1. Detection of fixed capacitors. A. Detecting small capacitors below 10pF is too small for fixed capacitors below 10pF. Measurements with a multimeter can only be qualitatively checked for leakage, internal short-circuit or breakdown. When measuring, you can use the multimeter R × 10k block, use two meter pens to connect the two pins of the capacitor, the resistance should be infinity. If the measured resistance value (the pointer swings to the right) is zero, the capacitor leakage is damaged or internal breakdown. B Detects whether the 10PF~001μF fixed capacitor has a charging phenomenon, and then judges whether it is good or bad. The multimeter uses R × 1k block. The beta values ​​of the two triodes are all above 100 and the penetration current is small. A composite tube of 3DG6 and other types of silicon triodes can be selected. The red and black test leads of the multimeter are respectively connected to the emitter e and the collector c of the composite tube. Due to the amplification effect of the composite triode, the charging and discharging process of the measured capacitor is amplified, so that the multimeter pointer swing amplitude is increased, thereby facilitating observation. It should be noted that during the test operation, especially when measuring the capacitance of a small capacity, it is necessary to repeatedly exchange the two points of the measured capacitor pins to contact A and B to clearly see the swing of the multimeter pointer. C For a fixed capacitance above 001μF, the multimeter's R×10k block can be used to directly test whether the capacitor has a charging process and whether there is an internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the magnitude of the pointer swinging to the right.
2. Detection of electrolytic capacitors Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, the appropriate range should be selected for different capacities when measuring. According to experience, in general, the capacitance between 1 ~ 47μF can be measured by R × 1k block, and the capacitance larger than 47μF can be measured by R × 100 block. B connects the multimeter red pen to the negative pole, and the black pen to the positive pole. At the moment of contact, the multimeter pointer deflects to the right with a large degree of skewness (for the same electrical block, the larger the capacity, the larger the swing), and then gradually turns to the left. Until stopped at a certain location. The resistance at this time is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical experience shows that the leakage resistance of electrolytic capacitors should generally be several hundred kΩ or more, otherwise, it will not work properly. In the test, if there is no charging in the forward and reverse directions, that is, the hands are not moving, the capacity disappears or the internal circuit is broken; if the measured resistance is small or zero, the leakage of the capacitor is large or the breakdown is broken. Can no longer be used. C? For an electrolytic capacitor whose positive and negative signs are unknown, the above method for measuring the leakage resistance can be used for discrimination. That is, first measure the leakage resistance arbitrarily, remember its size, and then exchange the test leads to measure a resistance value. The one with a large resistance value in the two measurements is the forward connection method, that is, the black meter is connected to the positive pole, and the red meter is connected to the negative pole. D? Using a multimeter electric block, using the method of positive and negative charging of the electrolytic capacitor, the capacity of the electrolytic capacitor can be estimated according to the magnitude of the swing of the pointer to the right.
3, the detection of variable capacitor A gently rotate the shaft by hand, should feel very smooth, should not feel sometimes loose or even stuck. When the axial direction of the load is pushed forward, backward, up, down, left, right, etc., the shaft should not be loose. B. Rotate the shaft with one hand and gently touch the outer edge of the group with the other hand. There should be no looseness. The variable capacitor with poor contact between the rotating shaft and the moving piece can no longer be used. C put the multimeter in the R×10k block, one hand connects the two test leads to the moving piece of the variable capacitor and the leading end of the fixed piece, and the other hand will slowly rotate the rotating shaft several times back and forth, and the multimeter pointer should be Do not move at infinity. In the process of rotating the shaft, if the pointer sometimes points to zero, it means there is a short circuit between the moving piece and the fixed piece; if it touches an angle, the multimeter reading is not infinite but a certain resistance value appears, indicating that the variable capacitor is moving. There is leakage between the film and the stator.
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