Precautions for Using Digital Multimeters, Advantages, and Causes of Damage
Digital multimeters are highly popular among radio enthusiasts due to their advantages such as accurate measurement, convenient reading, and comprehensive functions. A typical digital multimeter generally supports resistance measurement, continuity buzzer detection, diode forward voltage measurement, AC/DC voltage and current measurement, as well as transistor gain (hFE) and performance testing. Some advanced models even add functions like capacitance measurement, frequency measurement, temperature measurement, data memory, and voice reporting, which greatly facilitate practical inspection work. However, improper use of digital multimeters during actual testing can easily damage internal components and cause malfunctions.
Most damages to digital multimeters are caused by incorrect gear selection. For example, when measuring household AC power, if the multimeter is mistakenly set to the resistance gear, simply touching the live wires with the test leads can instantly damage internal components. Therefore, always verify the measurement gear before taking any readings. After use, set the multimeter to the AC 750V or DC 1000V gear. This precaution ensures that accidental mismeasurements 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 range. For example, measuring mains power with the AC 20V range can easily damage the multimeter's AC amplifier circuit, rendering it unable to measure 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 generally only blows the internal fuse of the multimeter without causing other damage.
Therefore, when measuring voltage parameters, if the approximate range of the voltage to be measured is unknown, the measurement range should first be set to the highest gear. After measuring the value, switch to a suitable range to obtain a more accurate reading. If the voltage to be measured far exceeds the maximum range of the multimeter, a high-resistance measuring probe should be used additionally. This is the case when detecting the anode high voltage and focusing high voltage in black-and-white color TVs.
