7Measurement Tutorial
276 Keysight 34420A User’s Guide
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. The table below shows common
thermoelectric voltages for connections between dissimilar metals.
Noise Caused by Magnetic Fields
If you are making measurements near magnetic fields, you should take the
necessary precautions to avoid inducing voltages in the measurement
connections. You should be especially careful when working near conductors
carrying large currents.
Copper-to- Approx. mV/ °C
Copper <0.3
Gold 0.5
Silver 0.5
Brass 3
Beryllium Copper 5
Aluminum 5
Kovar or Alloy 42 40
Silicon 500
Copper-Oxide 1000
Cadmium-Tin Solder 0.2
Tin-Lead Solder 5
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