Archived:CJC and Why Data Acquisition Boards and Signal Conditioning Unit Include a CJC Connection

Updated Feb 2, 2018

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Issue Details

While setting up my data acquisition device for thermocouple measurements I noticed that there is a CJC connection. What is a CJC and why is it important for thermocouple measurements?

Solution

Thermocouples operate on the principle that dissimilar metals generate a voltage when 
in contact with one another. There are many common types of thermocouples (K, E, J, etc.), 
which are comprised of specific metal pairings. Each combination of metal generates a 
known voltage related to the temperature of the junction that can be determined mathematically.

In a temperature measurement application, simply connecting a thermocouple to a data acquisition board or breakout box will add more dissimilar metal junctions, called cold junctions, to your circuit that may skew 
your measurement. Cold Junction Compensation (CJC) removes the effect of the voltages generated by 
these cold junctions for a more accurate temperature measurement.

Some data acquisition boards and signal conditioning units have a built-in CJC terminal, which is a 
temperature reference on the board used to calculate and remove the unwanted voltages.

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