Measurement-computing CB-7011 Instrukcja Użytkownika Pobierz pdf (Strona 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.

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Measurement-computing CB-7011 Instrukcja Użytkownika Strona 64