Correct method OF Cold JUNCTION compensation

Hello frnds

Is This the correct method of cold junction compenation

Vnet =VhOT -Vcold(ref)

therefore VhOT =Vnet+Vcold(ref)

so V ref at 30 deg celsius say X mv


watever O/p V R gettting v have to add X mv for cold junction compenation
in our PLC/DCS

Is IT RIGHT ?




REGRADS



jos

watever O/p V R gettting v have to add X mv

Click to expand...

What does this mean?

Check your PLC or DCS thermocouple input card, most of them take care of the cold junction compensation for you.

cold junction compensation

Dear Mr.Jose,
We have to consider the difference between the Actual temperature and Reference temperature (taken for calibration) of cold junction. However these are now being taken care in the AI cards.
RT

Electronic devices add the CJC to the thermocouple reading, so the formula is

temperature = thermocouple reading + CJC value

where CJC is the difference between the AI terminal block temperature and the freezing point of water (0°C).

Example:

The temperature being measured is 121°C

T/C hot end is 121°C
T/C cold end at AI input terminal block is 35°C.

The gradient across the thermocouple will be 121-35° = 86°C in equivalent millivolts, depending on the type of T/C.

The cold junction circuit measures the temperature of the terminal block, 35°C in this case. That value is added to the temperature represented by the millivolt value, 86°C, to get the hot end temperature value, 121°C.

121°C = 86°C + 35°C

Dan