122 34410A/11A/L4411A User’s Guide
4 Measurement Tutorial
Other Sources of Measurement Error
Settling Time Effects
The multimeter 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 multi–function calibrators use large parallel capacitors
(1000 pF to 0.1
μF) with high resistor values to filter out noise currents injected by their
internal circuitry. Non–ideal capacitances in cables and other devices may have much
longer settling times than expected just by RC time constants due to dielectric
absorption (soak) effects. Errors are measured when settling after the initial connection
and after a range change.
Loading Errors (ac volts)
In the ac voltage function, the input of the multimeter appears as a 1 MΩ resistance in
parallel with 100 pF of capacitance. The cabling that you use to connect signals to the
multimeter also adds capacitance and loading. The table below shows the multimeter's
approximate input resistance at various frequencies.
For low frequencies, the loading error is:
At high frequencies, the additional loading error is:
Input Frequency Input Resistance
100 Hz 1 MΩ
1 kHz 850 kΩ
10 kHz 160 kΩ
100 kHz 16 kΩ
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