Introduction to Common Faults and Countermeasures of Digital Multimeters
Most damage to digital multimeters is caused by incorrect measurement range selection. For example, when measuring household AC power, if the multimeter is set to the resistance range, touching the live wires with the test leads can instantly damage internal components. Therefore, always check the measurement range before taking any readings. After use, set the multimeter to the AC 750V or DC 1000V range. This precaution ensures that accidental mismeasurement of any parameter during the next use will not damage the digital multimeter.
Some damage to digital multimeters is caused by measuring voltages or currents that exceed their rated ranges. For example, using the 20V AC range to measure mains power (e.g., 220V AC) can easily damage the multimeter's AC amplifier circuit, rendering it incapable of measuring AC voltage. Similarly, exceeding the DC voltage range during measurement can also cause internal circuit failures. When measuring current, if the actual current exceeds the range, it typically only blows the internal fuse of the multimeter without causing other damage.
Therefore, when measuring voltage parameters of unknown magnitude, always start with the highest range first. After obtaining a rough reading, switch to a more appropriate range to achieve a more accurate value. If the voltage to be measured far exceeds the multimeter's maximum range, use a dedicated high-resistance probe (e.g., for measuring high-voltage components). This is particularly necessary when detecting anode high voltage and focus voltage in CRT (cathode-ray tube) televisions.
Most digital multimeters have a maximum DC voltage range of 1000V. Therefore, when measuring DC voltage, as long as the highest voltage is below 1000V, the multimeter is generally not damaged. If the voltage exceeds 1000V, the multimeter is likely to be damaged. However, the maximum measurable voltage may vary between different digital multimeters. If the voltage to be measured exceeds the range, a resistance voltage-divider method can be used for measurement.
Additionally, when measuring DC high voltages between 400V and 1000V, ensure that the test leads make good contact with the measurement points without any shaking. Otherwise, in addition to potential damage to the multimeter and inaccurate measurements, the worst-case scenario could cause the multimeter to display nothing at all.
