The use of multimeters in home appliance repair How to maintain multimeters
Use of multimeter
①Digital multimeter: Before measuring, switch to the measurement position. It should be noted that the range marked on the position is the maximum value.
②Mechanical multimeter: The method of measuring current and voltage is the same as the mathematical formula, but when measuring the cathode, the reading must be multiplied by the value on the gear to get the measured value. For example: the current gear is "X100" and the reading is 200, The measurement question is 200X100=20000Ω=20K, the "Ω" scale on the dial is from left to right, from large to small, while the others are from left to right, from small to large
Multimeter Precautions
① Adjust the "zero point" (only for mechanical watches). Before using the watch, first check that the pointer is on the "zero position" at the left end. Adjust the screw so that the pointer points to zero.
②When the multimeter is used, it should be placed horizontally (only for machines)
③Before the test, determine the measurement content, turn the range conversion knob to the corresponding gear for the measurement shown, so as not to burn the meter head, if you do not know the size of the measured physical quantity, start the test with a large range first.
④The test leads should be correctly inserted into the corresponding sockets.
⑤During the test, do not rotate the gear change knob arbitrarily.
⑥ After use, be sure to adjust the range change knob of the unused meter to the maximum range of AC voltage.
⑦When measuring DC voltage and current, pay attention to the positive and negative poles of the voltage, the flow direction of the current, and connect (when) correctly with the test leads.
The multimeter detects the open circuit fault of the lighting circuit
The multimeter detects the open circuit fault of the lighting circuit
When the lighting circuit is open, there will be no voltage in the circuit, the lighting will not light up, and the electrical appliances will not work. The reasons are: the fuse is blown, the wire is broken, the wire end is loose, the switch is damaged, etc.
When the multimeter detects the open-circuit fault of the lighting circuit, when the power is cut off, the multimeter can be used to measure the continuity of the circuit; or when the power is turned on, the multimeter can be used to measure the voltage of the AC voltage circuit to determine the fault point.
Open circuit faults of lighting circuits can be divided into three situations: total open circuit, partial open circuit and individual open circuit.
(1) All open circuits
This type of fault mainly occurs on main lines, in power distribution and metering devices, and within the range of household devices. Usually, the connection of each joint of the above-mentioned parts (including the melt terminal) should be checked in turn. Generally, the failure of the wire head to break away from the connection is the most common; secondly, check the opening and closing of the dynamic and static contacts of each line 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 shunt switch. If the cross-section of the shunt wire is small, it should be considered that the core wire may be broken in the insulating layer and cause a local open circuit.
(3) Individual open circuit
This type of fault is generally limited to the junction box, lamp holder, light switch, and the connecting wires between them. Usually, the connection of each joint can be checked separately, and the contact condition of the contacts of components such as lamp holders, light switches and sockets (for fluorescent lamps, the connection condition of each component should be checked).
