Multimeter can be said to be an essential instrument for electricians, but also to carry out maintenance tools, we often encounter some family circuit failure in the daily learning and living environment, the only thing on hand is through a national digital multimeter,how to test pcb board with a multimeter， how to improve the overhaul?

1. how to distinguish between firewire and zero line

The black stylus of the digital multimeter will be inserted into the public end, that is, the black hole on the multimeter, the red stylus will be inserted into the red hole, set to AC voltage 750V V gear, the left hand will be the black stylus touching the wall or the ground, the right hand holds the red stylus, the stylus touching the measured line or jack and other electrically charged points, to observe the readings of the multimeter. If the reading is around 220V, then this is the firewire. If the multimeter reads low, around 20V, then this is the zero line. If the multimeter reading is close to 0, then this is the ground.

2. Detecting short-circuit faults in lighting circuits

Lighting circuit short circuit, line current is very large, usually the fuse quickly blown, the circuit is cut off. But the detection of short-circuit point is still relatively troublesome. Repair should first find the short-circuit point, 1oz vs 2oz Copper the resistance of the multimeter can be used in the case of power outages, segmented, partitioned check circuit.

Place the multimeter in a resistance gear and measure the resistance of the control fire and zero wires. If the student reading way tends to zero, indicating that the travel line has a short circuit (or leakage) phenomenon. Rule out other short-circuit occurs after the point of failure, loaded with qualified fuses and then send power.

3. Detecting open circuit faults

When the circuit is open, the circuit has no voltage, the lighting is not open, the appliance can not work. Reasons are: fuse fuses, line circuit breakers, loose wires, switch damage.

When the multimeter detects an open-circuit fault in the lighting circuit, you can use the multimeter to perform electrical blocking and measure the circuit on and off when the power supply is disconnected; you can also use the multimeter AC voltage block to measure the line voltage to determine the point of failure when the power is on.

Lighting circuit open-circuit fault can be divided into full open-circuit fault, part of the open-circuit fault and individual open-circuit fault in three cases.

(1) all open circuit.

This type of fault occurs mainly in the trunk line, distribution and metering devices and domestic equipment range. Usually, the first step is to check the engagement of the connectors in the above parts (including the fused wire stack) in turn. General threaded head off the joints of the most common failure; secondly, check the line switch dynamic, static contacts open and close the situation.

(2) local open circuit.

This type of system failure problems mainly occur in a branch line range. Generally check the connection of each of our wires first, and then by checking the branch switch. If the tap conductor cross-section is small, due consideration should be given to the core wire may appear to break in the insulation layer and cause the impact of localized open circuit.

(3) Individual open circuit.

This type of fault is generally confined to the junction box, lamp holder, lamp switch and the connecting wires between them. In general, each connector connection can be checked individually, as well as the junction of components such as lampholders, light switches and sockets.

4. Lighting circuit leakage fault detection

Leakage occurs in the lighting circuit, not only waste of electricity, but also may cause electric shock. Leakage and short circuit of the same nature, but the accident development is different, serious leakage may lead to short circuit. When the leakage phenomenon is found, the cause should be identified in time to find out the point of failure and troubleshooting.

Lighting line leakage is mainly due to:First, the insulation of wires or electrical equipment is damaged by external forces; second, the line is run for a long time, resulting in aging and deterioration of the insulation; third, the line is attacked by moisture gas or pollution, resulting in poor insulation.

First of all, you can determine whether the business can indeed leakage. Can be placed on the digital multimeter cultural exchange work current block, series connected to the main switch, turn on all the switches, remove all the load (including light bulbs). If there is current, then the company has a leakage phenomenon. After determining the line leakage, can be analyzed and checked according to the following steps we continue to develop.

(1) to determine between the phase line and the zero line, between the phase line and the ground, or both. This method is to cut off the zero line, if the ammeter indication is unchanged, it is the leakage between the phase line and grounding; if the current indication is zero, it is the leakage between the phase line and the zero line; the current indication is small and not zero, it is the phase line and the zero line, it is the leakage between the phase line and grounding.

(2) Determine the scope of leakage. Remove the shunt fuse or open the circuit breaker. If the current indication is unchanged, it means that the bus is leaking; if the current indication is zero, it is a shunt leakage; if the current indicator becomes small but not zero, it indicates that there is a leakage on both the bus and the branch circuit.

(3) Find the leak. After the above checks, the circuit light switches are disconnected one after the other, and when the switches are disconnected the current indicator goes to zero, and then the branch circuit is leaking; if all the lights are off and the current indicator is unchanged, then the trunk line is leaking. In turn, in order to narrow down the scope of the accident, you can further check the connection parts of the line, as well as the wires through the wall and other places for leaks. Once the leak is found, troubleshoot the leak promptly.