Troubleshooting of Multimeter's Open Circuit
(1) Contact measurement method
Put the multimeter switch on the AC 250V or 500V gear, connect the first test lead to one end of the power supply, and the second test lead to the ground (such as water pipes, radiators, etc. or wet ground). If the grounding is good, when the multimeter reads around 220V, the first test lead is connected to the live wire of the power supply. If the pointer does not move, it means that the first test lead is connected to the neutral line of the power supply. Even if the grounding resistance of the second test lead is large, when the first test lead is connected to the live wire, the pointer will have obvious deflection.
(2) Non-contact measurement method
Put the switch of the multimeter in the AC 250V or 500V gear, connect the first test lead to either end of the power supply, place the second test lead in the air on the table, and hold the insulating rod part of the second test lead with your hands (be careful not to touch it with your hands) conductive parts). If the first test lead is connected to the live wire, the pointer on the meter head can generally be deflected by 2 to 10 divisions. The higher the sensitivity of the multimeter, the more obvious the deflection. If the first test lead is connected to the zero line, the pointer of the meter head will not deflect.
This method works with any model of multimeter. This method will not cause danger to the human body. Because the internal resistance of the pointer multimeter is 20K/V, if it is used to measure 220V voltage, the internal resistance of the pointer multimeter is 20K×220V=4400, which is relatively safe.
(3) Precautions for distinguishing live wire and neutral wire with a pointer multimeter
It is best to use a test pen to distinguish the live wire and neutral wire of the mains, which is a fast and safe method.
Be sure to pay attention to safety when using a pointer multimeter to distinguish the live wire and the neutral wire. Specifically, the insulation of the test lead line should be good, and the operator's hands and any part of the body cannot directly contact the metal part of the test lead to avoid the risk of electric shock.
Digital multimeter distinguish live wire and neutral wire
As we all know, the sensitivity of the AC voltage block of the digital multimeter is very high. Even if a weak voltage signal is sensed, it can be displayed on the LCD screen. Using the ACV block of the digital multimeter to find the live wire of the AC mains with the induction method is intuitive. , Rapid, accurate and safe features.
(1) Contact measurement method
Turn the digital multimeter to the AC 20V gear (or AC 2V gear), take off the black test lead, insert the black test lead into the V/Ω jack, hold the insulating rod of the red test lead in one hand, and touch the two jacks in turn with the tip of the test lead. The larger displayed value is the live wire, as shown in Figure 5-28.
(2) Non-contact measurement method
Sometimes, it is necessary to find the live wire from the outdoor lighting line; at this time, it is not necessary to peel off the insulation of the wire, and use the red test pen to touch the insulation of the two wires in turn, and the one with the larger reading is the live wire; because it is an induced voltage, the range It is best to choose AC 2V.
Multimeter testing lighting circuit and device
When testing lighting circuits and devices, it is generally used to measure the on-off condition of the circuit with electricity, and to measure the insulation of the circuit and the device; to measure whether the circuit or device has voltage and whether the voltage is normal with an AC voltage block.
Measuring line resistance value with electric barrier
Electric circuits and various circuits related to electricity can be measured with a multimeter. Because the resistance test has the characteristics of safety, convenience and ease, it is highly respected by circuit design and maintenance personnel. Determine whether the circuit is open or short circuit by testing the resistance value of the line; determine whether the component is good or bad by testing the normal resistance value of the component and the resistance value at fault and comparing it.
When testing the resistance of lighting circuits and devices, the device under test should be disconnected from the power supply before testing.
Measuring line voltage with AC voltage block
When we repair the lighting circuit and electrical appliances, by measuring the voltage value of the circuit, it can help us analyze the cause of the fault, such as the fault caused by the power supply voltage being too high or too low.
