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.
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