny metal rotor disk should haveblack painted stripes in the areas of measurement.For best accuracy, the IRt/c read-out device can becalibrated to the precise surface conditions by usinga Microscanner D-Series.

Vacuum Connection

Air

IRt/c


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IRt/c’s are Intrinsically Safe When Used withBarriers

IRt/c Monitors Plastic Injection Mold Clearing

In high volume plastic injection molding machinery,a molded part that does not clear the mold cancause serious problems, including a long down timeto clean up or make repairs.

A particularly useful property of the mold is itsshininess, which means low emissivity. Accordingly,the infrared radiation from an open mold is primarilyreflected from the room, and thus an IRt/c pointed atthe mold would not read much higher than roomtemperature. However, if a part is still in the mold,the IR radiation is far higher since the high emissivi-ty of the plastic part is easily seen by the IRt/c asthe temperature of the hot part. By mounting an IRt/cso that it can view the part as the mold opens, areliable and inexpensive part detection system canbe installed. Simply connect the IRt/c to a simplethermocouple controller with alarms interfaced to themold position. For efficient coverage of the mold,two IRt/c’s can be wired in parallel and connected toa single controller, so that a part viewed by eithersensor will alarm.

Tech Note

9

For harsh environments, the IRt/c.3x or IRt/c.5models with narrow field-of-view and built-in airpurge are recommended.

“Field Apparatus having energy storing or generat-ing characteristics of <1.2V, 0.1A, 25 mW or 25microJ shall be considered Simple Apparatus (non-energy storing). These general purpose devicesmay be used in a hazardous (classified) locationwithout further approval when connected to acertified intrinsically safe circuit.” -Quote from R.Stahl, Inc. Comprehensive Product Manual OnIntrinsic Safety Barrier and Repeater Relays .Examples of non-energy storing Intrinsically SafeApparatus are:

• Thermocouples, RTD’s, LED’s

• Dry Switch Contacts

• NAMUR Inductive Proximity Switches

• Non-inductive Strain Gauge Devices andResistors

The IRt/c falls into the category of thermocouples,since it generates its signal by converting theradiated heat energy to an electrical signal viaSeebeck effects, the basic driving force of thermo-couples. Like all thermocouples, it requires nopower source and generates signals measured inmillivolts of voltage, microamps of current andnanowatts of power. IRt/c’s have a small capaci-tance, but at one microFarad, the energy storage ismeasured in nanojoules and is a thousand timeslower than the 25 microjoule criterion.

Accordingly, the IRt/c qualifies as a Simple Appara-tus for use in hazardous locations, and with theappropriate barrier, qualifies as Intrinsically Safe.

Tech Note

10



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IRt/c Monitors Mechanical Drives for BearingFailure

IRt/c.3x Reduces Air Purge Air Consumptionby a Factor of 100

The small 1/4 inch (.6 cm) lenses of the IRt/c.3x andIRt/c.3SV make it possible to purge with as little as.01 CFM (.0003 cubic meters/min.) of air. With sucha small amount of air, it becomes possible to useinstrument air, if it is conveniently available, which isalready clean and dry, without adding the additionalhardware to clean and dry the IR purge air. Inaddition, the IRt/c.3x can be air purged with a smallinexpensive air pump (model APK-1), thus notrequiring a plant air source. At the very low flow rate,the IRt/c air cost is only approximately $1 per year,a 100-fold reduction over conventional IR devices.

Tech Note

11

Tech Note

12For certain highly loaded mechanical drive ele-ments, such as the main rotor drive for a helicopter,it is imperative that impending failure be detectedbefore a catastrophe occurs. A central element ofthe drive, such as a universal joint or coupling, willtelegraph its impending failure well in advance bydisplaying an increase in temperature. For example,if a drive transmitting 1000 hp (750 kW) of shaftpower with a universal joint loses only 0.1% in driveefficiency, the joint will increase in temperature asmuch as several hundred degrees until it is able todissipate an additional 750 watts of energy as heat.This increase in temperature is a direct and reliableindication of the increased inefficiency caused by adegradation in parts performance.

Monitoring the joint with an IRt/c provides a fast anddirect indication of joint temperature, and thus theincreasing inefficiency due to wear or failure. A moresensitive method of monitoring the joint is to employtwo IRt/c’s wired differentially (connecting the twominus leads together and measuring across the plusleads, see example), measuring the difference in

temperature between the joint and adjoining shaft.This difference is a direct measure of the heatcreated in the joint and will not be influenced byambient temperature effects, since the differentialpair arrangement cancels those effects. Accord-ingly, a very high precision can be achieved. AnIRt/c with built-in air purge is recommended if theenvironment is oily or dusty.

An air purge is ideal for keeping the lenses ofinfrared temperature sensing heads in continuousmanufacturing duty service clean, especially inparticularly dirty or oily environments. Even a smallamount of dirt or oil coating on a lens can affect thereading: if 5% of the lens area is covered, then 5%of the reading is lost. For conventional IR devices,with lens size of 1" (2.5 cm) or more, upwards of 1CFM (.03 cubic meter/min.) is required to maintaincleanliness. At typical costs for plant compressedair, a single continuous duty conventional IR sensoruses approximately $100 of air per year . Clearly, ifa plant has many IR installations, the cost of air is ofconsiderable concern.

Air

+

-

++

+ ---


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Monitoring Tire Temperature for RacingPerformance

Multiplexed Datalogging Applications

Tech Note

13

Tech Note

14An occasional problem introduced by switching-typethermocouple dataloggers is signal offset caused bythe switching transient. The IRt/c is a completelypassive device and produces an electrical signalentirely via thermoelectric effects, but does containboth resistance and capacitance above the levelsfound with conventional thermocouples. Manyinterface devices generate a small leakage current,which induces no shift in signal with conventionallow impedance (<100 ohm) thermocouples, but mayinduce an offset with the higher IRt/c impedance(~3K ohm). This type of offset is normally stable andis simply calibrated out by adjusting the device’sOFFSET or ZERO adjustment.

However, switching the thermocouple input can alsocause offsets in IRt/c readout due to the presence ofcapacitance, if the signal leads are connected in adifferential fashion to the amplifier input. A switchingtransient voltage stores a charge in the capacitance,which can cause the equivalent of leakage currentoffset. This offset could also be calibrated out, butmay not be stable. A preferred method is simply toground the negative side of the t/c input as shown.

The ground provides a path for the charge causedby the switching transient to dissipate, thus eliminat-ing the offset. The twisted shielded pair wire withshield connected to ground will compensate for anyloss of noise rejection, and thus provide a cleansignal.

due its small size, ruggedness, and low cost. It maybe connected to standard thermocouple read-outsystems. Installation should include connecting theshield to a suitable ground in order to avoid interfer-ence from the electrically harsh environment of aracing automobile. Mechanical installation shouldinclude attention to air flow patterns to minimize dirtbuilding on the lens. The IRt/c.3x or .5 are recom-mended because their narrower field of view allowsthem to be positioned further away

Tire temperature is of critical concern in automotiveracing for two reasons: the tire temperature directlyaffects its adhesion and its wear characteristics, andtire temperature patterns provide valuable informa-tion on the set-up and performance of the suspen-

sion. For example,excessive loading of atire caused by out-of-tune suspension willcause that tire tobecome considerablywarmer than theothers.

The IRt/c has provento be an ideal measur-ing device for on-board data acquisition,

Use three sensors for

profiling, one sensor for

brake rotor.

+

-

IRt/c Shieldapprox 1 microFarad Multiplexed Input

Connect (-) input to Ground

SwitchingTransient



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Why Offsets are Caused by Leakage Currents

Air Purging is Recommended When UsingWater Cooling

Some thermocouple readout devices produceleakage currents which can create offsets whenusing an IRt/c. The current originates from twosources within the device: leakage current actuallygenerated by the input amplifier, and leakagecurrent intentionally injected to the thermocouplecircuit to detect an open circuit due to wire breaks.These currents are normally of no consequence withconventional thermocouples with resistances < 100ohms. However, with the higher resistance of theIRt/c (~ 3KΩ), devices with high currents will createoffsets.

As an extreme example, a device producing 1microamp of current will result in less than onedegree offset with an ordinary t/c with 10 ohmsresistance. That same device reading an IRt/c at3KΩ will produce an offset of the order of 100°F(55°C). Most readout devices have considerablysmaller leakage currents and consequently smalleroffsets. As a general rule, the smaller the offset thebetter, and readout devices should be chosenaccordingly if other factors are equal.

Tech Note

15Very often the environment inside an oven containsvapors from the process which may condense oncooler surfaces inside the oven. When an IRt/c isused inside the oven to monitor the temperature ofthe process, the IRt/c must be cooled if the environ-ment is above 212°F (100°C). Using the convenientIRt/c Cooling Jacket Kit available, either air or watermay be used. For temperatures above 700°F(370°C) water is required, along with a small amountof purge air.

The purge air has two important functions:

1. It keeps the IRt/c lens clear of vapors that wouldcondense on its window, since the windowtemperature might be below the condensingtemperature of some of the vapors of the pro-cess.

2. The internal convective heat transfer characteris-tics are optimal for cooling at very high environ-mental temperatures.

The IRt/c.3x is particularly suited for this servicesince the air consumption required to keep its lensclean is as little as .01 CFM (300 cc/min). A smallconvenient self-contained air pump is available.

Tech Note

16The offset calibration procedure presented in theIRt/c Manual is recommended for field use. Fordesigners of readout devices, it is recommendedthat both sources of leakage current be reduced to10 nanoamps or less to minimize offset errors. Forrecommendations on low offset readout devicescontact Exergen.

I

Readout Device

Offset degrees = ( I x R ) / a

R

IRt/c

a = t/c coefficient in volts per degree= approx 22 microV / deg F (40 / deg C) for type K

= approx 28 microV / deg F (50 / deg C) for type J

Air

Water


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Detecting Hot Melt Adhesive in ProductAssembly, Packaging

IRt/c’s as Disposable Infrared Sensors

The IRt/c, how-ever, is ideallysuited for this typeof service.Its compatibilitywith thermocoupletelemeteringdevices, smallsize, ruggednessof construction, and overall reliability makes it anexcellent replacement for standard thermocouples.At one-tenth the cost of most conventional IRdevices, it is economical enough to be used in“disposable” applications.

Tech Note

17

Tech Note

18

continued...

Destructive testing is commonly used in a number ofindustries, including, for example military weaponstesting and fire safety testing. Thermocouples areroutinely used for temperature measurement, andare connected to telemetering equipment to transmitthe data before the sensor is destroyed in the test.Infrared would be preferred for a number of thesemeasurements because of speed, convenience,and non-contact capability, especially in measuringthe radiant temperature. However, the cost, com-plexity, and general fragility of conventional IRsystems have made such applications impracticaland prohibitively expensive.

which in turn is anexcellent indicationof the hot meltbonding power.Wired differentially,one IRt/c will give a(+) response to heat,while the other will give a (-) response to heat.

Fixture the (+) IRt/c to view the adhesive shortlyafter it is applied by the gun. Fixture the (-) IRt/c toview an area of the substrate in which there is noadhesive. The (-) IRt/c is called the Reference, sinceit automaticallycompensatesthe (+) unit forany changes insubstratetemperature,such that thenet signalprovided by the IRt/c pair is created only by the netheat of the adhesive being added to the substrate(the hot melt being applied properly to the carton,etc.).

Much of the production of modern society is heldtogether by means of adhesives, and without on-lineinspection equipment, modern high volume produc-tion machinery can quickly fill a warehouse withimproperly bonded scrap. Hot melt adhesive isprobably the most widely used because of itssolvent-free operation, high setting speed, andeconomy of use. With upwards of 100,000 hot melt“guns” in operation, there are many thousands ofinstallations that can benefit from on-line inspection.

Hot melt bonding power is a function primarily of hotmelt quantity and temperature. The more adhesiveapplied, the greater the area bonded. The hotter theadhesive, the less viscous it is - it becomes betterable to “grip” the substrate material. However, if thehot melt is too hot, it chars, forming a residue whichplugs the injection nozzles of the guns. Non-meltable contaminants also enter the meltingsystem at times. These contaminants also eventu-ally clog the nozzle or filters. Either way, the adhe-sive flow is blocked and poor product is produced.

A pair of IRt/c’s, wired differentially (connect theminus leads together and measure across the plusleads) reliably detects the infrared energy radiatedby the adhesive. This heat energy is proportional tothe amount and temperature of the adhesive it sees,

Hot Melt Gun

+ -

++

+-

IRt/c

Transmitter



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How the Pit Viper Measures Infrared Radiation

The Reference IRt/c is a verypowerful tool. It can be locatednext to the (+) IRt/c forcorrugated carton, on theunder side of a plastic basecup while hot melt is applied tothe top, or upstream of acoating head with the (+)downstream. The differentialpair of IRt/c’s will reliablyreport the presence orabsence of hot melt compared to a reference areaby the presence or absence of the characteristicheat signature. With set-up calibration, the pair ofIRt/c’s will also indicate quantitatively how muchhot melt is being applied.

The IRt/c.3x is usually the model of choice due to itssmaller tip, narrower field-of-view, and built-in airpurge for dirty environments, but any of the IRt/cmodels may be used. The output signal from thedifferential pair is in the range of 1 millivolt for atypical set-up. Any suitable amplifier can be used.

Since the IRt/c’s are measuringdifferentially, no cold junctioncompensation is required, andmight cause errors if present. Theamplified signal can be interfacedby computer, PLC, or othercontrol device. Be sure to “designin” adequate sensitivity adjust-ment. For best performance, it isrecommended that both IRt/c’sare mounted in a single aluminum

fixture in order to minimize any thermal differencesbetween them.

Set up and operation involve fixturing the IRt/c’s atthe desired inspection points, operating the adhesiveapplications at the minimum acceptable adhesivelevel, then adjusting the alarm limits to that level.

Tech Note

19Like the IRt/c, the pit viper has the ability to “see”infrared radiation.

Pit vipers comprise a family of snakes that share asophisticated thermal adaptation that stems fromthe evolution of specialized pit organs located neartheir eyes. These organs sense the infrared radia-tion of an approaching warm-blooded animal andsend signals to the snake’s brain. These signals areused with the visual picture provided by the snake’seyes, giving the snake more complete informationabout its environment.

Pit organs are small facial cavities covered by a thinmembrane of sensory cells that respond to tempera-ture differences between the target and the snake’sbody temperature. These sense organs are sosensitive they can resolve differences of just .003°C.Pit vipers can detect the presence of a warm-blooded animal at distances of up to 50 centimetersin total darkness simply from the animal’s infraredradiation. The pit viper quickly and accurately scansthe target with its infrared-sensing pit organs beforedeciding to strike to defend its nest or attack its prey.

+ -

Hot Melt Gun

IRt/c IRt/c

The non-contact temperaturecapability of both the pit viperand the IRt/c provides thesurvival edge in a fiercelycompetitive environment.


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otes

Contr olling Web Roller T emperature

Relative Humidity MeasurementTech Note

20

Tech Note

21The IRt/c infrared thermocouples have quicklybecome the sensors of choice for monitoring andcontrolling both web and roller temperatures. Hereare some tips on accurate roller temperaturemeasurement.

1. Uncoated Metal or Chrome Rolls

Shiny, uncoated metal rolls are a difficult surface forany infrared temperature sensor to properly mea-

sure, because thesensor will see toomany environmentalreflections. Thesolution is to simplypaint a small blackstripe on an unusedend of the roller. Aimthe IRt/c sensor at theblack paint stripe. Itwill then measure thetemperature accu-

rately and reliably regardless of changes in thesurface conditions of the rest of the roller.

If there is very little space on the edge of the roller,move the sensor closer and paint a very small blackstripe. The minimum spot size of the IRt/c is 0.3inches (8 mm), and for the IRt/c.3x it is 0.25 inches(6 mm) when the sensor is brought close to thesurface.

2. Dull Metal Rollers

Dull metal rollers can provide a reliable signal.However, it is best to test the surface, as the surfaceemissive properties may be changed by dirt,moisture, cleaning, etc. When in doubt, it is best tosimply paint a stripe to eliminate these variations.

3. Non-metallic Surfaced Rollers

These will provide a reliable IR signal at any pointthe IRt/c is aimed. No painted stripe is required.

water interface, and the wet bulb equilibriumtemperature is not materially affected by impurities.

The highest precision method is to employ an IRt/cwired differentially with a conventional thermocoupleto measure the quantity “wet bulb depression”. Thedifferential pair arrangement guarantees highaccuracy, since RH is a strong function of wet bulbdepression and a weak function of dry bulb tempera-ture. Standard psychrometric tables, charts, andsoftware algorithms can be used with the data toobtain accurate relative humidity for your environ-mental measurements.

IRt/c’s can be used to accurately and reliablymeasure actual relative humidity in many situationswhere there is a convenient source of water andflowing air.

An IRt/c aimed at a wet porous surface with ambientair blowing across the wet surface can actuallymeasure what is called “wet bulb” temperature forthat ambient area. (More precisely, wet bulb tem-perature is the equilibrium temperature of the air-water interface when a water film is evaporated.When air is moved over a wet surface, the watercools by evaporation until it reaches wet-bulbtemperature, then the cooling stops, no matter howmuch more air is moved over the surface. Thetemperature at which the cooling stops is the wetbulb temperature.)

The IRt/c measures the temperature of the air-waterinterface on a surface directly. The quality of thewater or of the absorbing material does not affectthe reading, since the IRt/c can directly view the air-

+

+

+

-

--

+

-

Wet BulbDepression

Temperature

Dry BulbTemperature

Air Flow



IRt/c Tech N

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Controlling Printed Circuit Board PreheatDuring Wave Soldering

Contr olling V acuum Forming andThermoforming Processes

Air

Tech Note

23

For forming plastics, radiantheat with an IRt/c is anexcellent combination ofheating method and control.They work extraordinarily welltogether, since both theheating and measuring occurright at the surface, where theplastic is located. The IRt/creading is unaffected byreflections from the heater,since the spectral response ofthe 6 to 14 micron IRt/c lensfilters out the shorter wavelengths of the radiantheater energy.

The IRt/c may be mounted in between ceramicheaters, or in the shroud or reflector of the radiantheater, such that it can see in between the ele-

Tech Note

22

Ceramic Heaters

IRt/c.2Air

The IRt/c is an excellent solution to the problem ofheater control for PC board preheat. IRt/c’s workparticularly well in this process, since both theheating and measuring occur right at thesurface, where the solder must flow. The IRt/creading is unaffected by reflections from theheater, since the spectral response of the 6-14 micron IRt/c lens filters out any shorterwavelengths of the radiant heater energy.

The IRt/c may be mounted in betweenceramic heaters, or in the shroud or reflectorof the radiant heater, such that it can see inbetween the elements. Select the IRt/c modelwith the field-of-view required to see past theelements to the PC boards. Care should be taken inmounting the IRt/c in such a way as to keep itstemperature below 200°F (93°C) and to keep thelens clean. The IRt/c.3x is the preferred model forthis application because of its small physical size

and built-in air purge. It can function in temperaturesto 250°F (121°C) when the air purge system is used.For still narrower fields of view, the IRt/c.5 andIRt/c.10 with 5:1 and 10:1 FOV respectively are verypopular.

ments. Select any of the IRt/cmodels, depending on thefield-of-view required to seepast the elements to thepainted surface. Care shouldbe taken in mounting the IRt/cin such a way as to keep itstemperature below 200°F(93°C) and to keep the lensclean. The IRt/c.3x is thepreferred model for thisapplication because of itssmall physical size and built-

in air purge. It can be used in temperatures up to250°F (121°C) when the air purge system is used.For still narrower fields of view, the IRt/c.5 andIRt/c.10 with 5:1 and 10:1 FOV respectively are verypopular.


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IRt/c Tech N

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Cooling Jacket Kit for Environments to 1000 °F(540°C)

IRt/c Controls Product Drying (Paper, Wood,Textiles, Film)

Tech Note

24In processing of products suchas paper, wood and textiles, it isimportant to be able to deter-mine quickly when the productsare sufficiently dry.

The surface temperature of a“wet” product will change (rise)very slowly as constant heat isapplied to the product. Thisoccurs because the moisture inthe product absorbs much of the heat energy as itevaporates. At the point that the product becomes“dry”, however, the same constant heat supply willquickly raise the temperature until it reaches thesame as the surrounding air, or higher if the heatsource is radiation. If temperature vs. time is plottedfor a heated drying process, the target “dry” tempera-ture point can clearly be seen as the beginning of arapid rise in surface temperature.

IRt/c’s can be used to monitor these changes insurface temperature. With their fast 0.1 secondresponse time, IRt/c’s can quickly detect when thesurface temperature begins to rise rapidly, anindication that the products have reached a lowmoisture content. (See also Tech Note No. 67)

A simple implementation method is to measure thedifference in temperature between the product andthe ambient air. Determine the delta T that results inthe correct dryness, and set the control system tomaintain that delta T.

The IRt/c is particularly convenient because it can bewired differentially with an ordinary thermocouple.

The combined signal can be fedto a single control channel.Alternatively, if absolutetemperature is preferred, theIRt/c and thermocouple can beread and controlled indepen-dently.

For hot, humid, dusty environ-ments, the IRt/c.3x is recom-mended because of its small

size and super-efficient purge air system.

Fully developed, patented IRt/c-based dryingsystems are available. Contact Exergen for referrals.

T

time (or position)

Tech Note

25Extraordinarily efficient indesign, the CJK requires only.05 gpm (190 cc/min) to protectan IRt/c at 1000°F (540°C). Asmall amount of air purgeinsures that optimum cooling ismaintained, and preventscondensation on the lens (seeTech Note No. 15).

The water cooling system consists of a seamlessmonotube, in order to eliminate the possibility ofleaking joints. For convenience, the seamless tubingincludes an extra 3 ft (1 m) tubing length.

A convenient and inexpensivekit makes it possible to useeither the IRt/c or IRt/c.3x withair, water, or both for service inharsh environments. Measuringonly 4.16" x 1" (106 x 25 mm)overall, the CJK-1 is physicallysmall enough to fit into tightareas and closely monitorprocess temperatures from theoptimum position - up close. With its all stainlesssteel housing, it can withstand the harshest environ-ments.

+

+

+

- TemperatureDifferential

Dry Air

+ +

-

Dry Air +

-

Temperature

Dry Air

Product

Air

Water



IRt/c Tech N

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Air Pump Accessory Keeps IRt/c’s Clean andCool

IRt/c Repeatability and Long-Term Accuracy Tech Note

26The ability of the measuring device to maintain itscalibration under service conditions and over a longperiod of time is of fundamental interest in tempera-ture control. The IRt/c is rated at less than 0.1°Crepeatability and has no measurable long termcalibration change, which makes it well suited forreliable temperature control. These attributes areinherent in the basic design and construction ofeach IRt/c.

Repeatability is defined as the ability of a measuringdevice to reproduce its calibration under identicalconditions. The IRt/c is a solid, hermetically sealed,fully potted system that does not change mechani-cally or metallurgically during service. There are noactive electronic components and no power sourceto produce the signal – only the thermoelectriceffects that produce a thermocouple signal.

Long term accuracy is influenced by the samethings that influence repeatability: mechanicalchanges and metallurgical changes. It is well knownthat thermocouples can change calibration over timedue to these effects.

Mechanical changes occur because conventionalthermocouples are gener-ally constructed as smalland light as possible toenhance response time,making them vulnerable todeformations that canchange the thermoelectricproperties. More importantlythe conventional thermo-

Thermocouple Probe at Product Temperature

IRt/c at Room Temperature

couple must operate at elevated temperature sinceit merely measures its own temperature.

The metallurgical changes which affect thermoelec-tric properties are a strong function of temperature;they are negligible at room temperature, but are ofserious concern at high temperature.

The IRt/c solves both problems by its design andbasic operation. Its solid fully potted construction ina mechanically rigid stainless steel housing, andoperation at near room temperature conditions,essentially eliminate the classical drift problems ofconventional thermocouples. Every IRt/c is double

annealed at temperatures above 212°F(100°C) to ensure long term stability,and tested five times prior to packaging.Barring a small percentage of failure, theIRt/c has essentially unlimited long termcalibration accuracy.

Tech Note

27For IRt/c installations in which a purge air source isnot convenient, or is too expensive to install, theIRt/c Air Pump Kit is ideal. The air pump is rated forcontinuous duty and produces 120 cubic inches/minute (2000 cc/min) air flow, which is more thansufficient for purging; and willcool an IRt/c.3x in environmentsup to 240°F (115°C). The pumpis available in both 120 VAC and12V DC versions, and issupplied with 10 ft (3 m) of vinyltubing, and horizontal/verticalmounting system.

The Air Pump Kit is recommended for installations inwhich dust, dirt, or vapors are present which mightcoat the IRt/c lens, or for situations in which longterm operation has been a problem due to fouling ofthe lens. At less than $100; requiring only a few

minutes to install; and its small 5"x 3.3" (13 x 8 cm) size; the AirPump Kit provides you a conve-nient and inexpensive assuranceof long term, trouble-free opera-tion of your IRt/c temperaturecontrol system.

Air

IRt/c.3x


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IRt/c Tech N

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IRt/c Trouble Shooting Guide

Symptom Action Result

1) Sensor reads high Check initialcalibration

Adjust zero offset ofreadout to bring readingback to normal.

2) Sensor reads low Clean lens ofsensor

If sensor does not correct,check points 3 and 4below.

3) Sensor readingdoes not change

Check impedanceof sensor

If sensor reads open,replace. If sensor hasimpedance of a few 10W,then there is a short in thet/c wire.

4) Sensor readingsuddenly drops byabout half

Check throughpoints 1 to 3above

If still reads low, replacesensor.

Tech Note

28

There are only three possible failure modes foran IRt/c sensor. If an IRt/c sensor is installed anddoes not function as expected the failure may bedue to something other than the sensor. It isrecommended that the sensor is checked out forresponse after installation to ensure that it isconnected to the readout instrument properly.This can be done simply by placing a hand or aheat source in front of the sensor after it isinstalled and making sure the reading changes(this is still valid even if the temperature is wellbelow the calibration point).

If the sensor gives a reading very different fromthe expected reading:-

1. Check initial calibration. If the controller hasbeen changed, or the offset adjusted after thesensor has been installed, the temperaturereading may be very different from the actualtemperature.

2. Check the sensor lens. If dirt has accumulatedon the lens over time, then the reading may belower than expected. Clean the lens using aQ-tip and alcohol. The lens needs to betreated gently, it can be easily scratched.

3. If the sensor reading does not change eventhought the target temperature is changing,the sensor may be burnt out. Check theimpedance of the sensor, if the impedance is>15kohm, then the sensor is probably burntout. If the impedance is <100ohm, then thereis a short in the thermocouple wire and thetemperature being measured is at the short.

4. If the temperature suddenly reads about halfof what it should, then the hermetic seal maybe compromised and the Xenon gas mayhave escaped.

For more information regarding the calibrationtesting of IRt/c sensors, see Tech Note #74. Forprocess control applications, the system can beprogrammed to check the sensor circuit every time itis powered up, see Tech Note #39.

If a PLC is used for process control, a sensor shortwill have the same effect as a “Heater Burn OutProtection” feature.



IRt/c Tech N

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What is Emissivity?

IRt/c Measures Vibrating Objects

IRt/c Can Measure Obliquely

Often, an area needs to be temperature monitored,but because of space limitations, the IRt/c cannot beplaced to view the target area squarely. In suchsituations the IRt/c can be angled obliquely to viewthe target area. The field-of-view then becomeselliptical instead of circular, and the IRt/c averagesthe temperature it sees.

Tech Note

30

Tech Note

29

continued...

Tech Note

31When you look in a mirror with your eyes, you seeonly reflections, nothing of the mirror itself. If themirror is perfect, it has 100% reflectivity. Therefore,it emits nothing because it reflects everything. Forthis condition, the emissivity is zero.

If we consider an imperfect mirror, the eye then seesmostly reflection, but also some of the imperfectionson the mirror surface. If, for example, we saw 90% ofthe mirror as a perfect reflector and 10% as imper-fections, 90% of the mirror would reflect; theremaining 10% would emit. Therefore, the emissivityequals 0.1.

Emissivity is a surface property which determineshow much radiation an object emits at a giventemperature compared to a blackbody at the sametemperature. Emissivity (along with backgroundthermal radiation) is a primary source of errors ininfrared temperature measurement. Emissivity canbe more easily understood if it is realized that infraredhas similar properties to visible light.

Mirrors figure prominently in the discussion of heatradiation and emissivity*. Since heat and lightradiation behave similarly, what we see with oureyes is similar to what the IRt/c sees.

To apply this method, be sure to estimate the size ofthe field-of-view footprint, and confirm that the IRt/c ismeasuring the area you wish to measure.

Measuring the temperature of objects that are nominally stationary, butvibrate, can be a difficult problem because of mechanical fatigue ofany contact device. An example is continuous monitoring of the casingtemperature of both the turbine and compressor side of a turbo-charger. Thermocouples or other contact devices fail after only a fewhours due to the high frequency vibration present during turbochargeroperation.

The IRt/c provides a simple and inexpensive solution. Mounting theIRt/c’s to a non-vibrating surface, they can monitor the turbochargertemperature without being subject to the destructive vibration.

Wherever there is a requirement for machinery monitoring, tempera-ture should be included; and for machines that vibrate, the bestsolution is the IRt/c.

Shape of Measuring Area


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IRt/c Tech N

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Where is the Emissivity Adjustment?

Consider for a moment theexact opposite of a perfectmirror, which is a perfectemitter. The eye looks at aperfect emitter and sees noreflection at all, only theemitting surface. Since 100% ofthe surface emits, and 0%reflects, the emissivity equals1.0. This type of object is calleda blackbody.

Finally, consider a good emitter. The eye sees asmall amount of reflection interspersed with thelarge amount emitting. If 10% of the surface did notemit, and instead reflected, we would have 10%reflecting and the remaining 90% emitting. There-fore, the emissivity equals 0.9.

Accordingly, we can state the following rule ofemissivity:

The emissivity of a surface is simply thepercentage of the surface that emits. Theremaining percentage of the surface reflects.

Shiny metal surfaces actlike mirrors, with emissivi-ties in the range 0.05 to0.2. Accordingly, they haveonly 4% to 25% emittingarea compared to reflect-ing area, and for thatreason are difficult to

measure with infrared methods. Non-metals,organic materials, and coated metals have emissivi-ties in the range of 0.8 to 0.95 and thus have 400%to 1900% emitting areacompared to reflecting area,and thus are much more easilymeasured successfully.

*See “Through the LookingGlass-The Story of Alice’sQuest for Emissivity” availablefrom Exergen.

Tech Note

32

Emissivity =1.0Reflectivity = 0.0

1.0

Blackbody

In the readout device.

The normal setup and calibration as shown in theIRt/c Operating Manual and Tech Note #1 automati-cally compensates for the emissivity and reflectivityof the material whose temperature is being con-trolled, and completely accounts for these effects atthe controlled temperature.

However, for processes in which the control tem-perature set-point varies, the control device willprovide higher accuracy over a wider range if itsSPAN or GAIN adjustment is used to calibrate theprocess. Accordingly, the calibration set-up shouldinclude a standard two point method of setting thespan.

1. Install IRt/c as close as possible.

2. Wire connections in standard fashion.

3. At low operating temperature, measure actualtemperature with D-Series.

4. Adjust OFFSET, ZERO, or LO CAL to matchreading on D-Series.

5. At high operating temperature, measure actualtemperature with D-Series.

6. Adjust SPAN, GAIN, or HI CAL to match readingon D-Series.

+-

1

2

3 45 6

Good EmitterEmissivity = 0.9

Reflectivity = 0.10.1

Emissivity = 0.1Reflectivity = 0.9

1.0

Poor Emitter



IRt/c Tech N

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Why the D-Series is Recommended for IRt/cTemperature Control Calibration

Tech Note

33

Because of its speed, accuracy, and its patentedAutomatic Emissivity Compensation System(AECS).

As in all infrared temperature control systems, IRt/cinstallations should be calibrated to the characteris-tics of the materials and the process being con-trolled, in order to insure that the control tempera-ture is accurate. Accordingly, the calibration refer-ence must be selected such that its accuracy isindependent of the variables that influence thetemperature control accuracy. In the case of infraredtemperature control, the major variables are emis-sivity and ambient reflections.

The Microscanner D-Series has the necessaryaccuracy and independence from emissivity andreflection errors, due to its AECS feature. Thereflective cup configuration of the sensing headautomatically corrects for emissivity by creating atiny blackbody at its point of measurement. By“trapping” the emitted radiation, and excluding theambient radiation (thereby replacing the reflectedambient radiation with reflected emitted radiation)the sensing eye sees a blackbody; and thus canreport the temperature precisely.

The result of AECS is illustrated below.

Effect of Ambient Temperature on Target Readingfor 100 F (38 C) Target with .8 Emissivity

Ambient T (F)

Target T (F)

90

94

98

102

106

110

0 20 40 60 80 100 120

Conventional Infrared

D-Series 38

43

32

(C)4 16 27 38

deg F

0

100

200

300

400

500

0.001 0.01 0.1 1 10 100 1000

Contact Error

D-Series

Conventional Thermocouple

260

200

150

90deg C

Time Comparison Between D-Series and ContactThermocouple for measuring a 500 F (260 C) Surface

Time from start of Measurement (sec)

For further information on Exergen’s MicroscannerD-Series Infrared Scanner/Thermometers call or faxExergen or your local Authorized IRt/c Distributor.

Effect of Emissivity on Temperature Reading for a500 F (260C) Target in 70 F (21 C) ambient

Emissivity

deg F

300

350

400

450

500

550

00.20.40.60.81

Conventional Infrared

D-Series using marker

D-Series w/o marker

Non-metals and Oxides Clean Metals

290

200

150

deg C

Conventional infrared devices are strongly influ-enced by both emissivity and ambient variation,while the D-Series remains accurate.

Additional factors in calibration accuracy are speedand contact error when using conventional thermo-couples. The D-Series overcomes both problems,and makes it possible to complete the temperaturecontrol set-up very quickly and accurately.

No AECSAECS active

When AECS is active, ambient radiation is excludedand replaced by reflections of emitted radiation.

D-Series are available in the compact 1-piece standard model, and in theremote sensor -RS version to be able to measure hard-to-reach areas.


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IRt/c Tech N

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Tech Note

34 Checking IRt/c Ambient Temperature

In many installations, it may not beclear whether cooling is required, and itmay not be easy to obtain the tempera-ture of the environment experienced bythe IRt/c. The IRt/c itself will tell youwhat its own temperature is, by usingthe procedure illustrated below.

The basic method is to temporarily“blind” the IRt/c using aluminum foil,so that it can only see itself. The tempera-ture that it produces is then its owntemperature only.

Before running this test, be sure tocheck for leakage current offsets asdescribed in the manual.

Tech Note

35 Air Purge and Air Cooling Requirements

The limiting air flow restriction for all of the IRt/cmodels and Cooling Jacket Kit is the air fittingsupplied with the unit. Accordingly, all IRt/c’s withbuilt-in air purge, and the Cooling Jacket Kit (CJK-1)all have essentially the same pressure vs. air flowcharacteristics, and the air flow chart applies to all.However, the air consumption requirements forpurging or cooling for each are somewhat differentdue to size and operation variables. Refer to thetable or chart for specific model requirements forminimum pressure for purging, or for cooling inelevated ambient conditions. IRt/c.xxx refers to allmodels with the 1.375” (34,9 mm) housing diameter.If water cooling is used with the Cooling Jacket Kit,air purge pressure only is required.

To convert to metric units

the following may be used:

1. Place IRt/c close to controller and cover IRt/c with aluminum foil.

2. Wire connections in standard fashion.

3. Short the input to obtain the leakage current offset (see Manual).

4. Adjust OFFSET, ZERO, or LO CAL to correct the offset as required.

5. Install IRt/c in operating environment and monitor the display temperature.

6. If below 200 F (100C) no cooling is required.

Model Air Purge Pressure

IRt/c.3x > 0.1 psig

IRt/c.xxx > 5 psig

Cooling Jacket > 0.1 psig

deg C = (deg F-32) x (5/9)

kPa = psig /.15

SCFM/35

Air Cooling Chart

Ambient Temperature (F)

Pre

ssur

e(p

sig)

1

10

100

0 200 400 600

IRt/c.xxx

Cooling Jacket Kit

Air Flow Chart

Flow (SCFM)

Pre

ssur

e(p

sig)

0.001

0.01

0.1

1

10

100

1000

0.01 0.1 1 10

+-

1 2 3

4

5

6



IRt/c Tech N

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IRt/c infrared thermocouples are designed to beused with all thermocouple readout devices andcontrollers, but due to the higher impedance levelsof the IRt/c compared to standard t/c’s, somecontrollers are better suited than others. Leakagecurrent generated by the controller (see Tech Note#16) creates an offset in reading which should beadjusted out for accurate temperatures. If the offsetproduced by the leakage current is larger than theavailable offset adjustment of the controller, theIRt/c will still produce repeatable readings and

control accurately, but the temperature indicationwill be incorrect. Accordingly, recommendedcontrollers are those which have low leakagecurrents and/or sufficient offset adjustment toproduce an accurate IRt/c reading (see chart forrelationship between leakage current and offset).

Following is a list of controller manufacturers withmodels known to have low leakage currents and arerecommended for use with the IRt/c:

Athena, Cal Controls, Eurotherm, Fenwal, Fuji,Honeywell, Love, Newport, Omega, Omron,Partlow, Red Lion, Syscon, Watlow, Yamatake-Honeywell, Shinko Technos

This list is not a comprehensive one - manufacturersare constantly improving their models. Contact yourlocal Authorized IRt/c Distributor for specific models,or the controller manufacturer to inquire as tosuitability of specific models for service with an IRt/c(sensor impedance of ~5KW).

Tech Note

36

Tech Note

37Selecting T emperature Controllers

Large Diameter Reflective Cup Used for SiliconWafer Temperature Measurement

Silicon wafer fabrication involves many operations,most of which require the accurate determination ofthe temperature of the silicon. The surface tempera-ture is an essential control variable for efficient highquality processing of material.

As the wafer is processed theemissivity of the surface can varyconsiderably due to the differentproperties of the substrate layers. Toenable the accurate rapid measure-ment of the wafer temperature, areflective cup was developed. Thereflective cup prevents ambientradiation from entering the sensor andreplaces it with reflected emittedradiation. By reducing errors causedby ambient reflections and emissivityvariations the measurement error canbe reduced by about a factor of ten.

The IRt/c.1X is a good sensor to use for this applica-tion, it is small and can easily be mounted to thereflective cup.

Leakage Current (microamps)2

200

100

100

AvailableOffsetAdjustment

50

100

F C

Recommended

RecommendedNot

o o

IRt/c.1x

REFLECTIVE CUP


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IRt/c Tech N

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A Software Method of Self-Testing IRt/c’s

How the IRt/c is Manufactured for Reliability

The IRt/c is designed and manufactured to provide a lifetime of reliableoperation in the most demanding service conditions. To assure thisperformance, every IRt/c is put through a rigorous process of manufac-ture, including seven separate test stages. At the end of this process,the IRt/c is ready to be installed, and is ready to provide you withreliable infrared temperature data for many years.

As an additional reliability feature, all IRt/c’s are manufactured with aXenon gas fill hermetically sealed into the sensing system. If thehermetic seal is broken by mechanical or thermal damage to thesensor, the Xenon immediately escapes, and the IRt/c radiationsensitivity (difference between target and sensor temperature) immedi-ately drops by more than a factor of two, thus providing an obviousindication of failure, rather than a gradual change which can causepoor quality service for a long period of time before a failure is de-tected.

Tech Note

38

For many OEM applications, it is important to beable to test the IRt/c for proper operation each timethe system is started, assuring the user that allsystems are functioning, much the same way that amicroprocessor can be programmed to check itselfwhen powered up. This feature is especially usefulto check for cleanliness of the lens in applicationswhere a user might inadvertently spill something onits surface.

The test is performed by applying a known powerinput to the target to be heated, and monitoring theinitial rate of change of temperature of the target asseen by the IRt/c. This rate of change is depen-dent only on the power level and independent ofthe initial temperature of the target, as long asthe target began at a uniform temperature .Sufficient time must be allowed after the previouspowerdown.

Tech Note

39

If the IRt/c is clean and functioning normally, it willreport the correct rate of change, and the machinebecomes operational. If the rate of change is lowerthan normal, the user is alerted to clean the lens. Ifthis still does not produce the desired response,service is required on the IRt/c or heater, target,control, etc.

Component Testing

Fabrication

System Testing

Potting Step #1

Cure Step #1

Calibration

Test

Potting Step #2

Cure Step #2

Hot Test

Intermediate Test

Cold Test

Inspect and Package

time

Initial Slope

Power

Temp



IRt/c Tech N

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IRt/c.5 Has 5:1 Field-of-View and Built-in AirPurge

Monitoring Plastic Extrusions

IRt/c’s are well suited for monitoring the temperature of plastic extru-sions, either at the point of extrusion to monitor correct extrusiontemperature, or after air cooling to monitor/control the cooling processprior to cutting to length. The model recommended depends on themonitoring geometry.

For extrusions of 1" (2.5 cm) width or more, the standard IRt/c may beused at a distance of 1/2" (1.3 cm), which is sufficient to keep the lensclean in a reasonably clean environment.

For smaller extrusions, or for up-reading; the IRt/c.3x is preferred dueto its smaller 0.25" minimum spot size (6 mm), and built-in air purge,which will maintain cleanliness even when very close to the hot plasticand pointed up.

For larger extrusions, in which more convenient positioning at greaterdistance is desired, the IRt/c.5 is recommended, due to its narrow 5:1field-of-view.

Tech Note

41

Tech Note

40

For drawings indicating field of view, mounting,

air purge path, etc., see the Catalog Section of

this book.

The IRt/c.5 model extends the range of applicationsfor infrared thermocouple thermometry to situationswhere geometry requires that the sensor bemounted remotely from the target. In addition to thenarrow 5:1 field of view (11° included angle), thismodel retains all of the ruggedness and elegantease-of-use features of the original IRt/c models, ishermetically sealed, and is equipped standard withan internal air cool/purge system. As do all IRt/c’s,this new model exceeds all applicable NEMAstandards, and is intrinsically safe.

Specifications (where different from other models):

Sensing Range: -50 to 1200°F (-45 to 650°C)

Field of View: 11° approx. (5:1)

Minimum Spot Size: 0.8"(2 cm)

Output impedance: 4 KW to 8 KW, varies bymodel

Weight: 6.5 oz with cable (184 gm)

IRt/c

IRt/c.3x

“Slot Spot”IRt/c.5

For the smallest extru-sions, the “Slot Spot”models, with their tightlyfocused optical systems,can measure to 2 mm (seeTech Note No. 80).

Slot Spot IRt/c Monitors Extrusion Temperature

Air


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Bread and Pastry Dough Mixing Temperature

Monitoring Dangerous Chemicals andHazardous Environments

Tech Note

42

Tech Note

43

Handling, processing, or storage of certain materialsinvolves an element of risk of fire, chemical damage,or explosion. Many times these materials aremonitored using pyroelectric, air temperature, orultraviolet devices to detect a fire situation, in orderto activate alarms and extinguishing systems. Thesedevices do not, however, provide the earliestpossible indication of a problem, because theycannot detect the initial heat prior to the fire.

The IRt/c, however, is capable of detecting even thesmallest temperature rise which must occur before afire starts, and transmit the information in as little as80 milliseconds to the thermocouple monitoringdevice, thus providing the maximum time to initiateextinguishing or cooling measures. The wide field-of-view standard IRt/c can average a wide area forbroad coverage of heat build-up, or the narrowerIRt/c.3x, .5, and .10 models can monitor specificareas from greater distances. Actual fire types and

Measuring the temperature of bread and pastry dough whilemixing is difficult at best with conventional contact thermocoupleprobes, due to breakage and possible contamination of the food.However, the temperature is quite important since too high atemperature will cause too much rise, leading to holes in thebaked product, and too low a temperature will not allow thedough to rise sufficiently, resulting in a product that is flat.

The IRt/c solves the problem by monitoring temperature withoutcontact, completely eliminating breakage and possible contami-nation. Wired into a temperature controller, the information can beused to control mixing speed motors to maintain proper doughtemperatures.

The recommended models are the IRt/c.3X and .5, since theirbuilt-in air purge keeps the lens clean even in the dusty interiorof the mixer. Hermetically sealed, the IRt/c can be washed downduring normal cleaning procedures. The recommended mount-ing location is the lid of the mixer, where the IRt/c has a clearview of the dough, and swings out of the way when loading andunloading.

special conditions should be evaluated prior toapplying IRt/c’s.

As a “simple device” all IRt/c models are ratedintrinsically safe (Tech Note #10), and as hermeti-cally sealed devices meet or exceed all applicableNEMA ratings.

IRt/c.55:1 Field-of-view

IRt/c1:1 Field-of-view

IRt/c.3x with Built-in Air Purg e



IRt/c Tech N

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Printing/Ink Drying

Induction Heater Control Tech Note

44

3. Part temperature: IRt/c models can be used tomeasure target temperatures up to 5000°F(2760°C). Select the correct model for thecontrol temperature desired.

4. Part surface material: For bare metal parts theLo E models are recommended. For coated ornon-metal surfaces the Hi E models should beused.

For high speed printing processes,the limiting factor on productivity ofthe equipment is usually ink dryingtime. With non-contact monitoringof the inked surface temperature,press production can be maxi-mized while assuring top quality.

The surface temperature of freshlyinked paper will be considerablycooler than ambient air tempera-ture, and will rise very slowly asthe paper absorbs heat. This occurs because the inksolvent absorbs much of the heat energy as itevaporates. At the point that the product becomes“dry,” however, the same constant heat supply willquickly raise the temperature until it reaches thesame as the surrounding air, or higher if the heatsource is radiation. If temperature vs. time is plottedfor a heated drying process, the target “dry” tem-perature point can clearly be seen as the beginningof a rapid rise in surface temperature.

Tech Note

45The IRt/c’s can be used to monitorthese changes in surface tempera-ture. With their fast response time,the IRt/c’s can quickly detect whenthe surface temperature begins torise rapidly, an indication that theink has dried, thus allowing pressspeeds to be maximized. Since allIRt/c’s are rated intrinsically safe(see Tech Note # 10), and arehermetically sealed to meet or

exceed all applicable NEMA ratings, they can beused in hazardous environments with alcohol-basedand other volatile inks. For tight areas, the IRt/c.SV orIRt/c.3SV is recommended.

The induction heating process can be readilycontrolled by the temperature of the part as mea-sured by an IRt/c non-contact infrared thermo-couple. Several issues should be considered in aninstallation:

1. The effect of the field on the IRt/c: since themeasuring signal is electrically isolated from thehousing, the IRt/c will operate in even a verystrong field. The shield wire should be attachedto a proper signal ground. If there isexcessive heating from the field,consider using the cooling jacketkit, with the same water source asis used to cool the coil.

2. The field-of-view: the preferredmethod is to view the part betweenthe coil turns or from the end.Select the IRt/c model that bestsuits the requirements. For smallgaps between coils, consider thefocused models

IRt/c.5

IRt/c.3x

Cooling Water

IRt/c

IRt/c.ACFIRt/c.AMFIRt/c.ALF

Temperature

time (or position)

WetDry

Ambient Air Temperature

IRt/c3.sv

Air Fitting


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IRt/c Tech N

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Electric Po wer Transmis sion and DistributionControl

Discrete Parts Monitoring

Parts on a moving conveyor can be monitored fortemperature either continuously – measuring anaverage of conveyor and part – or discretely – measur-ing each individual part. For parts which completely ornearly completely, cover the conveyor, measuringcontinuously will give good results.

A powerful method of improving the optical density ofthe product as seen by the IRt/c is to angle the IRt/csuch that it cannot see between the products. By doingthis, temperature monitoring and control can beperformed continuously with simple controllers, withoutthe requirement for additional logic.

However, for applications in which each individual partmust be measured for communication to a centralprocess control computer, additional devices are

required. The mostimportant are the partdetection device, which detects when thepart is within the field of view of the IRt/c;and the sample and hold device, whichholds the previous reading when the partis not in view. Suitable control modulesare available from various manufacturersto provide the necessary logic.

Heat = Energy Dissipated = I2R

Tech Note

46

Typical recommended system for discrete

part monitoring with IRt/c’s.

The capacity of highly loaded electric power conductors,especially switching and transforming equipment, is limitedby the temperature rise characteristics caused by the slightresistive losses. Accordingly, equipment utilization capacityis a direct function of the local temperature at critical points inthe equipment.

With continuous real time monitoring with IRt/c’s, criticalequipment can be used much more effectively. If the tem-perature is below operating limits, additional power may besafely routed through the equipment. With the non-contactcapability of the IRt/c, installation is simple, and live conduc-tors may be safely and easily monitored. Inexpensivestandard thermocouple transmitters and data collectionequipment may be used to transmit the information to acentral office where load switching decisions are made.

Angling the IRt/c permits it

to continuously monitor

bottle temperatures

Tech Note

47

IRt/cTransmitter

Part Detector

Track and Hold Module

Data Collectors

Network Manager

To Other Conveyors

Part Temperature

Conveyor Temperatue

Time

Average Temperature

R

I

IRt/c



IRt/c Tech N

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How the IRt/c Temperature Selection GuideWorks

Glass Monitoring

Glass processing, whether of sheets, bottles, orother forms, usually involves temperature as aprimary control variable. Since glass is impossible tomeasure by contact means, plants must use eitherambient temperature as an indirect approximation,or an infrared device to measure the glass directly.An often asked question is whether infrared devicescan measure glass correctly, since to the eye theglass is transparent.

The answer lies in the physics of glass and the wellknown “greenhouse effect.” The short wave radia-tion of visible light that we can see (~ 0.3 - 0.8microns) can pass through glass essentially unaf-fected. The much longer infrared wavelengths thatare normally measured for temperature assessment

(~ 5 - 20 microns) cannot pass through the glass,and are absorbed. As a consequence of the inabilityof glass to transmit the long wavelengths of infrared,the glass will emit those wavelengths created by itstemperature, and thus can be measured with anIRt/c. At much higher temperatures the infraredwavelengths become shorter, and some transmis-sion occurs.

If the glass is within the temperature range of theIRt/c, the sensor will measure its temperatureaccurately – just as if the IRt/c were looking at anopaque material surface. Follow the normal installa-tion and calibration procedures. The glass will haveemissivity in the range of 0.9 and above, andtherefore will provide good results.

All IRt/c’s are self-powered devices, which rely onthe incoming infrared radiation to produce the signalthrough thermoelectric effects. Accordingly, thesignal will follow the rules of radiation thermalphysics, and be subject to the non-linearities inherentin the process.

Tech Note

48

However, over a range of temperatures, the IRt/coutput is sufficiently linear to produce a signal whichcan be interchanged directly for a conventional t/csignal. For example, specifying a 2% match to t/c

continued...

The actual signal generated by the IRt/c can be

approximated with a fourth order polynomial

function of target temperature. This fourth power

dependence is due to radiation physics, and not a

limitation of the IRt/c.

The linear region matches the conventional t/c to

a specified tolerance.

Tech Note

49

IRt/c.5

Visible light transmitted

Infrared radiation absorbed

Infrared radiation emitted

millivoltoutput

Target Temperature

Linear region

Conventional thermocouple millivoltoutput

Target Temperature

Actual IRt/c Signal


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IRt/c Tech N

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Improving Mac hining T olerance

IRt/c.5

IRt/c.3x

linearity results in a temperature range in which theIRt/c will produce a signal within 2% of the conven-tional t/c operating over that range. Specifying 5%will produce a somewhat wider range, etc.

Each IRt/c model is specifically designed foroptimum performance in the region of best linear fitwith conventional t/c’s, but can be used outside ofthis range by simply calibrating the readout deviceappropriately. The output signal is smooth andcontinuous over its entire rated temperature range,and maintains 0.01°C repeatability over its entirerange.

The Temperature Selection Guide is a summary ofthe linear range performance of each IRt/c model.

Precision machining tolerances of metal and non-metal parts are substantially impaired by uncertaintyin part temperature, due to the dimensional changeswhich occur with temperature. For example, mostmetals have thermal expansion coefficients ofapproximately 10 ppm per °F (approximately 20ppm per °C). If a 10 inch (25 cm)part undergoing machiningincreases in temperature by only10 °F (5 °C) from the set-up, thepart will have increased in size by.001 inch (.025 mm). Accordingly,the best that the machine can do,regardless of the machine’squality, is + 0.0005" (+ 0.012 mm).If the temperature uncertainty is higher, the tole-rance increases in direct proportion. This effect isespecially important as the tool wears, and signifi-cantly more frictional energy is imparted to the part.

The IRt/c solves the problem by monitoring the parttemperature continuously, and reporting the tem-perature to the computer, which in turn adjusts theposition of the cutting tool accordingly. An additionalbenefit is detection of worn tools, due to the higherthan anticipated part temperatures, or rate of

change of temperature.

Any of the IRt/c models can beused, although the IRt/c.3x and.5 are preferred for their nar-rower fields of view and built-inair purge. Emissivity of the metalparts is normally not a problemdue to the presence of cuttingoils and coatings. If the parts are

completely clean, then a thin coating of oil will besufficient to increase the emissivity for accuratemeasurements.

Tech Note

50

Signal produced by the IRt/c-K-80F/27C

has its 2% linear range centered at

80°F (27°C), but produces a repeatable

signal to 1200°F (650°C).

Actual Temperature (C)

mill

ivol

tsof

sign

alou

tput

-10.00

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

-50 50 150 250 350 450 550 650

Target Temperature

* - ** - 440F/220C* - ** - 340F/170C* - ** - 280F/140C* - ** - 240F/120C* - ** - 180F/90C

* - ** - 50F/10C* - ** - 80F/27C* - ** - 140F/60C

* - ** - 98.6F/37C

0 100 200 300 400 500

Special Biomedical Calibration

100500 150 200 250

O F

CO

320 - 500F (160 - 260C)280 - 370F (140 - 190C)240 - 330F (115 - 165C)180 - 250F (80 - 120C)140 - 220F (60 - 105C)

0 - 85F (-18 - 30C)32 - 120F (0 - 50C)70 - 190F (20 - 90C)

Model Number Optimum Range



IRt/c Tech N

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Speed of Response

Asphalt T emperature Monitoring Tech Note

51

One of the outstanding features of the IRt/c is itsspeed of response – 0.1 to 0.2 seconds. Thisattribute makes it possible to monitor the tempera-ture of fast moving materials in production lines, andrapid heating and cooling. For applications in whichhigh speed is required, care should be taken inselection of the readout device, since most thermo-couple readouts are much slower than the IRt/c.

In applying the IRt/c, the dynamic characteristicscan be described mathematically as a pure expo-nential response, following the equation:

Accordingly, the IRt/c signal can be modeledanalytically for applications in which faster speedsare required. For any given IRt/c, the time constantwill be repeatable to within a few percent, and thuscan be successfully modelled.

A common limitation in applying the IRt/c to highspeed applications is the transit time of the targetacross the field of view. The characteristic timeconstant equation of response applies to the IRt/cresponse only. If the target requires time to com-pletely fill the field of view, the transit time must be

added to the IRt/c time constant. For best results,place the IRt/c as close as possible to the target tominimize the spot size, and therefore the transit timeeffect.

Tech Note

52

IRt/c.5

Asphalt properties are particularly sensitive to temperature, and it isimportant that the asphalt is applied at the correct temperature in orderto perform to its specifications. Accordingly, temperature monitoring isa common requirement, but the thermocouples normally used havesevere breakage problems due to the harsh abrasiveness of thematerial, and must constantly be replaced at high cost and interruptionof production.

The IRt/c solves this problem directly, since the temperature is moni-tored without contact. The normal thermocouple controller can be used– simply calibrate offset if necessary. The IRt/c.3x and .5 models arerecommended for their built-in air purge, which will keep the lens cleanby preventing vapors from condensing on the lens. The IRt/c.3x can bemounted in the chute to view the asphalt through a small hole, whilethe IRt/c.5 can be mounted some distance away due to its narrow 5:1field of view.

IRt/c.5

IRt/c.3x

Air

Air

IRt/c.5IRt/c.2IRt/c

mV

Time

Transit Time Effect

mV

Time

IRt/c Response

~ 0.1 sec

IRt/c.5IRt/c.2IRt/c

All Models

∆mV c et= − −( )/1 τ


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IRt/c Tech N

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How to Use Infrared Effectively

IRt/c Quick Selection GuideTech Note

53

Tech Note

54

1. How Large Is Your Target?

• If it is smaller than 0.8 inches (2 cm), you mustselect either the IRt/c.01, IRt/c.03, IRt/c.1x,IRt/c.3x, or focused model.

• If it is smaller than 0.3 inches (8 mm) you mustselect the IRt/c.3x or focused model.

• If it is larger than 0.8 inches (2 cm), select anyof the sensors.

2. How Close Can The Sensor Be Mounted?

• See Tech Note #36, Tech Note #41, and TechNote #55 and use the field-of-view drawingsshowing the distance from the sensor versusthe approximate diameters of the spot size.

• For example, the IRt/c.3x, at a distance of 3Xhas a spot size of 1X (at a distance of 1 foot,the spot size is 4 inches, at a distance of 1.5meter, the spot size is 0.5 meter).

• See Tech Note #29 if you wish to position anIRt/c at an angle other than 90° from yourtarget surface.

• If using a focused model, refer to individualmodel specifications for optimum distance.

3. What Is The Ambient Temperature WhereThe Sensor Is To Be Placed?

• If ambient is less than 160°F (70° C) chooseany sensor.

• If ambient is less than 212°F (100° C) chooseany sensor except IRt/c.01 and IRt/c.03..

• If ambient is greater than 212°F (100° C), seeTech Note #35 for air cooling flow requirementsfor the IRt/c Cooling Jacket Kit and IRt/c.XXXbuilt-in air purge/cool system.

• If ambient is greater than 500°F (260°C), it isusually best to specify an IRt/c or IRt/c.2sensor along with the Cooling Jacket Kit andutilize the water cooling feature. (Cooling thesmaller sensors with water is less expensiveover time, compared to cooling the IRt/c.5 withair.)

4. What Is Your Target T emperature?

• Use Temperature Selection Guide. See TechNote #49.

5. Choosing A T emperature Controller/InputDevice?

• See Tech Note #37 and Tech Note #14 for helpin selecting or using available thermocoupleinput devices.

As somewhat less commonly understood methodsof temperature measurement, infrared methodshave their own characteristics which lead to bothgood applications and difficult applications. Thethree simplified rules below will help you evaluatethe potential use of infrared techniques, andestimate of the degree of difficulty involved. Theserules apply to infrared physics in general, and arenot a limitation imposed by the design of IRt/c’sspecifically.

1. Simple Applications

• All non-metallic surfaces

• Food, Paper, Plastics, Coated Metals, Stone,Clay, Glass, Liquids, Textiles, etc.

2. More Difficult Applications*

• Bare Metals**

• Shiny, unpainted, uncoated metal surfaces**

3. “In Between” Applications*

• Dull Metal Surfaces

• Thin “See-through” Plastics

* For temperatures in the correct range, the Lo E modelsprovide very good performance if emissivity variationsare not too great.

** It is always repeatability that counts, and there arevarious “tricks” that can be used to improve repeatabil-ity in difficult applications, but experimentation isrequired.



IRt/c Tech N

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Calibrating with Thermocouple Sim ulators

Understanding Field-of-View

IRt/c’s are rated optically for their field-of-view by theactual dimensional equations describing theirconstruction. However there are, in practice, somesecondary effects which can influence performance,including optical scatter, unwanted reflections,atmospheric scatter, and others.

The graph illustrates the relative contribution to thesignal produced by the target and by the areasurrounding the target due to these effects. Notethat the sum of radiation from the target and radia-tion from the surroundings is always one, and as thesensor is placed further away than its rated field-of-view, there is less target signal and more surround-ings signal. Mathematically this effect is identical toa reduction in emissivity, and can be calibrated outthe same way, as long as the temperature of the

surroundings isrepeatable. Undertypical conditions,placing the IRt/csuch that the targetexactly fills thefield of view resultsin approximately80 to 90% targetsignal, and 10 to20% surroundingssignal.

A common convention in infrared thermometry, andthe one used to verify the optical performance ofIRt/c’s, is to define the field-of-view by the “1/2energy points” in an optical traverse experiment.The resultant data looks like a “Bell Curve” asindicated in theillustration. Thefield-of-view issimply the anglebetween the 50%energy points.

As always, closer isbest; use the closestpossible position forthe IRt/c.

Tech Note

55

IRt/c IRt/c.2 IRt/c.5100%

60%

20%

0%

40%

80%

Ratio: Distance/Target Size

Radiation from Target

Radiation from Surroundings

Typical Range of Operation

.1 .5 1 5 10 50

Poor Good Best

100% Energy

50% Energy

θ

θ

A common practice in thermocouple transmittercalibration is to set the 4 to 20 mA range on thebench before installation. The usual procedure is toemploy a thermocouple simulator which can beprogrammed to produce a thermocouple equivalentsignal of the desired type and temperature range. Inthis fashion, the 4 mA is set with the ZERO, and the20 mA with the SPAN for the desired range.

Bench calibration of a transmitter can be performedto operate with any IRt/c by adding the followingstep to the normal method:

• Measure the electrical resistance of the IRt/c tobe used with the transmitter, and add a resistorof the same value in series with the simulator.

Tech Note

56With this step, the simulator “looks” to the transmit-ter exactly the same as the IRt/c, and any offsetscaused by transmitter leakage currents can becalibrated out. Good practice is to check to makesure that the calibration remains stable on thebench, in case the transmitter leakage current is notconstant. As always with infrared devices, a finaltrim calibration should be performed in actualoperation (see Tech Note #1).

Resistor of the same value as IRt/c

Thermocouple Simulator

Thermocouple Transmitter


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IRt/c Tech N

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Measuring Objects Smaller Than theField-of-View

For some non-contact temperature monitoring tasks, the object to bemeasured is too small to adequately fill the field-of-view of one of theIRt/c models. The monitoring can still be successfully performed if twoconditions are met:

• The object size and distance from the IRt/c are constant.

• The area surrounding the object within the field-of-view of the IRt/chas a repeatable temperature.

The signal produced by the IRt/c represents the average temperaturewithin its view. Accordingly, the signal can be represented by theequation:

T = ( Tt A

t / A ) + ( T

s A

s / A )

where T is the output signal, Tt the target object temperature, At thetarget object area, Ts the surroundings temperature, As the surround-ings area as seen by the IRt/c, and A the total area seen by the IRt/c.

For example, to measure the temperature of a thin rubber strip 0.1"(2.5 mm) wide moving continuously 1" (25 mm) away from an IRt/c.2,at a temperature expected to be about 200°F (93°C), and a surround-ing temperature at 80°F (27°C). At 1" (25 mm) distance, the IRt/c.2spot size will be approximately 0.5" (13 mm).

Computing the results for the equation gives:

Tech Note

57

This result shows that the average signal will be 31°F (17°C)above the surroundings temperature, compared to an actualobject temperature of 120°F (67°C) above surroundings, orapproximately one-fourth, which is the ratio of object area tosurroundings area measured. Therefore, if the surroundings areexpected to be repeatable to 1°F (.6°C), the IRt/c signal will berepeatable to 4°F (2°C). For the final display on a controller, orother read-out device, calibrate in standard fashion by using theavailable offset adjustment. If the object is to be controlled over awide range of temperatures, calibrating with a span adjustmentwill yield greater accuracy.

If the target temperature falls within the range of one of the LoEmodels, the LoE model should be used, even if the target is notmetallic. Since a small target results in the same radiation math-ematics as low emissivity, a LoE model will reduce errors due tosize change and positioning by a factor of approximately 4. SeeTech Note 59.

At Tt

Output Signal = T

As Ts

T = + −( )(. )(. ) / [ (. ) ]) ( )[ (. ) (. )(. )] / [ (. ) ]200 5 1 25 80 25 5 1 252 2 2π π π

At Tt

Output Signal = T

As Ts



IRt/c Tech N

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Measuring High Temperatures with Immer sionThermowells

Tech Note

58

How To Use The IRt/c With A Thermowell

The technique is to mount an IRt/c sensor so that itaims directly into a hollow thermowell. The wellshould have a minimum inner diameter to accom-modate the minimum spot size of the sensorselected. Choose the appropriate sensor for thetemperature range and length of the well you areusing.

For example, to measure up to 2000°F (1100°C), 6feet (2 m) into a stack, use an IRt/c.100A-HiE sensorlooking into a thermowell of that length with aninside diameter of at least .8 inches (20 mm). Thespot diameter for the IRt/c.100A at 72 inchesdistance is .8 inches (at 2 meters distance, the spotdiameter is 20 mm.) The sensor can then “see” allthe way into the hollow well tube and monitor the tipend temperature, ignoring the sidewall tempera-tures.

Choose appropriate thermowell material (stainlesssteel, Hastelloy®, Inconel®, ceramic, etc.) to with-stand the temperature, oxidation and other rigors ofthe environment where it is to be placed.

If the thermowell is sealed with a sight glass, then aLo E model should be specified (see Tech NoteNo. 66).

Like ordinary thermocouples, the high temperatureIRt/c models can be used with immersion“thermowells” to measure high temperature gases orliquids, while maintaining the integrity of the vessel.However, the IRt/c has significant advantages overordinary thermocouples, RTDs, etc. in this applica-tion.

Survivability

Since the IRt/c sensor elements are positioned in anon-contact mode, outside of the heated area, andkept at a low temperature, the entire temperaturesensing system can be designed to survive for amuch, much longer period of time than conventionalthermocouples or RTD’s. The only part requiringmaintenance is the thermowell itself, an inexpensiveand easily replaced part. Users enjoy savingsbecause there are no replacement thermocoupleparts, no replacement labor, and no productionlosses from downtime for sensor replacement.

Sensor Stability and “Drift”

Even worse than sensor failure is a sensor thatreads incorrectly, feeding inconsistent or inaccurateinformation to your control systems. Sensor stabilityand drift can be significant problems with standardthermocouples when measuring high temperatures,due to chemical and metallurgical changes that longexposure to high temperatures causes. The IRt/c,however, is essentially immune to those effects,since the sensor remains at a low temperature – farbelow that of the contact device, and below thelevels which are the major sources of drift.

Sensor Speed

With its 0.1 to 0.2 secondresponse time, the IRt/c is farfaster than any conventionalthermocouple or RTD placedinside a well. Accordingly, forall practical purposes, thetemperature measurementspeed is the same as that ofthe well itself. To Thermocouple Transmitter

~ 100 F (~40 C)o o 2000 F (1100 C)o o


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IRt/c Tech N

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How the Lo E Filter Reduces Errors Due toEmissivity Variations

qhc

ech k Tλ λε π λ=−

−21

2 5

/

Emissivity is the property of a material’s surface thatdescribes its “efficiency” at emitting thermal radia-tion. An emissivity value of 1.0 represents emissionat 100%, and 0 describes emission at 0% (or perfectreflection - see Tech Note #31).

For non-metals and coated metals this efficiency ofemission, called emissivity, is very high (0.8 orgreater), and variations are usually not a problem.For example, for a production process in which anon-metallic material is to be controlled, and normalmaterial variations cause emissivity variations of±.01, the associated temperature error will be of theorder of .01 divided by .9, or ~1% of reading, anacceptable variation. In contrast, if we are to controlthe temperature of a metal with emissivity 0.2, thenvariations of ±.01 will produce an error of the orderof (.01/.2), or ~ 5% of reading. Additionally, metalfinishes, which play a significant role in emissivity,tend to cause more variations than changes in finishin non-metals.

The IRt/c Lo E Filter design filters out the effects ofthese emissivity variations on measured tempera-ture by approximately a factor of four, and thusreduces the errors by a factor of four. Thus, with theLo E Filter, the errors are of the same order as thosecommonly experienced for high emissivity targets.

The method takes advantage of the basic physics ofthermal radiation, in which the mathematical descrip-

Tech Note

59

Planck Function - Radiated Energy vs Wavelength

Wavelength

More emissivity sensitive

More temperature sensitive

qλ

If we compute the partial derivative of each expres-sion with respect to emissivity and temperature, weobtain the following relations for the slope of thesignal with respect to temperature divided by theslope of the signal with respect to emissivity:

tion of the energy distribution is by a formulacalled the Planck function:

where qλ is radiated energy at a given wavelength, εis the emissivity, T the absolute target temperature,λ the wave-length, and theother symbolsare for variousphysicalconstants. ThePlanck functionintegrates tothe morefamiliar Stefan-Boltzmanequation:

when all wavelengths are measured.

The Lo E Filter works by measuring the energycontent of the radiation, as described by the Planckfunction, over wavelengths that are more selectivelysensitive for temperature variations, and thereforeproportionately less sensitive to emissivity varia-tions, as follows:

*Radiated Energy= = =∞

q q d Tλ λ εσ0

4

Filtered Radiated Energy= q

where1

2

λλ

λ

λ εσ* ≈

>>

d Tx

x 4

∂∂ε

εσ σ ∂∂

εσ εσ εσσ

ε

∂∂ε

εσ σ ∂∂

εσ εσ εσσ

ε

( ) ( )

( ) ( ) ( )( )

T TT

T TT

T T

T TT

T x Tx T

T

x

Tx

x x x xx

x

4 4 4 33

4

11

44 4

4

= = ⇒ =

= = ⇒ =

>>

−−

,

where

.22 .20.19 .21

Emissivity Variations

Temp

time

Without Lo E Filter

Temp

time

With Lo E Filter

IRt/c

TM



IRt/c Tech N

otes

Set-up and Calibration Instructions forAdjustable Models

Accordingly, by optimum selection of the wave-lengths to be measured, the sensitivity to emissivityvariations can be significantly reduced, i.e. filtered,by enhancing the relative sensitivity to temperature.In practice, the best wavelengths are the shorterones, since they provide the most sensitivity totemperature, and the least sensitivity to emissivity,as is predicted by the integration of the Planckfunction.

The “filtering factor” for the IRt/c Lo E models isbased on the selection of .1 to 5 micron for themeasured wavelengths, and results in a factor offrom four to six error reduction, depending on targettemperature.

As an additional benefit of the Lo E Filter, errors dueto such factors as smoke, dust, moisture, etc. whichmay partially block the optical path to the target, arealso filtered. These factors behave mathematicallyidentically to emissivity, and therefore will be filteredby the same factor of four to six.

Tech Note

60

For all IRt/c Models with “A” in model designation(IRt/c.xxxA)

1. Connect air purge first if installing inprocess already at operating tempera-ture. Provide minimum 5 psig (30 kPa)air pressure.

2. Install IRt/c and align to view the desiredtarget. Bring target to operating tempera-ture if not already there. Connect leads toreadout device to be used (controller,PLC, etc.).

3. If the target temperature is not known, measure the targettemperature with an accurate reference. Remove the setscrew toexpose the calibration screw. Adjust the calibration screw toobtain reading desired. Replace the setscrew cover whencomplete. For final process adjustments, the ZERO or OFFSETadjustments available on readout devices can be convenientlyused.

Installation and calibration complete.

To maximize the linear range, see Tech Note #70 .

Calibration screw operates like a radio volume control: clockwise increasessignal.

Lo E Filter

Target F (C)

0.0

2.0

4.0

6.0

8.0

10.0

0 1000 2000 3000 4000

(500) (1000) (1500) (2000)

Performance

FilteringFactor

+

-

1

2

Air

3

Calibration Screw

Increase Signal

Decrease Signal


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IRt/c Tech N

otes

Why Color Does Not Affect Readings

How the Adjustable IRt/c Models Work

All IRt/c models with the “A” designator (example:IRt/c.10A-K-LoE) can be field calibrated for thespecific requirements of the application toprecisely indicate the actual temperature of thetarget, and to correct for reflective errors causedby ambient variations (see Tech Note #64).

The basic operation of the IRt/c adjustment is torescale the signal output until it matches theactual temperature for the thermocouple type inuse. In the vicinity of the calibration point, theoutput will match the linearity of the t/c. When theadjustment is made to actual temperature, theAutomatic Ambient Compensation System isautomatically correctly scaled.

The above chart shows the actual performance ofa .10A-HiE model as an illustration of the effect ofadjustment on the signal.

In many IRt/c installations, such as paint curing, webdrying, printing, etc., the temperature control systemmust be able to accurately measure materials with avariety of colors. Ideally the same calibration set-upwould be used for all colors, rather than having torecalibrate each time a new color is run.

Because the IRt/c measures the radiated wave-lengths that indicate temperature, which are gener-ally ten times longer than the wavelengths thatindicate color, color changes do notinfluence temperature readings. Even forsituations in which the target temperature issufficiently high such that appreciableenergy is radiated at visible wavelengths,all IRt/c models except Lo E completelyfilter out the visible wavelengths.

Except to the extent that color mightindicate a change in surface texture, andthereby affect emissivity, there will be noeffect of color on the reading.

Tech Note

61

0

20

40

60

80

100

120

140

0 400 800 1200 F

mV

Type K t/c

IRt/c SignalAdjustable

Adjustment

Output Signal200 400 600 C

Calibration Point

The energy contained in the radiation we see ascolor has nothing to do with the temperature (except ifthe target is hot enough to be incandescent), and issimply a function of which particular wavelengths arereflected to our eyes.

Tech Note

62

6 8 10 12 14 16 184 200 2 22 24 26

IRt/c

Wavelength in microns

Violet / Indigo / Blue / Green / Yellow / Orange / Red0.2 0.8

Colors"R.O.Y. G. B.I.V." backwards

IRt/c Hi E

IRt/cLo E



IRt/c Tech N

otes

Adjustable Models Compensate for ReflectiveErrors

Potential Errors Caused By AmbientTemperature Effects

Tech Note

63

Tech Note

64

continued...

If the ambient temperature of a temperature controlinstallation changes significantly, there are severalsources of potential inaccuracies that can beminimized by attention to installation details.

Reflective Errors: For situations in which the IRt/citself is at the same temperature as ambient sourcesof radiated energy, the patented design of the IRt/cwill compensate for reflected energy and maintainaccuracy. See Tech Note #64 for discussion.

If the ambient source of radiant energy is too hot foran uncooled IRt/c, the principal precaution to employis to take advantage of the generally specularcharacteristics of reflected energy. The term specularmeans “mirror-like,” and reflective errors can beminimized by avoiding viewing angles in which thesurface can reflect a hot source.

Leakage Current Effects: For installations in whichthe readout device generates appreciable leakagecurrent, there is a potential inaccuracy due to smallshifts in IRt/c impedance with ambient temperature.For example, if the readout device leakage current

generates an offset of 100°F (55°C), which iscalibrated out at installation, and sometime later theambient temperature for the IRt/c is much hotter, theIRt/c impedance might be a few percent differentthan it was at calibration. Accordingly, the tempera-ture offset caused by the leakage current will alsoshift by a few percent. If the original offset requirementis 100°F (55°C), then a shift of ~ 5% impedance willcause a shift in reading of ~ 5°F ( ~ 3°C). In general,always choose a readout device with the lowestleakage current available to avoid this potentialproblem. See Tech Note Nos. 14,16, 37, and 56 forfurther discussions of leakage current effects.

For high precision temperature control in applicationswhere the ambient temperature varies, reflectiveeffects may cause unacceptable errors under someoperating conditions. For example, an incubator isdesigned to warm a baby by measuring the child’sskin temperature, and modulate the ambient tem-perature inside the incubator to maintain the skinwithin the desired range. Even though skin has ahigh emissivity (> 0.9), there is potentially an error of±1°F (0.6°C) caused by changes in the reflective

component of the radiation as the ambient is modu-lated ±10°F.

The basic principles can be understood by consider-ing the radiation leaving a surface, as measured byany detector (including an eye). The total radiation qis made up of the reflected and emitted radiationcomponents as follows:

qa = ambient radiation = σσσσσ(T

a)4

qr = reflected radiation = ρρρρρqa

qe = emitted radiation = εσεσεσεσεσ(Ts)4

where r is reflectivity, ε is emissivity, σ is the Stefan-Boltzman constant, and Ta and Ts are absoluteambient and surface temperature respectively.

Radiant OvenPoor

Good

qr

qe qeq +rq =

qa


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IRt/c Tech N

otes

Painting Metal Surfaces to increase Emissivity

Since emissivity plus reflectivity is alwaysunity for non-transparent surfaces, the totalradiated energy can be written as:

q = qr + qe = (1-εεεεε)σσσσσ(Ta)4 + εσεσεσεσεσ(Ts)

4

This expression can be further simplified intoa linear approximation that applies to theambient temperatures over which the IRt/ccan operate uncooled:

T = (1-εεεεε)Ta + εεεεεTs

where T is the apparent surface temperaturemeasured by radiation. As indicated by the finalresult, if the emissivity is 1.0, the effect of ambienttemperature is zero. If the emissivity is 0.9, theeffect of ambient temperature is 10%, etc. (As anaside, this expression can be used to obtain theactual emissivity.)

Non-adjustable IRt/c’s are designed and calibratedto automatically compensate for this effect when the

Tech Note

65

Even with the availability of Lo E Filter models, as ageneral rule higher emissivities require less carefulattention to set-up details and calibration, and aremore “forgiving” in long term service using any IRtemperature measuring device. Accordingly it isrecommended that where possible, surface emissiv-ity should be increased. If it is not possible toincrease emissivity, then a Lo E Filter model shouldbe specified.

As an example, to control a metal roller temperature,paint either the end or an unused edge, and monitorwith an IRt/c.

A recommended paint for most service is

RUST-OLEUM®

7778

BAR-B-Q-BLACK

Rated to 800°F (427°C)

Temp

time

Ambient Apparent Surface

time

Without

Effect of IRt/c Automatic Ambient Compensation

With

emissivity is 0.9, a good general assumption formost non-metallic materials, and sufficient for goodaccuracy under most conditions. With the adjustablemodels, however, when the IRt/c is calibrated inplace it automatically compensates for the reflectiveerrors as indicated in the above equation for anyemissivity within its normal operating range. Thispatented automatic ambient compensation featuresignificantly improves the IRt/c control accuracy underreal world conditions of varying ambient temperatures.



IRt/c Tech N

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Measuring Location of Dry-Out Point in WebProduction

Looking Through Sight Windows with Lo EFilter Models

Commonly, many types of furnaces are equippedwith sight windows to permit visual inspection of theprocessing of the materials. These windows wouldconveniently provide a means for monitoring thetemperature if the IR sensor could deliver reliablereadings through the glass. Such glass can benormal window glass, tempered glass, quartz, etc.

Tech Note

66

0%10%20%30%40%50%60%70%80%90%

100%

0 1000 2000 3000 4000 F

500 1000 1500 2000 C

Approximate Signal Loss Through Sight Glass

Roll Mill Furnace Zones

800 C 1000 C 1200 C

IRt/c

Sight Window

Lo E IRt/c models can “see through” such windowsand will provide reliable readings if the losses are nottoo great. The adjustability feature of these modelsallow them to be calibrated to include the loss throughthe window. As a general recommendation, targetsabove about 500°C should provide good results, butthe only way to be sure is to actually install theappropriate IRt/c and monitor results. If there isinsufficient signal to read out the correct temperature,the OFFSET adjustment on the readout device maybe used to add signal.

1 2

34

5

6 7

For many types of continuous web productionprocessing, such as paper, printing, photographicfilm, textiles, etc., an important parameter for qualityand throughput rate is knowledge of the point atwhich “dry-out” occurs. More important even thanthe absolute temperature, the location of this pointprovides a highly precise indication of the rate ofheat input into the product, and allows direct controlof the energy input to force the dry-out point to aspecific spot in the drying process.

The IRt/c is particularly well suited to this applicationdue to its small size, low cost, outstanding speed,hermetically sealed construction, and its intrinsicallysafe character.

Connected to inexpensive multi-channel thermo-couple input cards for PLC’s or computers, the dry-out point is easily calculated by the intersection ofthe slopes of the temperature vs. position dataprovided by the IRt/c’s.

Tech Note

67

1 2 3 4 5 6 7

Web Temperature at IRt/c Locations

Dry-out Point


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IRt/c Tech N

otes

Fail-Safe Control Installation MethodsTech Note

68

controller is highly recommended, since it not onlywill protect against short circuits, but also againstany other possible failure in the IRt/c which mightmaintain electrical continuity, but renders it blind tothe process.

Calibration Drift

There are no known processes that can cause asignificant calibration drift in the IRt/c. Since thereare no active electrical components, the signal isgenerated entirely by thermoelectric effects, and thematerials are kept at comfortably low temperatures.A significant feature of the IRt/c design and con-struction is the presence of a Xenon gas fill in thedetection system, which provides an immediate anddramatic change in sensitivity (factor of ~ 3) ifmechanical damage occurs sufficient to cause aleak (see Tech Note #38). A common apparentsource of drift can be a dirty lens, since the opticalsignal will degrade in direct proportion to the lensarea blocked. Employing the built-in air purge featureof most IRt/c’s prevents this problem.

Although extraordinarily reliable, like any othermeasuring device, an IRt/c installation should bedesigned to “fail-safe” under all foreseeable situa-tions. Accordingly, the possible failure modesshould be considered as part of the installationdesign, as recommended in the Operating Prin-ciples Manual supplied with every IRt/c.

Open Circuit Detection

As in all thermocouple installations, a primaryprotection recommended is open circuit detection,which will alert if wires are broken, or if the IRt/c isphysically damaged to the point of opening theelectrical circuit. Standard circuit techniques involveusing a small leakage current that generatesnegligible voltage when the circuit is closed, butdrives the input amplifier into saturation if the circuitopens. Only a very small amount of current isrequired, ~ 1 nanoamp, which produces a negligiblesignal offset with the higher impedance of the IRt/c,although some devices produce far more currentthan required, and thus produce more offset (seeTech Notes #16, 37).

Short Circuit Detection

Also a commonly available feature of thermocouplecontrol devices, this safety feature detects if the loadis on solidly for a time that is too long for the normalprocess requirements. This would be the case if athermocouple were shorted somewhere betweenthe measuring junction and the controller, and thusnot reporting the temperature of the process, but thetemperature at the short. This safety feature in a



IRt/c Self-Test

A powerful method of checking an IRt/c installationis to test the response against an expected range onevery measurement cycle. This option is highlyrecommended if there is computing power available,since it takes full advantage of the fact that anyfailure of the IRt/c will result in a dramatic change insensitivity; and thus failure to respond to normalthermal processes will be easy to detect. Refer toTech Note #39 for further details.



IRt/c Self Test



IRt/c Tech N

otes

Selecting Hi E or Lo E Based on EmissivityTable

Tech Note

69

Note: Lower emissivity surfaces require more stableconditions than high emissivity surfaces for accuratetemperature control. These tables include approxi-mate values, which can vary significantly withsurface condition. For best results, install an IRt/cand test. Emissivity data from Heat, Mass, andMomentum Transfer by Rohsenow and Choi(Prentice-Hall, 1961).

Metals EmissivityRange

IRt/cSelection

Aluminum

highly polished plate, pure 0.04 - 0.06 Lo E

oxidized at 1110 F (600 C) 0.11 - 0.19 Lo E

commercial sheet 0.09 Lo E

Brass

highly polished plate, pure 0.1 Lo E

oxidized at 1110 F (600 C) 0.61 - 0.59 Lo E

Chromium, polished 0.08 - 0.36 Lo E

Copper

polished 0.05 Lo E

heated at 1110 F (600 C) 0.57 Lo E

Gold, pure, highly polished 0.02 - 0.03 Lo E

Iron and steel (excluding stainless)

iron, polished 0.14 - 0.38 Lo E

cast iron, polished 0.21 Lo E

cast iron, oxidized at 1100 F (600 C) 0.64 - 0.78 Lo E

wrought iron, polished 0.28 Lo E

wrought iron, dull oxidized 0.94 Hi E

iron plate, rusted 0.69 Lo E

steel, polished 0.07 Lo E

steel, oxidized at 1110 F (600 C) 0.79 Lo E

rolled sheet steel 0.66 Lo E

steel plate, rough 0.94 - 0.97 Hi E

Lead, gray oxidized 0.28 Lo E

Mercury 0.09 - 0.12 Lo E

Molybdenum filament 0.10 - 0.20 Lo E

Nickel

polished 0.07 Lo E

plate, oxidized at 1110 F (600 F) 0.37 - 0.48 Lo E

Platinum

polished plate, pure 0.05 - 0.10 Lo E

wire 0.07 - 0.18 Lo E

Silver, pure, polished 0.02 - 0.03 Lo E

Stainless steel

polished 0.07 Lo E

type 310, oxidized from furnaceservice

0.90 - 0.97 Hi E

Tin, bright 0.06 Lo E

Tungsten filament, aged 0.03 - 0.35 Lo E

Zinc

commercial pure, polished 0.05 Lo E

galvanized sheet 0.21 Lo E

Nonmetals EmissivityRange

IRt/cSelection

Asbestos

Brick

0.93 - 0.94 Hi E

red, rough 0.93 Hi E

fire clay 0.75 Hi E

Carbon

filament 0.53 Hi E

lampblack, rough deposit 0.78 - 0.84 Hi E

Glass (Pyrex, lead, soda) 0.85 - 0.95 Hi E

Marble, light gray, polished 0.93 Hi E

Paints, lacquers, and varnishes

white enamel 0.91 Hi E

flat black lacquer 0.96 - 0.98 Hi E

aluminum paints 0.27 - 0.67 Lo E

oil paints, 16 colors 0.92 - 0.96 Hi E

Porcelain, glazed 0.92 Hi E

Quartz, opaque 0.68 - 0.92 Hi E

Water 0.95 - 0.96 Hi E

Wood, oak, planed 0.90 Hi E


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IRt/c Tech N

otes

Calibrating for Wide Linear Range with Adjust-able Models to Standard Thermocouple Inputs

Tech Note

70

All IRt/c models with the “A” designator (example:IRt/c.10A-K-Lo E) are equipped with a calibrationadjustment feature that makes it possible to preciselycalibrate the IRt/c to the temperature control require-ments. However, for installations in which monitoring oftemperature rather than control is desired, a wide linearrange is convenient. Accordingly, the proceduredescribed below can be used to produce a very widelinear range when using controllers, meters, PLCs,transmitters, etc. for temperature monitoring. The onlyrequirement is that an OFFSET, ZERO, LO CAL, orequivalent adjustment be available to offset thereading.

The method involves simply “rotating” the output curveof the IRt/c to better fit the linear thermocouple require-ment over a wider temperature range, as shown in thegraph. The steps are as follows:

1. Set the readout device to the offset valueshown in Table I.

2. Adjust the calibration screw on the IRt/c to thecorrect target temperature.

3. Calibration complete.

Example: Apply a Lo E model to monitor steel at 1800°F (980°C). Cover the IRt/c with aluminum foil such that itcannot see the target, then set the readout device offset so that the display reads approximately 75% of targettemperature: .75 x 1800 = 1350°F (.75 x 980 = 735°C). Remove foil, point IRt/c at intended target, and adjust thecalibration screw on the back of the IRt/c until the readout display reads the correct temperature, or within a fewpercent of the correct temperature. Fine tune the reading at the readout device as required. The calibration iscomplete, and the linear range over which the reading will be within 2% of actual is approximately 1800°F ±250°F(980°C ±140°C).

mV

mV

Temperature

Signal

Signal

Thermocouple

IRt/c

After

Before

Offset

Linear Range

Linear Range

Models: IRt/c.xxxA(Applies to allAdjustable Models)

Target Temperature°F (°C)

Optimum Offset(% of Target

Temperature)

Approximate 2% LinearRange (from Target

Temperature), °F (°C)

Lo E 800 (425) ~ 75% ± 100 (60)

1000 (540) ~ 75% ± 150 (80)

1600 (870) ~ 75% ± 200 (110)

2000 (1100) ~ 75% ± 300 (170)

2800 (1540) ~ 75% ± 400 (220)

3600 (2000) ~ 75% ± 400 (220)

Hi E 200 (90) ~ 60% ± 25 (15)

500 (260) ~ 60% ± 50 (30)

1000 (540) ~ 60% ± 200 (110)

1500 (820) ~ 60% ± 500 (280)

2100 (1150) ~ 60% ± 600 (330)

3000 (1650) ~ 50% ± 800 (440)



IRt/c Tech N

otes

Printing Press Applications

IRt/c infrared thermocouples are revolutionizing theprinting industry because their small size allowsthem to be mounted in the tight spaces typical ofboth web and sheet fed presses, and their low costallows economical installation and control on eventhe smallest of presses. Additionally, since manypresses are already equipped with thermocouplecontrollers and PLC thermocouple inputs, the IRt/cis a simple installation.

Applications include not only printing onto paper, butalso cloth, plastic, and any other printing webapplication.

Location 1: INK ROLLERS, PLA TENS

CONVENTIONAL PRESSES (water/ink)

On conventional presses (water/ink processes), thequality of the process is very dependent on thedifference in surface tension between water and ink,and this surface tension is highly temperaturesensitive. When presses operate, heat is generateddue to friction in the pressing area. Heat build-upcan significantly alter the surface tension of thewater/ink resulting in a deterioration in print quality.

IRt/c sensors easily monitor any roll surface tem-peratures within presses. Connected to a displaywith alarm signal, they can alert the operator ofdeteriorating temperature conditions before poorquality impressions are made. Connected to atemperature controller, PLC or computer, the IRt/cquickly signals an installed press temperaturecontrol system to provide cooling to the press area,or signal cooling systems to provide cooling to theink and/or water supplies to maintain proper surfacetension.

Temperature is also important when there is risk ofthin wall cylindrical platen(s) becoming loose orsloppy due tothermal expansion(or contraction). Onlarge diametermetal cylinders, asmall temperaturechange can resultin a significantchange in thecircumference ofthe roll, and thusaffect the proper“fit.” By measuring

Tech Note

71the surface temperature of the roll, the proper fit ofthe plate can be maintained by either (1) cooling thearea or (2) slowing down the press so friction heatdecreases to a low enough level to maintain printquality.

WATERLESS INK PRESSES and CONVERSIONS

“Waterless” ink technology involves the use ofspecial inks to eliminate the need for the water/inkcombination. This technology has significant costand performance advantages for the printer inelimination of waste treatment, and higher qualityproduct. The waterless ink technology can beapplied to virtually all types (web and sheet fed) andsizes of presses from large multi-color pressesdown to the small presses.

Conventional presses can be converted to usethese inks by providing a method to control thesurface temperature of the rolls where the ink isapplied to the platens. This is typically done by usinghollow rolls and supplying chilled water through therolls to keep the surface at a desired temperature.The IRt/c is a key component of the packagerequired to convert a press, since waterless inks arevery temperature sensitive and must be applied withstrict ink and surface temperature control.

The surface temperatures are easily monitored byan IRt/c. The output signal is sent to a discretetemperature controller, PLC, or custom computercontrol system to regulate the refrigerated circula-tors providing cooling water.

The IRt/c sensing system is precise enough to alsoallow manipulation of color characteristics forwaterless printing. For example, running a particularwaterless ink at different temperature extremesallows for choosing between brilliant or softer colors.

Press locations for IRt/c: 1) Ink Rollers,

Platens; 2) Drying/Curing; 3) Chill Rollers;

4) Bindery.


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IRt/c Tech N

otes

OEM Low Cost Interface

Location 2: DRYING/CURING

After ink is applied to the paper (or cloth, plastic,etc.) in the printing area, the web (or sheet) typicallytravels through a drying/curing process. IRt/csensors are used where they (1) “look” directly at theweb or sheet while it is inside the dryer or (2) at theweb just as it exits the dryer. Either method can beused to control drying temperature or UV curing.

For web presses, a much more accurate way is alsopossible. By using multiple IRt/c sensors along theweb while in the dryer, the actual “Dry-Out” point canbe located and controlled within the dryer. See TechNote #67.

Location 3: CHILL ROLLERS

For web offset printing, as the web leaves the dryer,it runs through a chill roller(s) to cool the web so thatthe paper (cloth, plastic, etc.) can be cut andstacked, or rolled, without the material stickingtogether.

By using IRt/c sensors to measure the surfacetemperature of the web at the point where it is beingchilled, the IRt/c signal can control the amount of

Designing the advantages of infrared temperaturesensing into your OEM equipment is now easier andmuch, much lower cost than it has ever been. TheIRt/c product line can be conveniently interfaced withmany standard thermocouple devices at the compo-nent level for custom board design. For example,Analog Devices, Inc. manufactures numerous low-cost thermocouple input components that work wellwith the IRt/c, such as the following two models.

Model AD1B60 Intelligent Digitizing Signal Conditionerfor the IRt/c

• Complete IRt/c sensor-to-digital signal condi-tioning and data conversion

• Directly connect up to 4 IRt/c’s per chip

• Cold junction compensation built in

Tech Note

72

• Software switchable open thermocoupledetection

• Allows IRt/c linearization over completetemperature sensing range

• Digital output

• Under $50 in 100 piece quantities

Small size fits into tight press area. The model

IRt/c.3SV is recommended due to its convenient side

view and extraordinary ability to keep itself clean in the

harshest ink spray environments.

chilling. This control will eliminate “over chilling”(condensation problems due to high ambienthumidity common in press rooms) and“underchilling” problems, automatically.

Location 4: BINDERY

Hot melt glue guns and applicators periodically “plugup” or run out of glue. Properly used IRt/c sensors oran Exergen AAM system can instantly alert machineoperators prior to products being glued improperly.See Tech Note #18 and/or the section on theExergen AAM Series (Applied Adhesive Monitors) inThe IRt/c Book.

IRt/c.3SV

Chill Rolls

Drying/CuringPress Area

Web Offset



IRt/c Tech N

otes

Flame Detection

Model AD594 (type J), AD595 (type K) IRt/c Amplifier withCJC

• Direct connection with IRt/c sensors

• Built-in cold junction compensation

• 10 mV/deg C output (0 to 10 V output)

• Under $7 per unit in 100 piece quantities(AD594AQ)

For more information about component level IRt/cdesign, or assistance in board level design forinterface with the IRt/c product line, please contactExergen directly.

Contact Analog Devices directly for information onthese and other models: Analog Devices, Inc., OneTechnology Way, PO Box 9106, Norwood, MA02062 (Phone: 800-262-5643, 617-329-4700)

Many industrial processes involve highly flammable materials and area constant potential hazard. As a result, for safety and loss prevention,flame detection devices arespecified to alert or shut downthe process in the event of a fire.The IRt/c, alone or in conjunctionwith other devices can provide agood solution. Since the IRt/c isintrinsically safe, it can bemounted in the hazardous areawhen used with the appropriatebarrier (see Tech Note No. 10),thus making it suitable forlocations not possible with otherflame detection devices.

The recommended model is theIRt/c.10A-K-LoE. With spectralsensitivity of 0.1 to 5m, thismodel will measure the shortwave radiation created by aflame, while filtering out thechanges in ambient targettemperature.

It is strongly recommended that the system be tested for the desiredresponse and control set-up. For example, the ability of the system todetect a plumber’s propane torch flame at 10 ft (3 m) can be tested,resulting in an indicated temperature rise of the order of 50°F (30°C).The monitor/controller can be set appropriately, and all flames that arelarger or more luminous than the torch will alarm. Customary testing,redundancy, etc. should be observed, as required for the application.

Tech Note

73

IRt/c.10A-K-LoE

Plumber’s Torch Test

Thermocouple to copperconnections at localambient temperature.

Twisted shieldedpair of copper leads.

If thermocouple controller used,keep in a stable environment. Ifnon-thermocouple (millivoltinput), environment has no effect.

Averages the signalin a one ft (.3 m)

diameter target at 10ft (3 m) distance.


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Calibration T esting ProceduresTech Note

74ing the signal. If it was already clean, additionalcleaning doesn’t let any more light through, andthe signal remains the same.

• If the durable IRt/c hermetic seal somehow fails,the Xenon gas will immediately escape. For evena small leak, the Xenon will escape quickly, withinseconds. It is a “fail-safe” design. The Xenon gaswill not leak gradually. If this occurs, the mVoutput sensitivity will immediately drop to approxi-mately 50% or less of normal signal. For example,if a type K-180F/90C sensor looks at a highemissivity 212°F (100°C) surface and readscorrectly on a thermocouple meter, or gives you3.3 mV on a DVM, then the sensor is withinspecifications. If the signal is only approximately1.7 mV, or reads in the neighborhood of 140°F(60°C) with a thermocouple meter (and the lens isclean), the fail-safe gas seal has been compro-mised.

The fail-safe feature is quite important, since abreach of the sensor gas seal would permitcontaminants to enter the sensitive detectionsystem and cause unpredictable drift.

Conducting Pass/F ail Testing

For your convenience, 212°F (100°C) is recom-mended as a test target temperature, even though itmight be outside the 2% linear range of the IRt/cbeing tested, since the strict repeatability of the IRt/cpermits it to be tested at any temperature within itsspecified range. A digital volt meter (DVM) with atleast 0.1 mV resolution is recommended instead of athermocouple readout, since the DVM will be faster,and will not generate a leakage current that cancause readings to vary from sensor to sensor due toresistance variations. An electronic ice pointreference is desirable, but not necessary for pass/fail testing.

Equipment

Best: Accurate Blackbody at 212°F (100°C).

Good Alternative: Pot of boiling water.

Procedure

Make sure the sensor window is clean. If it is not,then clean with a mild solvent such as alcohol andwipe dry. Clip the DVM test leads to the IRt/c andpoint at the target, bringing the IRt/c as close aspossible to be sure that the IRt/c sees only thetarget, taking care that the clip lead connections (theeffective cold junctions) remain at room tempera-

For many OEM and general temperature controlapplications it is sometimes desirable to testsensors before being placed into service, or toconduct routine checking while they are in service.Accordingly, recommended procedures are pre-sented to allow easy checking with commonlyavailable equipment. However, prior to testing, it isimportant to understand what indications an actualIRt/c failure might cause.

Factory Calibration

The pre-calibrated IRt/c sensors (models without the“A” suffix that indicates user adjustability) arecalibrated under conditions that optimize perfor-mance in actual use: target emissivity = 0.9 (a goodgeneral value for non-metals), and ambient tem-perature elevated to approximately 1/4 of theelevation of target temperature above room tem-perature (accurately simulates the effect of reflectedenergy). Since this type of test would requirespecialized devices, the procedures outlined havetest standards that are slightly different, since theyuse blackbodies, or test surfaces/ambients whoseproperties vary to some extent.

What to Look For When Testing

Open Circuit: An open circuit (resistance > 15 KΩ)indicates a broken wire, and open circuit detectionsystems will perform normally to detect it.

No Response to Thermal Radiation: Sensor readsambient temperature accurately, but does notrespond when pointed at a hot target. This fault issimilar to a short circuit with an ordinary thermo-couple, in that the circuit is complete, but is measur-ing the ambient temperature at the short, and not atthe measuring junction. For the IRt/c, this fault is thesame as if the sensor were covered with foil, thusblinding it.

Sensor Reads Low: There are only two ways anIRt/c can shift after factory calibration: the lensbecomes dirty; or the sensor loses its hermeticallysealed Xenon gas.

• If the lens becomes dirty, the signal loss is directlyproportional to the amount of dirt on the lens.Infrared energy is a form of light and therefore thesituation is similar to ordinary window glassbecoming dirty and blocking out sunshine. Ifconsiderably dirty before cleaning, the window willlet more light through after cleaning, thus increas-



IRt/c Tech N

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Checking Calibration of IRt/c or D-Series withBoiling W ater

ture. Immediately read the DVM for the correctreading. For details of test set-up for the boilingwater, see Tech Note No. 75.

In-Service Inspection Methods

Measure the surface temperature of the target (withthe target at normal operating temperature) with aMicroscanner D-Series infrared thermometer. Makenote of the temperature. Check the IRt/c displaydevice and make sure the reading reproduces theoriginal value that was obtained at installationcalibration. If the IRt/c reading is incorrect, clean the

lens with a cotton swab and alcohol (or similarcleaner) and recheck the display. If the reading issignificantly lower, the fail-safe Xenon charge hasescaped, indicating that the sensor should bereplaced.

Calibration Values

For specifications for the mV signals that should beobtained for the test conditions obtained above, forany given model IRt/c, please fill in the data below,and fax to Exergen. The specifications will be returnfaxed to you.

Name

Company

Phone Fax

IRt/c Model

Target Material and Temperature

continued...

Tech Note

75

Exergen’s Microscanner D-Series are designed ashighly accurate and reliable temperature referencesas well as fast easy-to-use infrared scanners. Sinceall components making up a D-Series are drift-freethere is never a requirement to calibrate the instru-ment once it leaves the factory, and no calibrationmeans is provided on the instrument (except certainhigh temperature models). Accordingly, if the D-Series calibration has shifted from its factory setting,it requires repair since a component has failed.Similarly, non-adjustable IRt/c models are factorycalibrated for life, and if they do not reproduce theircalibration, they should be considered failed.

Unless you have technical experience with andhave a laboratory infrared “blackbody,” this calibra-tion checking technique is recommended by the

factory. Boiling water is a physical constant, easilyused, and requires no technical set-up of elaborateequipment or checking of traceable standards.

Boiling Point of Water

The open boiling point of (reasonably pure) water isaffected by only one factor: barometric pressure.The standard 212°F (100°C) boiling point is for abarometric pressure of 30.00 inches of Hg (mer-cury), or in metric terms, 1 Bar (1000 millibars). Thisis “normal” at sea level. Barometric pressure can beaffected by elevation above sea level, and byweather conditions.

Elevation Correction: The boiling point of water islowered by approximately 2°F (1°C) for every 1000 ft(300 m) above sea level with no unusual weather


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IRt/c Tech N

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4. Bring the water to a RAPID boil. Tilt the coverSLIGHTLY so that the water does not boil over.The condensing steam on the inside of the potalong with the rapidly boiling water will force theoutside surfaces of the pot to be within a fractionof a degree of the temperature of the boilingwater. (The temperature drop through the wallthickness of the average pot for boiling water isvery small and can be ignored.)

5. Briefly touch the nosepiece flat onto the blackmark and note the temperature reading. For anIRt/c, bring the sensor as close as possiblewithout touching.

The reading should be within ±2% of the actualboiling point (for example ±2°C for 100°C boilingpoint). If the reading is not within these limits, theinstrument has a failed component and should bereturned to Exergen for repair. Please call for anRMA number prior to shipment. For the IRt/c refer toTech Note No. 73 for specifications.

conditions. If your weather is “normal” and you arenot using the barometric pressure method, you cansimply use the following corrections.

Weather Conditions: If you use this method, you donot need to put in a correction for elevation abovesea level. It will be automatic by using the currentbarometric pressure dominating your area. Baromet-ric pressure can be much lower during especiallystormy conditions (low pressure areas), and muchhigher during extremely cool and dry conditions(high pressure areas). Consult the weather reportson TV, in your local newspaper, or call a weatherservice office for current barometric conditions inyour area. Barometric pressure correction factors:

• 2°F / inch Hg (1°C / 30 millibars) change from 30.00in. Hg (1 Bar)

• Add to the boiling temperature for higher thannormal pressure.

• Subtract for lower than normal pressures.

Checking Calibration

Required Equipment:

• Metal pot with cover, minimum 4" (10 cm) tall.

• Solid paint marker or thin opaque tape.

1. Use a metal pot, with cover, for boiling water.

2. Fill the pot at least 1/2 fill with water.

3. Use the solid paint marker supplied with your D-Series, or a piece of opaque (non-see through)tape, or a thin electrical tape, to put a measuringspot at least 1in. (25 mm) in diameter on theoutside surface of the pot. Make sure themeasuring spot is at, or slightly below, the waterlevel.

Note: Always clean the sensor lens prior

to calibration testing. A cotton swab with

a mild cleaner such as alcohol works well.

100

D-Series Checking

IRt/c Checking

Elevation Boiling Temperature

Sea level 212°F 100°C

1000 ft (300 meters) 210 99

2000 ft (600m) 208 98

3000 ft (900 m) 206 97

4000 ft (1200 m) 204 96

5000 ft (1500 m) 202 95



IRt/c Tech N

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Increasing T emperature Range, ImprovingAdjustment Sensitivity, and Reducing theMinimum Spot Size with the Aperture Kit

Tech Note

76

For all IRt/c adjustable models an Aperture Kit is provided to offer theability to extend the target temperature range, improve the adjustmentsensitivity of the adjustment potentiometer, and reduce the minimumspot size to as small as 1/4 in. (6 mm).

The kit consists of one 1/2 in. (13 mm) and one 1/4 in. (6 mm) stainlesssteel apertures and two retaining rings. The apertures and retainersare installed as shown, taking care that the retainers sit and lockbetween the internal threads. The precise axial location is not critical.Install only one aperture, based on the requirements of your applica-tion.

The function of the aperture is to reduce the quantity of radiated energyentering the IRt/c optical system, thus increasing the rated maximumtarget temperature before burn-out. In addition, since less signal isproduced at a given temperature, the adjustment will be less “tweaky”when calibrating the IRt/c installation. The table below lists the range oftemperatures for each model recommended with and without theapertures. These recommendations are approximate, since the actualsignal level will depend on the actual target characteristics (emissivity,etc.). If there is insufficient adjustment range available with the smallaperture installed, simply replace it with the large one, or remove it. Ifthe adjustment is too sensitive, install an aperture. Use the table belowto set up your installation initially, to make sure that the IRt/c is notdamaged by excessive radiation, then adjust up or down as required tomeet your calibration requirements. The ranges below assume thatyou are using the technique described in Tech Note #70 or an equiva-lent calibration method.

Model No Aperture 1/2" (13mm) Aperture 1/4" (6mm) Aperture

IRt/c.10A- ** - HiEIRt/c.xxxACF- ** - HiEIRt/c.xxxAMF - ** -HiE

to 700°Fto 370°C

500 to 1500°F260 to 820°C

1300 to 2500°F700 to 1370°C

IRt/c.10A- ** - LoEIRt/c.xxxACF- ** - LoEIRt/c.xxxAMF - ** -LoE

to 1400°Fto 760°C

1200 to 1800°F650 to 980°C

1600 to 2500°F870 to 1370°C

IRt/c.20A- ** - HiEIRt/c.xxxALF - ** -HiE

to 1200°Fto 650°C

1000 to 2500°F540 to 1370°C

2300 to 3000°F1260 to 1650°C

IRt/c.20A- ** -LoEIRt/c.xxxALF - ** -LoE

to 1800°Fto 980°C

1000 to 2500°F540 to 1100°C

2500 to 3500°F1370 to 1930°C

IRt/c.100A- RS -HiEIRt/c.xxxAXLF - RS -HiE

to 2500°Fto 1370°C

2000 to 4000°F1100 to 2200°C

3500 to 5000°F1930 to 2760°C

IRt/c.100A- RS -LoEIRt/c.xxxAXLF - RS -LoE

to 3500°Fto 1930°C

2500 to 4500°F1930 to 2500°C

4000 to 5000°F2200 to 2760°C


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IRt/c Tech N

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IRt/c Tested for Vacuum and MicrowaveCompatibility

IRt/c Tested at 5000 psig (340 bar) Pressure

For some types of processes, it is necessary tomonitor temperatures of materials subjected to highgas pressures. Conventional contact devices aredifficult to employ under these conditions andconventional IR devices are unsuitable becausetheir optical and electronic components are unableto withstand high pressures.

With its elegant simplicity and solid construction, theIRt/c provides a solution. It has been tested atpressures up to 5000 psig (340 bar). A simple ferruletype tubing fitting may be used to provide a pres-sure-tight seal around the IRt/c housing. If using anIRt/c model with a lensed optical system (IRt/c.5;IRt/c.10; etc.), pierce the lens at its edge with aneedle to provide pressure equalization.

Tech Note

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Tech Note

78

Tests for compatibility performed by customerscontribute greatly to our understanding of howIRt/c’s perform in some of the unusual environmentswhere non-contact temperature measurements arerequired. Exergen has a policy of providing sensorsfree of charge to any laboratory for test purposes, inreturn for a copy of test results. This series of testswas performed by a customer who required theperformance, and had the facility to test the IRt/c.The test was conducted in a 4 ft. by 4 ft. (1.2 m by1.2 m) chamber in the following sequence:

First Test

1. Vacuum exposure (15 minutes at 40 Torr)

2. Microwave Exposure (5 minutes, 3 KW at 2450MHz)

3. Chamber load (15 pounds H2O)

Second Test

1. Vacuum exposure (10 minutes)

2. Microwave Exposure (30 seconds, 3 KW at 2450MHz)

3. Microwave Exposure (10 seconds, 3 KW at 2450MHz)

4. Chamber load (1 pint H2O)

The IRt/c showed no ill effects and operatedflawlessly when checked after the test sequence.

Ferrule typetube fitting

IRt/c(can also beplaced entirelyinside chamber)

5000 psig(340 bar)Chamber



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Unique “Slot Spot” IRt/c’s Measure SmallRectangular Spots

IRt/c’s Withstand 1000G Shock

With simple “O-ring” mechanical supports, IRt/c’scan withstand up to 1000 g shock without damage,and without shift in calibration. Such robustnessmakes them well suited to heavy duty applicationswhere high levels of shock and vibration are com-mon.

More modest forces of 10 g can be withstood on acontinuous basis, but fatigue of the cable can be aproblem. Mechanical support, coiling, or otherappropriate cable management is recommended.

Tech Note

79

IRt/c.2/15ACF-HiE for Non-Metal Targ ets, 0 to 2500 °F(-18 to 1370°C)

IRt/c.2/15ACF-LoE for Metal Targ ets, 500 to 2500 °F(260 to 1370°C)

Specifically designed for measuring temperatures ofvery small objects, the unique Slot Spot IRt/c makesit possible to monitor and control such difficulttargets as small extrusions, yarn, thread, wire, glassfiber, and others.

To use, followall of thestandard set-up and calibra-tion instruc-tions suppliedfor all of theadjustableIRt/c models.Use the linesscribed on the

back of the sensor to align the field-of-view on thetarget. The alignment can be fine-tuned by movingthe sensor (closer, farther, rotate slightly) until amaximum signal is obtained. For convenience a

Tech Note

80

handheld t/c meter or millivolt meter can be used.The sensor is positioned optimally when the maxi-mum signal is obtained on the meter.

The Aperture Kit provided with the sensor may beused to extend the temperature range, or improvethe resolution of adjustment. The wide linear rangecalibration technique specified in Tech Note 70 isrecommended. The table shows the temperaturelimits for each aperture.

For monitoring targets which are outside the focalplane, the field-of-view can be approximated byintersecting planes in both views with an included

continued...

1000 G’s

Elastomeric O-Ringscommonly used for seals

1.375 (34,9) DIA.

Range Adjustment Screw

AIR PURGE/COOL FITTING

2.02 (51,3)

1.7 (43)

AIR PURGE PATH

30o

0.6 (15)

0.1 (2)

DETAIL OF FOCAL PLANE

Lines Indicating Long Axis of View

Slot Spot IRt/c Monitors Extrusion Temperature

Aperture None 1/2” (13 mm) 1/4 “ (6 mm)

IRt/c.2/15ACF-HiE(Non-Metal Targets)

0 to 700°F(-18 to 370°C)

500 to 1500°F(260 to 820°C)

1300 to 2500°F(700 to 1370°C)

IRt/c.2/15ACF-LoE(Metal Targets)

500 to 1400°F(260 to 760°C)

1200 to 1800°F(650 to 980°C)

1600 to 2500°F(870 to 1370°C)


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Side View Model Designed for Monitoring WebProcesses

Tech Note

81

angle of approximately 30°. Thisresults in one-half of the distancefrom the focal plane being added toeach dimension. For example, if thetarget is 1” (25 mm) from the focalplane, 1/2” (13) would be added toboth dimensions, resulting in a spotsize 1.1” (28) long by 0.6” (15) wide.This feature makes the Slot Spotparticularly well suited to monitoringtemperature of a target through anyopening that is slot-shaped.

IRt/c.SV

In heating, drying, coating, cooling, or any otherthermal processing of webs of paper, plastic,metals, textiles, film, etc., often there is very littlespace available for a sensor to monitor webtemperature. In a space as small as 0.56 in.(14.2 mm) the IRt/c.SV Infrared Thermocouplecan be installed to monitor temperature of themoving web, and reliably control the process tomaximize quality and throughput of product.

The IRt/c.SV has all of the same specificationsas the standard IRt/c, including no powerrequirement, rugged stainless steel hermeticallysealed construction, intrinsically safe, fullelectrical shielding, ~0.1 second response time,and ability to operate uncooled in environmentsup to 212°F (100°C). It is available in J,K,T,Ethermocouple types, with linear range selectionsthe same as the standard IRt/c. The solid filled1/2 in. (12.7 mm) tubular housing can be heldsecurely with convenient tube fittings or stan-dard clamps to mount the sensor over the targetarea.

1

Increase inspot size is ~

1/2 of distancefrom focal

plane.

.56 (14,2)

2.27 (57,8)

~ 2

~ 1.500 (12.7) Dia.



IRt/c Tech N

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Grounding and Shielding for ElectrostaticProtection and Noise Suppression

Applies to All Models With Stainless SteelHousing

All IRt/c models with stainless steel housing are builtwith complete electrical shielding of both thehousing and cable, with the measuring elementselectrically isolated from the housing (as in aconventional ungrounded thermocouple). Byadhering to standard good practice in grounding andshielding techniques, IRt/c’s can provide outstand-ing performance in the most severe electricalenvironments commonly found in productionprocesses.

Q. When is attention to grounding and shieldingrequired?

A. If the IRt/c must operate in extreme environ-ments, employ long t/c cable runs, the measuringsystem is utilizing the high speed capability of theIRt/c, or if the process can generate high staticelectricity fields . For most installations, the built-innoise rejection characteristics of the IRt/c aresufficient to insure good performance, especially ifthe readout device is heavily filtered with a longinput time constant.

Q. Can I operate ungrounded?

A. Yes, but it is not recommended, especially inapplications where the process can generate highstatic electricity fields . Examples are web pro-cesses of all types, including printing, laminating,film drying, etc. Without either the housing or shieldgrounded to drain away the charge, a static chargecan build in the housing, which may eventuallydischarge through the IRt/c sensing elements, andcan cause damage to the sensor.

Q. How do I use the shield correctly?

A. The most important rule is to be sure the shield isgrounded at only one point, preferably at the signalinput ground. Keep in mind that the housing isconnected to the cable shield, and if the housing iselectrically in contact with machinery at the mount-ing point, that point will be a ground, and the shieldwire should not be connected at the instrument end.

For best possible performance, electrically isolatethe IRt/c at the mounting point and ground the shieldat a suitable ground on the readout instrument.

Q. Can I ground the shield to the negative (red)thermocouple lead instead of to a chassisground?

A. Yes, but test both alternatives in your applicationand use the one that gives the cleanest signal. Besure that the housing is electrically isolated, other-wise ground loop currents may cause errors.

Q. Should the extension cable be shielded?

A. As indicated above, if the installation requireshigh speed performance, twisted shielded extensioncable and connectors with ground straps should beused throughout. Aluminum foil is a suitable materialto complete a shield if their are gaps in the shieldcoverage.

Tech Note

82

No

Yes

Yes

Insulator

Yes

Insulator

No

Insulator


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IRt/c Tech N

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Side View Model Designed for MonitoringTemperature in Dirty or Vapor-FilledEnvironments

Tech Note

83

IRt/c.3SV

In heating, drying, coating, cooling, or any otherthermal processing of webs of paper, plastic,metals, textiles, film, etc., often there is very littlespace available for a sensor to monitor web tem-perature, and the harsh environment requires ahighly efficient air purge design to prevent fouling ofthe IR lens. In a space as small as 0.7 in. (18 mm),and in areas where ink or paint are being applied,the IRt/c.3SV Infrared Thermocouple can reliablecontrol the process to maximize quality and through-put of product.

The IRt/c.3SV has all of the same specifications asthe standard IRt/c, including no power requirement,rugged stainless steel hermetically sealed construc-tion, intrinsically safe, full electrical shielding, ~0.1second response time, and ability to operateuncooled in environments up to 212°F (100°C). It isavailable in J, K, T, E thermocouple types, withlinear range selections the same as the standardIRt/c. The solid filled 1/2 in. (12.7 mm) tubularhousing can be held securely with convenient tubefittings or standard clamps to mount the sensor overthe target area.

Ideal applications are offset printing, where thepresence of inks and physically tight locations makethe IRt/c.3SV the sensor of choice. Targets thatmust be monitored “upside down” are also idealapplications, since the narrow field of view and airpurge will prevent debris from blocking the lens.Only 5 psig (.3 bar), which consumes less than 1SCFM (.03 m3/min) is required for direct paint sprayenvironments.

3~ 2

~1

∅ .50 (12,7)

.68(17,3)

2.27 (57,7)

1.93 (49,1)

17° Approx.

Air Chamber Designrequires only 5 psig (.3bar) air pressure toprevent any directlysprayed paint or ink toadhere to the lens.

Upside-down Application

IRt/c.3SV

Printing Press Application



IRt/c Tech N

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IRt/c.01 Selection and Application Hints forOEMs

Using the IRt/c.01 in a High Electrical Noise Area

1.28 (32.5).06 (1.5)

.550 (14.0)

.935 (23.7)

1.02 (25.9)

.22 (5.6)

.25 (6.4)

O.D. 0.725 x 18 T.P.I. REF.(DIN PG 11 THREADS)

.497 (12.6)

LOCKNUT MATERIAL:MOLDED TYPE 6/6 NYLON.

BLACK ABSPLASTIC

Tech Note

84

Tech Note

85

Applies to All Models With ABS Plastic Housing

In applications where the low cost of the IRt/c.01 isimportant, and the other performance requirementsare met by the sensor, there are occasional con-cerns that electrical noise in the environment canaffect the readings. By employing one or morestandard techniques, IRt/c.01’s can provide out-standing performance in the most severe electricalenvironments commonly found in machinery.

1. Employ Filtering in the Readout Device.

If the readout device is heavily filtered with a longtime constant, there is normally never a problemwith noise. Response time constants in the range of1 second are in common use in temperaturecontrollers, and are usually more than enough toprevent any significant noise interference.

2. Add a Shield to either the IRt/c.01 or the EMI Source.

With aluminum foil, conduit, etc. the IRt/c.01 can be

shielded from the source of electromagnetic radia-tion directly. Be sure to properly ground the shield.Refer to Tech Note No. 82 for recommendations.

3. Consider Substituting a Fully-Shielded IRt/c Model.

If none of the above options provide the necessaryperformance, especially for high speed applications,select one of the fully shielded stainless steel IRt/cmodels for the application.

To assist you in specifying an IRt/c.01 model foryour application, the following sequence of steps isrecommended:

Locate the IRt/c.01 close enough to make themeasurement accurately.

Referring to the 1:1 field-of-view specification, besure that the target is large enough, or the sensorclose enough such that the target is larger than themeasuring spot. The IRt/c.01 can be physicallyclose as to nearly touch the target, and is limitedonly by physical space and local temperature.Normal mounting is with the supplied locknuts (2supplied), but alternative methods may be used tohold the cylindrical section or the flats, whichever ismore convenient in locating as close as practical.For hot targets in close proximity (~ 1 inch or 2,5 cm)permit adequate ventilation of the mounting to keepthe IRt/c.01 below its 160°F (70°C) rating. If thesensor face is likely to become dirty, mount in sucha fashion to permit occasional cleaning with a mildsolvent such as alcohol.


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IRt/c Tech N

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Inexpensive Infrared Scanning Arrays withIRt/c.01

request a copy of the IRt/c Signal Output Table foryour model, which has the data necessary tolinearize over the entire operating range of theIRt/c.01.

Calibrate just once!

Referring to Tech Note No. 1, best practice is toinstall the IRt/c.01, operate the process undernormal conditions, and calibrate the read-outsystem based on the reading from a reliable refer-ence (the D-Series is recommended). As long as thetarget materials are consistent, and there is noleakage current offset from the electronics, the initialcalibration will be valid for all subsequent installa-tions.

Investigate low cost thermocouple interfaces.

Prices per channel for computer A/D cards andPLC input cards for thermocouples have fallen towell under $100, and are available for as little as$30 for some systems. If the application is for highvolume OEM equipment, consider using a board-level chip such as the Analog Devices AD594/5,available at under $7 (see Tech Note No. 72).

For single channel use, consider IRt/c’s in parallel.

Wired in parallel to a single input channel, an arrayof IRt/c’s produces an output signal which indi-cates the average temperature of the targetsscanned. This attribute is particularly convenientfor monitoring and controlling wide webs, whichcannot easily be covered by a single sensor. Touse, simply wire all of the red (-) t/c leads to thenegative input terminal, and the other (+) leads tothe positive input.

Tech Note

86

Select the linear range required .

Referring to the Temperature Selection Guide,choose the model that has the center of its linearrange closest to the control point for your applica-tion, and select the thermocouple type you prefer.If your applicationincludes monitor-ing and controlover a range ofmore than ~100°F (~ 50°C),and your thermo-couple interfacehas computa-tional ability,

With the low cost of the IRt/c.01 and itsdirect compatibility with inexpensive,widely available thermocouple inputdevices, powerful infrared scanningarrays can now be considered forapplications in which thermal signaturesare desired for process monitoring andcontrol. Such applications include webdrying, printing, laminating, paint curing,and any other thermal processing ofmoving material. Multiple input monitor-ing and control devices include dataacquisition systems, personal computers, PLC’s,and custom OEM cards. By taking advantage ofthe low cost performance of the IRt/c.01 andstandard available components, infrared scanningarrays can be put to work controlling your processfor approximately $100 per channel.

Some tips on setting up an IRt/c infrared scanningarray:

Be sure to use identical models for each sensor in anarray .

This will keep all of your signals internally consis-tent within the software you use, and avoid anyinterpretation errors. Also, if you employ theavailable IRt/c Signal Output Tables, one table orcurve will apply to all the sensors in an array.IRt/c’s of the same model are interchangeable to< 1% of reading.

For web drying, printing, laminating, paint curing, etc.



IRt/c Tech N

otes

Two-Color Pyrometry with IRt/c’s Tech Note

87

IRt/c.L2 Method uses energy content of twowavebands to calculate temperature: a short waveband which is strongly sensitive to temperature andweakly to emissivity; and a long wave band stronglysensitive to emissivity and weakly to temperature.

An initial calibration has to be performed with bothdevices viewing the same known target tempera-ture. The value for εεεεε is immediately computed by theSLW equation, and the value for A by the SSW equa-tion. A variety of computational methods can beemployed to compute εεεεε and T continuously from thetwo equations in two unknowns, with the simplest

being a computation of differen-tials in signal relative to theinitial calibration. The onlyassumption required for themethod to work in its differentialform is that the ratio of emissivi-ties for the two wave bandsemployed remain constant, i.e.(εSW/εLW) = constant. For theexample and recommendedcombination of IRt/c.10A-LoE(short wave), and IRt/c.2-K-440F/220C (long wave) thesewavelength bands are 0.1 to 5

micron and 6.5 to 14 micron respectively. Note thatthe emissivity coefficient can include any effectthat is not wavelength dependent, such as inter-vening dust, partial obstruction, or target smallerthan the fields-of-view.

IRt/c.L2 Method uses energy content of two wavebands

to calculate temperature: a short wave band which is

strongly sensitive to temperature and weakly to

emissivity; and a long wave band strongly sensitive to

emissivity and weakly to temperature.

The IRt/c.L2 Method

short wave band

For many bare metal temperature monitoringapplications, emissivity variations are too extremefor even the IRt/c-LoE models to provide reliableinformation. A common problem is aluminum, sinceemissivity is low and variable due to alloying,surface oxidation, surface finish variations, etc.

The traditional non-contact infrared solution hasbeen two-color pyrometry, since this method yieldssignificant improvements over single wavelengthdevices by ratioing signals at two nearby wave-lengths, and thus deducing temperature from theratio. The major drawbacks of conventional two-color systems are size, complexity, and cost. TheIRt/c innovation, and theavailability of inexpensivecomputational power, havemade possible a simple, reliablesubstitute for conventional twocolor pyrometry at a smallfraction of the cost and smallfraction of the size.

The IRt/c.L2 method of two-color pyrometry incorporates thefollowing:

• A short wave (LoE) IRt/cmodel and long wave IRt/cmodel viewing the sametarget area.

• Two thermocouple input channels to a computeror PLC.

• Computational ability to solve two equations intwo unknowns on-line.

Depending on the models selected, the cost forsuch a system can be well under $1000.

The equations to be solved are as follows:

For the short wave (LoE) model:

SSW = A( εεεεε/.25)(1.771E-17 T6 - 6.584E-14 T5 +2.062E-10 T4 + 1.625E-07 T3 - 5.366E-05 T2 +

1.116E-02 T - 8.615E-01)

For the long wave model (example IRt/c.2-K-440F/220C):

SLW

= (εεεεε/.9)(-5.335E-16 T6 + 8.684E-13 T5 - 4.670E-10 T 4 + 4.446E-08 T3 + 8.892E-05 T 2 + 1.622E-02 T

+ 1.300E+00)

where SSW

and SLW

are signals produced in millivolts(referenced to 0°C cold junction compensation), εεεεε isemissivity, T is target temperature, and A is anarbitrary calibration constant that represents theposition of the adjustment screw for the adjustableLoE model.

long wave band

Conventional Two-Color Pyrometer

IRt/c Pair

Planck Function - Radiated Energy vs Wavelength

Wavelength

qλ


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IRt/c Tech N

otes

Measuring Tire Tread Internal Temperature

Internal Temperature= 160°F (71°C)

Surface Temperature= 140°F (60°C)

Ambient Temperature= 70°F (21°C)

Model IRt/c.5-HBT -J-80

By its very nature, infrared measures surfacetemperature, but most material properties of interestrelate to internal (bulk) temperatures. For manymaterials, such as metals, the gradient between thesurface andinternaltemperaturesis smallenough toignore. Forother materi-als, such asrubber prod-ucts, thegradient can bequite largewhen thematerial is exposed to an ambient temperature thatis much different from its bulk temperature. Thisproblem is particularly acute in the manufacture andtesting of tires, since surface temperature may notbe a reliable indication of internal tread temperature,which is the property of interest, due to the action ofrapid convection and radiation at the surface, andslow conduction internally.

The IRt/c Heat BalanceSeries Infrared Thermo-couples actually calculatethe internal temperature bysolving the equation thatdescribes the heat balancebetween internal, surface,and ambient temperatures,and produce an unpoweredthermocouple signal thatrepresents the internaltemperature!

This breakthrough methodwas first developed andpatented by ExergenCorporation for use in themedical field to solve theproblem of obtaining humancore body temperature non-invasively, and is in use in literally hundreds of

thousands of clinical infraredthermometers. The applicationto tire temperature measure-ment is the first industrialapplication of the method.

Mathematically, the IRt/c-HBemploys what is called theHeat Balance Equation, whichfollows from the basic heattransfer electrical analogcircuit shown:

The Heat Balance Equation is continuously solvedby the IRt/c, and produces a thermocouple millivoltsignal that represents Tc. For the IRt/c.5HBT-J-80,the signal is a type J, and the K is programmed tocalculate temperature approximately 1/4” (6 mm)deep.

All of the other outstanding characteristics of theIRt/c, including unpowered simplicity, ruggedhermetically sealed system, intrinsic safety, andcompatibility with standard thermocouple interfaceswith PLC’s, computers, controllers, etc., makes theHeat Balance Series an outstanding selection forthe measurement of tire temperature, and theimproved performance made possible by accuratemeasurements.

Set-up and Calibration

System set-up and calibration is the same as for allother IRt/c models except that the referencetemperature is obtained with a probe type unit to

Tech Note

88with the IRt/c-HB (Heat Balance)™ Series Infrared Thermocouple

Tc

Ts

Ta

T K T T T

RR

c s a s= − +

=

( )

where K 1

0

Conduction

Radiation

Convection

Ta

Ts

Tc

R0

R1

Heat transfer to or from thematerial.

Heat transfer model usingelectrical analogy.

Tc

Ts

Tc=Ts=Ta



IRt/c Tech N

otes

IRt/c Specifications: Real World PerformanceAccuracyThe table below summarizes some of the majordifferences between how IRt/c’s are designed andcalibrated, compared to conventional infrareddevices, with the objective of providing the bestpossible accuracy under actual real-world condi-tions.

Why the IRt/c is Different

The concept of a black-body is a highly useful andessential mathematical construction in the applica-tion of infrared radiation physics, and has had firmtheoretical support from the time of Max Plancknearly 100 years ago. However, in the real worldapplication of infrared methods for temperaturecontrol, IR devices do not measure black-bodies.

More realistically, real-world measurements areperformed on targets that approximate what istermed a gray-body, i.e. materials which have anemissivity less than 1. Gray-bodies also have thefurther characteristic that emissivity is constant at allwavelengths of interest. Then for gray bodies:

qgb = qbb εεεεε

at all wavelengths, where qgb and qbb are radiatedenergy from a gray-body and black-body respec-tively.

An important element which is missing whenworking with black-bodies, but present with gray-

Tech Note

89

continued...

• Measure internal temperature with insertion probe.

• Adjust readout device OFFSET, or ZERO untilIRt/c reading agrees with probe.

Calibration complete.

The new technology embodied in the IRt/c HeatBalance Series can be used in other applicationswhere internal bulk temperature is required.

penetrate to the depth of measurement. FollowingTech Note No. 1, the process is as follows:

• Install the IRt/c in the location it will be used.

• Wire IRt/c to readout device.

• Place tire to be measured in normal location. Tiretemperature must be significantly different fromambient for the calibration to be accurate.

Radiated Energy vs Wavelength

Wavelength

qλ

Black-body

Gray-body

AIR PURGE/COOL FITTINGAIR PURGE PATH

.500 DIA.(12.7)

.558 (14.17)

#10-32MOUNTINGHOLES

1.00 (25.4)DIA. BOLTCIRCLE

1.375(34.9) DIA.

5X1X

1.40(35.5) 2.85

(72.3)2.59

(65.8)

3.39(86.1)

SPOT SIZE IS .8" (20)DIA. AT FOCAL PLANE.SPOT SIZE INCREASESWITH APPROX. 11 DEGINCLUDED ANGLE AWAYFROM FOCAL PLANE.

11


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IRt/c Tech N

otes

bodies is reflectedradiation. For non-transparent materi-als, emissivity plusreflectivity alwaysequals one:

εεεεε + ρρρρρ = 1

Accordingly, for ablack-body εεεεε = 1,and therefore ρρρρρ = 0.But for a gray-body

εεεεε < 1 and therefore ρρρρρ > 0, and the reflected radiationdue to ambient temperature must be considered.Refer to Tech Note No. 64 for further details.

IRt/c’s are specifically designed to be accurate andreproducible under real world conditions of targetsthat approximate gray-bodies, with ambient tem-peratures that vary, thus with reflected radiation thatvaries. The performance specifications of the IRt/c,unlike conventional infrared devices, include gray-body effects.

Mathematically the signal output of an IRt/c is acomplex function of target temperature, ambienttemperature, target emissivity, reflected energy,thermocouple type, etc. To clarify the specificationswe can represent the change in signal with respectto a variable of interest, while holding all othervariables constant, as a partial derivative.

Ambient T emperature Coefficient Specification

The variation in output signal with ambient tempera-ture, which is the Ambient Temperature Coefficientspecification, can be represented as below:

where S is the output signal and Ta is the ambienttemperature. This equation describes the output ofthe IRt/c, including a gray-body assumption ofemissivity = 0.9, and that the sensor itself is at thesame temperature as the environment.

What this means in practice is that when an IRt/c isinstalled and calibrated in place (Tech Notes No. 1,64), the IRt/c body tends to change temperature withthe ambient background that the target sees, theninternally applies the correction required to reduceerrors. Without this feature this error could be manytimes higher, and cause unwanted shifts in processcontrol temperature.

For example, waterless printing processes requirethat the ink application roll to be temperaturecontrolled in order to maintain high quality. If thetemperature is tobe controlled at80°F (26.7°C), andthe press enclosurecan vary over therange 70 to 100°F(21.1 to 37.8°C)due to warm-up,weather, airventilation, etc.;then a conventionalIR device willproduce an error ofabout 3°F (1.7°C),while an IRt/c willproduce an error ofonly 0.2°F (0.1°C).Thus, the IRt/cprovides ten times more accurate control than theconventional device.

To estimate the improvement in control accuracyproduced by the IRt/c for a specific application, thefollowing approximation can be applied:

qa = ambient radiation = σ(T

a)4

qr = reflected radiation = ρq

a

qe = emitted radiation = εσ(T

s)4

Gray-body Equations

Real World – IRt/c Conventional IR

10 0004

S

S

TC

a

o∂∂∂∂

≤ . /

IR Temperature Control

Accuracy:

Conventional IR≈≈≈≈≈3°F (1.7°C)

IRt/c≈≈≈≈≈0.2°F (0.1°C)

Compensating for Emissivity Variations

A common assumption for conventional IR ther-mometry is that emissivity is constant with changesin target surface temperature. Real materials do nothave this characteristic. The average value for non-metals for which the change in emissivity withrespect to surface temperature has been reported, isapproximately - 2% per 100°F target temperaturechange (- 3% per 100°C).1

10

S

S

Ta

∂∂∂∂

=

≈

for laboratory

up to 10% or more

for real surfaces

1

S

S

Ta

∂∂

qr

qe qeq +rq =

qa

Temp

time

Ambient TIR Reading

Actual T

Temp

time

Ambient T IR Reading

Actual T Error( )( )( )

( ) ( )

Error with Conventio nal IR

Error with IR t c

≈ − −

≈ −

−

1

0 910

ε

ε

∆

∆

T T T

TT T

a s a

as a.



IRt/c Tech N

otes

Applying the partial derivative mathematical formula-tion, the emissivity variation is:

range, where the effect of emissivity change isaccounted for in the linearity specification, and theuser is confident that his process control will beaccurate. Note that testing an IRt/c with a blackbody will not give the same linear range as a real-body.

A second effect on linear range is the effect of targetsurface temperature on ambient temperature, andtherefore the reflected component of radiation to thesensor. As target temperature increases within aprocess, the increased radiation heat transfer to thesurroundings will cause the target ambient radiantbackground to also increase in temperature.

For example, a laminating process that has severaltemperature control settings that depend on thematerial and feed speeds, may operate with targettemperatures that are 100°F (56°C) different. As thematerial changes temperature, the backgroundradiation in the vicinity of the measurement will alsochange temperature, and influence the IR reading.

Accordingly, the variation in signal with targettemperature has the additional component asfollows:

continued...

Real World - IRt/c

Conventional IRReal World – IRt/c

Real World - IRt/c Conventional IR

Conventional IR misses this effect, and will causeprocess control errors.

The signal produced by the IR device is proportionalto the radiation emitted by the surface:

S=εεεεε qbb (conventional IR assumption)

then the change in signal with respect to targetsurface temperature may be presented as follows:

Note that the conventional IR device loses one termof the signal change with respect to surface tem-perature. When the IR signal is converted to atemperature indication, the signal in the conven-tional device is linearized, whereas in the IRt/c thesignal is unchanged.

Since real-world emissivity for most non-metalmaterials decreases with temperature, the constantemissivity assumption of conventional IR devicesproduces errors in readings that are not obvious tothe typical IR user and can be highly misleadingover a wide temperature range. The IRt/c, however,is specified for a useable specific temperature

For a typical case of e = 0.9,

the change in signal is ≈≈≈≈≈2.5%, which is accounted for

in the ambient compensation

system over the linear range.

The 2.5% error is

present, but not

accounted for in the

design or calibration,

thus resulting in

process control error.

Conventional IR

Comparison to Standard Thermocouples

Standard thermocouples are generally specified asadhering to ASTM and ANSI specifications, whichprescribe a basic accuracy of ±2.2°C, or 0.75% of

ε

Temperature

Slope≈ -0.03/100 °C

Actual emissivity

ε

Temperature

Slope = 0(constant emissivityassumption)

Error

1ε

∂ε∂Ts

≈ −

≈ −

0.02 / 100 F

0.03 / 100 C

o

o

10

ε∂ε∂Ts

=

S

Actual Surface Temperature

Actualemittedradiation

IRt/c SignalS

Actual Surface Temperature

Conventional IRconstant emissivity assumption

Actualemitted

radiation

Error

∂∂

∂∂ε

∂ε∂

∂∂

∂∂

∂ε∂

ε∂∂

ST

ST

Sq

qT

qT

qT

s s bb

bb

s

bbs

bb

s

= +

= +

∂∂

∂∂ε

∂ε∂

∂∂

∂∂

ε∂∂

ST

ST

Sq

qT

qT

s s bb

bb

s

bb

s

= +

= +0

( )

( )

( )

∂∂

∂∂

∂∂

∂∂∂∂

ε

∂∂

ε

∂∂

ε

ST

ST

TT

TT

c

ST

S

ST

S c

c

SST

s a

a

s

a

s

a

s

s

=

=

= −

= −

≈

= −

by test

1

1

0 25

10 25 1

.

.

∂∂TT

a

s

= 0

Ta

TT


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IRt/c Tech N

otes

reading, whichever is higher2 . Likewise, IRt/c’s arealso specified to be within the same ±2.2°C limits, orto the percentages stated in their specifications,whichever is higher.

However, it is important to note that when an IRt/c iscalibrated to installation, this error disappears.

Repeatability and Interchangeability

The cardinal requirement for the IRt/c, as in anymeasuring device, is to repeat its calibration. Therepeatability of IRt/c’s is specified at <0.1°C.

Interchangeability uncertainty from one device toanother is 2% maximum, since each individualdevice is built and tested to conform to standardswith a ±1% tolerance, so is therefore able to producea maximum of ±2% difference between any twodevices. Typical interchangeability uncertainty,determined by test, is described statistically withstandard deviation of approximately 0.5°C.

Summary

1. The IRt/c is a different type of device comparedto conventional IR, since it is carefully designedand built to produce real world accuracy fortemperature control, with some subtle featuresthat make a significant improvement overconventional IR.

2. In-place calibration is always recommended, asit always is with any IR device due to uncertain-ties in emissivities and ambient temperature.

3. For OEM applications, or multiple same-useapplications in a factory, once the initial systemhas been qualified and calibrated, IRt/c’s of thesame model can be substituted without thenecessity of recalibration.

4. An added benefit of the IRt/c is its specifieduseable linear range per model. (A user is notled into believing that his measurement is

accurate over a wide temperature range, acommon misunderstanding with conventionalIR. Thermal physics and scientific data demon-strate that trying to track real-world surfacetemperatures over a range greater than approxi-mately 100°F (56°C) involves accounting forincreasing errors that cannot be handled byconventional IR devices. This includes not onlypermanently mounted IR sensors, but portablehandheld IR devices, also.) There is oneexception to this rule, however, theMicroscanner D-Series portable IR scanners.(See Tech Note #91, #33) They have the largestuseable target temperature ranges with theleast amount of possible errors due to emissivityand ambient reflections. Use of theMicroscanner D-Series is recommended forcalibrating and checking IRt/c sensors intemperature ranges less than 1600°F (850°C).

5. An IRt/c’s full performance cannot be accuratelychecked with a black-body. Standard laboratoryblack-bodies can be used for pass-fail orreproducibility testing only. Contact Exergen foravailability of specialized test devices.

6. An IRt/c’s full performance cannot be accuratelychecked with a conventional handheld portableIR device, there are too many external sourcesof error. See Tech Note #91.

Notes

1. Thermal Radiative Transfer and Properties, MQBrewster ed., John Wiley & Sons, 1992.

2. ASTM Standard E230, ANSI MC96, Manual onthe use of Thermocouples in TemperatureMeasurement, Fourth ed., ASTM 1993.

TIR

Actual Temperature

IRt/c Signal onReal-body

± 1% Limit givesmaximum ± 2%

Interchangeabilityuncertainty.

TIR

Actual Temperature

ThermocoupleSignal

IRt/c Signal onReal-body

± 2.2°CThermocoupleLimits of Error



IRt/c Tech N

otes

IRt/c’s More Accurate than Conventional IR inReal World

A common misunderstanding amongst evenexperienced manufacturers and users of infraredtemperature measurement equipment is that theaccuracy of temperature measurement is solely aspecification of the infrared device. This statementis correct only in the laboratory under controlledconditions with blackbody(emissivity = 1.0, reflectivity = 0)targets. In the real world, designsand specifications that areapplicable in the laboratory canbe misleading and sometimesoutright incorrect. Following is asummary of the key points ofaccuracy in a comparisonbetween the IRt/c and conven-tional IR (detailed mathematicaldevelopment is presented inTech Note No.89).

1. Real-world materials have emissivity < 1,and therefore have reflectivity > 0, whichcauses errors from varying backgroundtemperatures.

Even non-metals, with emissivity approximately 0.9and reflectivity approximately 0.1, must reflect about10% of the energy incident from the backgroundambient. This reflected energy, unrelated to thetarget temperature, is nevertheless measured by theinfrared sensor, and therefore will introduce signifi-cant errors if the ambient temperature changes, as itdoes in the real world. Conventional IR devices,calibrated with blackbodies, usually ignore thiseffect, and thus are subject to the error. IRt/c’s arespecifically designed and tested to include acorrection for this effect and thus improves theirreal-world accuracy.

2. Real-world materials have emissivities thatchange significantly with temperature, whichcauses significant errors even with perfectcalibration and linearization.

Probably the most misleadingconcept in infrared thermo-metry is that emissivity isconstant with varying tem-perature. Real-world materialshave emissivity variations thatrange from an average of 2%

per 100°F (60°C) temperature change for non-metals, to 10% per 100°F (60°C) temperaturechange for some paints, and well over 100% per100°F (60°C) temperature change for some metals.1

Accordingly, accuracy of real-world temperaturemeasurements should be considered valid only for a

limited temperature range.Specifications of accuracy forconventional infrared devicesspecified over wide targettemperature ranges are largelymeaningless. (The sole exceptionis Exergen’s D-Series, due to itsAutomatic Emissivity Compensa-tion System.)

IRt/c’s are specifically designedand tested to maintain very highaccuracy over a limited tempera-ture range, and specifically not

specified to imply accuracy over a wide targettemperature range. For this reason IRt/c’s areoffered in a variety of temperature range selections,each of which is optimized for a specific limitedtemperature range, which correctly reflects the real-world material characteristics, and maximizes theaccuracy.

3. Real-world temperature control is mostaccurate if the IR sensor is designed, built,calibrated, and tested at factory conditionsthat are designed to reflect actual fieldconditions.

Conventional IR devices are designed, built, andtested to standards traditionally defined by black-bodies, which do not include the errors caused byreflected energy and emissivity variations of real-world materials. IRt/c’s are designed, built, andtested to standards that include elevated andvariable ambient background temperatures, andreal-world target materials that change emissivity

with temperature, thus max-imizing the accuracy of tem-perature measurement andcontrol.

1. Thermal Radiation HeatTransfer. R Siegel and JR Howell,ed., second edition, HemispherePublishing Corporation 1981.

Tech Note

90

Emissivity

Target Temperature

Non-metals

Metals

qa = ambient radiation = σ(T

a)4

qr = reflected radiation = (1-ε)q

a

qe = emitted radiation = εσ(T

s)4

qr

qe qeq +rq =

qa


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IRt/c Tech N

otes

Drying P aper Webs With Jets of Air Controlledby IRt/c’s

Disposable Window

A not uncommon problem in some industrialenvironments, such as foundries, is maintainingoptical cleanliness during washdown, or protectingthe lens from debris when air purge is impractical orinsufficient. In addition, sometimes a barrier isnecessary between the process to be monitoredand the IRt/c.

Windows made of common materials such as glass,etc. will significantly attenuate infrared radiationfrom targets below about 1000°F (540°C) and arenot generally suitable for low temperature service.However, windows made ofpolyethylene willtransmit very efficiently atall temperatures if they arethin enough. “Thin” meansgenerally less than about0.005 in. (0.1 mm).

An excellent material is acommonly available plasticwrap brand called GladCling Wrap®, which can

easily be wrapped around the IRt/c for cleanliness,or formed into a window. If the polyethylene is dirtyor damaged, it can easily be replaced. With maxi-mum temperature rating at about 212°F (100°C),this material can be used in many processes.

The transmission coefficient of such thin polyethyl-ene is in the neighborhood of 90%, and thereforeonly a small recalibration of the readout device maybe required. Other brands of plastic wrap are notrecommended, unless you can confirm that they aremade from polyethylene.

Tech Note

91

Tech Note

92

A basic problem in controlling moisture content ofpaper webs is non-uniformity of drying across theweb. Standard methods cannot address thisproblem because typically the entire web is mea-sured for moisture content, and the process isadjusted to insure that no part of the web has toomuch or too little moisture. Accordingly, the overallbasis weight and paper properties are not optimum,since there are significant non-uniformities. IRt/c’s,along with inexpensive PLC’s or other computingpower, makes it possible to eliminate these non-uniformities and maximize the value of the paper.

The method consists of spanning the web with aseries of simple modules consisting of an IRt/c anda controllable air jet configured to dry the stripscanned by the IRt/c. The IRt/c signal is the input toa temperature control system which controls the airjet based on local temperature and other process

parameters. By individually drying each strip to thesame standard, the web can maintain uniformity andtherefore high quality. Any IRt/c model with built-inair purge is suitable. Where mounting spacepermits, the IRt/c.5 sensor is the recommendedmodel.

IRt/c’s

Polyethylene wrap



IRt/c Tech N

otes

In-line Pre-Calibrated Transmitter for Easy,Reliable Installation

mitter should be located in a an environment nohigher than 158°F (70°C) in temperature.Additional t/c extension wire may be added asrequired. Use of twisted shielded t/c wire isrecommended (same as on the IRt/c andtransmitter), and maintain shield connections.

3. Check load on transmitter and power supplyvoltage for correct range (10 VDC minimum @10Ω; to 22 VDC minimum @ 1KΩ).

4. Set readout device (controller, computer, PLC,etc.) for 4 to 20 mA range to match the t/c.XMTRmodel range.

5. Perform final calibration of IRt/c installation inaccordance with IRt/c instructions, using offseton current loop readout device.

6. Installation complete.

Tech Note

93

∅ .50 (12,7)3.4 (86)

3 ft (1 m) 26 AWG strandedtwisted shielded pairthermocouple wire.

10 ft (3 m) 22 AWGstranded twisted pair wire.

IRt/c Side Loop Side

4 - 20 mA

12 - 36 VDC

1000 OhmMax Load

t/c connector

t/c.XMTR

Any Model IRt/c

Model t/c.XMTR- * - ** 4-20 mA Transmitter

Current loop transmitters for thermocouples havetraditionally been designed as “hockey pucks” inorder to fit thermowell heads, thus complicatinginstallation for applications not using athermowell, and requiring a housing for protec-tion. Additionally, they generally have to becalibrated to a specific range, usually with thermo-couple simulators or other such device, thusrequiring significant set up time and the possibility ofunauthorized recalibration.

The t/c.XMTR is designed to overcome both of thecostly inconveniences:

• In-line design is only slightly largerthan the cable and requires nomechanical support.

• Precalibrated for thermocouple typeand temperature range eliminatesall adjustments, requirements forsimulators, etc.

• Hermetically sealed stainless steel construction issuitable for the harshest service without anyadditional packaging.

The t/c.XMTR is specifically designed to interface toany model IRt/c (or any conventional thermocouple)by a simple thermocouple connector or splice. The2-wire current loop can be used in any conventionalcurrent loop circuit that is scaled for the temperaturerange of interest.

Model Selection

1. Select the correct IRt/c model for theapplication: target temperature, targetmaterial, field-of-view.

2. Select the t/c.XMTR model for the t/c typeand temperature range from the tablebelow. Example: t/c.XMTR-K150

Installation

1. Install IRt/c as normal.

2. Connect IRt/c output cable tothe thermocouple input side ofthe transmitter using standardt/c connector, splice, or otherstandard method of connectingthermocouple cables. Trans-

Model NumbersExample: t/c.XMTR-J-150

J150K150

J500K500

J1200K1200

K2000 S3000

Temperature at 4 mA 32°F

Temperature at 20 Ma 150°F(65°C)

500°F(260°C)

1000°F(540°C)

2000°F(1100°C)

3000°F(1650°C)


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IRt/c Tech N

otes

Easy Upgrade of Existing Temperature ControlSystems with IRt/c and t/c.XMTR

Tech Note

94

• Replace conventional infrared sensing systemsfor superior accuracy, reliability, and low cost.

• Replace contact temperature sensors for non-contact measurement of actual product tempera-ture instead of oven temperature.

• Retrofit using existing PLC analog inputs (4-20mA, 0-5 V, 0-10 V).

The t/c.XMTR is specifically designed to makereplacement or retrofit simple and inexpensive:

• In-line t/c.XMTR design is only slightly larger thanthe cable and requires no mechanical support.

• Precalibrated for thermocouple type and tempera-ture range eliminates all adjustments, require-ments for simulators, etc.

*For OEM’s, IRt/c’s and t/c.XMTR can be factorysupplied wired together.

• Hermetically sealed stainless steel construction issuitable for the harshest service without anyadditional packaging.

• Use any existing wiring, including thermocouple,RTD, etc.

The t/c.XMTR is specifically designed to interface toany model IRt/c (or any conventional thermocouple)by a simple thermocouple connector or splice. The 2-wire current loop can be used in any conventionalcurrent loop, 0-5V, or 0-10V circuit that is scaled forthe temperature range of interest.

t/c connector or splice*

t/c.XMTR

Any Model IRt/c

4 - 20 mA

12 - 36 VDC

Load

Any Existing Wire Pair



IRt/c Tech N

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Add “PC” Suffix to Any Type K Adjustable Model

Non-adjustable IRt/c’s are particularly attractive inapplications where reproducibility and interchange-ability are important, or where tamperproof sensorsare desired. For low temperature applications, themany non-adjustable IRt/c models available providethe user with a wide selection to fit such needs.However, many higher temperature applications,with both high and low emissivity targets alsorequire precalibrated non-adjustment features. Inaddition, for systems in which linearization softwareis employed in the readout device, the installationcalibration can be performed more conveniently insoftware rather than making an adjustment on theIRt/c.

Tech Note

95

To take advantage of these models, the following isrequired:

1. Thermocouple input to programmable readoutdevice (or 4-20 mA if transmitter is employed).

2. Signal output lookup table for either HiE - PC orLoE - PC IRt/c models.

The following models are available with the PCcalibration designation, with the same signal outputat all temperatures. The maximum recommendedtarget temperature for all models is 2000°F(1100°C). The minimum recommended targettemperature depends on the precision of thethermocouple input amplification system, but areasonable lower limit is 700°F (370°C) for the HiEand 1000°F (540°C) for the LoE. For other specifica-tions, refer to the Model Selection Chart or theindividual model specification sheet.

Precalibrated Hi E and Lo E Models for OEMApplications

IRt/c.10A-K-HiE-PCIRt/c.10A-K-LoE-PC

IRt/c.20A-K-HiE-PCIRt/c.20A-K-LoE-PC

IRt/c.2/15ACF-K-HiE-PCIRt/c.2/15ACF-K-LoE-PCIRt/c.4ACF-K-HiE-PCIRt/c.4ACF-K-LoE-PCIRt/c.8ACF-K-LoE-PC

IRt/c.2/18AMF-K-HiE-PCIRt/c.2/18AMF-K-LoE-PCIRt/c.6AMF-K-HiE-PCIRt/c.6AMF-K-LoE-PCIRt/c.12AMF-K-LoE-PC

IRt/c.2/15ALF-K-HiE-PCIRt/c.2/15ALF-K-LoE-PCIRt/c.4ALF-K-HiE-PCIRt/c.4ALF-K-LoE-PCIRt/c.7ALF-K-HiE-PCIRt/c.7ALF-K-LoE-PC


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IRt/c Tech N

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Tech Note

96

IRt/c infrared thermocouples can accurately control the temperature of rotating and movingstainless steel heaters common in the packaging industry, without touching the heaters.

Typically, uncoated stainless steel heaters are difficult for IR sensors to measure reliablybecause of reflected infrared signals that can change after after a heater surface is cleaned.The solution to this problem is simple:

Choose an unused location on the heaters, as close as possible to the surface you wish tomeasure. Mechanically mount a surface that is reliable for the IRt/c to measure.

There are at least two choices for a reliable infrared target surface that meet the needs ofthe packaging industry (able to withstand repeated daily cleanings, durable to provideyears of service):

IRt/cTM Non-Contact Heat Sealing TemperatureControl for Packaging Machinery (OEM & Retrofit)

IRt/c

IRt/c

Run Speed IRt/c

Heaters

Run Speed IRt/c

IRt/c

IRt/c

Heaters

Fin Seal Fin Seal

Run Speed IRt/c Run Speed IRt/c

IRt/c

IRt/c

IRt/c

HeaterHeater

IRt/c



IRt/c Tech N

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1. Black, hard-anodized aluminum coated surface

A black, hard-anodized aluminum hoop, ring, disk, or strip can be used. The surface must be “hard-anod-ized”. It can be mounted in place onto the steel heaters by using thermal epoxy, small screws, or othersuitable mounting methods.

This method is very good for “retrofit” situations. The IR target surface can be added right onto existingheaters.

2. Teflon coating, directly applied onto an unused part of the stainless steel heaters

This is an excellent choice for OEMs that already use teflon coatings in other parts of their machines.Simply have a teflon coating added to the best target area prior to installing the heaters.

“Open and Close” Heaters/Cutters - IRt/c control

For jaw heaters/cutters that “open and close”, attach a small piece of coated metal to each heater head.This strip will come to the same temperature as the heater head as heat is conducted through the attach-ment point. The length of the strip should be just long enough so that the IRt/c sensor constantly looks atthe strip during each “open and close” cycle giving a constant update of the temperature of the heaters.

High Speed / High Performance

Heat SealingFor Rotating Heaters and for Stationary Strip Heaters , an additional IRt/c can be added tocontrol the sealing much more accurately as the machine begins to increase speed. Thetechnique is as follows:

1. During start-up, control the heaters using the sensors directly measuring the heaters.

2. As the machine speeds up, switch temperature measurement for the heater controlsystem to a “run speed IRt/c ”. This sensor is aimed directly at the actual fin seal, or lapseal, just after it is formed by the heaters. The “run speed IRt/c” will measure the actual sealtemperature directly from the seal itself.

StationaryStrip Heater

Run Speed IRt/cLap Seal

IRt/c

Heater IRt/c

IRTargetIRt/c


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IRt/c Tech N

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Explanation

By measuring the actual temperature of the sealduring high speed running, the heater control can bevery precise, on the order of a few degrees. This willallow very tight tolerance heat sealing. This systemwill automatically reduce the following possiblesources of high speed heat seal error:

• Dirt build-up on the heater sealing surfacethat impedes heat transfer to the seal

• Packaging material changes in thickness

• Changes in pressure applied to the seal

The control accuracy of this type of high perfor-mance system can also allow the use of a widervariety of packaging material compositions on thesame machine.

IRt/c’s - Reliable, Durable

The rugged IRt/c sensors need no power supply,and are designed for years of trouble-free operationin industrial environments

No maintenance is required. The sealed IRt/csensors can even be steam-cleaned.

For “dusty” packaging environments, we recom-mend using the IRt/c.3X or other IRt/c models withbuilt-in air-purge system. With a small amount of air,the sensor window will remain clear.

With the Exergen IRtc2132 temperature controllers,even small packaging machines can now benefitfrom reliable IRt/c temperature control for thermalsealing of packaging.

If additional technical assistance is needed, pleasecontact Exergen.



IRt/c Tech N

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By using IRt/c sensor technology, a dramatic increase in high quality output of web processing can beachieved.

· Increase drying speeds up to 20% or more

· Reduce scrap up to 75% or more

· Faster setup time when a new material is setup for processing

· Greater variety of web materials to be processed on the same machine

BACKGROUND

A common problem in high speed manufacturing of packaging films, paper and textiles, is dryer oven controlfor high speed drying of adhesives, inks and coatings onto the material.

With transparent films, IR sensors tend to “see” right through the film. And the amount of “see through” canvary with the thickness and composition of the film. With metallic films, IR sensors tend to see mostlyreflections. These reflections can vary due to the surface condition and composition of the metallic compo-nent of the particular film. Measuring the true temperature of transparent and reflective films is extremelydifficult, even with expensive IR sensors with special filtering. Measuring the drying pr ocess, however, iseasy with IRt/c sensors.

HOW IT WORKS

The key to measuring the drying process of webs is to use multiple IRt/c sensors to get a relative tempera-ture profile. Multiple IRt/c sensors installed in the dryer, allow you to controll the drying process with theutmost precision.

What the IRt/c’s see: When a coating, even a thin coating, of glue, ink, or other finish is added to a surface,the coating itself becomes visible to IRt/c sensors. The drying characteristics of the coating can be seeneven on reflective and transparent films. Even if it is a partial coating, the sensor can still “see” it. (Thereason for this is that liquids, even very thin layers of liquids, are highly “emissive”, in other words theyabsorb and emit IR very well.)

Because the IRt/c can see this thin layer, it then becomes easy to use multiple sensors to graphically, ornumerically, display a “trend” of what occurs on the surface of the web. It is this “trend” that is important incontrolling the drying.

Tech Note

97 Web Drying - IRt/c’s TM for Transparent& Reflective Films, Paper & Textiles (OEM & Retrofit)

Install multiple IRt/c'sinside the dryer.

1 2

7

3

64 5


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IRt/c Tech N

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A trend plot of relative temperatures in a drying process will always show a lower relative temperature whilethe coating is drying. The heat energy of the oven, goes into evaporating the carrier of the coating, so therelative temperature indication by the IRt/c is “lower”.

As soon as the coating becomes dry,however, evaporation stops. The heatenergy of the oven then goes into heatingthe coating and substrate. The relativetemperature indication by the IRt/c be-comes “higher”. These “lower” and “higher”relative temperature indications of thedrying process by the IRt/c sensor aretotally independent of the emissivity andtransmissivity problems for “see through”and “reflective” films. Because of this, therelative temperature information of the IRt/csensors can reliably be used for accuratedrying control.

For opaque, non-metallic web materialssuch as paper and textiles, the IRt/csensors will also display true web tem-perature along with the trends.

MANUAL WEB DRYING CONTROL

Install each IRt/c with an IRtc.2132controller/display unit, or with an appropri-ate data acquisition display system, (orother means of display). No calibration isnecessary for relative temperature data.The machine operator can then quicklyobserve the relative temperature trendsshown by the IRt/c’s and decide if, andwhere, the web is being dried. To make adecision, the operator simply looks for thecharacteristic relative temperaturechange, sensor to sensor , to see wherethe evaporation process stops.

If the sensors show relatively littlechange, (sensor to sensor ) all the waythrough the oven, then the web isn’t beingdried (i.e. evaporation isn’t complete).

If the sensors show a steady increase inweb temperature from the first sensorposition, then the coating is missing, or, isdrying so fast that overdrying occurs (andwasting energy!).

Using the sensor display information, theoperator can then manually adjust thedryer controls so that the web dryout pointis both moved to, and maintained within,the desired location inside the dryer.Manual adjustments based on our sensordisplay information allow the user tomaximize production efforts whileminimizing energy costs.

1 2 3 4 5 6 7

100 100 101 102 109 116 123

GraphicDisplays

DisplaysDigital

Dry-out Point Location

Relative temperature at IRt/c Locations

1 2 3 4 5 6 7

100 105 110 115 120 125 130

GraphicDisplays

DisplaysDigital

Alarm! Not Drying

1 2 3 4 5 6 7

100 105 110 115 120 125 130

GraphicDisplays

DisplaysDigital

Alarm! Overdrying



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AUTOMATIC WEB DRYING CONTROL

Install the IRt/c sensors and connect to a PLC or industrial computer. No calibration is necessary for relativetemperature data. Write a short program to calculate the temperature difference from sensor to sensor inthis way:

((T3-T2)-(T2-T1)), ((T4-T3)-(T3-T2)), ((T5-T4)-(T4-T3)), etc. These calculations represent the change in“slope” from sensor-to-sensor for relative temperatures of each sensor.

The maximum value found for ((T3-T2)-(T2-T1)), ((T4-T3)-(T3-T2)), ((T5-T4)-(T4-T3)), etc., tells preciselywhere the “dryout point” of the web is occurring in the oven.

With some quick tests on actual product, the program can be further refined to fit the drying profiles moreprecisely, such as setting a minimum or maximum value for the changes in slope for startup conditions,high speed, etc.

INSTALLATION GUIDELINES

1. Select enough sensors to give relative temperature indication over the length of the oven. For maximumcontrol of long ovens, we recommend at least one sensor every 20 inches (0.5 meters). For compact, highspeed drying ovens where control has to be very precise because drying must occur within a very shortdistance on the web, we recommend sensors be spaced about every 6 inches (15 cm), or less.

2. We recommend that the sensors be installed right inside the oven, if possible, as close as possible to theweb. By mounting sensors close to the target web, other minor sources of IR errors are minimized. (IRt/csensors can be installed inside drying ovens up to 750 F (450 C) with air cooling alone.) We recommendusing the IRt/c.3X model for web drying.

If this is not possible, IRt/c’s can be installed outside the oven, looking through a sight tube at the web.Select an IRt/c model with a field of view thatcan look down the sight tube at the web.

3. For internal oven air drying temperaturesup 212 F (100 C), the sensors can beinstalled inside the oven with no air cooling.Select the IRt/c.3X (or IRt/c.3SV for tightspaces) sensors and use the built-in airpurges to keep the sensor window clean forzero maintenance.

4. For internal oven air drying temperaturesabove 212 F (100 C) select the IRt/c.3Xsensor with the CJK-2 (air cooling jacket kit).This combination will allow the sensor to bekept clean and cool in up to 750 F (450 C)drying ovens with air only.

IRt/c’s - RELIABLE, DURABLE

The rugged IRt/c sensors need no powersupply, no periodic calibration, and aredesigned for years of trouble-free operationwith all types of dryer ovens. For additionaltechnical assistance, please contactExergen.

t/c WIRE

6mm TUBING OR1/4" O.D. S.S. TUBING(NOT INCLUDED)

SHROUD AND HOUSING ASSEMBLY

COOLING AIR PASSAGE

PURGE AIR PASSAGE

INCOMING AIR SUPPLY

ANY LENGTH

3.00(76.2)

4.15

(105.4)

1.00 DIA.(25.4)

CJK-2

IRt/c.3X


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IRt/c Tech N

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Tech Note

98

By using IRt/c sensor technology, a dramatic increase in high quality output of web processing can beachieved. Use the IRt/c’s with chrome-plated, stainless steel, or other uncoated metal rollers as well as withcoated rollers. IRt/c systems enable the user to:

· Increase throughput speeds up to 20%, or more, on the same machine

· Reduce scrap up to 75% or more

· Shorten set-up times

· Process a greater variety of web materials on the same machine

Applications / Processes that would benefit from the use of IRt/c technology:

· Textile Processing

· Paper Processing

· Opaque Films Processing

· Any continuous web processes using heated (or cooled) rollers

Use of Exergen’s unique patented, non-contact infrared sensors solves past technical difficulties associ-ated with temperature measurement of shiny, uncoated metal rollers (due to the high infrared reflectivity ofthe uncoated metal surfaces). Exergen has developed and tested a two stage approach to accuratelymeasure and control the heat output of heated (or cooled) metal rollers using our IRt/c’s—even at very highspeeds.

Stage 1: START-UP and STAND-BY T emperature Control

During start-up and stand-by conditions, the temperature of the heated roller will become fairly uniformthroughout the roller surfaces. Because of this, the temperature can be reliably measured at any convenientlocation on the surface, or the edge, of the rollers.

So, for Stage 1 , simply install an IRt/c so that it can see a reliable signal from the roller.

IRt/c

Add Target Area

Uncoated heated Roller Coated heated RollerIRt/c

OR

Stage 1: Start-up, Stand-by

METAL

IRt/c’s TM -- Use With Heated Metal Rollers / WebProcesses To Increase Production (OEM & Retrofit)



IRt/c Tech N

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UNCOATED METAL ROLLERS

On an unused edge of the roller, install a durable non-metallic target surface finish. This can be done with:

(a) a durable epoxy paint

(b) the addition of a thin metallic hoop, or ring, with a Teflon coating

(c) or the addition of a thin hoop, or ring, of black, hard-anodized aluminum.

Install an IRt/c sensor so that it looks at this coated surface. Use this sensor to control the temperature ofthe roller during start-up and stand-by modes

COATED METAL ROLLERS (silicon coating, Teflon, any non-metallic coating, etc.)

Install an IRt/c to aim at the center, or any convenient location, on the surface of the roller.

Stage 2: RUNNING Temperature Control

For Stage 2 , install an additional IRt/c sensor to look directly at the web surface after it contacts the heatedroller. As the web begins to move, (or, at a preset rpm) the temperature control system for the rollershould be switched over to a control system connected to this IRt/c sensor.

This IRt/c sensor should be mounted so that it looks at the side of the web material that is heated by theroller. For webs heated on two sides, sensors should be mounted on each side to control each heatedroller.

For wide webs: multiple IRt/c sensors can be installedacross the web.

For multi-zone rollers: use at least one IRt/c for eachzone across the web.

Explanation

The most common errors in web processing are asfollows:

Temperature Measurement Errors - errors due toincorrect temperature measurement.

• Thermocouple “Slip ring” signal errors

• Internal temperature sensor location errors

Heat Transfer Errors - errors caused by variations ofheat transfer to the web.

• Web material changes in thickness, moisturecontent, etc.

• Dirt build-up on the heater roller surface that can impede heat transfer to the web

• Changes in pressure applied to the web as it contacts the heated roller

As the roller speeds up, heat is removed from the roller surface by the web material. Temperature gradi-ents appear inside the roller, and on the roller surface. Conventional embedded, surface, or edge tempera-ture sensors cannot adequately track and compensate for all these temperature variations, nor can theyadequately measure the amount of heat transferred to the web material.

Exergen’s Two Stage IRt/c Sensor & Control System automatically reduces all these sources of webtemperature processing errors. Thus, the actual temperature of the webs can be both tightly (to within afew degrees) and consistently controlled through the use of IRt/c sensor technology.

The rugged IRt/c sensors need no power supply, no periodic calibration, and are designed for years oftrouble-free operation. For additional technical assistance, please contact Exergen.

Stage 2: Running

Heated

IRt/c


800-422-3006 • 617-923-9900 • Fax 617-923-9911

IRt/c Tech N

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Tech Note IRt/c TM Heat Balance Seriesfor Medical Applications

The Heat Balance (HB) Series of IRt/c infraredthermocouples have the ability to measure theinternal temperature of the target material, non-invasively , by employing a patented heat balancetechnique. A typical application in medical equip-ment is monitoring or controlling the temperature offluid transported through disposable tubing whenwarming or cooling:

• Transfusion systems

• IV warming systems

• Dialysis systems

• Cardio-pulmonary bypass systems

• ECMO systems

• Blood analyzers

The IRt/c.01HB model pictured, actually measures the internal fluid temperature by measuring both tubingsurface and ambient temperatures then calculating the internal temperature necessary to maintain the heatbalance. A convenient clip head provides a reproducible mounting location for the sensor and can bequickly attached to new tubing and removed from used tubing.

99

IRt/c.01 StyleSensor with Heat

BalanceCapability

Tubing clip toposition sensor toview tubing, sized

for tubing used

Standarddisposable

tubing



IRt/c Tech N

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Principles of OperationFluid at temperature T

f flowing in tubing transfers heat via convection through thermal resistance R

f to the

tubing inside surface, which in turn conducts heat to the tubing external surface through thermal resistanceR

t, which then transfers to the environment via radiation and convection thermal resistance R

o. The tem-

peratures of the wetted surface of the tubing, outside surface of the tubing, and the local ambient are givenby T

w , T

s, and T

a, respectively.

Employing the method of thermal analysis with electrical analogs: current = heat flow, and voltage = tem-perature, the heat transfer equation may be written as follows:

The IRt/c-HB Series measures both Ts and Ta, and solves this equation automatically for fluid temperatureTf, providing a highly accurate method of monitoring or controlling the temperature of interest.

The configuration shown above is the model IRt/c.01HB-J-37C with its convenient tubing clip. Any of theIRt/c models can be configured for the HB calculation. Contact the factory for further details.

TaTsTf

Rf Rt Ro

Tw

Radiation +ConvectionHeat Transfer

q

( )

( )

( )

qR R R

T T

RT T

Accordingly

TR R R

RT T T

f t of a

os a

ff t o

os a a

=+ +

−

= −

=+ +

− +

1

1

and via heat balance:

,

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