Fault Causes and Preventive Actions for Digital Multimeters
① Most damages to digital multimeters are caused by incorrect measurement range selection. For example, if the resistance range is selected when measuring AC mains voltage, once the probes touch the mains supply, the internal components of the multimeter will be damaged instantly. Therefore, always verify that the measurement range is correct before taking any measurement. After use, set the selector switch to the AC 750 V or DC 1000 V position. This prevents damage to the digital multimeter even if the wrong parameter is accidentally measured next time.
② Some digital multimeters fail because the measured voltage or current exceeds the range limit. For instance, measuring mains voltage on the AC 20 V range can easily damage the AC amplifier circuit and disable the AC measurement function. When measuring DC voltage, values exceeding the rated range may also cause internal circuit faults. When measuring current, an over-range current usually only blows the internal fuse without causing further damage. When measuring voltage with an unknown approximate value, start with the highest range, then switch downwards after obtaining a rough reading to get a more accurate result. If the target voltage far exceeds the maximum range of the multimeter, use high‑voltage high‑resistance probes. This applies to measuring the CRT anode high voltage and focus high voltage of black‑and‑white or color televisions.
③ Most digital multimeters have a maximum DC voltage range of 1000 V. Measurements below 1000 V generally will not damage the meter. Voltages exceeding 1000 V carry a high risk of damage. However, the maximum measurable voltage varies among different models of digital multimeters. For voltages beyond the meter's range, use a resistor voltage divider for measurement. Additionally, when measuring high DC voltage between 400 V and 1000 V, ensure firm contact between the probes and test points with no shaking. Shaky contact may lead to inaccurate readings or meter damage; in severe cases, the display may go blank.
④ Never perform resistance measurements on live circuits.
