Notes on Operation of Handheld Digital Multimeters
Handheld digital multimeters feature accurate measurement, convenient readings and complete functions, so they are very popular among radio enthusiasts. Ordinary handheld digital multimeters generally support resistance measurement, continuity beep test, diode forward voltage measurement, AC and DC voltage and current measurement, as well as transistor amplification factor and performance measurement. Some digital multimeters are added with functions such as capacitance measurement, frequency measurement, temperature measurement, data storage and voice readout, which greatly facilitate practical testing work. However, improper use of portable digital multimeters can easily damage internal components and cause faults during testing. Based on real cases of digital multimeter damage, Jintai Keyi has summarized operating precautions for beginners to refer to, so as to avoid damage to handheld digital multimeters as much as possible.
Most damages to digital multimeters are caused by incorrect range selection. For example, if the resistance range is selected when measuring AC mains supply, once the test probes touch the mains power, the internal components of the multimeter will be damaged instantly. Therefore, always check that the measuring range is correct before taking measurements. After use, set the selector switch to AC 750 V or DC 1000 V. This setting prevents instrument damage even if wrong parameters are measured accidentally next time.
Some digital multimeter failures are caused by voltage or current exceeding the measuring range. For instance, measuring mains voltage on the AC 20 V range can easily damage the AC amplifier circuit and disable the AC voltage measurement function. Excessive DC input voltage may also trigger internal circuit faults. When measuring current, over-range current usually only blows the built‑in fuse and will not cause other damage. When measuring voltage with unknown approximate value, select the highest range first, then switch to a lower range after getting a rough reading for more accurate results. If the voltage to be measured far exceeds the maximum range of the multimeter, special high‑resistance test probes shall be equipped, such as for measuring CRT anode high voltage and focus high voltage of black‑and‑white and color televisions.
Most digital multimeters have a maximum DC voltage range of 1000 V. Generally, DC voltage below 1000 V will not damage the meter, while voltage exceeding 1000 V is highly likely to cause damage. The upper measurable voltage limit varies for different multimeter models. Resistance voltage division can be adopted for measurement if the voltage exceeds the meter's range. In addition, when measuring high DC voltage from 400 V to 1000 V, the test probes must maintain stable contact with the measured point without shaking. Otherwise, inaccurate readings or instrument damage may occur. In severe cases, the multimeter may show no display at all.
