Explanation of Common Misunderstandings in the Use of Digital Multimeters
Digital multimeters are very popular among radio enthusiasts due to their advantages such as accurate measurement, convenient value reading, and comprehensive functions. The most common digital multimeters generally have functions like resistance measurement, continuity sound detection, forward conduction voltage measurement of diodes, AC and DC voltage and current measurement, measurement of the amplification factor and performance of transistors, etc. Some digital multimeters have additional functions such as capacitance measurement, frequency measurement, temperature measurement, data memory, and voice reporting of values, which bring great convenience to actual detection work. However, due to improper use, digital multimeters are prone to damage to internal components and malfunctions during actual detection. Based on the actual situations of digital multimeter damage, I have summarized the precautions in the use of digital multimeters for beginners to refer to, so as to prevent the damage of digital multimeters as much as possible.
Some digital multimeters are damaged because the measured voltage and current exceed the range. For example, measuring the mains voltage in the 20V AC gear is very likely to cause damage to the AC amplifier circuit of the digital multimeter, making the multimeter lose its AC measurement function. When measuring the DC voltage, if the measured voltage exceeds the measurement range, it is also likely to cause a fault in the internal circuit of the meter. When measuring the current, if the actual current value exceeds the range, generally only the fuse inside the multimeter will be blown, and no other damage will be caused. Therefore, when measuring voltage parameters, if you don't know the approximate range of the measured voltage, you should first set the measurement gear to the highest range, and then change the gear to measure after getting an initial reading, in order to obtain a more accurate value. If the voltage value to be measured far exceeds the maximum range that the multimeter can measure, a high-resistance measuring probe should be equipped additionally.
Most of the damage to digital multimeters is caused by incorrect measurement gear selection. For example, when measuring the AC mains voltage, if the measurement gear is set to the resistance gear, once the probes touch the mains voltage, the internal components of the multimeter will be damaged instantly. Therefore, before using the multimeter for measurement, you must check whether the measurement gear is correct. After use, set the measurement selection to 750V AC or 1000V DC. In this way, no matter what parameters are mismeasured during the next measurement, the digital multimeter will not be damaged.
The upper limit of the DC voltage range of a digital multimeter is 1000V. Therefore, when measuring the DC voltage, as long as the highest voltage value is below 1000V, the multimeter will generally not be damaged. If it exceeds 1000V, the multimeter is likely to be damaged. However, the upper limit of the measurable voltage of different digital multimeters may vary. If the measured voltage exceeds the range, the method of resistance step-down can be adopted for measurement. In addition, when measuring the DC high voltage between 400V and 1000V, the probes must make good contact with the measurement point and there should be no jitter. Otherwise, in addition to the possible damage to the multimeter and inaccurate measurement, in severe cases, the multimeter may have no display at all.
