1. DMMs are the tape measure of the new millennium. That’s because they measure volts, ohms, and amperes easily and instantaneously.
2. Different types of DMMs have different resolutions and accuracy to enable more detailed measurements. The terms "digits" and "counts" are used to describe a meter’s resolution.
3. A DMM uses Ohm’s Law to directly measure and display ohms, amps, or volts.
4. If a DMM has manual ranging only, it is necessary to select the highest range so as not to overload the input.
5. When measuring resistance with a DMM the measurement must be made with the circuit power off — otherwise the meter or the circuit could be damaged and create and dangerous situation.
6. Common situations that often lead to DMM failure include:
- Contact with AC while test leads are plugged into current jacks
- Contact with AC power source while in resistance mode
- Exposure to high voltage transients
- Exceeding maximum input limitations (voltage and current).
7. Some DMMs will detect an overload condition and protect the meter, but will not recover until the operator performs and operation on the meter such as replacing a fuse.
8. DMMs with a low impedance capability, let technicians safely troubleshoot sensitive electronic or control circuits and help to prevent false readings from circuits that may contain ghost voltages.
9. Ghost voltages occur from having energised circuits and non-energised wiring in close proximity to each other. If a digital multimeter does not have the ability to recognise ghost voltage, troubleshooting circuit problems can result in a waste of time, money, and effort.
10. A DMM should be used for troubleshooting purposes in high-energy three phase distribution panels or for testing whether a circuit is energised. Traditional solenoid testers should not be used in these situations. AS61010 outlines the minimum safety requirements for the design of test instruments and classifies them on their typical operating environment e.g. CAT IV 600V.
Answers supplied by Fluke Australia.
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