Multimeter - small knowledge of electrolytic capacitor detection
The capacity of electrolytic capacitors is much larger than that of ordinary fixed capacitors. When measuring, choose a suitable range for different capacities. Under normal circumstances, the capacitance between 1 and 47 pF can be measured with R×1k gear; the capacitance greater than 47 ptF can be measured with R×100 gear. The smaller the capacity of the capacitor, the larger the selection of the blocking factor should be. The capacitor should be fully discharged before measurement, that is, the two pins of the electrolytic capacitor should be short-circuited to discharge the residual charge in the capacitor. The two pins of the capacitor can be short-circuited with a multimeter pen, and the schematic diagram of the capacitor discharge method is shown in Figure 3. Bulk capacitors must be discharged from the metal part of a screwdriver. After the capacitor is fully discharged, connect the red test lead of the pointer multimeter to the negative pole, and the black test lead to the positive pole. At the moment when it is first turned on, the pointer of the multimeter should deflect to the right by a large angle, and then gradually return to the left until it stops at a certain position. The resistance value at this time is the forward insulation resistance of the electrolytic capacitor, which should generally be above several hundred thousand ohms. Change the test leads to measure, the pointer repeats the previous phenomenon, and the last indicated resistance value is the reverse insulation resistance of the capacitor, which should be slightly smaller than the forward insulation resistance.
In the above measurement, if the pointer of the multimeter does not move during the measurement, it means that the capacitance of the capacitor disappears or the internal circuit is broken; if the forward and reverse insulation resistance of the capacitor is very small or zero, it means that the capacitor has a large leakage current or an internal short circuit, and it cannot be used any more. . For electrolytic capacitors with unknown positive and negative signs, the method of measuring insulation resistance can be used to distinguish, that is, first touch the two pins of the capacitor with two test leads of the multimeter, and measure the insulation resistance of the capacitor. After changing the test leads, measure again. The larger value is the forward insulation resistance. At this time, the black test lead is connected to the positive pole of the capacitor.
