Voltage and Current Measurement with a Multimeter
① Measuring AC Voltage with a Digital Multimeter: Connect the black test‑lead to the "‑" or ground terminal (marked inside the test‑lead jack), and the red test‑lead to the AC jack (or the jack marked with "V" followed by a tilde "~"). Turn the selector switch to the 750 V range (some models show 1000 V) under the AC~ section for measuring 220 V mains voltage. Touch the two test‑leads to the two holes of the power socket respectively; the displayed reading is the AC‑voltage value.
② Measuring AC Voltage with an Analog Multimeter: Connect the black test‑lead to the negative or ground terminal and the red test‑lead to the positive terminal. Set the selector to the AC~ 500 V range. Perform measurement in the same way as with a digital multimeter. Read the scale corresponding to the maximum full‑scale value on the right‑hand side. For the 500 V range, refer to the scale row marked "50" at its maximum. If the pointer points to 20, the actual reading is 200 V.
③ Measuring DC Voltage with a Digital Multimeter: The test‑lead connection is similar to AC‑voltage measurement, except that the red test‑lead shall be inserted into the positive jack and touch the positive pole of the power supply. Set the selector to the DC range (marked with "V" and a short horizontal bar). Select an appropriate measuring range, starting from the higher range downwards. For example, select the 2 V range for an AA battery. If the polarity is reversed, a minus sign "‑" will appear in front of the reading.
④ Measuring DC Voltage with an Analog Multimeter: The measuring procedure is similar to that of a digital multimeter, and the reading method follows the rules for AC‑voltage measurement described above. When the DC‑voltage polarity is unknown, first treat it as AC voltage for measurement without paying attention to the reading. Reverse the test‑leads and measure again. Observe which measurement produces forward pointer deflection; this connection corresponds to the correct positive‑and‑negative polarity. Then switch to a suitable DC‑voltage range and take the formal reading.
Digital multimeters are widely popular among radio‑electronics enthusiasts for their high‑measurement accuracy, convenient readout and comprehensive functions. Ordinary digital multimeters generally support resistance measurement, continuity buzzer test, forward‑conduction voltage measurement, AC / DC voltage and current measurement, as well as transistor gain and performance testing.
Certain digital multimeters add extra functions such as capacitance measurement, frequency measurement, temperature measurement, data storage and voice readout, bringing great convenience to practical testing work.
Nevertheless, improper operation may easily damage internal components and cause faults of digital multimeters.
Based on real‑world damage cases of digital multimeters, the following precautions are summarized to minimize instrument damage.
Most digital‑multimeter failures are caused by wrong range selection. For instance, if the resistance range is selected while measuring AC mains voltage, internal components will be instantly damaged once the test‑leads touch the mains supply.
Therefore, always verify that the measuring range is correctly set before taking any measurement.
After use, set the selector switch to AC 750 V or DC 1000 V. This setting prevents damage even if incorrect parameters are measured by mistake in the next operation.
Some failures occur when measured voltage or current exceeds the rated range. For example, measuring mains voltage under the AC 20 V range will readily damage the AC amplifier circuit and disable the AC‑measuring function of the multimeter.
