Instructions and Precautions for Using Digital Multimeters
Digital multimeters are widely favored by radio enthusiasts for their high measurement accuracy, convenient reading and complete functions. A standard digital multimeter generally supports resistance measurement, continuity buzzer test, forward voltage drop measurement of diodes, AC and DC voltage & current measurement, as well as transistor gain and characteristic testing. Some upgraded models add capacitance measurement, frequency measurement, temperature measurement, data storage, voice reading and other functions, which greatly facilitate practical testing work. However, improper operation can easily damage internal components and cause faults during measurement.
Some digital multimeters break down because the measured voltage or current exceeds the rated range. For example, measuring mains voltage on the 20 V AC range will very likely damage the AC amplifier circuit inside the meter and disable its AC measurement function. Exceeding the range during DC voltage measurement may also lead to circuit faults. When measuring current, an over‑range condition usually only blows the internal fuse without further damage. Therefore, if the approximate voltage value is unknown, start with a higher range, then switch to a lower range for a more precise reading. If the target voltage greatly exceeds the maximum measurable range of the multimeter, use high‑voltage high‑resistance probes.
Most failures of digital multimeters result from incorrect function selection. For instance, if the resistance range is selected for mains AC voltage measurement, internal components will be instantly damaged once the probes touch the live mains. Always verify the correct range before measurement. After use, set the selector switch to 750 V AC or 1000 V DC. This setting prevents damage even if an incorrect measurement is made next time.
The maximum DC voltage range of most digital multimeters is 1000 V. Measurements below 1000 V normally will not damage the meter, while voltages above 1000 V carry a high risk of damage. Note that the upper voltage limit varies between different models. For voltages beyond the rated range, use a resistor voltage divider for measurement. When measuring high DC voltage between 400 V and 1000 V, ensure stable, reliable contact between the probes and the test point without shaking. Otherwise, readings may be inaccurate, the meter may be damaged, and in severe cases, the display may go blank.
