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Users manual
5. Measurement Guide
5.1 DC Measurement Considerations
5.1.1 Thermoelectromotive force error
Thermal voltage is the most common error source in low-level DC voltage measurement, which
will be caused when you use heterogeneous metals to connect circuit under different
temperatures. And each joint between each metal will produce a thermocouple and a voltage
proportionable to the joint temperature. You have to take necessary precaution measures to
reduce thermocouple voltage and temperature change during low-level voltage measurement.
And the best connecting method is copper-copper crimping, for the multimeter input terminal is
made from red copper. The following table lists common thermal voltage during heterogeneous
metal connection.
Copper With
Welding of cadmium
and stannum
Copper
Gold
Silver
Brass
Beryllium copper
5.1.2 DCV load error
If resistance of the equipment under test approximates multimeter internal resistance, it will
cause measurement load error which is listed in the following figure.
Vs=Ideal voltage under test
Rs=Resistance of voltage source under test
Ri=Multimeter input resistance (10MΩ or >10GΩ)
ET3260 and ET3260A
mV
/
℃
(approximate value)
0.2
<0.3
0.5
0.5
3
5
6 1/2 Digit Multimeter
Copper With
Aluminum
Welding of stannum
and plumbum
Kovaralloy or alloy
Silicon
Copper oxide
39
mV
/
℃
(approximate value)
5
5
40
500
1000
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