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Appendix B. Thermocouple
When two wires composed of dissimilar homogeneous metals are joined at one end,
a thermoelectric electromotive force (emf) appears that depends only on the metals
and the junction temperature. This is called the Seebeck effect. A pair of different
metals with a fixed junction at one end constitutes a thermocouple. For small
changes in temperature, the emf is linearly proportional to the temperature. This
implies that the temperature reading can be obtained by measuring the emf.
We cannot measure the emf, V1, directly because when a voltmeter is connected to
the thermocouple, another emf, V2, is created at the (cold) junction of the
thermocouple and the voltmeter. The cold junction compensation method is used to
resolve the problem. Using another sensor, e.g. a thermistor, to measure the cold
junction temperature, T2, we can calculate the emf, V2, which corresponds to T2.
The thermocouple emf, V1, can be obtained by adding V2 to that measured by the
voltmeter and then the temperature.
Summary of Contents for OME-ET-7000 Series
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