Digital multimeters include a lot of features to improve the accuracy of resistance measurements. Unfortunately, most of these features add additional measurement time. In order to make good decisions, trading off speed for accuracy, you need to have a good understanding of each type of measurement error and the features incorporated into the multimeter to limit these errors. Following are nine tips for making better resistance measurements.
Tip 6: Settling time Effects
Modern multimeters have 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 mF) with high resistor 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 and after a range change. You may need to increase the delay time before a measurement in these situations. The amount of delay can typically be set from the front panel or programmatically.