Capacitor detection methods and experience

1 fixed capacitor Detection
A is a small capacitor below 10 PF. Because the capacity of the fixed capacitor below 10 PF is too small, the multimeter can only be used for measurement to check whether there is leakage, internal short circuit or breakdown. During measurement, you can use a multimeter r×10k block, and use two pen to connect two pins of the capacitor separately. The resistance value should be infinite. If the measured resistance value (pointer swinging to the right) is zero, it indicates the capacitor leakage is damaged or internal breakdown.

B detection 10pf ~ 0 01 u f fixed capacitor charging phenomenon, and then determine whether it is good or bad. The multimeter uses the r × 1k block. The Beta values of the two transistors are over 100, and the penetration current is small. You can choose 3dg6 and other models of silicon three-member composite tube. The red and black table pens of the multimeter are connected to the emission pole E and collector C of the composite tube respectively. Due to the amplification of the composite transistor, the charge-discharge process of the tested capacitor is amplified, which increases the pendulum range of the multimeter pointer for easy observation. It should be noted that during the test operation, especially when testing a small capacity capacitor, the tested capacitor pins should be repeatedly switched to contact a and B, to see the pendulum of the multimeter pointer.

C for Fixed capacitors above 0 0000μf, use the r × 10k block of the multimeter to directly test whether the capacitor is charged and whether there is internal short circuit or leakage, the capacity of the capacitor can be estimated based on the amplitude of the pointer swinging to the right.

 

2 electrolytic capacitor Detection
A because the capacity of the electrolytic capacitor is much larger than that of the general fixed capacitor, the appropriate range should be selected for different capacities during measurement. Based on experience, generally, 1 ~ The capacitance between 47 μF can be measured using the R * 1k block, and the capacitance larger than 47 μF can be measured using the R * 100 Block.
B. Connect the multimeter red table pen to the negative pole, and the black table pen to the positive pole. In the moment of contact, the multimeter pointer is deflected to the right to a greater degree (for the same electrical block, the larger the capacity, the larger the swing ), then gradually turn to the left until it stops at a certain position. The resistance value is the forward leakage resistance of the electrolytic capacitor, which is slightly greater than the reverse leakage resistance. Actual use experience shows that the leakage resistance of electrolytic capacitors should generally be several hundred kb or above. Otherwise, it will not work properly. In the test, if there is no positive or reverse charge, that is, the table needle does not move, it indicates that the capacity disappears or the internal circuit breaker; If the measured resistance is small or zero, it indicates that the capacitor has a high leakage rate or is broken down and cannot be used any more.

C For electrolytic capacitors with unclear positive and negative signs, the above method for measuring the leakage resistance can be used for identification. That is, first test the leakage resistance, remember its size, and then exchange the table pen to measure a resistance value. The one with a large drag value in the two measurements is the positive connection method, that is, the black table pen is connected to the positive electrode, and the red table pen is connected to the negative electrode.

D. Use A multimeter for electrical blocking. Use the forward and reverse charge method for the electrolytic capacitor. The capacity of the electrolytic capacitor can be estimated based on the size of the swing margin to the right of the pointer.

 

3 Variable Capacitor Detection
A uses a hand to gently rotate the rotating shaft. It should feel very smooth and should not feel sometimes tight or even stuck. When the load axis is pushed forward, back, up, down, left, right, and other directions, the shaft should not be relaxed.

B uses one hand to rotate the shaft, and the other hand gently touches the outer edge of the animation group. It should not feel relaxed. A variable capacitor with poor contact between the rotating shaft and the Dynamic Disk cannot be used any more.

C. Place the Multimeter in the r * 10k block. One hand connects the two table pens to the dynamic part and the picking end of the fixed part respectively, and the other hand slowly rotates the rotating shaft several times back and forth, the multimeter pointer should be in an infinite position. In the process of rotating the shaft, if the pointer sometimes points to zero, there is a short circuit between the dynamic disk and the fixed disk. If you encounter a certain angle, the multimeter reading is not infinite, but has a certain resistance value, it indicates that there is leakage between the dynamic and fixed slices of the variable capacitor.