How to Measure Resistance with a DMM, Digital Multimeter

- measuring resistance with a digital multimeter is straightforward, but there are a few essential hints and tips to make sure the readings are accurate.

Resistance measurements are one of the common measurements that need to be made in an electronics laboratory or workshop.

Knowing how to measure resistance with a digital multimeter is quite straightforward, although there are a number of precautions and hints and tips that can make the measurements more reliable and accurate.

Digital multimeter resistance tests

When making a resistance measurement, the digital multimeter supplies current to the item under test and measures the response. The more current the device is able to draw, the lower the resistance.

Often the digital multimeter will possess several ranges. Typically it is best to opt for the lowest range that does not overflow the display.

Basic resistance measurements

For accurate measurements of resistance, the item to be tested should not be affected by other components within the circuit.

In the very basic circuit shown below, other components will affect any readings made.

Simple circuit for test using a digital multimeter
Simple circuit for test using a digital multimeter

Accordingly the component should be removed from the circuit to enable accurate testing to be undertaken, free from the effects of other components within the circuit.

Measuring the resistance of the component using a digital multimeter
Measuring the resistance of the component

Similarly never measure resistance when the circuit is powered, as power from the circuit will not only distort the reading, but could damage the meter.

Continuity testing

It is possible to use many digital multimeters for continuity testing. Often there is a special switch position for this facility. When in this mode, the DMM sounds when there is continuity between two points. This makes it much easier to test for continuity when probing contacts within an item of test equipment.

When using the continuity test function, it is possible to keep one's eyes on the areas being probed, rather than having to glance away each time to look at the resistance reading.

By listening for the sound of the tester, it is possible to quickly tell when there is continuity between two points. The other advantage is that it is not necessary to glance away, and possibly misplace the probe position. Often the movement of glancing away leads to the probe slipping as eyes are not on the probes and the circuit board.

By Ian Poole

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