At the heart of gas detection systems DRÄGERSENSOR®ˆger-sensoren-… · sor at ambient...

At the heart of gas detection systems

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DRÄGERSENSOR®

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When there’s

danger in the air ...


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... this can quickly pose a high risk to humans, the environment, and alltypes of property and systems. Recognize the threat before it is too late.


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Detecting hazards – quite simple in principle

WHY IT IS WORTH KNOWING MORE ABOUT GAS

DETECTION SENSORS

Our sensory organs are often unable to detect air-borne hazards, or cannot do so early enough. Toxicor flammable gases and vapors can build up,reaching hazardous concentrations, or there maybe insufficient oxygen in the air. Both of these sce-narios can have life-threatening consequences.

The reliability with which harmful airborne sub-stances can be detected depends to a large extenton the sensors that are used. It is essential for thegas detector and sensor to be adapted perfectly toeach other. Hazards must be identified in goodtime and dependably, and false alarms leading toproduction downtime and the like must be avoided.You entrust the safety and protection of your per-sonnel, equipment and property to a perfectlyworking sensor.

MEASURING GASES IN ELECTRICAL UNITS

The sensor is the most important component insidea gas detector. It converts the measured variable,e.g. a gas concentration, into an electrical signal.Depending on the sensor type, this is achieved byeither chemical or physical processes. To obtain ameaningful and informative measured value read-out, many factors have to be taken into account.Response times must be short, susceptibility toerror low, and reliability high. The better the sensor,gas detector and central unit are designed to worktogether in accordance, the more reliable themeasurement results will be. In industrial gasdetection applications, three sensor technologiesin particular are used on account of their excellentproperties: electrochemical, catalytic and infraredmeasurement.

In former times, miners took canaries with them into the mine shaft.They made hazardous changes in the air underground easily visible:while the bird sat on its perch, everything was fine, but if it was lyingon the floor, there was the threat of danger. The birds tended to cometo a sticky end, and the miners were only able to escape the samefate if they were able to get to safety in time. This very simple methodof hazard detection was unable to identify which airborne substancesposed the threat, nor their concentrations. Most importantly, however,the warning often came too late for effictive protective steps such asescape, ventilation or oxygen supply to be taken.

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The electrochemicalsensor principle


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ELECTROCHEMICAL SENSOR

Electrochemical sensors work in a similar way tobatteries. When the target gas is present, a smallelectrical charge is generated chemically betweentwo electrodes, and displayed in the measuringhead. The signal strength is proportional to theconcentration.

One fundamental requirement is to achieve a stablesensitivity and good selectivity under all normalambient conditions. The sensors must be able toreliably withstand the tough conditions prevailing inan industrial setting, and do this 24 hours a day, allyear round.

Over the years, Dräger has developed and placedon the market many different sensors for all kindsof gases and applications. We make the know-howwe have built up and the individual performance ofthe sensors available so that you can perform yourmonitoring tasks. To this end, every sensor isequipped with an electronic memory chip (EEP-ROM) containing individual information: look-uptables for measured value compensation, coeffi-cients for mathematical calculations, timing ele-ments for process control and control bits for vari-ous special functions.

This intelligence means that a high signal qualitycan be achieved, which in turn results in a longservice life with minimal maintenance requirements.This minimizes the overall costs of ownership ofthe gas warning system.

PLUG-AND-PLAY EQUALS SMART SENSOR

Once a sensor has been manufactured, it is testedin the production department using the target gas.The individual data collected during this process,as well as many other standard parameters, arerecorded and logged in the sensor memory. Whenthe sensor is later connected to an intelligentDräger transmitter, the instrument reads out thisdata and can perform the necessary configuration.

The adopted settings guarantee the highest possi-ble measurement performance and user-friendlyconfiguration. The calibration is stored in the sen-sor before leaving the factory, meaning that thesensor is ready for use immediately.

On the basis of this plug-and-play principle, Drägeroffers its customers electrochemical sensors formore than 100 toxic gases and oxygen, all of whichcan be used with the same universal transmitter.This gives you maximum flexibility and quick readi-ness for use.

Because the sensor and the transmitter are devel-oped and manufactured by Dräger under one roof,the different properties of the two components canbe designed to function perfectly together, result-ing in the greatest possible customer benefit interms of performance characteristics.

Cross-sectional diagramElectrochemical Dräger Sensor

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Memory chip

Pressure release

Electrochemical component

Selective filter


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Stored intelligence

PRESSURE COMPENSATION FOR A LONGER

SERVICE LIFE

Electrochemical Dräger Sensors can be used in atemperature range of – 40 °C to + 65 °C ( – 40 °F to+ 150 °F). To achieve such an extreme temperaturespan, sophisticated mechanical and electroniccompensation mechanisms are needed. A patentedporous housing made of Teflon surrounds the sensorand, in the event of changes in pressure, allows theenclosed air to equalize pressure with the ambientair without any of the chemicals escaping. In caseof temperature changes, air pressure fluctuationsand the absorption of water due to humidity in theair, mechanical stress is completely eliminated.

The result is a constant level of sensitivity and anoutstanding service life of several years.

Demonstration of pressure compensation Immersion in warm water: on the left, chemicalsreleased due to positive pressure; on the right,effective compensation of positive pressure with-out damage to the sensor.

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ORGANIC ELECTROLYTE OPENS THE DOOR TO

PPB MEASUREMENT

Not all gases can be detected using standard elec-trochemical technology, so for special applicationsDräger has developed an organic electrolyte on apolycarbonate basis. Thanks to their better signal-to-noise ratio, these sensors can detect extremelylow gas concentrations in the 10 ppb (parts per billion = 1:1,000,000,000) range. What is more, thesensors show less cross sensitivity to standardtoxic gases which can be present in very low con-centrations in the ambient air. This results in lowerdetection limits, while nonetheless virtually rulingout false alarms.

FUNCTIONAL SAFETY WITH PATENTED

SENSOR TEST

The gas detector regularly performs a sensor test.This test is controlled on the basis of individualdata from the memory device to ensure optimaltesting of every sensor type in accordance with itsproperties. The test involves using an electricalpulse to stimulate the sensor, similar to exposingthe sensor to gas. The sensor must now respondby emitting the corresponding output signals. Thisensures that the correct measurement signal willbe generated when gas reaches the sensor'smeasurement electrode. The test has no effect onthe sensor's normal measurement function.

This guarantees a high level of reliability and avail-ability of the electrochemical measurement function.

SELECTIVE FILTERS TO PREVENT FALSE ALARMS

Exchangeable selective filters increase sensor per-formance in terms of selectivity. Once a filter isused up, it can easily be removed for a replace-ment filter. This is an effective means of suppress-ing certain irritating cross-sensitivities.

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Sensor test Test pulse (top) and sensor response(bottom).

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The catalyticsensor principle


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HOW CAN FLAMMABLE GASES BE MEASURED?

Easy – by burning them. But not, of course, using anaked flame, as they are supposed to be detectedbefore they form a flammable mixture with air.Chemists describe this process as oxidation, whichrequires air (oxygen), fuel and a substance whichwill enable a reaction between the two, namely acatalyst which is attached to a heat-resistantceramic body.

Yes, this is just the sort of catalytic converter whichyou would find in your car. The only difference isthat it is of virtually no interest whether the catalyticconverter in your car becomes even hotter than it isalready as a result of the oxidation reactions (e.g.when hydrocarbons which have not yet combustedbecome water vapor and CO2) – all that matters isthat it should be as effective as possible.

We, on the other hand, are interested in the slightincrease in temperature which occurs during thistype of oxidation process because, as is commonlyknown, any oxidation involves a heat of reaction,which is a measure of the number of reactions thathave taken place. And a few clever tricks are all thatis needed to actually coax a measurement signalout of a catalyst which allows the proportion offlammable gas in the ambient air to be determined.

First, we need a much smaller catalyst and a lot ofoxygen, which we extract from the volume of asmall and highly porous ceramic bead which firsthas to be baked. This involves making a “dough”out of optimized catalyst and metal salts and usinga special production process to ensure a high level

of porosity. After heating for a short time, the resultis a stable ceramic body which contains anextremely finely distributed catalyst. The bead isonly about 1 mm in size, and roughly as permeablefor the gas as fired clay.

To heat the bead to the perfect temperature for theintended oxidation process, it contains a miniatureimmersion heater, a small electrically heated platinum coil. The current is carefully selected toensure that the bead will not become too hot, butalso not too cold – the perfect temperature toobtain the highest possible measurement signal isroughly 450 °C (850 °F).

Measurement signal? Yes, because platinumchanges its electrical resistance very precisely inrelation to temperature. If the resistance is known,the temperature is known, and if the temperature isknown, the concentration of the oxidized gas isknown.

Unfortunately, however, the ambient temperaturealso changes, and by a great deal more than thetemperature caused by the heat of combustion(which is just a few °C). To be able to use the sen-sor at ambient temperatures of – 50 °C to + 85 °C(– 60 °F to + 185 °F), the ambient temperature addi-tionally needs to be measured. To do this, a similartype of bead is used, though this time of coursewithout a catalyst.

Principle of operation of a catalytic sensor

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Methane

Oxygen

Platinum coil

Electrical connections

Pellistor carrier


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Absolute reliability

Such beads are known as pellistors, a made-upterm created from the words pellet and resistor.The pellistor without the catalyst (compensator) isused to measure the ambient temperature, whilethe pellistor with the catalyst (detector) is used tomeasure the ambient temperature plus heat ofcombustion, where the difference between the twosignals – a measure of the gas concentration – is generated electrically.

For pure air, the difference must of course be zero,which is why this is set to zero in the associatedelectronics. When both pellistors are then exposedto, for example, 0.85 % by volume propane, theassociated electronics only has to be adjusted sothat it displays “50 %LEL”. Thereafter the settingsare left unchanged, and the detector is "calibratedto propane".

In this context, 50 %LEL means that the propanegas concentration is already hazardous but far fromflammable. Only once the LEL (the lower explosionlimit) is exceeded by 100 % can propane ignite inair, i.e. only above 1.7 % by volume.

Although there is virtually no end to the possibili-ties offered by catalysts, the main priority whenmanufacturing high quality catalytic bead sensorsis to attain sensor properties such as high effec-tiveness, signal stability, solidity, resistance to cata-lyst poisoning, reproducibility and, above all, out-standing durability and short response times –Dräger achieves this with its extensive know-howacquired during the course of 30 years. After all,catalytic bead sensors need to be operated contin-ually for months at a time, without requiring mainte-nance, and must be able to reliably detect veryslight temperature differences – frequently in hos-tile climatic conditions.

What is more, the sensor must of course notbecome an ignition source itself in the event thatconcentrations in excess of 100 %LEL are present.The two beads, at temperatures of roughly 450 °C(850 °C), would no doubt be able to ignite manygases and vapors, were it not for the ignition pro-tection measures in place. Thanks to the solidexplosion proof design and the gas-permeable sin-tered metal discs, flashback into the hazard area isreliably prevented – that is true explosion protection.

Dräger produces three types of sensor designedfor gas detection systems:

THE ALL-ROUNDER

The Dräger Polytron SE Ex PR M detector headhas become the universal industry standard. It isused wherever there is a probability that flammablegases and vapors will be released in order toactively prevent a potentially explosive atmospherefrom occurring (this is known as preventive explo-sion protection). The operator is alerted by the central unit, while at the same time a pre-alarm(e.g. 20 %LEL) causes countermeasures to be acti-vated (e.g. fresh air is blown in to reduce the con-centration of the flammable gas). If this measurefails, the concentration continues to rise and themain alarm is triggered (e.g. when 40 %LEL isreached), resulting in a forced shut-down. TheDräger Polytron SE Ex PR M with the central unitsDräger REGARD Ex and Dräger Polytron SE Exwere type-examined for suitability for this applica-tion by an independent testing authority.


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Explosion protection means reliably excluding atleast one of the three prerequisites for ignition.

Gas/vapor In sufficiently high concentration (above LEL).

Air/oxygenIn sufficiently high concentration.

Ignition sourcee.g. ignition spark with sufficient energy or sufficiently high temperatures.

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THE EARLY-WARNING INSTRUMENT

The Dräger Polytron SE Ex LC M (LC = Low Con-centration) detector head is suitable for reliablydetecting very low gas concentrations. It is usednot so much for preventive explosion protection asfor the early detection of flammable gases andvapors with concentrations far below 10 %LEL. Typical alarm thresholds are 3 %LEL and 5 %LEL,equivalent, for example, to 300 ppm and 500 ppmhexane respectively. The explosion proof sensorcontains complex amplification electronics whichare individually calibrated during production to anumber of different parameters.

THE HEAT RESISTANT INSTRUMENT

The Dräger Polytron SE Ex HT M (HT = High Tem-perature) detector head is approved for use atambient temperatures of up to 150 °C (300 °F). It isnormally used in applications where extremely hightemperatures are commonly found, especially fordetecting leaks in the immediate vicinity of gas tur-bines. The temperature-resistant connection termi-nals are located in a galvanized cast iron housing.

ALSO AVAILABLE AS REMOTE SENSORS

The sensing heads described above, when com-bined with transmitters like the Dräger Polytron Exor the Dräger PEX 3000, can also be operated asremote instruments, i.e. in areas which are difficultto access the sensor can be operated separately tothe transmitter electronics.

SUITABILITY TESTING

The catalytic bead sensor has been tested for suit-ability for detecting many different gases andvapors by a recognized testing authority (NotifiedBody as stipulated by the ATEX Directive):methane, propane, acetone, acetylene, ammonia,petrol 065/095 (FAM normal gasoline), benzene,1,3 butadiene, n-butane, n-butyl acetate, cyclo-propane, diethyl ether, dimethyl ether, ethanol, eth-ylene (ethene), ethyl acetate, ethylene oxide, n-hexane, methanol, methyl ethyl ketone (MEK),n-nonane, n-octane, n-pentane, i-propanol, propy-lene (propene), propylene oxide, toluene andhydrogen.

In all, more than 200 different flammable gases andvapors can be reliably detected using catalyticbead sensors.


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The infraredsensor principle


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INFRARED ABSORPTION

Whenever substances contain both carbon (C)and hydrogen atoms (H), i.e. hydrocarbons, theirC-H bonds can briefly absorb part of the infraredlight radiation. This slightly weakens the intensity ofthe emitted light.

Light-sensitive pyrodetectors are able to registerthis weakening, while downstream electronics cancalculate a signal on this basis which serves as areliable indicator if a gas concentration is present.

The concentrations that can be measured bymeans of infrared absorption range – dependingon the substance in question – from a few hundredppm (parts per million) up to 100 % by volume.

This method is often used to detect flammablegases and vapors within their 0 to 100 %LELranges, though it can also be used for the earlydetection of even small leaks (in coolant circuits,for example) so that more serious damage can beavoided.

FAIL-SAFE OPERATION

All the components needed to perform the meas-urement – light sources, detectors, signal ampli-fiers, processors, memory chips, heating elementsetc. are protected against external influences.

In most IR gas detectors, a solid explosion proofstainless steel housing acts as a hermetic seal,protecting the interior components from dirt, mois-ture, corrosive gases and other factors which mightimpair the measurement.

The constant readiness for use of the componentsis continuously monitored internally, and any com-ponent failure immediately triggers a fault alarm –ensuring true “fail-safe” operation!

Many Dräger IR transmitters feature SIL (SafetyIntegrity Level) certification, and have beenapproved by the independent testing authoritiesexida and TÜV. They confirm that this sensor tech-nology is ideally suited to applications wheredemands for functional safety are high.

Our customers can rely on the reliable readinessfor measurement.

Schematic diagram of the DrägerPolytron IR (explosion proof)

Only the green part of thelight radiation is filtered outand its intensity measured.

If a gas absorbs the greenpart of the light radiation, its intensity is measurablyreduced.

Principle of operation of infrared absorption (measurement cuvette)

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IR sources Sapphire window

Heated mirror

Gas

Flameproof enclosure

Beam-splitter

Measurement detector

Reference detector

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Precise reflection

STABLE – EVEN UNDER ADVERSE CONDITIONS

A stable measurement signal – even a “stable zero”if no hydrocarbons are present – is one of the keyrequirements in industrial applications. Falsealarms are simply unacceptable, as they can resultin emergency shutdowns, production downtime andeven plant evacuations.

Dräger sets global standards with its forward-look-ing innovations, such as double compensation oftemperature and ageing effects, the 4-beam tech-nology for high resistance to contamination, andthe beam block warning for preventive mainte-nance.

For more than 15 years, we have succeeded timeafter time in meeting our customer’s exactingrequirements and continuously raising the bar justa little bit higher each time: one typical challengewhen it comes to IR gas detectors, for example, isto prevent contamination in the measurementcuvette from negatively affecting the measurementsignal.

The Dräger PIR 7000 achieves a new quality andperfect balance between signal strength and con-tamination resistance in this respect: thanks to itsperfectly harmonized multi-mirror optics, the instru-ment maximizes its use of the available light, mean-ing that even a significant build-up of dust or dirtparticles has no effect on its measurement proper-ties.

BEST POSSIBLE LINEARITY AND CONVENIENT

OPERATION

Due to the non-linear absorption behaviour of thegreat majority of hydrocarbons, individual linearizedcharacteristics would theoretically need to bedescribed for every single substance. The goalmust be to enable the IR transmitter to calculate asignal which, as far as possible, increases propor-tionally to the rise in gas concentration.

To this end, the Dräger Polytron IR type 334 fea-tures a “gas library” containing 38 substances,which offers the world's biggest choice of lineariza-tions (27 substances have additionally been testedand certified for measurement performanceaccording to ATEX).

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And even if the substance to be monitored has notyet been included in the gas library, there is at leasta very good chance of finding among the 38 differ-ent linearizations one which comes very close tothe required absorption behaviour.

And best of all, calibration of sensitivity can still beperformed conveniently with standard test gases(e.g. methane, propane or ethylene). The DrägerPolytron IR automatically converts the different gasparameters of the desired target gas and the stan-dard test gas accordingly – approved according toATEX.

INFRARED – THE FIRST CHOICE

Infrared gas detectors are therefore the first choicenowadays for stringent industrial requirements (e.g.in chemical plants or in the automotive industry)and for applications with adverse ambient condi-tions (e.g. on offshore oil rigs).

Hydrocarbons, and indeed carbon dioxide (CO2)and nitrous oxide (N2O), can be reliably and accu-rately detected using infrared sensor technology.

The combination of monitored operational readi-ness, stable measurement characteristics, durabledesign and minimal maintenance requirements hasproved persuasive for our customers, and hasresulted in more than 100,000 installed infraredsensors worldwide.


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Made in Germany

Gas detection technology requires a high level of precisition. Not onlythe integrity of systems and machines, but also human lives depend onthe reliability of a gas warning system.

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Dräger is one of the world's pioneers in the devel-opment and pushing ahead of sensor technology.In its own laboratories at the company's Lübeckheadquarters, Dräger conducts basic research andtechnology studies.

Dräger strives constantly to improve all its safetytechnology. Whenever current technologies, newmaterials, changed production processes ortougher legal regulations give rise to additionalrequirements, Dräger has already found ways ofmeeting them.

Besides developing highly specialized niche prod-ucts, we research ways of reducing cross-sensitivi-ties and lowering detection limits. We are alsoimproving economic aspects continuously, e.g. byreducing costs of ownership.

We forge lasting relationships with our customers.For over 110 years, mutual trust has been the basisfor our path together into the future.


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Sensor technology cannot be viewed on its own. Just like in a car, it isnot the engine alone which determines driving comfort. It is only whenall the individual components work together in harmony that you achievean optimal system.

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The whole is morethan the sum of its parts


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At Dräger, an entire team of engineering specialistsand sensor experts always works together on thedesign and development of gas warning systems.The team takes account of current technologiesand devises new systems of hazard prevention.Solutions are planned which are tailored preciselyto the relevant customer requirements.

The modular design of Dräger systems guaranteesthat your safety concept will meet all existing andfuture requirements long-term. New instrumentsand sensors can be added into existing systems,while systems using today's components can beexpanded, changed or modernized at virtually anytime.

Besides offering a uniquely wide range of sensors,measuring instruments and technical components,Dräger provides every possible kind of support.


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The perfect safety system is not automatically created simply by combining good quality equipment.

Professional system engineering provided by experienced Dräger specialists, plus detailed planning, will help you identify the best solution for your particular challenge.

From commissioning to maintenance, trained service staff are at your disposal all over the world,ready to perform all the services you need.

Experience cannot be learnt


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aAHEADQUARTERSDräger Safety AG & Co. KGaARevalstrasse 123560 Lübeck, Germany

www.draeger.com

GERMANYDräger Safety AG & Co. KGaARevalstrasse 123560 LübeckTel +49 451 882-2794Fax +49 451 882-4991

FRANCEDräger Safety France SAS3c route de la Fédération, BP 8014167025 Strasbourg Cedex 1Tel +33 3 88 40 59 29Fax +33 3 88 40 76 67

SINGAPOREDraeger Safety Asia Pte Ltd67 Ayer Rajah Crescent #06-03Singapore 139950Tel +65 68 72 92 88Fax +65 65 12 19 08

UNITED KINGDOMDraeger Safety UK Ltd.Blyth Riverside Business ParkBlyth, Northumberland NE24 4RGTel +44 1670 352 891Fax +44 1670 544 475

SYSTEM CENTERS

P. R. CHINABeijing Fortune Draeger SafetyEquipment Co., Ltd.A22 Yu An Rd, B Area, Tianzhu Airport Industrial Zone,Shunyi District, Beijing 101300Tel +86 10 80 49 80 00Fax +86 10 80 49 80 05

USADraeger Safety, Inc.505 Julie Rivers, Suite 150Sugar Land, TX 77478Tel +1 281 498 10 82Fax +1 281 498 51 90


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At the heart of gas detection systems DRÄGERSENSOR®ˆger-sensoren-… · sor at ambient...

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