B&B Electronics Network Device I-7011 - Manual (Page 64)

64
I-7011, I-7018 User Manual Rev:B1.0
To measure the Seebeck voltage directly is not available
because we must first connect a voltmeter to the thermocouple,
and the voltmeter leads themselves create a new thermoelectric
circuit. Therefore we need to eliminate the junction thermoelectric
to measure the correct Seebeck voltage, and this is called “Cold
Junction Compensation”.
For most thermocouples, the Seebeck voltage is 0V while
in 0°C. One simple way to cancel the junction voltage is to put the
junction into 0°C enviroment and the junction voltage is 0V. Nor-
mally, this is not a good method for most application. Typical method
is to measure the junction temperature by thermistor, and measure
the junction voltage from the junction temperature. Then we may
get the Seebeck voltage from measured thermocouple voltage and
junction voltage, and we may calculate the temperature from the
Seebeck voltage.