The principle of thermocouple is base on the binding ability of metal atoms(ions) to free electrons in metals related to temperature, different kinds of metal atoms(ions) have different binding abilities to free electrons. The metal on both sides of the fusion interface after two kinds of metals are welded together has different binding ability to free electrons, the large one is positively charged and the other side is negatively charged. There is electromotive force (EMF) difference between the two sides of metals that be changed with the temperature, the value of EMF is small but can be accurately measured.
1.The practical use of thermocouple is not as simple as the above principle, sometimes the thermocouple need to be extended, the materials of thermocouple extension wire is not necessarily the same as the thermocouple metal material, as long as the temperature of the positive and negative joint is the same, it has no effect on temperature measurement.
2.Since the instrument measure the electromotive force, there is no current in the thermocouple wire in principle.
3.Since the EMF is very small, it is susceptible to various electromagnetic interferences in many cases, so be attention to this.
4.In some case, it is necessary to measure the temperature of the charged object, such as the temperature of wire joint, power terminal block, There are many instruments that can directly measure the temperature, but the thermocouple alloy wire has a high voltage that could be dangerous to the personnel, therefore the wires from the instrument to measured object need to be insulated from the personnel during the measurement, it must be powered off when adjust the contact points of the instrument and the measuring points. Get more information from www.super-instrument.com.
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