Relationship between temperature and voltage of Type T thermocouple

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Discussion Overview

The discussion revolves around the relationship between temperature and voltage output of a Type T thermocouple, specifically addressing how to determine the temperature corresponding to a specific voltage output, such as 1.5 mV. The scope includes theoretical understanding, practical calibration methods, and considerations of experimental setups.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Experimental/applied

Main Points Raised

  • One participant suggests calibrating the thermocouple by measuring its output in ice water and boiling water to establish a relationship, noting that the response may be linear but is uncertain.
  • Another participant provides a reference indicating that 1.496 mV corresponds to approximately 37.2°C (99°F) and suggests that 1.5 mV is roughly between 37 and 38°C.
  • A participant emphasizes that the output of a thermocouple is dependent on both the temperature at the junction of the wires and the temperature at the cold junction, indicating that the relationship may not be straightforward.
  • It is noted that cold junction compensation is typically part of thermocouple systems, and the absence of this could affect the accuracy of readings.
  • One participant raises the point that the purity of the metals used in the thermocouple can influence the voltage output.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the relationship between temperature and voltage output, with some suggesting linearity while others indicate uncertainty. There is no consensus on the exact relationship or the best method for determining temperature from voltage output.

Contextual Notes

Limitations include the dependence on specific setups, such as cold junction compensation, and the potential variability due to the purity of the metals in the thermocouple. The discussion does not resolve these factors.

TheAnalogKid
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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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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.!
 
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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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.
 
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.
 
Also, the purity of the metals in the TC will make a difference in the potential it produces.
 

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