Testing Open-Circuit Faults in Lighting Circuits with a Multimeter
Lighting circuit open circuit faults can be divided into three situations: complete open circuit, partial open circuit, and individual open circuit.
(1) All open circuits
This type of malfunction mainly occurs on the main line, in distribution and metering devices, and within the range of incoming devices. Usually, the first step is to check the connection points of each joint in the above section (including the melt connection pile) in sequence, and the common fault is the disconnection of the wire end from the connection point; Secondly, check the opening and closing status of the dynamic and static contacts of each circuit switch.
(2) Partial open circuit
This type of fault mainly occurs within the range of branch lines. Generally, check the connection of each wire head first, and then check the branch switch. If the cross-sectional area of the branch wire is small, it should be considered that the core wire may break inside the insulation layer and cause a local open circuit.
(3) Individual open circuit
This type of fault is generally limited to the range of junction boxes, lamp holders, light switches, and the connecting wires between them. Usually, the connection of each joint, as well as the contact status of components such as lamp sockets, light switches, and sockets, can be checked separately (for fluorescent lamps, the connection status of each component should be checked).
1. Use a multimeter to determine the positive and negative poles of the speaker
Firstly, set the pointer multimeter to the DC 0-5mA range, and then connect the two probes to the two solder pads of the tested speaker. Gently press the paper tray of the speaker with your hand and observe the direction of the multimeter pointer's swing. If the pointer deflects in the positive direction, the red probe is connected to the negative terminal of the speaker, and the black probe is connected to the positive terminal of the speaker. On the contrary, the red probe is connected to the positive pole, and the black probe is connected to the negative pole.
Piezoelectric ceramics are a type of artificially synthesized piezoelectric material. When subjected to external pressure, charges are generated on both sides, and the amount of charge is proportional to the pressure. This phenomenon is called the piezoelectric effect. Piezoelectric ceramics have piezoelectric effect, which means that they will deform under the action of an external electric field, so piezoelectric ceramic pieces can be used as sound emitting elements.
By utilizing the piezoelectric effect of piezoelectric ceramic plates, a multimeter can be used to determine their quality.
Lead two wires out of the two poles of the piezoelectric ceramic piece, then place the ceramic piece flat on the table, connect the two leads to the two probes of the multimeter, set the multimeter to the minimum current mode, and then gently press the ceramic piece with a pencil eraser. If the multimeter pointer swings significantly, it means the ceramic piece is intact; otherwise, it means it is damaged.
