I purchased a temperature module for the reading of thermocouple. But unfortunately i did not notice that there is written 20 deg. C. internal on the existing module though there is a TC compensator which is externally connected with the module. The module which i purchased it came with 20 deg.c. external and without any
TC compensator. So this module is not working in the system. So i am at a loss.

Could anybody explain properly what is the real meaning of 20 deg.c. external & internal?

 

The internal/external compensation is your cold junction. If you don't understand thermocouple operation, do a search for thermocouple theory.

Mat

 

A T/C generates a mV output which is the difference between the "hot end" (process end) and the "cold end" (where the measurement is made).

The "mV to temperature values" reference tables that are used by electronic instrumentation assume that the cold end is at the freezing point of water (0°C or 32°F). Both 'ice point compensation' and 'cold junction compensation' are terms used to describe techniques to compensate for the fact that the cold end of the T/C, the connection point where the mV measurement is made, is typically not at the freezing point of water.

In the old days, a separate T/C junction was immersed in a bucket of ice water to achieve "ice point" for a reference. This is an example of external compensation - the ice bucket provides cold junction compensation external to the measurement device. The millivolt reading from the standard tables is correct when cold junction is taken into account.

Without the ice bucket, one would have to measure the physical temperature of the junction/connection block at the cold end, look up the millivolt signal generated by that type T/C for that temperature, and then add that mV value to the signal measured without any cold junction compensation.

The next development was external electronic devices for specific thermocouple types that would measure the junction block temperature. These were considered "external" compensation because they were separate devices outside the measuring device (the controller or the recorder or the indicator).

Present day commercial T/C devices use electronic sensors to measure the temperature of the junction block and do exactly that. Most, if not all are considered "internal" compensation, because these are part of the measuring device, not something the user attaches to the connection points.

For backwards compatibility, many present day temperature commercial T/C devices allow configuration for either external or internal compensation.

Unless you have a little "black box" cold junction compensator that is to be wired to the junction strip where the T/C terminates, your device most likely has ice point compensation built into it as internal compensation.

Bud

 

There was already a good explaination of TC compensation posted, so I will skip that part.

A quick check to see if compensation is working is to short the TC input with a short lenght of copper wire. Your TC readout should read about room temperature. (Atctually it should read the temperature of the TC input terminals.) If it does, your compensation is working. If not, we need to explore this further.

Don't forget that red is negative in TC land.

Dave [email protected]

 

Bud, It's August 2015 and I am reading your explanation. I just wanted to say THANK YOU.