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11-5
Maintenance
11
Temperature Measurement When Using an RTD
Decade resistance box
The resistance of three lead wires must be equal.
+/A
/b
Input terminals
−/B
Temperature Measurement When Using a Thermocouple
Thermocouple wires or TC extension wiresCopper wires
DC voltage standard
+
–
Input terminals
+
−
Thermocouple
wires
Copper
wires
(0°C standard temperature device)
RJC of TC input
As the measurement terminal of the recorder is generally at room temperature, the
actual output of the thermocouple is different from the values given on the
thermoelectromotive force table based on 0°C. The recorder performs compensation by
measuring the temperature at the input terminal and adding the corresponding
thermoelectromotive force to the actual output of the thermocouple. Therefore, when the
measurement terminal is shorted (equivalent to the case when the detector tip is 0°C),
the measured value indicates the temperature of the input terminal.
When calibrating the recorder, this compensation voltage (thermoelectromotive force of
0°C reference corresponding to the input terminal temperature) must be subtracted from
the output of the DC voltage standard before application. As shown in the figure, by
using the 0°C standard temperature device to compensate the reference junction at 0 °C,
you can input the thermoelectromotive force of 0 °C reference from the DC voltage
standard and perform the calibration.
11.4 Calibrating the Recorder