Post on 23-Dec-2015
transcript
presented by:
Bill Griffith
Product Characterization Through Data Logging
Product Characterization Through Data Logging
April 3, 2002
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• Why perform product characterization
• Data logging system overview
• Sensors
• Signal Conditioning
• Multiplexing / Switching
• Analog to Digital Converter
• PC Connectivity
• An example of characterizing a power supply
• Questions and answers
Product characterization through data loggingDAC Back to BasicsDAC Back to Basics
And, how to make better
measurements!
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• Does it meet design goals?
• Does it meet standards (UL,CUL,CSA, GS/TUV,CE, etc.)?
• Is it reliable?
• Can it be manufactured ?
• Is it energy efficient?
• Is the product safe?
The use of measurements on a product or design to verify proper operation
What is Product CharacterizationWhat is Product Characterization
Automated test can collect more data
and will have more repeatable results
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Product CharacterizationProduct Characterization
• PC board / Components
• Life / Durability tests
• Operation vs. temp and humidity
• Noise, accuracy, gain checks
• Incoming value screening
• Battery Tests
• Charge / Discharge rates
• Life test
• Temperature Rise
Some examples
Temperature is the most common
measurement- typically changes
slowly
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Product CharacterizationProduct Characterization
• Mechanical Enclosures• Heat rise, hot spots
• Cooling effectiveness
• Air flow
• Whole Product• Environmental tests (extreme
temp and humidity)
• Standards (UL, CE, etc.)
• Specification development - through margin analysis
• Reliability - Vibration, Stress Tests
Some more examples
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• Reliability
• Changes in temperature create mechanical stress
• Strain will lead to failure
• Possible safety issues
• Temperature changes can occur during power up or thermal gradients caused by hot spots
Temperature can affect reliabilityWhy Product CharacterizationWhy Product Characterization
• Hot spots can be caused by:
• Components
• Dead air spots
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• Performance
• A change in temperature can cause frequency drift
• In addition, voltage can change with temperature
• Temperature can affect energy efficiency
Temperature can affect performanceWhy Product CharacterizationWhy Product Characterization
• Solutions - reduce differences in temperature
• Add vents
• Add fan - optimize design (size, cost, quiet operation, power consumption, magnetic flux)
Hitachi has developed what it says is the first water cooled laptop. The machine has no fan to cool its CPU.
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• Power Supply - unique challenges• Smaller transformer often more desirable
• drawbacks include less efficiency and more heat
• Transformers create more heat at lower frequencies
• Measurement challenges• Magnetic flux and RF energy can interfere with
temperature measurements • Parts maybe grounded creating potential ground
loops with instruments used to measure temperature
An example of product characterizationWhy Product CharacterizationWhy Product Characterization
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• Most common measurements include:• Temp, DCV, Current, ACV, Frequency, and Events
• Measurement characteristics include:• Multiple inputs: typically < 20 channels
• Relatively slow reading rates: ~ 1 channel/sec
• Standalone or PC-connected: Most analysis done in a PC
• Data storage: Electronic memory or documented on paper
Product characterization is the process of using electrical and physical measurements to gain insight and improve a design
Why Product CharacterizationWhy Product Characterization
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OverviewData Logger System ArchitectureData Logger System Architecture
TransducerSignal
ConditioningMultiplexer
Digital Multimeter
(DMM)
Display Analysis & Reporting
A/D 28.32 C
MON
VIEW
SCAN
Consider PC connectivity - Cables - Adapters - SW
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Data Logger System - TransducersData Logger System - Transducers
• Temperature
• Flow
• Pressure
• Strain
• Position
• Weight
• Speed
TransducerTransducer
• dc Volts
• ac Volts
• dc current
• ac current
• Resistance
• Frequency
Physical Parameters Electrical Signals
Physical parameter to electrical signal
Choose the correct sensorMount it correctlyPosition it correctly
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Data Logger System - TransducersData Logger System - Transducers
• Thermal mass• Don’t let the measuring device
change the temperature of what you are measuring
• Response time is a function of the mass of the sensor and the mass of object being measured
Temperature background
Dewar• Glass is a poor conductor• Gap reduces conduction• Metallization reflects radiation• Vacuum reduces convection
• How is heat transferred
Sensor
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Data Logger System - TransducersData Logger System - Transducers
• What is your normal temperature?
• Thermometer resolution, accuracy
• Contact time
• Thermal mass of tongue, thermometer
• Human error in reading
Making temperature measurements
97.6 98.6 99.6 36.5 37 37.5
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Data Logger System - TransducersData Logger System - Transducers
• Need accurate, sensitive measurements--
• J-type thermocouple
at room temp = < 1 mV
• A 1C change at 0C =
50.38 V• To see a 0.1C change
in a J-type TC at 0C, your instrument must be able to resolve down to 5 V.
Thermocouples
VVABAB
++
--
Metal AMetal A
Metal BMetal B
• Good junction•Thermal shunting• Noise and leakage current•Thermocouple specs• Calibration of TC
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Data Logger System - TransducersData Logger System - Transducers
Thermocouples - Gradient Theory
Metal AMetal AVVAXAX++ --
Metal BMetal B
TXTA
TB
• The wire is the sensor, not the junction
• Heating one end of a wire creates a voltage Vax
• The voltage is a non-linear function dependent on wire type and the temperature difference from one end of the wire to the other
• The Seebeck coefficient (e) is used to quantify the voltage that is created
VVABAB
++
--
Ta
Tx
Tx
Tb
+eAdT eBdTVAB =
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• If a “thermocouple junction” is made with two wires of the same metal - what voltage would the TC produced (VAB)?
a) 2*VAX - twice the gradient voltage of metal A
b) No voltage
c) Can’t determined without knowing the temperature difference
d) Can’t determine without knowing the metal type
Data Logger System - TransducersData Logger System - Transducers
Thermocouples - Gradient Theory
VVABAB
++
--Metal AMetal A
TxTa
Tb
Metal AMetal AVVAXAX++ --
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Data Logger System - TransducersData Logger System - Transducers
• We are taking a deeper look at how measurements are made - a lot of the details are handled by the data logger
• The architecture that we have presented makes it possible to connect any type of transducer to any channel.
• Simply setup the data logger with the type of transducer and channel information
• The data logger will make the necessary measurements, conversions and display the correct results in scientific units
A modern data logger will make it easy to make measurements
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Data Logger System - TransducersData Logger System - Transducers
• For more details on making temperature measurements - see application note 290.
More information is available
• Having a good understanding of transducers will allow us to make better measurements• In order to make good measurements - care has to be taken
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Data Logger System - TransducersData Logger System - Transducers
Thermocouples - Gradient Theory
• If a thermocouple was made of a single metal Metal A the TC would produce zero volts
• Two different metals are combined to create a TC
• How do you measure a TC?
VVABAB
++
--Metal BMetal B
TxTa
Tb
VVAXAX++ --Metal AMetal A
VV++
--
Metal AMetal A
Metal BMetal B
Metal CMetal C
Metal CMetal C
Tx
Click to edit Master subtitle style• Create a reference
junction
• Measure Tref using thermistor
• Lookup Vref for TC at reference junction
• Compute Vx = V+Vref
• Solve for Tx using Vx 0 Tref
Vx
Vref
Tx
ComputeVx=V+Vref V
o
Data Logger System - TransducersData Logger System - TransducersThermocouples - How to measure a TC
Tref
VVXX
Metal AMetal A
Metal BMetal B
Metal CMetal C
Metal CMetal C
Tx VV++
--
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Data Logger System - TransducersData Logger System - TransducersThermocouples - Common Types
0 500 1000 2000
mV
deg C
20
40
60
EE
R
NKJ
E
ST
Platinum T/CsBase Metal T/Cs
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Data Logger System - TransducersData Logger System - Transducers
• Better accuracy and more expensive
• Absolute temperature
• A common thermistor
type has 5000 at
25C with 4%/ C
• 1C = 200 • 10 of lead resistance
would cause a .05 C error
Thermistor
RRmeasmeas
++
--
Rtemp
Often physically small mass• Won’t cause thermal loading • A large measurement current will cause self heating
Rlead
Rlead
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Data Logger System - TransducersData Logger System - Transducers
• RTDs • Absolute measurement• Accurate measurement• A common RTD has 100
at 0C with .385 / C • 10 of lead resistance
would cause a 26 C error
RTD - Resistance Temperature Detector
• Avoid self heating, a 5 mA current source would create 2.5 mW of power in our RTD. • At 1 mW/ºC, that is an error of 2.5/ºC
iRtemp
Rlead
Rlead
VV++
--
RTD
+ Vlead -
+ Vlead -
DMM
R=V/i
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Data Logger System - TransducersData Logger System - TransducersRTD - Four wire ohm measurement
I=0
I=0
iRlead
Rlead
Rlead
Rlead
R=V/i
V V
++
--Rtemp
RTD
• For more information on 4-wire ohm measurements see application note 1389-2
DMM
V=Vtemp=i*Rtemp
Rtemp=V/i
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Data Logger System - TransducersData Logger System - Transducers
• Linear change in voltage or current with change in temperature
• 10 mV/K (voltage IC)
• Room temp approx. 3V with
a 10mV/°C change
OR
• 1 A/K (current IC)• Need an external power
source• Absolute measurement
IC - Temperature sensor
VVtemptemp
++
--
• Have limited temperature range < 150 C• Fairly large mass
10mv/K v
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Data Logger System - TransducersData Logger System - Transducers
+ Most accurate
+ Most Stable
+ Fairly linear
- Expensive
- Slow
- Needs I source
-Self heating
-4-wire meas.
RTD Thermistor IC Thermocouple
Temperature sensors
+ High output
+ Fast
+ 2-wire meas.
- Very nonlinear
- Limited range
- Needs I source
- Self-heating
- Fragile
+ High output
+ Most linear
+ Inexpensive
- Limited variety
- Limited range
- Needs V source
- Self-heating
+ Wide variety
+ Cheap
+ Wide T. range
+ No self-heating
- Hard to measure
- Relative temperature only
- Nonlinear
- Special connectorsAbsolute temperature sensors
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Data Logger System - TransducersData Logger System - Transducers
• Your designing an electronic device and have included an IC temperature sensor in your design and want to verify the accuracy of the IC sensor - what type of sensor would you use with your data logger to make the measurement?
A) Thermocouple
B) RTD
C) Thermistor
D) IC Sensor
Polling Question
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OverviewData logger System ArchitectureData logger System Architecture
TransducerSignal
ConditioningMultiplexer
Digital Multimeter
(DMM)
Display Analysis & Reporting y
A/D 28.32 C
MON
VIEW
SCAN
V
V
Wiring errors
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Data Logger System - Wiring ErrorsData Logger System - Wiring Errors
• Extension wires are less expensive, more rugged, but have slightly different temperature curves than the thermocouple
Thermocouple extension wires
Long rugged extension wiresSmall diameter measurement wires Possible problem
• Keep the junction of the extension wire and the thermocouple wire near room temperature
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Data Logger System - Wiring ErrorsData Logger System - Wiring Errors
Metal AMetal A
Metal BMetal B
Common Mode Errors
DMMZL
ZH
Icom
•Make ZL as large as possible
•Avoid connections to grounds
• Common mode errors create a current into both the high and the low measurement paths
• Typically caused by a difference in grounds
H
L
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Data Logger System - Wiring ErrorsData Logger System - Wiring ErrorsNormal Mode Errors
DMM
Inorm
magneticcoupling
• Normal mode noise introduces a current that is in the same direction as the measurement current
• Magnetic flux or RF energy are common sources of normal mode errors
Reduce the size of the measurement loop - twisted pair wire - move measurement hardware closer to the source - run measurement wiresperpendicular to high current wires
V
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Data Logger System - Wiring ErrorsData Logger System - Wiring ErrorsNormal Mode Errors
Electrostatic noise
• Large ZL is important to avoid capacitance coupling through tip of thermocouple
Shielding will provide an alternative path for electrostatic energy - Only ground one end
DMM
Inorm
ZL
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OverviewData logger System ArchitectureData logger System Architecture
TransducerSignal
ConditioningMultiplexer
Digital Multimeter
(DMM)
Display Analysis & Reporting y
A/D 28.32 C
MON
VIEW
SCAN
V
V
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Data Logger - Signal ConditioningData Logger - Signal Conditioning
• Convert signal to be compatible with system• Thermocouple
reference junction
• Filter• Strain gauge bridge
completion circuit• Shunt resistor for
indirect current meas.
• Amplifier / Attenuator• AC converter
VV++
--
Metal AMetal A
Metal BMetal B
Metal CMetal C
Metal CMetal CIsothermal Reference Junctions
Signal Conditioning - Examples
VV++
--
I
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Data Logger - Signal ConditioningData Logger - Signal Conditioning
• Reduce noise that has been coupled into the signal “normal mode error”
• Allow for filter settling time
Filtermagneticcoupling
Inoise
Include lead and switch resistance,
plus lead and switch capacitance
when calculating settling time
I < InoiseV
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OverviewData logger System ArchitectureData logger System Architecture
TransducerSignal
ConditioningMultiplexer
Digital Multimeter
(DMM)
Display Analysis & Reporting y
DMM 28.32 C
MON
VIEW
SCAN
V
V
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Data Logger System - MultiplexingData Logger System - Multiplexing
2-wire, 4:1 MUX
H
L
H
L
H
L
H
L
4-wire, 2:1 MUX
H
L
H
L
H
L
H
L
1-wire, 4:1 MUX
Multiplexing - Examples
H
L
H
L
H
L
H
L
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Data Logger System - MultiplexingData Logger System - Multiplexing
FET
SolidState
Reed 300 V50 mA
6 µV1
500 ch/s 10 M16 V1 mA
25 µV1 k 100k ch/s Infinite
300 V1 A
3 µV3 200 ch/s Infinite
Armature 300 V1 A
3 µV1 60 ch/s 10 M
Typical
MAXVoltage Offset Speed Life
Switch characteristics
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OverviewData logger System ArchitectureData logger System Architecture
TransducerSignal
ConditioningMultiplexer
Digital Multimeter
(DMM)
Display Analysis & Reporting y
DMM 28.32 C
MON
VIEW
SCAN
V
V
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Data Logger System - DMMData Logger System - DMM
• Reduce the complexity of signal condition
• May only need one RMS converter
• May not need additional attenuation and amplifiers in signal conditioning
DMM - Digital Multimeter
Control and reading memory
A/D Converter
Amplifier, attenuator and shunt resistors for current
AC RMS
Current Source for resistance
H
L
ZL
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Data Logger System - DMMData Logger System - DMMNormal Mode Errors
A/D Converter
Inorm
magneticcoupling
• Normal mode noise introduces a current that is in the same direction as the measurement current
•An integrating A/D can be used to reduce normal mode noise
When using an integrating A/D the integration period will be set to line frequency - Use at least 1 PLC to reject noise - Higher frequency noise will be integrated and reduced along with power line noise
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• Normal mode noise is typically generated by large currents that have the same frequency as line frequency - integrating over one Power Line Cycle will make Vnoise=0
• Can trade off reading rate (speed) for resolution
• 1 line cycle = 60 rdgs/s
• 10 line cycles = 6 rdgs/s
Data Logger System - DMMData Logger System - DMM
VTemp
Integrating A/D Converter
Vnoise
V
T
1 PLC
2 PLCNPLC
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Data Logger System - DMMData Logger System - DMMMeasurement Characteristics• Resolution - How many bits or digits the ADC/system produces
• Repeatability - How consistent results are reading-to-reading
• Accuracy
Relative accuracy - statistical determination of error (deviation from norm)
Absolute accuracy - statistical determination of error from a traceable source
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OverviewData logger System ArchitectureData logger System Architecture
TransducerSignal
ConditioningMultiplexer
Digital Multimeter
(DMM)
Display Analysis & Reporting
DMM 28.32 C
MON
VIEW
SCAN
System error is a sum of the error from each component - avoid noise sources!
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• Quickly setup data logger• Self guiding menus
• Make sure that you are collecting valid data• Verify setup / possibly monitor a channel• Set limits and alarms
• Upload results to PC• Create final reports in Microsoft applications
• Use away from bench• Display viewing angle• Bright in multiple lighting conditions
• Save channel setups and easily modify
Data Logger System - Reporting TasksData Logger System - Reporting TasksCommon reporting tasks
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Data Logger System- Reporting TasksData Logger System- Reporting Tasks
• Connecting to data logger• RS-232
• USB
• LAN
• GPIB
• Software• Easy to use
• Create documentation
• Compatible with Microsoft Office Apps
PC Connectivity
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Data Logger System - Reporting TasksData Logger System - Reporting Tasks
• Typically report results in Microsoft Office applications; Excel, Word, or PowerPoint
• Need a way to cut and paste graphical data into these office applications easily
• Could create a program or use an off-the-shelf application designed for the task
Creating reports
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Data Logger System - Reporting TasksData Logger System - Reporting Tasks
• Although a common interface RS-232 has a couple of drawbacks
• RS-232 can be slow
• Can be difficult to find the correct cable
• USB has become prevalent and addresses the common problems of RS-232
Using RS-232 / USB
• USB to GPIB converters have made it possible to take advantage of USB and create an opportunity to take advantage of portable computers away from the bench
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Data Logger System - Reporting TasksData Logger System - Reporting Tasks
• LAN connectivity has several advantages
• Fast - although not tuned for measurement data like GPIB
• Can be used over long distances
• Allows resources to be shared
• LAN to GPIB converters can take advantage of LAN capability
Using LAN connectivity
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PC Software Summary
Textual language
T&M graphical language
Free to $300
Time intensive
Medium Medium
Great
Great $600 to $1,400
Data logger SW
Quick QuickLow - product specific
Software Create Report
Make 1st Reading
Flexibility Cost
Time intensive
$300 to $1,000
Data Logger System - Reporting TasksData Logger System - Reporting Tasks
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PC Connectivity Summary
USB
$0 to Low
Yes
RS-232 Yes Yes Low
Interface Common to PC
Common to Instr.
Speed Cost
$500
Distance
Short
Need an adapter
Medium Short
LAN Yes $1100Need an adapter
Fast Long
GPIB Need an adapter
$400 to $600
Yes Fast Short
Data Logger System - Reporting TasksData Logger System - Reporting Tasks
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• Specified an OEM power supply to speed product development. Requirements include:
• 100 Vac - 240 Vac +/- 10% line voltage
• Characterize temperature measurements in critical areas
• Voltage stability under full load
• Voltage regulation under low line voltage
Data Logger System DemoData Logger System DemoOEM Power Supply Characterization
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• Test setup
• Data acquisition / switch unit connected to:
• Four temperature measurements using T-type thermocouples
• Four dc voltage measurements
• A PC with USB/GPIB converter
• Data logger software
• Create a report, Temperatures vs. Time, Voltage vs. Time
Data Logger System DemoData Logger System DemoOEM Power Supply Characterization
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• Getting Started
• Use front panel of DAC system to quickly verify voltage and temperature setup
• The PC and SW is used to automate the measurements over time
• Varied line voltage manually
• The data logger screen images were then cut and pasted into a Microsoft Word document for the final report
Data Logger System DemoData Logger System DemoOEM Power Supply Characterization
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Power Supply TestData Logger System DemoData Logger System Demo
A/D 28.32 C
MON
VIEW
SCAN
Vab-
Vcd-
Vef-
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TransducerSignal
ConditioningMultiplexer
Analog-to- digital
converter
Display
28.32 C
MON
VIEW
SCAN
A/D
Summary - System AccuracySummary - System Accuracy
Transducer errors
Thermal gradient
Ref transducer accuracy
Thermal EMF / Offsets
DMM - offset, noise, linearity, resolution, accuracy
Data logger temperature conversion algorithm
System accuracy is the sum of the measurement errors for each component
Additional cable errors
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• Data logger may include PC cables and software
• Data logger will make thermocouple measurements easy - built-in conversion routines, reference junction, reading storage, monitor data from display
• Data logger may specify system accuracy - to determine complete error add transducer error
• For our example the data logger specifies the system error for a T-type TC as 1oC. The TC has an error of 1oC or .75% which ever is greater. So the total error is 2oC
SummarySummaryModern Data logger - Can help
Work to minimize external sources of error