Multimeter to test the quality of household appliances
When using the resistance range of a multimeter to measure the on-off status of the power input terminal (plug) of a household appliance, according to the control mode of the power switch of the electrical appliance, when the switch is turned off, it may be possible to measure whether the two pins of the plug are connected or not (pointer Swing or not swing): When the power switch directly cuts off the power supply of household appliances, such as desk lamps, TV sets, DVDs, etc., when the switch is turned off, the power supply is directly cut off, so when the ammeter measures, the two pins of the plug should not be connected ; But in the standby state of TV, DVD, refrigerator, fully automatic washing machine, etc., when not working, the internal power supply is not completely cut off, that is, it is in standby state, so some circuits are still working, (such as refrigerator After the power is plugged in, as long as the door is opened, the internal lighting will be on. As long as the refrigerator door is opened, the light bulb is normal. , it may be still connected; you need to check the electrical schematic diagram of the appliance to judge whether the deflection of the pointer is normal or not according to the actual situation. For example, the small DC power supplies that are often in contact with at present (external power supply for radio recorders, mobile phone chargers, etc.), basically do not have switches, and are directly plugged into live sockets for use. There is also a switching power supply that outputs a stable DC voltage. Because of their different working principles, the two power supplies that have the same input AC 220V and output DC parameters are also the same. The volume and weight of the former are larger than the latter. In the case of resistance, the former is directly connected to the primary coil of the transformer because 220V is connected, and the resistance value should be only about a few hundred ohms in normal conditions. If the pointer does not move, or the resistance value is large, there is a problem with the power supply; For the DC power supply, if the measurement input terminal of the general meter below the 1K range is connected and the pointer is swinging, the power supply is most likely damaged. This is due to the difference produced by different circuit structures. Different electrical appliances, different brands, circuit structures are not the same, and whether there are faults is also different. This is the reason why sometimes it is connected and sometimes it is not connected when measuring.
