Keysight DAQ970A Guide D'utilisation page 235

4 Measurement Tutorials
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 above section).
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.
High-resistance measurement errors
When you are measuring large resistances, significant errors can occur due to insulation resistance and surface
cleanliness. You should take the necessary precautions to maintain a "clean" high-resistance system. Test leads and
fixtures are susceptible to leakage due to moisture absorption in insulating materials and "dirty" surface films. Nylon
and PVC are relatively poor insulators (10
nylon or PVC insulators can easily contribute a 0.1% error when measuring a 1 MΩ resistance in humid conditions.
The table below shows several common insulating materials and their typical resistances.
Insulating material
PTFE
Nylon
PVC
Polystrene
Ceramic
Glass Epoxy (FR-4, G-10)
Phenolic, Paper
235
9
ohms) when compared to PTFE insulators (10
Resistance range
1 TΩ to 1 PΩ
1 GΩ to 10 TΩ
10 GΩ to 10 TΩ
100 GΩ to 1 PΩ
1 GΩ to 1 PΩ
1 GΩ to 10 TΩ
10 MΩ to 10 GΩ
13
ohms). Leakage from
Moisture absorbing
No
Yes
Yes
No
No
Yes
Yes
Keysight DAQ970A/DAQ973A User's Guide