Four Examples of Using Digital Multimeter

　　The AC voltage range of a digital multimeter is very sensitive, and it can display even a small induced voltage around it. Based on this feature, it can be used as a test pen. Usage is as follows: Set the multimeter to the AC20V range, leave the black test lead in the air, and hold the red test lead in contact with the line or device on the side. At this time, the multimeter will display. If the displayed number is between a few volts and more than ten volts (different multimeters will have different displays), it means that the line or device is energized. If the display is zero or very small, it means that the line or device is not energized.

2. Distinguish whether the power supply line is the live wire or the neutral wire

　　The first method: You can use the above method to judge: the larger number is the live wire, and the smaller number is the neutral wire. This method requires contact with the circuit or device being measured.
　　The second method: No contact with the circuit or device being measured. Set the multimeter to AC2V, with the black test lead suspended in the air, hold the red test lead and slide the tip along the line gently. If the meter shows a few volts, it means that the line is the live wire. If it shows only a few tenths of a volt or even less, it means that the line is the neutral wire. This judgment method does not directly contact the line. It is not only safe but also convenient and quick.

3. Find the breakpoint of the cable

　　When a breakpoint occurs in a cable, the traditional method is to use the resistance block of a multimeter to find the breakpoint of the cable section by section. This not only wastes time, but also greatly damages the insulation of the cable. The inductive characteristics of a digital multimeter can quickly find the disconnection point of the cable. First, use the resistance block to determine which cable core wire is broken. Then connect one end of the broken core wire to an AC220V power supply, then turn the multimeter to the AC 2V position, leave the black test pen in the air, hold the red test pen and slide the pen tip gently along the line. At this time, if the meter shows a voltage of several volts or a few tenths of a volt (depending on the cable), if the display on the meter suddenly drops a lot when it moves to a certain position, record this position: Generally, the breakpoint is between 10 and 20 cm in front of this position.

This method can also be used to find the breakpoint of the resistance wire of a faulty electric blanket.

4. Measuring the frequency of UPS power supply

　　For UPS power supply, the stability of the voltage at its output end is an important parameter, and its output frequency is also very important. However, it cannot be measured directly with the frequency block of a digital multimeter , because the voltage that its frequency block can withstand is very low, only a few volts. At this time, you can connect a 220V/6V or 220V/4V step-down transformer to the output end of the UPS power supply to reduce the voltage without changing the frequency of the power supply, and then connect the frequency block to the output of the transformer to measure the frequency of the UPS power supply.