48
34405A User’s and Service Guide
3
Measurement Tutorial
DC Measurement Considerations
Thermal EMF Errors
Thermoelectric voltages are the most common source of error in low–level
DC voltage measurements. Thermoelectric voltages are generated when you
make circuit connections using dissimilar metals at different temperatures.
Each metal–to–metal junction forms a thermocouple, which generates a
voltage proportional to the junction temperature. You should take the
necessary precautions to minimize thermocouple voltages and temperature
variations in low–level voltage measurements. The best connections are
formed using copper–to–copper crimped connections, as the multimeter’s
input terminals are a copper alloy. The table below shows common
thermoelectric voltages for connections between dissimilar metals.
Copper to
–
Approx. mV / °C
Copper to
–
Approx. mV / °C
Cadmium-Tin Solder
0.2
Aluminum
5
Copper
<0.3
Tin-Lead Solder
5
Gold
0.5
Kovar or Alloy 42
40
Silver
0.5
Silicon
500
Brass
3
Copper-Oxide
1000
Beryllium Copper
5
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