Tutorial 7
Keysight 34970A/34972A User’s Guide 307
Sources of Error in Resistance Measurements
External Voltages
Any voltages present in the system cabling or connections will affect a resistance
measurement. The effects of some of these voltages can be overcome by using
offset compensation (as described on the previous page).
Settling Time Effects
The internal DMM has the ability to insert automatic measurement settling delays.
These delays are adequate for resistance measurements with less than 200 pF of
combined cable and device capacitance. This is particularly important if you are
measuring resistances above 100 kΩ. Settling due to RC time constant effects can
be quite long. Some precision resistors and multifunction calibrators use large
parallel capacitances (1000 pF to 0.1 μF) with high resistance values to filter out
noise currents injected by their internal circuitry. Non-ideal capacitances due to
dielectric absorption (soak) effects in cables and other devices may have much
longer settling times than expected just by RC time constants. Errors will be
measured when settling after the initial connection, after a range change, or when
using offset compensation. You may need to increase the channel delay time
before a measurement in these situations (for more information on channel delay,
see page 119).
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