Relationship between temperature and voltage of Type T thermocouple

In summary, the conversation discusses the relationship between temperature and the output of a type T thermocouple, and how to determine this relationship. The suggestion is made to calibrate the thermocouple by testing it in iced water and boiling water and noting the mV readings. Various resources and data sets are provided as references. It is noted that the output of a thermocouple depends on the temperature at the joint and the cold junction, and that the purity of the metals in the thermocouple can affect the potential it produces.
  • #1
TheAnalogKid
10
0
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.
 
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  • #2
you could calibrate the thermocouple.
put it in iced water, along with another thermometer. read the mV's and note the temp
then boil the water, read the temp, note the mV's.
i think the response is linear, but it may not be.!
 
  • #3
The might help - http://www.omega.com/temperature/Z/pdf/z223.pdf and 1.496 mV corresponds to 99°F (37.2°C).

It looks like it's supposed to read ~0 V at freezing or ~32°F.

I would recommend what phlegmy suggested. Try it in ice water and boiling water as a test.

Type T (Copper Constantan) thermocouples.
http://www.veriteq.com/thermocouple-data-logger/type-t.htm

The Principles and Methods of Using Thermocouples
http://www.iotech.com/mcjun96.html

http://srdata.nist.gov/its90/download/type_t.tab (in Celsius).

Looking at this last dataset, 1.5 mV is between 1.486 and 1.528 mV, which correspond to 37 and 38°C, so 1.5 mV ~ 37.5°C (99.5°F)
 
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  • #4
The output of a thermocouple depends on the temperature of the termocouple ( the point where the two wires are joint ) and the temperature where the two wires connect to the circuit ( the "cold junction" ). The output is a function ( linear ? , I don't know ) of the difference of temperatures. So there is no answer to your question.
 
  • #5
It depends on the set up. Most TC systems have a cold junction compensation function. However, the OP should specify what the actual set up is. If there is a bare bones set up, the cold junction compensation is likely to be forgotten. Then the tables will be useless.
 
  • #6
Also, the purity of the metals in the TC will make a difference in the potential it produces.
 

1. How does the temperature affect the voltage output of a Type T thermocouple?

The voltage output of a Type T thermocouple is directly proportional to the temperature difference between the two junctions. This means that as the temperature increases, the voltage output also increases. The relationship between temperature and voltage can be described by the Seebeck effect, where a voltage is generated when there is a temperature gradient between two different metals.

2. What is the range of temperatures that a Type T thermocouple can measure?

A Type T thermocouple is suitable for measuring temperatures ranging from -200°C to 350°C. However, the accuracy and reliability of the measurements may vary depending on the specific type of thermocouple and the environment in which it is used.

3. Can the voltage output of a Type T thermocouple be affected by external factors?

Yes, the voltage output of a Type T thermocouple can be affected by external factors such as electromagnetic interference, humidity, and vibrations. These factors can introduce errors in the voltage output and may need to be compensated for in order to obtain accurate temperature measurements.

4. How do I convert the voltage output of a Type T thermocouple to a temperature reading?

The voltage output of a Type T thermocouple can be converted to a temperature reading by using a thermocouple reference table or a thermocouple calculator. These tools take into account the voltage output and the type of thermocouple being used to provide an accurate temperature reading.

5. Are there any precautions I should take when using a Type T thermocouple?

Yes, it is important to handle a Type T thermocouple with care as it is made of delicate materials and can be easily damaged. It is also recommended to calibrate the thermocouple periodically to ensure accurate measurements. Additionally, attention should be paid to any external factors that could affect the voltage output, as mentioned in question 3.

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