Introduction to Key Points for Using Digital Multimeters
Digital multimeters are well‑received by radio electronics enthusiasts for their high‑measurement accuracy, convenient reading and comprehensive functions. Ordinary digital multimeters generally support resistance measurement, continuity buzzer test, diode forward‑voltage measurement, AC/DC voltage and current measurement, as well as measurement of transistor amplification factor and performance.
Some digital multimeters add extra functions including capacitance measurement, frequency measurement, temperature measurement, data memory and voice readout, which bring great convenience to practical testing work.
However, improper operation may easily damage internal components and cause faults during testing.
Based on real‑world cases of digital‑multimeter damage, precautions for operation are summarized to minimize instrument damage.
Most digital‑multimeter failures are caused by incorrect range selection. For instance, measuring mains AC power with the resistance range.
Once the test probes touch mains voltage under such condition, internal components of the multimeter will be damaged instantly.
Therefore, always double‑check that the measurement range is correctly set before taking any measurement.
After finishing measurement, set the function selector to AC 750 V or DC 1000 V. This setting prevents multimeter damage even if wrong parameters are selected for the next measurement.
Some multimeter damages are caused by voltage or current exceeding the measuring range. For example, measuring mains voltage on the AC 20 V range will easily burn out the AC amplifier circuit and disable the AC‑measurement function. Exceeding the DC‑voltage measuring range will also lead to internal circuit faults.
When the actual current exceeds the current‑measurement range, usually only the internal fuse will blow, and no other damage will occur.
Therefore, when measuring voltage with unknown approximate magnitude, start with the highest range, then switch to a lower range after reading the rough value for higher‑accuracy results.
If the voltage to be measured far exceeds the maximum measuring range of the multimeter, high‑voltage high‑resistance test probes shall be used, such as for measuring the second‑anode high‑voltage and focus high‑voltage of black‑and‑white color televisions.
