# What is Thermocouple: Definition and 49 Discussions

A thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of Seebeck effect, and this voltage can be interpreted to measure temperature. Thermocouples are widely used as temperature sensors.Commercial thermocouples are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of temperature measurement, thermocouples are self powered and require no external form of excitation. The main limitation with thermocouples is accuracy; system errors of less than one degree Celsius (°C) can be difficult to achieve.Thermocouples are widely used in science and industry. Applications include temperature measurement for kilns, gas turbine exhaust, diesel engines, and other industrial processes. Thermocouples are also used in homes, offices and businesses as the temperature sensors in thermostats, and also as flame sensors in safety devices for gas-powered appliances.

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1. ### Can a type K thermocouple be used with cryo?

Hi. I can not understand why type K tc can not be used with cryogenic temperatures? If for example calibrated with liquid nitrogen and ice, can it be used from 0 C to -200 C accurately? I understand that there is a non-linear characteristic a lower temperatures, but then one could make a...
2. ### Calculating the resistance in a compensating circuit for a thermocouple

Homework Statement:: A K-type thermocouple is connected as shown to sense temperature. The temperature zone is at 25°C. The RTD has a resistance of 100 at 0°C and a TCR coefficient of 0.00385. A 5V power supply drives the circuit. Calculate R2 for proper compensation. What is the emf produced...
3. ### Temperature Measurement: Are All Thermometers Created Equal?

What is the difference in temperature with different thermometers for the same object? Thanks !
4. ### How does a thermocouple exploit the Seebeck effect?

Homework Statement descibe the operational principle of a thermocouple Homework EquationsThe Attempt at a Solution A thermocouple works using the seebeck affect. Two dissimilar metals joined together at one end forming a "hot" junction this is where the temperature is measured. At the other end...
5. ### How to determine the wire gauge of thermocouple wires?

Homework Statement A resistance thermometer bridge circuit shown below has a designed maximum temperature of 150°C, ignoring the effects of connecting wire resistance. If the connecting loop is 200 m determine the smallest gauge (swg) of copper wire which must be used if the indicated maximum...
6. ### Temperature rise calculation for electrical devices

There are 2 types of temp rise measurement for electrical devices, 1)resistance type 2) thermocouple type (direct measurement) My query is 1) which method is superior and please explain me the reason. 2) Which gives higher value of measurement? Thanks in advance.
7. ### Removing thermocouple from stovetop

Our gas burners have thermocouples so the gas turns off if the flame goes out. Our power burner has an undiagnosed issue that causes the gas supply to get cut off even if the flame is burning. We've replaced the thermocouple, cleaned the (clean) flame spreader, and unclogged the (clear) gas...
8. ### Thermocouple Type-K: 3 Wires & Ceramic Shield?

I have a type-K thermo-couple. In all the thermocouple, I have seen so far there is just two wires and a joint. But in the one I got, there is third wire which is connected to the joint and is twisted around the ceramic shield of the thermocouple. I do not know what does it do? Any idea...
9. ### Fitting a thermocouple to a motor

Hi. It's my first post I work in a manufacturing plant where a hydraulic pump motor has failed. The cause was bearing failure and the motor locked up. The motor still insulation tested ok, but is being sent out for rewind and new bearings I am looking at ways to predict early failure? I want...
10. ### Thermocouple time to indicate temp

Homework Statement Homework Equations The Attempt at a Solution I do not know exactly how to start this problem. I would really appreciate it if you could give me some hints. I know that e^ - t/tau=T(t)-Twall/Ti-Twall where tau=m*cp/hA where h=convective heat tr.coeff and T(t) is desired temp...
11. ### Mathematical relationship of a thermocouple

Homework Statement The graph shows the response of a bare thermocouple which has been subjected to a step change in temperature from 50°C to 10°C. Assuming that the bare thermocouple behaves as a single transfer lag system, determine the mathematical relationship between the temperature (T) and...
12. ### Sensitivity of a thermocouple from thermometric function

Homework Statement In what range of temperature will this thermocouple be more sensitive (i.e. having a measureable voltage for a small change in temperature)? Homework Equations The thermal electromotive force (E) of a thermocouple is described in terms of temperature by the function: E =...
13. ### Temperature variation within thermocouple in Seebeck mode

Hi guys, I posted a thread a while ago asking for advices to create a Finite Element model of a radioisotope thermoelectric generator. I've basically finished this model mainly using conduction and radiation at the boundaries. I am wondering something though: currently my heat gradient is very...
14. ### Okay to twist thermocouple wires?

I am trying to make some K-type thermocouples. I have wire. Is it okay to twist the ends together at the sensing tip? There is no tension in the wires, so is it okay? I don't see why everyone says to weld them or solder them. I don't have a welder and the solder won't stick (yes I used flux).
15. ### Thermocouple Applications to generate current to run a very small led ?

Can I use a thermocouple which has a temperature difference of 1 degree to generate current to run a very small led.
16. ### How would you calculate the energy generated by a thermocouple?

Say you had a thermocouple 2" wide by half a meter long and the temperature gradient was 2000 degrees Celsius how much electricity would it generate? If it was hot enough could a non metal plasma be used as the secondary conductor rather than a second type of metal?
17. ### T type thermocouple for Delta T measurement

I am working on an experiment where I need to measure the Delta T across a heat ex-changer. I have two independent T Type thermo couple, one at the inlet and the other at the outlet. Both tied to an Agilent data logger. I normally put the data into an excel sheet and generate Delta T = T1 - T2...
18. ### K type thermocouple malfunction at 800-1000K

Hey Everybody, So we have a PID heating system with K-type thermocouples running through labview. We have a chassis that has 6 DAQ cards for Tc inputs (2 daq cards), flowcontroller in/out, an output for the heating elements for the PID control, and another input for a pressure transducer...
19. ### How Can Insulation Thickness Prevent Condensation in a Thermocouple System?

Dear Seniors and Friends We have a thermocouple consisting of two pipes . In the inner pipe there is the flue gas and the outer pipe we have a cooling water . Currently we are facing a problem that gases are being condensed below 100 C because of cooling water .We have to apply insulation...

Are there any cons with the thermo-couple? Like in the mercury thermometer, it absorbs some heat from the source, etc.
21. ### Control system - Thermistor, thermocouple, PT100

I'm 95% sure I got it all correct, but I'd appeciate another set of eyes Homework Statement 1) What's a thermistor? What is its principle of action? 2) What's a thermocouple, and what is its principle of action? 3) How does temperature transducer act based on the bimetal principle...
22. ### Explaination of thermocouple chart ?

The Y axis represents the temperature of the measurement junction in a thermo couple chart and what does the X axis represents ? http://www.pyromation.com/downloads/data/emfk_c.pdf. This is a chart for K type thermocouple. Does it represent the temperature of the refernce junction , if...
23. ### Calibration of a Thermocouple and the Seebeck Effect

Homework Statement We were asked to calibrate a J type thermocouple. In order to do that our reference junction was kept at 1°C while in the other junction the temperatures were raised from 22°C to 93°C (we registered the voltage every 2°C) then we plotted the data in a graph with the...
24. ### Can a thermocouple be used as a power cable?

I am trying to find out if type K thermocouple is capable of transmitting power from an external power supply to a camera and some lamps attached on the end. I have 3 pairs of thermocouples. One pair for the camera supply. One pair for the video output. One pair for the lamps. I have tried...
25. ### Thermal gradients in electrical paths of thermocouple conductors

I recently inherited a problem related to temperature measurement. Thermcouples (d- and k- type) are being used in a high-pressure, high-temperature environment, with the measuring junction suspended in an electrically-insulating solid. The leads of conductors A and B extend out of the...
26. ### Maximizing Accuracy in K Type Thermocouple Measurements

Hello all, I'm looking to buy an accurate K Type thermocouple and I have a couple questions concerning accuracy before I make my decision. -If it is a K Type thermocouple, does it matter how the probe is configured? e.g. length etc.? -Is there any discrepency in accuracy between different...
27. ### Optimizing Thermocouple Connections for Accurate Temperature Measurement

I want to measure the temperature of a metal stage where I am holding a sample. What I have done is to clamp both wires from a thermocouple against the stage using a bolt and washer. Supposedly this is not the best practice but I don't see why this would be a problem. I have read that you are...
28. ### Thermocouple Accuracy and Noise?

I'm looking to use the MAX31855 thermocouple-to-digital converter, to measure temperatures in the range of 0-350C. According to the manufacturer, the ADC inside the chip is identical for every different type of thermocouple, just a different sensitivity is programmed in depending on the type of...
29. ### Electrical DIY - Thermoelectric Peltier Seebeck Thermocouple?

I'm trying to build a DIY working model of TEG/TEC generator similar to the exhaust pipe designs that recover energy from extremely hot exhaust pipe or light those antique candle powered radios. I have 400 (1 inch) pieces of copper wire and 400 (1 inch) pieces of paper clip steel wire. I will...
30. ### Can You Measure Temperature Without Completing the Circuit with a Thermocouple?

I really need someone to tell me I'm wrong and why here or this is going to keep bothering me. As far as I'm aware, a thermocouple works by heating the same side of two different materials, one p-type and one n-type. Since charge carriers also serve to conduct thermal energy, the charge...
31. ### Tool-Work Thermocouple: Why Voltage Appears Measuring Lathe Process?

Why there are voltage appear when use it to measure lathe process by doing this way?
32. ### Problem deal with accuracy of thermocouple

How i am going to confirm or make sure the accurate of thermocouple before i use it for measurement in experiment? Is it ok if ... I put it in ice in order to get 0 Celsius and put in boiling water to get 100 Celsius? In the idea case, i should get 0 and 100 Celsius from thermometer.. but...
33. ### Thermocouple in inductive surrounding

We use induction furnaces to melt aluminium. I want to be able to read the temperature of the water in the pipe flowing in and out of the furnace. I am looking at a spot about 3m away but the induction from the furnace registers about 20mV on a scope which the thermocouples equate to 400V...
34. ### Thermocouple in metal cutting measurement

There are lots of for metal cutting measurement. However, thermocouple is not in the list of metal cutting measurement. Anyway, is it possible to measure the temperature for turning machine by using K-type thermocouple. Can i put the thermocouple at the end of cutting edge to measure ? can it...
35. ### Calibrating a thermocouple HELP

Calibrating a thermocouple HELP! Homework Statement I have to describe a procedure on calibrating a thermocouple system if excess temperature were required in degrees Celsius Homework Equations The Attempt at a Solution I was not sure really sure on how to calibrate the system...
36. ### How Does a Thermocouple Interface with an ECU to Control Fuel Injection?

Hi everyone, please let me know if this posting belongs elsewhere. I have a car that runs a motronic 2.7 fuel injection system and with that there is a thermocouple probe in the exhaust pipe (standard K-type thermocouple). This thermocouple goes into a black box which then sends out a signal...
37. ### Can Thermocouple Junctions Cool Down When Supplied with Current?

is it possible that instead of heating the junction ... of thermocouple... we supply the current n the juntion cools down... which when touched felt cold... according to the supply of current...?? if not then is there any method of doing that
38. ### Which Is Better for Micro-Calorimeters: Thermistor or Thermopile?

Hallo I am going to make a micro-calorimeter and in this micro-calorimeter I need a very sensitive temperature sensor. I think I am going to use a thermistor or a thermopile. But which one to choose? With which temperature sensor do I get the highest sensitivity? And with which temperature...
39. ### Which Thermocouple Type Is Best for Measuring Water Temperature Dynamics?

Hey guys, First post so be nice :smile: I am building a system to measure the temperature of water in a tank. I will be using a thermocouple probe inside a thermowell. My very crude diagram shows the set-up; The temperature range is obviously 0-100 degC which seems to fall into...
40. ### Thermocouple voltage compensator

Hey, Anyone know where I might be able to get a thermocouple voltage compensator (an electrical "ice bath" circuit) for cheap or if I may be able to make one? For a T and/or K type thermocouple. I am looking in the range of \$30 or less. Here is a description of what I'm talking about. Just...
41. ### Building a Simple Transistor Amplifier: Tips and Tricks

Hello, I would like to build a Voltage Amplifier, I did one with 2 Transistors but doesn´t work, it doesn´t amplify. Do you know pleas how to build an Amplifier with transistors and resistors? an easy one with no more then 2 or 4 transistors please. Do you all think it´s possible? Ciani
42. ### How Do You Calculate Temperature Difference Using a Thermocouple?

Homework Statement The one end of the thermocouple is placed in 45C water, the other end in oil of unknown temperature. Of the voltmeter connected to it's end I got 1.35mV. If the sensitivity of the thermocouple is 0.05mV/C, what will the difference of temperature of the liquids be...
43. ### Relationship between temperature and voltage of Type T thermocouple

I have a friend who was asked what temperature corresponds to an output of 1.5mV from a type T thermocouple. What is the relationship and how do you get the relationship? This is an academic problem, so datasheets aren't really the answer I'm looking for.
44. ### Appropriate thermocouple in measuring superheated steam

i want to know which type of thermocouple is used in measuring superheated steam temperature coming out of boiler? this temp sensor is used in accordance with desuperheater to reduce the temperature of excessive superheated steam... can u provide with its range, accuracy, and resolution
45. ### Carpc: Please help me locate the thermocouple on this circuit board

Hi. I have a carpc with a motorized LCD touchscreen monitor (MTSVO-SC). The problem is that I live in Canada and when the temperature is too low, the monitor will refuse to open. It makes a beeping noise and does not open until the temperature is above -5C. I would like to override this...
46. ### Checking thermocouple knowledge

Hello to all. I want to check my knowledge about theory nad principles of thermocoupels. Please can you read .pdf file in attachment and comment? Thank you very much in advance.
47. ### Thermocouple Errors in Temperature Controller

I recently made a Type K thermocouple (Chromel-Alumenel type) and am trying to see if it is working correctly. I do not have the necessary equipment or time to use cold junction compensation, so I was told by my professor to just test the temperatures and voltage readings at room temperature (20...
48. ### How do I measure surface temperature with a thermocouple on a filament bulb?

Can some 1 pls tell me how to measure the surface temperature of the filament bulb with a thermocople, do you put the sensor on the surface or what. As i am new to this can u pls help. Thanks you
49. ### Thermocouple to measure the temperature of glass

Is it wrong to use a thermocouple to mesure the temperature of glass that will range from 20-300oC? as the range of the thermocouple is much higher, does this make it inaccurate? :confused: