The Four Laws of K-type Thermocouple Wires

The Four Laws of K-type Thermocouple Wires
Law of homogeneous conductor
The K-type thermocouple wire is welded at both ends of the same homogeneous material (conductor or semiconductor) to form a closed circuit. Regardless of the conductor cross-section and temperature distribution, no contact potential will be generated, and the temperature difference potential will cancel out, resulting in a total potential of zero in the circuit.
It can be seen that thermocouples must be composed of two different homogeneous conductors or semiconductors. If the material of the hot electrode is uneven, an additional heating potential will be generated due to the existence of a temperature gradient.
Law of intermediate conductor
In the K-type thermocouple circuit, a middle conductor (third conductor) is connected. As long as the temperature at both ends of the middle conductor is the same, the introduction of the middle conductor has no effect on the total potential of the thermocouple circuit. This is the law of middle conductor.
Application: According to the law of intermediate conductor, in the actual temperature measurement application of thermocouples, the form of hot end welding and cold end open circuit is often used. The cold end is connected to the display instrument through a connecting wire to form a temperature measurement system.
Some people are concerned that using copper wires to connect the cold end of the thermocouple to the instrument to read the mV value may cause additional measurement errors due to the contact potential generated at the connection between the wire and the thermocouple. According to this law, there is no such error!