Keithley 2700 User Manual

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 T
1
and T
2
. To determine the thermal EMF generated,
the following relationship may be used:
E
T
= Q
AB
(T
1
– T
2
)
where: E
T
= Generated thermal EMF
Q
AB
= Thermoelectric coefficient of material A with respect to material B (µV/
°C)
T
1
= Temperature of B junction (°C or K)
T
2
= 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
HI
LO
E
T
= Q
AB
(T
1
– T
2
)
E
T
T
1
T
2
A
B
2182
CH1
2700

Keithley 2700 Specifications

General

Type	Digital Multimeter
Measurement Functions	DC Voltage, AC Voltage, DC Current, AC Current, Resistance, Frequency, Temperature
DC Voltage Range	100 mV to 1000 V
AC Voltage Range	100 mV to 750 V
Frequency Range	3 Hz to 500 kHz
Temperature Range	-200°C to +1372°C
Display	Vacuum Fluorescent Display
Connectivity	IEEE-488, RS-232
Channels	10
Power Supply	100V to 240V AC, 45Hz to 66Hz
DC Current Range	10 µA to 3 A
AC Current Range	10 µA to 3 A
Temperature Measurement	Thermocouple, RTD