Thermoelectric Generation - Keithley 2750 User Manual

Model 2750 Multimeter/Switch System User's Manual

Thermoelectric generation

Figure E-1
made of the A material, while the source under test is the B material. The temperatures
between the junctions are shown as T
the following relationship may be used:
E = Q
T
where: E
In the unlikely event that the two junction temperatures are identical, no thermal EMFs
will be generated. More often, the two junction temperatures will differ, and considerable
thermal EMFs will be generated.
A typical test setup will probably have several copper-to-copper junctions. As pointed out
earlier, each junction can have a thermoelectric coefficient as high as 0.2µV/°C. Since the
two materials will frequently have a several degree temperature differential, it is easy to
see how thermal potentials of several microvolts can be generated even if reasonable pre-
cautions are taken.
Figure E-1
Thermal EMF generation
2750
CH1
shows a representation of how thermal EMFs are generated. The test leads are
(T – T )
AB 1 2
= Generated thermal EMF
T
Q = Thermoelectric coefficient of material A with respect to
AB
material B (µV/°C)
T = Temperature of B junction (°C or K)
1
T = Temperature of A junction (°C or K)
2
E = Q (T
T AB
A
HI
E
T
LO
T
2
B
and T . To determine the thermal EMF generated,
1 2
- T )
2
1
T
1
Measurement Considerations E-3