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Model 2700 Multimeter/Switch System User’s Manual
Measurement Considerations
E-3
Thermoelectric generation
Figure E-1 shows a representation of how thermal EMFs are generated. The test leads are
made of the A material, while the source under test is the B material. The temperatures
between the junctions are shown as T1 and T2. To determine the thermal EMF generated,
the following relationship may be used:
ET = QAB (T1 – T2)
where: ET
QAB
T1
T2
= Generated thermal EMF
= Thermoelectric coefficient of material A with respect to material B (µV/°C)
= Temperature of B junction (°C or K)
= Temperature of A junction (°C or K)
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
precautions are taken.
Figure E-1
Thermal EMF generation
ET = QAB (T1 – T2)
2700
2182
A
HI
CH1
ET
LO
T1
T2
B