General precautions when measuring resistance

As with any measurement, when measuring resistance, there are some precautions to observe. In this way damage to the multimeter can be prevented, and more accurate measurements can be made.

· Measure resistance when components are not connected in a circuit: It is always advisable not to measure the resistance of an item that is in a circuit. It is always best to make the measurement of the component on its own out of the circuit. If a measurement is made in-circuit, then all the other components around it will have an effect. Any other paths that will allow current to pass will affect the readings, making them inaccurate to some degree.

· Remember to ensure the circuit under test is not powered on Under some circumstances it is necessary to measure resistance values actually on a circuit. When doing this it is very important to ensure the circuit is not powered on. Not only will any current flowing in the circuit invalidate any readings, but should the voltage be high enough, the current resulting could damage the multimeter.

· Ensure capacitors in a circuit under test are discharged. Again when measuring resistance values in a circuit, it is necessary to ensure that any capacitors in the circuit are discharged. Any current that flows as a result of them will cause the meter reading to be altered. Also any capacitors in the circuit that are discharged may charge up as a result of the current from the multimeter and as a result it may take a short while for the reading to settle.

· Remember diodes in a circuit will cause different readings in either direction

When measuring resistance in a circuit that includes diodes the value measured will be different if the connections are reversed. This is because the diodes only conduct in one direction.

· Leakage path through fingers can alter readings in some cases.

When making some resistance measurements it is necessary to hold a resistor or component onto the multimeter test probes. If high resistance measurements are being made the leakage path through the fingers can become noticeable. Under some circumstances the resistance path through fingers can be measured at just a few megohms, and as a result this can become significant. Fortunately the levels of voltage used in most multimeters when measuring resistance is low, but some specialised meters may use much higher voltages. It is wise to check.

Measuring resistance with a multimeter is very easy and convenient. When looking at how to measure resistance, it is quite straightforward for both analogue and digital multimeters and the process is virtually the same in both instances, although readings may not be quite as easy to take if the resistance is high and the measurement needs to be taken where the calibrations are close together. Nevertheless whatever test equipment is used, resistance is easy to measure.

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