Application law of thermocouple temperature measurement
The thermoelectric characteristics are used to measure the actual temperature, there are several laws derived from the experiment, which have great practical value, collectively referred to as the application of thermocouple temperature measurement laws, they are:
The Seebeck potential of a closed loop consisting of a pair of uniformly oriented conductors depends only on the temperature of the two contacts, not on the temperature distribution along the conductor.
Homogeneous conductor law A closed loop of homogeneous conductors, regardless of their cross section and length, and regardless of their temperature distribution, cannot produce Seebeck effect. That is, two conductors of the same material cannot form a thermocouple.
In a thermocouple circuit, as long as the temperatures at both ends of the middle conductor are equal, the middle conductor is connected without any effect on the thermoelectric potential of the thermocouple circuit. By extension, a fourth or fifth intermediate conductor can be introduced into a closed loop composed of two conductors.
In A thermocouple circuit, if the thermal electrodes A and B are connected to the connecting wires C and D, respectively, and their contact temperatures are T, T1, and T0, respectively, the total thermoelectric potential of the circuit is equal to the algebraic sum of the respective potentials.
In the law of connecting conductors, when the thermoelectric characteristics of A and C, B and D are the same, the position can be changed, and this law is commonly used to correct the temperature at the reference end of the field temperature measurement with thermocouples.
The thermocouple composition law uses three different conductors A, B, C each paired with each other to form three closed circuits, if the thermoelectric potential of the closed circuit composed of thermal electrodes A and B is known, then the thermoelectric of the closed circuit composed of thermal electrodes A and B.
According to this rule, the thermal electrode C is usually used as the standard electrode, which is made of a material with high purity and very stable physical and chemical properties.