7Measurement Tutorial
284 Keysight 34420A User’s Guide
Offset Compensation
A resistance measurement involves measuring a voltage (E) induced across the
resistance by a known current source.
Thermal EMF caused by dissimilar metals can create a parasitic voltage in the
measurement circuit (V
EMF
). (See page 276 for a description of thermal EMF). The
thermal EMF can be caused by the input lead connections or internally in resistor
R. In general, this voltage will not change with the current applied to the resistor.
The voltage measured, and so the resistance calculated, is in error by V
EMF
. Using
offset compensation can reduce the errors caused by V
EMF
. To make an offset
compensated measurement, the meter makes two voltage measurements, one
with the current source on and one with the current source off, and subtracts the
two measurements. The actual voltage drop across the resistor, and the
calculated resistance are obtained by:
First Reading - Second Reading = ( I * R + V
EMF
) - V
EMF
= I * R
Offset compensation can be used in 2-Wire or 4-Wire ohms measurements.
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