Causes of Failures and Preventive Measures for Digital Multimeters
Most damage to digital multimeters is caused by incorrect range selection. For example, if the multimeter is set to the resistance range while measuring AC mains voltage, touching the live circuit with the probes will instantly damage internal components. Therefore, always check the measurement range before use. After use, set the selector to AC 750V or DC 1000V to prevent damage from accidental incorrect measurements during the next use.
Some digital multimeters fail because the measured voltage or current exceeds the rated range. For instance, attempting to measure mains voltage on the AC 20V range easily damages the AC amplifier circuit, disabling the AC measurement function. Excessive DC voltage can also damage internal circuitry. Overcurrent during current measurements typically only blows the internal fuse without further damage.If the approximate voltage level is unknown, always start from the highest range, then adjust downward for an accurate reading. For voltages far beyond the multimeter's maximum rating, use high‑voltage, high‑resistance test probes - such as when measuring the high anode and focusing voltages in black-and-white and color televisions.
Most digital multimeters have a maximum DC voltage rating of 1000V. Voltages below this level generally will not damage the unit, but voltages above 1000V are very likely to do so. Maximum input voltages may vary by model. If the voltage exceeds the meter's range, use a resistive voltage divider for measurement.In addition, when measuring high DC voltages between 400V and 1000V, ensure firm, stable contact between the probes and the test points. Loose or shaky connections can cause inaccurate readings, internal damage, or even a completely blank display in severe cases.
Never measure resistance while the circuit is live.
