Thermocouples Istvn Seres Szent Istvn University Gdll Department

Thermocouples István Seres Szent István University, Gödöllő, Department of Physics and Process Control

The thermocouple as an electrical circuit 2

The thermocouple as an electrical circuit The contact voltage Metal A Metal B E 3

The thermocouple as an electrical circuit The principle of the operation The contact voltage depends on the temperature + T U 1 A B VAB(T, T 0)=U 1 -U 2 T 0 U 2 + 4

The thermocouple as an electrical circuit The classically used calibration function VAB(T, To) = a (T-To)+b (T-To)2+g (T-To)3+. . . 5

The physical laws should be valid for thermocouple Law of homogenous metal: VAA(T, To) = 0 Law of isothermocouple: VAB(T, T) = 0 Antisymmetrical law: VAB(T, To) = - VAB(To, T) Law of the inner metal : VAB(T, To) = VAC(T, To) +VCB(T, To) T U 1 A B T 0 U 2 + - Law of the inner temperature: VAB(T 1, T 3) = VAB(T 1, T 2) +VAB(T 2, T 3) VAB(T, To) = a (T-To)+b (T-To)2+g (T-To)3+. . . 6

The thermovoltage function based on the function equation theory Sinzow: F(x, z) = G(x, y) + H(y, z) F(x, z) = h(z) - f(x). The functions with “eliminating” property can be written as the subtraction of two one-variable function. 7

The thermovoltage function based on the function equation theory Sinzow: VAB(T, T 0) = VAC(T, T 0) +VCB(T, T 0) VAB(T, T 0) = f(T) - g(T 0) Anti-symmetry: VAB(T, T 0) = -VAB(T 0, T) VAB(T, T 0) = f(T) - f(T 0) 8

The thermovoltage function based on the Fermi-Dirac statistics WF 0 The energy distribution function of the Fermi-Dirac statistics 9

The thermovoltage function based on the Fermi-Dirac statistics = With the given notation of x, it can be proved that (not detailed here): 10

The thermovoltage function based on the Fermi-Dirac statistics The potential holes and the Fermi energies before contacting the two metals 2004. 05. 17. 11

The thermovoltage function based on the Fermi-Dirac statistics The potential holes and the Fermi energies after contacting the two metals The Galvani voltage between the two metals: 12

The thermovoltage function based on the Fermi-Dirac statistics The Galvani voltage between the two metals: U 2 -T 2) + b(T 4 -T 4)+g(T 6 -T 6) (T, T ) = a(T AB 0 0 13

The check of the calibration function for the basic laws U 2 -T 2) + b(T 4 -T 4)+g(T 6 -T 6)+… (T, T ) = a(T AB 0 0 UAA(T, To) = 0 a, b, g = 0 UAB(T, T) = 0 UAB(T, To) = - UAB(To, T) UAB(T, To) = UAC(T, To) +UCB(T, To) UAB(T 1, T 3) = UAB(T 1, T 2) +UAB(T 2, T 3) 14

The new calibration function check for the data of the TC producer Mérőponti hőmérséklet 15

Practical application of thermocouples vacuum cooling of mushroom 16

Continue next week ! 17