The principle of thermocouple compensating conductor

Before understanding the principle of thermocouple compensation wire, we should first know the thermocouple temperature measurement principle of

in the practical application, the measurement and control instrument is a certain distance from thermocouple total. As shown in figure 2.

the need in the thermocouple ( A and B in figure) Pick up again after a period of wire, the signal of thermocouple received temperature

table. C and D in the diagram to connect the thermocouple wires and thermometer table.

in the figure, the working end temperature T1, A, B and C, and D junction temperature of T2, measuring instrument ( The reference side) Temperature for T0.

we can put the total loop total electromotive force is divided into two period of thermoelectric emfs and E, A and B are represented by A, thermoelectric emf of the EAB ( T1, T2) , C, D for another section, thermoelectric emfs for ECD ( T2, T0) , namely:

E = the EAB ( T1, T2) + ECD（ T2, T0) （ Thermocouple conductor among law) （ 1)

in the diagram above, if the material of C, D and A, B, or C to A, D is the B, is equal to the thermocouple in T2 (A, B The middle temperature) Creates a connection point, at this point, the loop total potential:

E = the EAB ( T1, T2) + EAB（ T2, T0) = EAB（ T1、T0) （ Thermocouple temperature among law) （ 2)

from type ( 2) We can see that as long as it is the same thermocouple, among the connection point, the total potential and the connection point temperature ( The middle temperature) Has nothing to do, but work only with the client and refer to the temperature. This is what we want. In thermocouple wiring, we don't need to consider the middle have the join point, also don't need to consider the connection point of temperature, but with a thermocouple connected to the medium and measuring instrument.

to comparison, 2) Type ( 1) 。 If we can find some material C, D, it can satisfy the:

ECD ( T2, T0) = EAB（ T2, T0) （ 3)

type ( 1) Be:

E = the EAB ( T1, T2) + ECD（ T2, T0) = EAB（ T1, T2) + EAB（ T2, T0) = EAB（ T1、T0) （ 4)

content type ( 3) Material C and D we called thermocouple compensating conductor of A and B.

type ( 4) Also tells us, the use of the compensating conductor, we will T2 extends to T0, but in the end of our measurement result has nothing to do with T2, so that we can understand, because we use the wire C, D, is it compensated the T2 connection of additional potential, and we do not need to consider the final measurement T2, which is why C and D is called the cause of the compensating conductor.

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