How to Measure AC and DC Using a Multimeter
① Measuring AC Voltage with a Digital Multimeter: Connect the black test lead to the COM or ground jack (marked on the meter terminal), and insert the red test lead into the AC jack (marked V with a wavy line underneath). Turn the selector switch to the 750V AC range (some models are 1000V) for measuring 220V mains power. Touch the two test probes to the two sockets of the power outlet. The displayed reading is the AC voltage value.
② Measuring AC Voltage with an Analog Multimeter: Connect the black test lead to COM or ground and the red test lead to the positive jack. Switch to the 500V AC range. Take measurements in the same way as with a digital multimeter. Read the value from the maximum range mark on the right side of the dial. For the 500V range, read from the scale row with a maximum marking of 50 on the right of the dial. If the pointer points to 20, the reading is 200V.
③ Measuring DC Voltage with a Digital Multimeter: The operation is similar to AC voltage measurement, except the red lead connects to the positive jack and touches the positive terminal of the power source. Select the DC range (marked V with a horizontal line underneath). Choose the proper range from high to low according to the object under test. For example, select the 2V range to measure an AA battery. If the polarity is reversed, a minus sign will appear before 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 AC voltage measurement described above. When the positive and negative polarity of DC voltage cannot be confirmed, you may tentatively treat it as AC without recording the reading. Reverse the two probes and test again. The test with forward pointer deflection indicates the correct polarity. Then switch to the proper DC voltage range to take the formal reading.
Digital multimeters are popular among radio enthusiasts for their high measuring accuracy, convenient reading and complete functions. Ordinary digital multimeters generally support resistance measurement, continuity buzzer test, forward voltage drop measurement of diodes, AC/DC voltage and current measurement, as well as measurement of transistor amplification factor and performance.
Some digital multimeters add functions including capacitance measurement, frequency measurement, temperature measurement, data hold and voice readout, bringing great convenience to practical inspection work.
However, improper use of digital multimeters may easily damage internal components and cause faults during testing.
Based on real cases of digital multimeter damage, a set of usage precautions is summarized to prevent meter damage.
Most digital multimeter failures are caused by incorrect range selection. For instance, measuring mains AC voltage with the resistance range. Once the probes touch mains power under this setting, internal components of the multimeter will be damaged instantly.
Therefore, always verify the selected measuring range before taking any measurement with the multimeter.
After use, set the selector switch to 750V AC or 1000V DC. This setting can prevent damage to the digital multimeter even if you mistakenly select a wrong parameter in the next measurement.
