
The voltage representing temperature T
H
is obtained due to the thermoelectric effect in the leads
when zero current flows, i.e. the potentiometer is balanced and J
I
¼ 0. At zero current, as previously
discussed, the electromotive force (emf) at the potentiometer (or DVM) equals the thermal emf
generated by the thermocouple.
From Eqn (20.48), the potential difference between each end of a wire of material M is related to
the temperature difference between the points by the following equation.
dεÞ
J
I
¼0
¼S
M
dT
J
I
¼0
(20.50)
where S
M
is the value of S* for material M.
Equation (20.50) can be applied to each wire in the system shown above, to give the following ...