* Question
| How to detect capacitors? |
* Answer
| 1. Detection of fixed capacitors. A detects small capacitors below 10pF.Since the fixed capacitor capacity below 10pF is too small, the measurement with a multimeter can only be qualitatively checked for leakage, internal short circuit or breakdown.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.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.The detection of electrolytic capacitor A because the capacity of electrolytic capacitor is much larger than the general fixed capacitor, so when measuring, the appropriate range should be selected for different capacities.According to experience, under normal circumstances, 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.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.
For an electrolytic capacitor in which the 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 and then 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.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.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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