Problems with multimeters that test household appliances to see if they are good or bad
When using the multimeter resistance file to measure the household appliances power input (plug) on and off, according to the appliance power switch control mode, the switch can appear in the switch off, the measurement of the plug between the two feet is connected or not connected (pointer swing or not swing): when the power switch directly cut off the power supply into the household appliances, such as table lamps, televisions, DVDs, etc., in the switch off, the power supply is directly cut off, so the meter measurement should not be connected; but in the standby state of television, DVD, refrigerators, automatic washing machines, etc., is not in a state of all being cut off. So when the meter measurement, the plug should not be connected between the two feet; but in the standby state of the TV, DVD, refrigerator, automatic washing machine, etc., when not working, the internal power supply is not all cut off, that is, in the standby state, so part of the circuit is still working, (for example, refrigerator, power plugged in as long as the door is open, the internal light is bright, as long as the refrigerator door is open, the bulb is normal, measurement) (For example, refrigerator, power plugged in as long as the door is open, the internal light is bright, as long as the refrigerator door is open, the light bulb is normal, measurement of the refrigerator plug feet equal to the measurement of an open lamp, the meter should be measured through) this type of appliances in the measurement of the power supply plug feet, it may be that it is still in the connecting state; specific need to view the electrical schematic diagram of the appliance, according to the actual situation in order to determine the deflection of the needle with or without the representation of normal. For example, at present often contact with the small DC power supply (recorders external power supply, mobile phone chargers, etc.), they basically do not have a switch, directly into a powered socket to use, but from the internal structure, there is the use of transformer step-down and then rectified, regulated output; there is also the use of switching power supply, the output of a stable DC voltage, the two because of the principle of operation is different for the same input 220V, the output of the same DC parameters of the two kinds of power supplies, the former volume, weight is more than the same. Power supply, the former volume, weight is larger than the latter, when using a multimeter to measure the resistance of the 220V input, the former because 220V directly to the primary coil of the transformer, the normal resistance value should only be a few hundred ohms or so, if the pointer does not move, or a large value of resistance, the power supply has a problem; but for the latter use of the principle of switching power supply dc power supply, the general meter 1K file below the measurement of the input side is on! , the pointer is swinging, the power supply is very likely to have been damaged. This is due to the different circuit structure of the differences. Different appliances, different brands, the circuit structure is not the same, whether there is a failure is also different, this is the measurement of sometimes through, sometimes not the reason.
