Principles of Infrared Thermocouples How do they measure temperature? INTRODUCTION All IRt/c’s have a proprietary infrared IRt/c INFRARED detection system which receives the THERMOCOUPLES – heat energy radiated from objects the A REVOLUTIONARY NEW TEMPERATURE SENSING sensor is aimed at, and converts the heat passively to an electrical potential. Z TECHNOLOGY A millivolt signal is produced, which is scaled to the desired thermocouple The IRt/c product line represents a characteristics. dramatic breakthrough in temperature sensing technology. The IRt/c sensors Since all IRt/c’s are self-powered are unpowered, low cost, and can devices, and rely only on the incoming measure surface temperatures of infrared radiation to produce the signal materials without touching. They can through thermoelectric effects, the be directly installed on conventional signal will follow the rules of radiation thermocouple controllers, PLCs, thermal physics, and be subject to the transmitters, and other readout devices. non-linearities inherent in the process. However, over a range of temperatures, the IRt/c output is sufficiently linear Actual IR/tc Signal to produce a signal which can be millivolt interchanged directly for a conventional output t/c signal. For example, specifying a 2% match to t/c linearity results in a temperature range in which the IRt/c OS36 Series will produce a signal within 2% of the ,, yy conventional t/c operating over that Target Temperature range. Specifying 5% will produce a The actual signal generated by the IRt/c can somewhat wider range, etc. be approximated with a fourth order polynomial yy ,, function of target temperature. This fourth power dependence is due to radiation physics, and Linear Range *** not a limitation of the IRt/c. 2% 5% Conventional thermocouple > 5% millivolt Linear region output millivolt output Actual IR/tc Signal Target Temperature The linear region matches the conventional t/c to a specified tolerance. Target Temperature yy ,, Temperature Selection Guide 90.00 Linear Range *** ,, yyy y yy yy ,,,,, 80.00 2% 5% > 5% 70.00 millivolts of signal output Sensor - Type - Temperature 0° 50° 100° 150° 200° 250° 300° C 60.00 yyy, yyyy ,,,, ,,, yy, ,, 50.00 * - ** - 220C/440F * - ** - 170C/340F 40.00 * - ** - 140C/280F 30.00 * - ** - 120C/240F ,,, , y yy yyy 20.00 * - ** - 90C/180F * - ** - 60C/140F 10.00 * - ** - 27C/80F 0.00 * - ** - 10C/50F –10.00 * - ** - 37C/98.6F Special Biomedical Calibration ±0.2 C (35.5-39.4), ±0.3 C (25-40C) –50 50 150 250 350 450 550 650 0° 100° 200° 300° 400° 500° 600° F Actual Temperature (C) * Select OS36, OS36-2, or OS36-5 Target Temperature ** Select Type J, K, E, T The OS36-K-80 has its 2% linear range *** Temperature Range in which IRt/c output is linear centered at 80°F (27°C), but produces a compared to conventional t/c, within stated % (of reading). repeatable signal to 1200°F (650°C). Z-76 Principles of Infrared Thermocouples Cont'd Each IRt/c model is specifically Long term accuracy is influenced by the percentage of failure, the IRt/c has designed for optimum performance same things that influence repeatability: essentially unlimited long term in the region of best linear fit with mechanical changes and metallurgical calibration accuracy. conventional t/c’s, but can be used changes. It is well known that outside of those ranges by simply thermocouples can change calibration QUICK INSTALLATION GUIDE calibrating the readout device over time due to these effects. appropriately. The output signal is Mechanical changes occur because All infrared-based sensing systems smooth and continuous over its entire conventional thermocouples are must be calibrated for specific material rated temperature range, and maintains constructed generally as small and surface properties (for example, the 1% repeatability over its entire range. light as possible to enhance response amount of heat radiated from the target time, thus making them vulnerable surface, environmental heat reflections, The Temperature Selection Guide to deformations that can change etc.). This calibration is performed by is a summary of the linear range the thermoelectric properties. More measuring the target surface temperature performance of each IRt/c model. The importantly, the conventional with a reliable independent surface user selects the IRt/c model and type, thermocouple must operate at temperature probe. The easiest and and the target temperature range for elevated temperature since it merely fastest method of accurately calibrating the application. The normal offset measures its own temperature. out these effects is to use an OMEGA adjustments on the thermocouple OS91 hand-held Infrared Thermometer readout device are used to calibrate with a patented Automatic Emissivity the installation for emissivity and Compensation System to give a true background effects. reading regardless of emissivity. How reliable are these new devices? The following procedure is recommended: Of fundamental interest in temperature 1. Install IRt/c as close as practical to control is the ability of the measuring view the target material to be measured. device to maintain its calibration under service conditions, and over a long 2. Wire IRt/c to controller, PLC period of time. The IRt/c is rated at Transmitter, etc. in standard fashion 1% (of reading) repeatability and to The IRt/c gives repeatable static (including shield). As in conventional have no measurable long term and dynamic readings. t/c’s, red wire is always (–). calibration change, which makes it well suited for reliable temperature control. The metallurgical changes which affect 3. Bring process up to normal operating These attributes are inherent in the thermoelectric properties are a strong temperature and measure actual basic design and construction of each function of temperature, being negligible temperature of target material with IRt/c. at room temperature, and of serious OS90 Series Infrared Thermometer. concern at high temperature. 4. Adjust “input offset,” “zero,” The IRt/c solves both problems by “low cal,” on the readout device to its design and basic operation. Its match the OS91 reading. solid fully potted construction in a mechanically rigid stainless steel Installation complete. housing, and operation at near room temperature conditions, essentially eliminates the classical drift problems of conventional thermocouples. Every IRt/c IRt/c at Room Temperature is double annealed at temperatures above 100° C to ensure long term Thermocouple Probe at Product Temperature stability, and tested 5 times prior to packaging. Barring a very small Conventional thermocouple operating at elevated temperature is subject to long-term drift, while the IRt/c operating at room temperature is stable. Quick Installation Guide 2 Repeatability is defined as the ability of a measuring device to reproduce its calibration under identical conditions. + The IRt/c is a solid, hermetically sealed, – fully potted system that does not change either mechanically or metallurgically during service. There are no active electronic components and no power source to produce the signal – only the 3 1 4 thermoelectric effects that produce a thermocouple signal. The 1% rating is a conservative value based on the practical difficulty of demonstrating tighter tolerances under test conditions, rather than a true limitation of the device. Z-77 IRt/c SETUP WITH AUTO-TUNE TEMPERATURE CONTROLLERS In many applications, heating elements 10,000 V 60 Hz are employed to heat a product in an oven, furnace, or with jets of hot air. Conventional control devices using contact thermocouples measure and control the oven air temperature, IR IRt/c heating element temperature, or air jet temperature in an effort to maintain product temperature and therefore, quality; often with less than satisfactory results. Fast Meter Z Heat Input 1000 ft (300 m) Twisted Shield Pair t/c Wire IRt/c CAN BE USED WITH IRt/c’S ARE INTRINSICALLY SAFE UP TO 1,000 FT (300 M) OF WHEN USED WITH BARRIERS Product Temperature THERMOCOUPLE EXTENSION WIRE “Field Apparatus having energy storing or generating characteristics of <1.2V, With twisted shielded pair thermocouple 0.1A, 25 mW or 25 microJ shall be Time extension wire, an IRt/c can be mounted considered Simple Apparatus (non- as far as 300 meters (1,000 ft) from energy storing). These general purpose Replacing the contact thermocouple, the readout device, even in a very devices may be used in a hazardous (for example measuring oven fierce electrical noise environment. A (classified) location without further temperature) with a non-contact IRt/c demonstration test was performed with approval when connected to a certified measuring product temperature directly, a 300 m (1000 ft) coil of twisted shielded intrinsically safe circuit.” – Quote from will insure that product temperature is pair of extension wire, with 30 m (100 ft) R. Stahl, Inc. Comprehensive Product maintained. Some readjustment of the unwound, connecting an IRt/c to a fast Manual On Intrinsic Safety Barrier controller parameters is required (100 msec. response) A/D conversion and Repeater Relays. Examples of because of differences in sensor module to a computer. As a noise non-energy storing Intrinsically Safe response times (an IRt/c is much generator, a 60 Hz 10,000 volt transformer Apparatus are: faster), and time required to heat the and spark generator was set up to spark product compared to the original sensor within 15 cm (6 inches) of the wire. • Thermocouples • RTD’s • LED’s (slower). After installing the IRt/c and • Dry Switch Contacts calibrating the controller reading using The test results showed less than 0.1°C • NAMUR Inductive Proximity Switches an OS91 Infrared Scanner (see Quick of noise at any relative position of the • Non-inductive Strain Gage Devices Installation Guide below), initiate the wire, spark, and transformer. The and Resistors self-tuning cycle of the controller and extraordinary noise suppression check to see that the control is stable characteristics designed into the IRt/c The IRt/c falls into the category of and accurate. If it will not self tune make it possible to locate it at very long thermocouples, since it generates its properly, manually adjust the control distances, without the necessity of a signal by converting the radiated heat coefficients to achieve stable control. transmitter. The IRt/c housing is electrically energy to an electrical signal via Because the product temperature is isolated from the signal leads and is Seebeck effects, the basic driving likely to change temperature more connected to the shielded ground of the force of thermocouples. Like all slowly than the original sensor, start extension cable. For long distances, thermocouples, it requires no power with slowly increasing the “D” of the twisted shielded extension cable should source and generates signals measured PID coefficients. be used, and the shield connected to a in millivolts of voltage, microamps of good electrical ground. current and nanowatts of power. IRt/c’s have a small capacitance, but at one IRt/c’s are intrinsically safe when used microFarad, the energy storage is with barriers measured in nanojoules and is a thousand times lower than the 25 microjoule criterion. Accordingly, the IRt/c qualifies as a Simple Apparatus for use in hazardous locations, and with the appropriate barrier, qualifies as Intrinsically Safe. IRt/c Barrier Z-78 Principles of Infrared Thermocouples Cont'd IRt/c IRt/c RELATIVE HUMIDITY MEASUREMENT CONTROLLING WEB ROLLER TEMPERATURE APPLICATION NOTES IRt/c’s can be used to measure actual The IRt/c infrared thermocouples have IRt/c MONITORS relative humidity in many situations quickly become the sensors of choice TIRE TEMPERATURES FOR where there is a convenient source for monitoring and controlling both web of water and flowing air, and measure and roller temperatures. Tips on accurate RACING PERFORMANCE it accurately and reliably. roller temperature measurement: An IRt/c aimed at a wet porous surface 1. Uncoated Metal or Chrome Rolls – with ambient air blowing across the wet Shiny, uncoated metal rolls are difficult surface, can actually measure what is for any infrared sensor to properly called “wet bulb” temperature for that sense the true temperature (the sensor ambient area. (More precisely, wet will see too many environmental bulb temperature is the equilibrium reflections). The solution to the problem temperature of the air-water interface is to simply: paint a small black stripe when a water film is evaporated. When on an unused end of the roller. Aim the air is moved over a wet surface, the IRt/c sensor at the black paint stripe. water cools by evaporation until it It will then measure the temperature reaches wet-bulb temperature, then accurately and reliably regardless of Tire temperature is of critical concern in the cooling stops, no matter how much changes in the surface conditions of the automotive racing for two reasons: the more air is moved over the surface. The rest of the roller. tire temperature directly affects its temperature at which the cooling stops adhesion and its wear characteristics; is the wet bulb temperature.) and tire temperature patterns provide valuable information on the set-up and The IRt/c measures the temperature performance of the suspension. For of the air-water interface on a surface example, excessive loading of a tire directly. The quality of the water or of caused by out-of-tune suspension will the absorbing material does not affect + cause that tire to become considerably the reading, since the IRt/c can directly warmer than the others. view the air-water interface, and the wet bulb equilibrium temperature is not The IRt/c is an ideal measuring device materially affected by impurities. for on-board data acquisition, due to its small size, ruggedness, and low cost. The highest precision method is to It may be connected to standard employ an IRt/c wired differentially If there is very little space on the edge thermocouple read-out systems. with a conventional thermocouple of the roller, move the sensor closer and Installation should include connecting to measure the quantity “wet bulb paint a very small black stripe. The the shield to a suitable ground in order depression”. The differential pair minimum spot size of the IRt/c is 8 mm to avoid interference from the arrangement guarantees high (0.3 inches) and for the OS36-2 it is electrically harsh environment of a accuracy, since RH is a strong function 4 mm (0.16 inches) when the sensor is racing automobile. Mechanical of wet bulb depression and a weak brought close to the surface. installation should include attention to function of dry bulb temperature. air flow patterns to minimize dirt building Standard psychrometric tables, 2. Dull Metal Rollers – Dull metal on the lens. The OS36-2 or OS36-5 are charts, and software algorithms rollers can provide a reliable signal. recommended due to their narrower can be used with the data to obtain It is best to test the surface for reliability, field of view, thus allowing you to accurate relative humidity for your though, as the surface emissive position it further away. environmental measurements. properties may shift via dirt, moisture, cleaning, etc. It is best, if in doubt, to simply paint a stripe to eliminate these variations. Relative Humidity Measurement + 3. Non-metallic Surfaced Rollers – + Wet Bulb These will provide a reliable IR signal at – Depression any point the IRt/c is aimed. No painted – Temperature stripe is required. + – Air Flow + Dry Bulb Temperature – Z-79 CONTROLLING IRt/c CONTROLS PRINTED 2. The field-of-view: the preferred VACUUM FORMING AND CIRCUIT BOARD PREHEAT method is to view the part between THERMOFORMING PROCESSES DURING WAVE SOLDERING the coil turns or from the end. Select the IRt/c model that best suits the For forming plastics, an excellent An excellent solution to the problem of requirements. combination of heating method and proper heater control for PC board control is radiant heat with an IRt/c for preheat is an IRt/c. They work 3. Part temperature: both the OS36-2 control. They work extraordinarily well extraordinarily well together, since both and OS36-5 models can be used to together, since both the heating and the heating and measuring occur right target temperatures of 1100°C (2000°F), measuring occur right at the surface – at the surface – where the solder must and have linear ranges to 260°C (500°F). where the plastic is located. The IRt/c reading is unaffected by reflections from flow. The IRt/c reading is unaffected by reflections from the heater, since the ASPHALT TEMPERATURE Z the heater, since the spectral response spectral response of the 6-14 micron MONITORING of the 6-14 micron IRt/c lens filters out IRt/c lens filters out any shorter the shorter wavelengths of the radiant wavelengths of the radiant heater energy. Asphalt properties are particularly ,,,, yyyy heater energy. sensitive to temperature, and it is important that the asphalt is applied Air at the correct temperature in order OS36-2 OS36-2 to perform to its specifications. ,,,, yyyy Air Ceramic Heaters Accordingly, temperature monitoring is a common requirement, but the thermocouples normally used have severe breakage problems due to the harsh abrasiveness of the material, and must constantly be replaced at high cost and interruption of production. For this application, the IRt/c may be mounted identically to Vacuum Air Forming/Thermoforming (above). ,,, yyy OS36-2 The IRt/c may be mounted in between INDUCTION HEATER CONTROL ceramic heaters, or in the shroud or yyy ,,, reflector of the radiant heater, such that The induction heating process can be Air it can see in between the elements. readily controlled by the temperature Select the IRt/c standard, OS36-2 of the part as measured by an IRt/c or OS36-5 model, depending on the non-contact infrared thermocouple. field-of-view required to see past the Several issues should be considered elements to the painted surface. Care in an installation. OS36-5 should be taken in mounting the IRt/c in such a way as to keep its temperature below 93°C (200°F) and to keep the IRt/c lens clean. The OS36-2 is the preferred model for this application because of The IRt/c solves this problem directly, its small physical size with built-in air Cooling Water since the temperature is monitored purge. It can be used in temperatures to OS36-5 without contact. The normal thermocouple 121°C (250°F) environments when the controller can be used – simply calibrate air purge system is used. Its narrower OS36-2 offset if necessary. The OS36-2 and field-of-view allows more leeway in OS36-5 models are recommended due positioning, and thus more flexibility in to their built-in air purge, which will keep installation. For still narrower fields of the lens clean by preventing vapors view, use the OS36-5 with its 5:1 FOV. from condensing on the lens. The OS36-2 can be mounted in the chute 1. The effect of the field on the IRt/c: to view the asphalt through a small since the measuring signal is electrically hole, while the OS36-5 can be mounted isolated from the housing, the IRt/c will some distance away due to its narrow operate in even a very strong field. 5:1 field of view. The shield wire should be attached to a proper signal ground. If there is excessive heating from the field, consider using the optional cooling Reproduced with permission of jacket kit, with the same water source Exergen Corp. as is used to cool the coil. OS36-2 and OS36-5 models feature built-in air purge to keep these quality thermocouples functioning efficiently and accurately, even in dirty environments Z-80 One Omega Drive | Stamford, CT 06907 | 1-888-TC-OMEGA (1-888-826-6342) | firstname.lastname@example.org www.omega.com UNITED KINGDOM www. omega.co.uk Manchester, England 0800-488-488 UNITED STATES FRANCE www.omega.com www.omega.fr 1-800-TC-OMEGA Guyancourt, France Stamford, CT. 088-466-342 CANADA CZECH REPUBLIC www.omega.ca www.omegaeng.cz Laval(Quebec) Karviná, Czech Republic 1-800-TC-OMEGA 596-311-899 GERMANY BENELUX www.omega.de www.omega.nl Deckenpfronn, Germany Amstelveen, NL 0800-8266342 0800-099-33-44 More than 100,000 Products Available! 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