Omega RD100B Temperature Measurement When Using a Thermocouple, RJC of TC input, Maintenance 11-5

11.4 Calibrating the Recorder

Temperature Measurement When Using an RTD

The resistance of three lead wires must be equal.

/b	−/B +/A
		Decade resistance box
Input terminals
	Temperature Measurement When Using a Thermocouple
	Copper wires	Thermocouple wires or TC extension wires

+

–

	Copper
DC voltage standard	wires

− +

Thermocouple	Input terminals
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

Maintenance

11-5