Precautions, Advantages and Damage Causes of Digital Multimeters
Digital multimeters are well‑received by radio enthusiasts for their accurate measurement, 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 triode amplification factor and performance. Some advanced models add functions such as capacitance measurement, frequency measurement, temperature measurement, data storage and voice readout, which bring great convenience to practical testing work. Nevertheless, improper operation may easily damage internal components and cause malfunctions.
Most damages to digital multimeters stem from incorrect range selection. For example, if the resistance range is selected for measuring AC mains power, internal components will be instantly damaged once the probes touch the live mains. Therefore, always verify that the measurement range is correct before taking measurements. After use, set the selector switch to AC 750 V or DC 1000 V. This prevents damage even if wrong parameters are selected accidentally in subsequent measurements.
Some failures occur when measured voltage or current exceeds the instrument's range. Measuring mains supply at the AC 20 V range, for instance, can burn out the internal AC amplifier circuit and disable the AC‑measuring capability. Exceeding the DC‑voltage range may also trigger internal circuit faults. When measuring current, an over‑range condition usually only blows the built‑in fuse without further harm. Hence, when the approximate magnitude of target voltage is unknown, start with the highest range. After obtaining a rough reading, switch downwards for higher‑accuracy results. If the voltage far exceeds the meter's maximum rating, use dedicated high‑voltage probes, such as when measuring CRT anode high‑voltage and focus high‑voltage for black‑and‑white or color televisions.
Most digital multimeters have a maximum DC‑voltage range of 1000 V. Measurements below 1000 V normally do no harm, whereas voltages above 1000 V carry a high risk of damage. Note that maximum measurable‑voltage limits vary among different models. Resistor voltage‑divider networks can be used for voltages beyond the meter's native range. In addition, for DC high‑voltage measurements between 400 V and 1000 V, ensure firm, stable probe‑to‑circuit contact with no shaking. Otherwise, inaccurate readings and meter damage may occur; in severe cases the display can go completely blank.
Never perform resistance measurements on energized circuits.
