In case of accurate thermocouple measurement, its a common practice to reference the cold junction temperature at ice point (0 Deg C) so that copper leads may be connected to an EMF readout device. This procedure avoids the compensation of cold junction temperature at the terminal of read out which may not be constant and the measurement may not be very accurate.
Thermocouple output is dependent of temperature of hot junction and temperature of cold junction.
The Cold junction temperature needs to be known to get the hot junction temperature.
To reduce the uncertainity of cold junction measurement Reference junction boxes are used.
A reference junction box terminates the thermocouple cold end at a known and constant temperature. This can be 0 deg or 60 Deg C, as per user requirement.
The EMF of the reference junction is fixed and is added on to the output of the thermocouple.
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