Digital Temperature Indicator Calibration (Thermocouple) - Using a reference junction

N

neoth

#1
hi all,

what is the difference between using an reference junction and without an reference juntion when calibrating a digital indicator??
 
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BradM

Leader
Admin
#2
Re: Digital Indicator Calibration

Hello, Neoth!

Are you talking about a thermocouple indicator? If so, thermocouples work off of millivolt potential being created by a difference between the measuring and sensing end. The ambient temperature at the sensing junction has to be measured and accounted for. So, enter the cold junction compensator CJC.

You can simulate a millivolt signal into the indicator and verify the meter is working correctly. Then you can short out the junction (use a paper clip or something) and measure the room temperature using the CJC.

In today's instruments, CJC really don't change too much. But... if you have an indicator/controller that is drifting alot (assuming it's not 30 years old :tg:), it may have some issues with the CJC.

With thermocouples, you need the CJC. If you don't use it, you will have error in the readings equivalent to the room temperature. If it's in a panel or something (seeing hot and cold conditions), then that error is increased.:)
 
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