 # How to do the calculation of mv to temperature in a thermocouple

Explain how to convert mv to temperature in a thermocouple

You can multiply Temperature with the sensitivity of the thermocouple and you will get mV.

The sensitivity of different types of thermocouple are below

1. K type- 41 microvolts/ •C

2. J type- 51

3. E type-68

4. B, R, S types-10

The formula is mV=sensitivity X temp.

The mV = sensitivity * Temp equation assumes the mV reading is cold junction referenced, when in most cases when people ask this question, they’re asking how do I know what temperature is when I measure the voltage at the cold end of a thermcouple whose hot end is in the process.

The mV reading of a thermocouple in a process has no cold junction reference so whatever means is used convert mV to temperature will be have an error on the low side (assuming the T/C is measuring a temperature above freezing) which is the difference between the temperature of the thermocouple leads and the freezing point of water.

Any modern electronic measurement of a thermocouple has a cold junction (CJ) reference circuit that measures the temperature of the terminal block where the thermocouple wires connect and that temperature is added to the mV conversion temperature to create the ‘reported’ temperature.

Years ago, techs calibrating the CJ circuit would carry a small liquid-in-glass thermometer that would sit right on the terminal block and they would tweak the CJ measurement to match the thermometer reading.