Measurement Computing CB-7011 - Manual (Page 64)

64
CB-7011/CB-7011D, CD-7018 User’s Manual
linearly proportional to temperature.
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
(cold) junction. Therefore we need to eliminate the junction ther-
moelectric to measure the correct Seebeck voltage, and this is called
“Cold Junction Compensation”.
For most thermocouples, the Seebeck voltage is 0V while
at 0°C. One simple way to cancel the junction voltage is to put the
junction into 0°C environment and the junction voltage is 0V. Nor-
mally, this is not a good method for most applications. The typical
method is to measure the junction temperature with a thermistor,
and measure the junction voltage from the junction temperature.
Then we can get the Seebeck voltage from measured thermocouple
voltage and junction voltage, and we can calculate the temperature
from the Seebeck voltage.