Companies and households rely on heat sensors to function properly. It is employed in the manufacturing industry and laboratories across the nation. Even household appliances and auto parts use these sensor types to remain operative and accurate.
Thermocouples are most commonly used temperature sensor used in many types of thermometers and many of our day to day appliances some of which you might not even be ware of. Based on use
they can be divided into industrial and home TC. There working principle is universal but their make and body type are different for different purpose.
Most objects that rely on heat are probably using this device to manage heat convection, regulate temperature, and remain safe. It can measure in almost all type of environment. Ex-hot, cold, harsh, smooth, high pressure, low pressure etc. There are many types but based on use they come for industrial and home use. Otherwise there are standard grade available.
At home they are used in devices like ovens, heaters, refrigerators etc. In industries they come in the form of probes to insert in the temperature measurement region. They are used in power plants, Metal ore smelting, glass industries, nuclear furnace and any other machines or region where monitoring the temperature is necessary for safety or controlling purposes.
What are tcs?
They are the most common type of temperature sensors using plain metallic wires. Their wires are chosen so as to produce a large electromotive force that varies linearly with temperature. There is no known metal or alloy that has all of these desirable features, although some are very close to it.
Since there are no product with this perfect behavior, all electromotive force curves deviate from a straight line or linear response to some degree. In industrial applications, the choice of materials used to manufacture a range is dependent on the temperature to be measured, the type of atmosphere exposed to the material and the required accuracy of measurement.
Why they are called so?
Tcs are formed by coupling together a pair of metal and works on the application of thermal energy. Hence the name.
How were they discovered and what is their principle of operation .
There discovery date back to 1822-23 when Thomas seebeck observed a deflection in a compass needle kept near a closed circuit of two metallic wires whose two junction are at different temperature.
He also discovered that the Potential difference generated was almost directly proportional to the difference in the two temperatures for particular range depending on the type of material of which it is made.
But he thought it to be of magnetic nature .Anyhow the effect was termed Seebeck effect. Later in same century Leopoldo Nobili and Macedonio Melloni continued his work and made a device to measure heat radiation. It was simple group of metal junction in series like a thermopile combined with galvanometer. It may be the first tc made for any measuring purpose.
If two metals of different wires are joint at two ends and if temperature of the junctions are different then a current flows through the wires.
For small changes in temperature within the operating region the Seebeck voltage or the EMF (electromotive force) is directly proportional to temperature. Voltage temperature relationship can be approximated as
T= a1( V)+a2(V)^2+a3( V)^3+….. up to N terms.
However a1(V) is quite large as compared to other coefficient and so the relationship is approximately linear for quite long range of temperature. Lot of math here huh!
However Measuring the Seebeck voltage directly is not possible because we must first connect a voltmeter to the lead wires ,and the voltmeter leads themselves create a new thermoelectric circuit at the contact point of voltmeter and tc leads.
Determining the Temperature of by measuring the voltage output.
How to nullify the effect of extra junction produce
Measuring voltage is an indirect measure of temperature .But it is not possible directly. Consider the diagram above as an example.To measure the temperature we have to connect two wires of say constantan to copper (Red) and Iron to copper (Blue). And then the two ends to a voltmeter.
But Since Constantan to copper and iron to copper will itself generate some voltage it forms another junction as shown above. So we cannot determine exact temperature unless we subtract that the extra voltage difference generated at constantan- copper(Red) and Iron-copper(Blue) junction.
This is only possible if we know the temperature of reference. One way to employ this is to put the junction at reference temperature and thus know in advance the voltage which will be generated at two junctions and thus subtract it eventually to get voltage generated at target surface ie, Iron-Copper junction.
What causes sebeck effect ?
Here is a demo
Suppose a metal wire is heated at one end then electron which are free to move will tend to be denser at cold junction and less denser at hot.
So an electron gradient will be created. And so a net potential difference but since no current can flow in open loop the the potential difference is maintained by balancing two currents inside the metal wire thermal gradient current and current induced by potential difference(ohms law) caused by difference in density of electrons.
Now when two wire of different metal but at identical temperatures at hot and cold junction are joined current flows. Voltages of hot and cold junction of different metals may not be same since it depend the type of metal. So a current is established at two ends.
But the flow of electron at hot and cold junction are opposite since metal with higher hot junction potential will be having lower colder junction potential and vise versa. So the polarity of voltage difference will be opposite at two ends. This is because wire at higher voltage means higher positive charge which implies more negative charge at opposite end than the other wire.
3 Laws of Thermocouples
When connecting wires in tc circuits there are three rules or laws to keep in mind. They are
Law of homogeneous material
A current cannot flow in a single wire loop made of same material by
application of heat alone.S o if there is a temperature difference between two points along the length of a homogenous wire there will not be a voltage difference.
Law of intermediate materials
At uniform temperature the algebraic sum of the thermoelectric emfs in a circuit composed of any number of dissimilar materials is zero .So if a third metal is inserted in either of two wires and if the two new junctions are at the same temperature, there will be no net voltage generated by the new metal.
Law of successive or intermediate temperatures
Provided T1<T2<T3 then if a thermal emf1 is produced by tc made by two dissimilar homogeneous materials whose junctions are at T1 and T2 and emf2 is produced when the junctions are at T2 and T3 , the emf generated when the junctions are at T1 and T3 will be emf1 + emf2.
Advantage of using
The advantages include wide temperature ranges, inexpensive costs, variety, rugged exterior, and simple, self-powered design. The cons, however, are low voltage measurements, non-linear voltage-to-temperature conversion chart, reference requirements, low stability, and low sensitivity.
Industrial temperature measurements ranging between -200°C (-328°F) and over 1450°C (2462°F) is normally achieved with them. They are the only sensors that can be used at very low temperatures, particularly in applications where the accuracy is adequate.
Here is comparison of various sensors most common in use
Junctions types and errors in thermocouples
There are three kinds of thermocouple junctions
Grounded junction –
This junction is in direct contact (welded) to the outer sheath of the probe. Useful where the environment is corrosive and the response time requires is low ie fast acting probe. It gives fast response because the junction is more in contact wit the medium.
Useful in areas where very fast response time is required. But the nature of gas is preferably non corrosive. It is so because since the junction is exposed it is fast but may corrode away easily. The junction is in direct contact with environment as it extends from a opening in the outer sheath. This opening is tightly sealed to prevent any moisture or the surrounding inside the sheath which may cause error.
Ungrounded junction -this type is used only in potentially electrically hazardous place like transformers etc. The junction completely insulated electrically from the outer sheath. The enclosed junction makes it suitable for it to used in corrosive environment.
What is response time?
It is how much time the sensor takes to reach 63.2% of the sudden change in temperature It is analogous to time constant in electrical circuit. So it has been derived that the temperature rises in the junction takes place exponentially as a capacitor of circuit is charged. At about 5 time constant the temperature of junction is equal to the actual temperature value.
Response time depends on the exposure of junction with the medium and the probe diameter. Smaller the diameter and more expose the junction lesser is the response time.so exposed junction will have least response time
Errors in thermocouples
The following type of error may creep into thermocouple temperature measurement which may add up and affect overall accuracy.
Wire error: Thermocouple wire may not be uniform and homogeneous in its material .It may contain some impurity or other manufacturing defects. So all the thermocouple of same type may not show the reading.nIn this respect type T are considered most accurate with maximum 1.0 °C. error over the range -65 to 130 °C .
Reference junction error: This error is produced to faltering cold junction temperature due to faulty heating or cooling device at junction at cold junction compensation box.
Voltage measurement error: the measuring device which measure voltage and convert it to other form like a transmitter may be faulty and inducing errors.
Linearization error: For all the range of temperature for a particular type of thermocouple the relation between emf and (milllivolts) and temperature is not linear. So depending on the method or formula used to convert the millivolt to temperature the errors are in temperature is affected.
These errors are errors of a newly bought thermocouple. In long term emf drifts and leads to decalibration.
Thermocouple drift and decalibration
When thermocouple is placed in the high temperature region for considerable long time we cannot be sure of the reading of the temperature shown by it.This is because the emf produced by the TC can change over time even though it is at same temperature.This change in emf is called thermocouple drift.
Causes This change is due to change in chemical and metallurgical properties of metal of thermo elements at its surface or at volume or both. It result in change in seebeck coefficient in the some or entire regions of the thermo elements.
At surface following may occur
- Oxidation of surface material mainly if the thermocouple wires are not protected by sheath or where open wire configuration is used.
- Corrosion or depletion because of the gas or chemical around the thermo elements.
- Chemical reaction with the insulator or sheath.
Inside of the thermocouple ie in its bulk changes may occur because
- The metal of the thermo element may change is metallic phase like.it may undergo allotropic change or diffusion of foriegn material.
- Metal can undergo grain growth.
- Continuous stress may cause the internal lattice to undergo deformation and develop voids etc.
- Ordering transformation which is change in order or symmetry to disorder of the lattice when heated.
Following things are to be noted about thermal drift
It is not 100 % avoidable.
Drift is not caused if seebeck constant changes near the hot end of the thermoelement.
Drift s mainly caused if the thermo elements in between the thermocouple wire undergo change in seebeck constant.
This is because the temperature profile that at hot and cold end region of Tc the temperature in uniform.So any
No effect of change in seebeck coefficient. But at the middle region if seebeck coefficient changes drift may occur.
To ensure reliable and stable operation during its life time enclosure such as sheath thermo wells or protection tubes are used. But some of the noble metal thermocouple are more susceptible to contamination and may cause drift.
A thermocouple drift is irreversible. While after the drift you can change the probe but the detection of drift is important because a faulty reading can make process work incorrectly causing faulty operation of the process.
Sometimes temperature may go higher than the safer limit and may ultimately burn the thermocouple. This may also be caused when the drift is low and thus forcing the controller to raise the temperature further. This may cause halting in process causing loss to business.
For detecting thermocouple drift redundancy of reading can be used. This can also reduce human error in reading. Some controllers like honeywell uses loop resistance method to detect the drift. A drifted thermocouple will have higher resistance then the normal.
Periodic checking of temperature at installation can be done.
How thermocouple calibration is done
Thermocouples calibration is not the same as other instruments.
In fact when the term calibration with respect to thermocouple is used in laboratory it basically implies the validation of the thermocouple to produce required voltage which should match with values in TC emf chart.
It is done by comparison of the two curve the ideal and the plotted.
1.)Put thermocouple in a thermal bath at different temperature
2.)Measure thermal emf produced.
3.) Plot that emf with the temperature on X axis. Subtract emf equivalent of ambient temperature from the emf measured.
4.)Find the new equation for the curve obtained .The curve will be approximately linear. If higher accuracy is required find the coefficients of the higher powers.
If it does not matches or show some deviation sometimes the controller or display device which reads local temperature like thermometer, controller, data acquisition system etc is programed again to match that voltage to the actual temperature. The device does that by readjusting its voltage equation.
So in effect it is calibration of the thermocouple instruments like thermometer, controller, data acquisition etc
For temperature bath
We use Standard temperature source large enough so that the thermocouple can be inserted into it like ice bath. We can use the boiling and or freezing point of a series of pure solvents as those temperatures are well known at STP. Use an accurate thermometer to note down temperature.
Another such heat source is thermocouple calibration furnace. They have fast heating time. Accurate temperature display of about+-0.5decC. Also they can be used to calibrate multiple thermocouples at the same time.
Ok but what does a calibrator does.
It is a thermocouple meter plus simulator.
It is an instrument which reads temperature when TC wires is connected to its input and the calibrator is set to correct TC type.
Also it can simulate and reproduce ideal thermocouple sensor millivolts at its output when set to a temperature and type.
1.)To check that the instrument is reading correct temperature .If not the instrument is adjusted to read correct temperature.
2.) To compare the value read by TC under test and actual temperature reading eliminating the use of charts.
How to read the chart
It consist of rows of values showing millivolt.
The reference junction(cold junction) is Zero degree C for all data.
Each row consist of eleven values
Voltage value is for temperature corresponding to the row containing that voltage value plus the temperature corresponding to column containing that voltage value.
Generally thermocouple probe is enough to sense the temperature of the environment. Working condition in plants etc however is not so favorable for probes and they can be easily damaged For example places like high pressure steam, Flowing fluid etc can easily corrode away the probe Also it is required that the process is not disturbed when we insert a probe through a hole .
So insertion must be airtight. For this reason a thermowell is used. They provide protection from corrosion and are also useful for easy replacement of probe without opening up the process. For this reason they are installed airtight into the system.
They are of 3 types based on installation method.
1.) Welded 2.)Flanged 3.) Threaded
You can easily identify them by picture .
While selecting a thermowell you should watch out
1.)Length Thermocouple are tip sensing unlike rtd which are stem sensing. Therefore length is important to consider because while using thermocouple probe the tip of the probe should be touching the well bottom otherwise it will increase the time delay in measurement which in fact is unavoidable because of the insertion of thermowell but it should be minimized to reduce errors.
There are two types of length stated manufacturer.
Insertion length. or “U”length This is the length of well in the process of measurement. A properly installed element: in liquid, the element should be immersed up to point where it is most sensitive plus one inch. In air or gas, the element should be immersed up to point where it is most sensitive length plus three inches.
Extension length This length is called “T” length and is the extending length which is to extend thermowell and probe through wall or insulation of material. Between two length is the connection mechanism which is flanged threaded or welded.
Bore size used is greater then the size of probe so that more that one probe can be inserted.
They are of 3 types based on installation method.
1.)Welded This connection can be used when the process is not corrosive and routine removal is not required because welding frequently is not economical and is time consuming. This technique is suitable for high temperature & pressure application. As welding make thermowell quite airtight.
2.)Flanged Appropriate for large pipe diameter. Preferable if there is a need for more frequent well replacement such as high corrosion rates. So flanged connection is economical and easy to reinstall. Such a technique is more for high-pressure application.
2.) Threaded suitable for smaller diameter well. Threaded well are easy to install when diameter of well is small., which are not likely to be changed frequently
For high corrosive environment flanged is used where frequent changing is for non corrosive environment and smaller diameter.
You van easily identify them by picture
Stepped Tapered or straight.
Stepped is used to increase time response. Reduced diameter causes easy thermal flow.
Tapered is in between strength (vibration resistance) and time response.
Tapered length are more resistant to vibration of fluid. Vibration is caused from a phenomenon called wake frequency. Actually fluid flowing around well forms a kind of turbulence and if the frequency of wake is equal to (something called the) natural frequency of well the well may vibrate with maximum amplitude and break of. So the natural frequency quoted as velocity rating of well supplied by the supplier should be higher that the fluid velocity .
So in places like high speed fluid like outlet of high power motor a tapered connection will be better to use.
Material according to the corrosiveness of the environment.
There are corrosion charts available from thermowell manufacturers that list the preferred material for different conditions.
Here is detail about the the thermocouple accessories needed for complete installation of thermocouple at industries.
These type of TC don’t have any perrmanent fittings at end. It is just a sheated probe with wire at other end. So to mount them compression fitting is supplied separately.
Fittings let you adjust the depth of your probe into a system for temperature readings. Use fittings for straight-shaft probes and metal tubing only. These are sort of plumbing instruments used to connect tubes carrying thermocouple probe or wire to comparatively larger length.
These fitting allows to vary the insertion depth of the probe. They are generally made of brass or copper ferrule of size equal to probe and nuts to tighten the ferrule to probe. Its main specifications are Diameter. Choose your fitting according to the diameter of probe its measurement is NPT(National pipe thread).
Compression do not require soldering, so they are comparatively quick and easy to use so disassembling or partial removal for maintenance is easy.
They work at higher pressures and with toxic gases.
In these types of fittings extruder type TC are used which are generally used in plastic industries.
Another application is injection in molding machines or presses in rubber industry.
The thermocouple has a spring loaded adjustable depth bayonet cap and long lead protected with stainless steel flexible armor. This type of arrangement is used because the length can has to readjusted along extruders and the same thermocouple will serve the purpose.
The use of this transmitter is generally recommended when the cost of thermocouple wire and plc input card exceeds the cost of the transmitter and common wire. This transmitter receives the voltage from the thermocouple and converts it into a scalable 4-20 mA analog output.
Different type can be
4-20 ma transmitters
Programmable transmitters Some transmitters are field programmable, while others have a specified range, and are programmed at the factory.
TC temperature transmitters are used to convert millivolt (mV) output of a thermocouple to a reliable 4-20 mA DC current signal. This way Noise, voltage and other effects are defeated.
Transmitters are available according to base metal type because each type represents different temperature range.
Various specifications are included like analog voltage, analog current, resistance, and temperature which tells what transmission method ex-0 – 10 VDC. Devices that receive analog current 4 – 20 mA or resistance like as 0 to 10 ohms.
Mounting styles are different for different type of TC Ex thermohead/thermowell , DIN rail cabinet or rack or on on computer boards
Connectors jaks and plugs
While using extension wires often they deferent pieces of wires need to be connected. So for that purpose jacks and plugs are available. Connect TC wire or temperature sensor instrumentation with a temperature controller or process control HMI automation panel. Specifications for thermocouple connectors include
Contact plating and
For each type or thermocouple, the appropriate connector is attached to the thermocouple terminals.
Thermocouple connector plug or jack with ANSI color code are
Type K Yellow
Type J Black
Type T Blue
Type E Purple
Type N Orange
Type R/S Green
Type C Red
Connection are of two main types contact and crimp.
Contact-type devices have
a)Pins or plugs-designated as male connectors
b)sockets or receptacles- termed female
Crimp connectors is the physical compression (deformation) of a contact around a conductor to form an electrical and mechanical connection. Some thermocouple connectors feature quick wiring caps that allow the user to insert wires into the caps and then tighten the screws.
General Home appliances which uses tcs
Gas space heaters,Room heaters,Boilers
These type of appliances uses screw in, clamp or push in pilot burners. Choose the required model from the available probes but refer your manual for replacement and model type before making a purchase.
These are different type of space heaters which require a specially made probes to fit in the stove.
Gas/electric oven or stove used in household cooking
They are located under the burner. You can locate it after opening the lower panels given in ovens. Most modern oven come with electronic temperature control. They are required to cook your food at required temperature So a thermostat is used to control the temperature. Their design may be different depending upon the company or model of oven. Ovens or stoves have special type of probe which is thin and long. They are connected with a thermostat which is responsible for the controlling action. Complete set of probe and thermostat are available.
These type of stove uses pellet or wood pieces for lighting .Another tcs are used for its temperature control.
For pyrometer or kilns.
These types have high temperature applications.
For exhaust gas temperature monitors
Generally used to monitor the temperature the exhaust gas of automobile or internal combustion engine so that driver have an indication of air-fuel ratio which should not be higher than required. If it is so then the exhaust temperature will be higher then normal.
For refrigerators (Lagering and brewing)
Generally to replace the tc of your refrigerator you need the model number and company of the fridge. But many times you need to control the temperature of your freezer for certain application like brewer making wine making etc.For that certain general purpose probes with thermostat are available.
Surface tc probes
These types are used to measure the surface temperature of hot plates griddles, central heating radiators etc.They are also helpful in plumbing applications like measuring the temperature of pipes, radiators, boilers etc to maintain an efficient heating system.
For meat (Food processing/catering)
Your food items may require to measure its temperature for culinary purpose. Correct temperature improves its taste and prevent from damage.
Types of thermocouples
Thermocouples are categorized based on their use, sensitivity and temperature range. They can be easily identified by using the color chart.
Type K (Chromel / Alumel)
Sensitivity -41 µV/°C.
Temperature range –270 to 1372°C.
Use: General purpose use like process plants etc. It is oldest and therefore most commonly used. Its probes are of all varieties and have its temperature range is quite wide making it applicable in relatively vast processes. Its can readily be used in oxidizing or inert environment. However in reducing or vacuum it can deteriorate. Nickel part of the probe is magnetic so its show abrupt variation in emf above temperature around 220.
Type E (Chromel / Constantan)
Sensitivity (68 µV/°C) Highest sensitivity in terms of EMF /°C or °F of any of the thermocouples
Overall range –270 to 1000°C useful range 95-900 degrees C
It is mainly used for cryogenics or very low temperature measurement .Another advantage is Its none of the wires are magnetic. Suitable in oxidizing environment which are clean and not partially oxidizing or frequent change in environment from oxidizing to reducing.
Type J (Iron / Constantan)
Useful range (-45 to +760 °C)
Use: Equipment that can not accept ‘modern’ thermocouples.it is magnetic so above curie temperature around 750 it can loose calibration. Reducing, Vacuum, Inert environment .It can detoriate at high temperature at high temperature in oxidizing or sulphurous environment below zero temperature application is also not suitable because of iron conductor may rust or form embritllement. So it is used upto 450 °C.
Type N (Nicrosil / Nisil)
650 -1260 degrees C –270 to 1300°C
Use: It is stable as it does not show abrupt emf change like type k. Also at high temperature it does not oxidizes. was made as a better replacement of type K. Type B s or R are TC are also stable type of thermocouple but their sensitivity is not so good at low temperature so the are mostly used for high temperature. Also N type is much cheaper.
Type R/S/B (Platinum type thermocouple)
These are noble metal thermocouple and one of the most stable types. But they are best applicable at high temperature because of the flat or constant emf response at temperature below 40-50°C Doe snot oxidizes in oxidizing condition like hot air. It is not enclosed in metal tubes because of high susceptibility to contamination ie diffusion of unwanted material etc.
They are mainly used in glass, semiconductor or steel industries to monitor the temperature of arch of this melting chamber of furnace where glass or steel is melted. They are generally enclosed in ceramic tube.
R (Platinum / Rhodium)
Overall range –50 to 1768°C.Useful range 870-1450 degrees C
S (Platinum / Rhodium)
Overall range –50 to 1768°C Useful range 980-1450 degrees C
sensitivity (10 µV/°C)
They are particularly used as standard for calibrating in melting point of gold.
B (Platinum / Rhodium)
Overall range 0 to 1820°C.Useful range1370-1700 degrees C (approx 10 µV/°C)
Type T (copper-constanan)
Overall range –270 to 400°C.Useful Range 200-350 degrees C.
Sensitivity 43 µV/°C.
They are good at low temperature so cryogenics very low temperature) application is its standard characteristics. They are Particularly useful where long presence of moisture in unavoidable such as food industries. Can be used in all types of environment inert, oxidizing or reducing provided they are mild and not extreme.
Type C tungsten 5% rhenium – tungsten 26% rhenium)
Overall range 0 to 2320°C.Useful range 1650-2315 degrees C
Well-suited for vacuum furnaces at extremely high temperatures. Not useful in presence of oxygen above 250 °C. They are used vehicle for space, nuclear reactor core, heating in industrial process etc. Tungsten is combustible at very high temperature so cannot be used in oxidizing environment. They are used in inert or hydrogen environment. Also in rigorous process of heating and cooling may cause embrittlement which then may cause breakage of wire due to vibration. This limits it to be used in all type of industrial heating.
Type M nickel alloy for each wire
0-1287 degrees C
Use: These thermocouples are used in vacuum furnaces for the same reasons as with type C.
This chart shows the various color codes for identifying the type of wire and its polarity based on the type of wire. These color codes are different in different countries and Also different for different types of thermocouples. You can identify the type of thermocouple by noticing the insulation color and the color used for different polarities wire.
Omega All range and types of Tc and other sensors. Complete range of instruments for industrial instrumentation.
Conac technologies Temperature sensors and compression seal fittings solution.
ABB TC and TC transmitters.
Danfoss Sensors valves Heating and refrigeration control of appliances at home. Sensors switches and instrument for Industrial automation.
Fluke Handheld instruments loggers, Calibrator, Thermometer, Surface Tc probe and local reading instruments.
Watlow Electric heaters and Temperature sensors and temperature controllers
Agilent technologies TC pressure or vacuum gauge. Industrial automation and lab service.
Calex electronics limited
United electrics controls
Gefran Industrial automation, controllers ,inverter for drives and sensors(temperature, pressure, position, force transducers(load cell) etc)
Thermal detection Temperature sensors for process and manufacturing industries.(Pharmaceuticals temperature probe, industrial straight TC, fitting.
Madison level pressure and temperature sensor(Tc, RTD, switch, thermistors) manufacturing
Lab facility Complete range of instruments for TC and TC accessories. Connectors, cables, sensors, transmitters, fittings etc
bocon Temperature sensors. Limited variety of TC designed
Ust sensor industrial sensors(temperature, pressure etc)
West control solution
Tecpel Handheld TC for multimeters
H.heinz meb wider stande gmbh
Phoenux Tm gmbx
digitron Haldheld reading and data logging
CMR Sensors for diesel and gas engines. Bearing temperature, exhaust gas temperature etc.
B+B Temp, pressure, humidity sensors
Rossel mestechnik Temp sensors for various industries.
Temsens instruments TC and other temperature sensors
Pixsys Bayonate type TCs
Murphy Stainless steel straight TCs
Athena All range of TC design(straight, wires, extruders etc)
Ihne and tesch
Fischer messtecnik Straight TC for process control and Tc transmitters.
Pico technology TC with handle or plug type or expose wire with connectors for use with data loggers at local reading
Rototherm Mineral insulated straight Tc with assemblies.
Nor cal products
Hoover dam technologies