#WishIknew How do you calibrate a thermocouple?

Temperature

When you have a question about process automation that needs a short answer, let us know with #WishIknew and #Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, and reviews if you want to know more.

I wish I knew how to calibrate a thermocouple!

You have several ways that apply to all thermocouple types, but the right way for you depends on your conditions. However, you always need a calibration furnace. So let’s go through the options.

Standard voltmeter

If you have a lab with the thermocouple and voltmeter in the same ambient temperature, you can use a compensating cable. Put your sensor in the calibration furnace and set the furnace to increase and decrease the temperature. As the voltmeter measures the millivolts, you can find the temperature using a reference table.

Multimeter Thermocouples
Courtesy of Conrad

Cold junction 

Usually, the factory lab calibrates your sensor using a cold junction for higher accuracy. It uses zero degrees Celsius as a reference point because the reference tables base their values on that point. This should give you an accurate millivolt value.

Cold junction compesation thermocouples How do you calibrate a thermocouple
Courtsy of Mosaic Industries

Comparative calibration + external reference junction

Here you have a second thermocouple connected to an external reference junction. Thus, you can compare your sensor output with the reference sensor. Both will start at zero degrees Celsius again.

External reference junction How do you calibrate a thermocouple
Courtesy of FLUKE

Digital calibrator

You can connect the sensor directly to a digital calibrator, which will compensate for the ambient temperature. You can also find calibrators that work with the calibration furnace to increase and decrease the temperature and collect all the data automatically.

Fluke Calibrator How do you calibrate a thermocouple
Courtesy of FLUKE

This video will tell you more about thermocouple calibration: