Dc Measurement Considerations - Agilent Technologies 34405A User's And Service Manual

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.
48
Copper to –
Cadmium-Tin Solder
Copper
Gold
Silver
Brass
Beryllium Copper
Approx. mV / °C
0.2 Aluminum
<0.3 Tin-Lead Solder
0.5 Kovar or Alloy 42
0.5 Silicon
3 Copper-Oxide
5
Copper to –
34405A User's and Service Guide
Approx. mV / °C
5
5
40
500
1000