Capacitor detection skills sharing

Capacitor detection methods are mainly divided into three categories: detection of variable capacitors, detection of electrolytic capacitors, and detection of fixed capacitors.

1. Detection of variable capacitors

A. Gently rotate the shaft by hand, it should feel smooth, and it should not feel loose and tight and stuck. When the carrier shaft is pushed forward, backward, up, down, left, right and other directions, the rotating shaft should not be loose.

B. Rotate the shaft with one hand, and touch the outer edge of the moving plate with the other hand. There should be no looseness. A variable capacitor with poor contact between the shaft and the rotor cannot be used.

C. Put the multimeter in the R×10k block, connect the two test leads to the moving piece and the fixed piece of the variable capacitor with one hand, and slowly rotate the shaft with the other hand. The infinity position does not move.In the process of rotating the shaft, if the pointer sometimes points to 0, it means that there is a short-circuit point between the moving piece and the fixed piece;If a certain angle is encountered, the multimeter reading is not infinite but a resistance value, indicating that there is leakage between the variable capacitor moving plate and the fixed plate.

2. Detection of fixed capacitors

A. detection of small capacitors below 10pF is due to the small capacitance of fixed capacitors below 10pF, so using a multimeter to measure, can only qualitatively check whether there is leakage, short circuit or breakdown inside.When measuring, you can use the multimeter R×10k block, and use two test pens to connect the two pins of the capacitor at will, and the resistance value should be infinite. If the measured resistance value (the pointer swings to the right) is 0, it means that the capacitor is damaged by leakage or breakdown inside.

B. Detect whether the 10PF~0.01μF fixed capacitor is charged, and then judge whether it is good or bad. The multimeter selects R×1k block.The β values of the two triodes are both above 100, and the penetrating current can be made of 3DG6 and other silicon triodes to form a composite tube. The red and black test leads of the multimeter are respectively connected to the emitter e and collector c of the composite tube.Due to the amplification effect of the composite triode, the charging and discharging process of the capacitor under test is amplified, so that the pendulum of the multimeter pointer is increased, which is convenient for observation. It should be noted that: in the test operation, when measuring a capacitor with a small capacity, it is necessary to repeatedly exchange the pins of the tested capacitor to contact points A and B, so that the swing of the multimeter pointer can be clearly seen.

C. For fixed capacitors above 0.01μF, the R×10k block of the multimeter can be used to directly test whether the capacitor has a charging process and whether there is a short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.

3. Detection of electrolytic capacitors

A. Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, when measuring, appropriate ranges should be selected for different capacities. According to experience, in general, the capacitance between 1 ~ 47μF can be measured in R×1k block, and the capacitance larger than 47μF can be measured in R×100 block.

B. Connect the red test lead of the multimeter to the negative electrode and the black test lead to the positive electrode. At the moment of first contact, the multimeter pointer will deflect to the right by a large degree (for the same electrical block, the larger the capacity, the larger the swing), and then gradually turn to the left, until it stops at a certain position.The resistance value 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 more than a few hundred kΩ, otherwise, it will not work properly.In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the needle does not move, it means that the capacity disappears or the circuit is broken; can not be used.

C. For electrolytic capacitors whose positive and negative signs are unknown, the above method of measuring leakage resistance can be used to identify them. 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 the larger resistance value in the two measurements is the forward connection method, that is, the black test lead is connected to the positive electrode, and the red test lead is connected to the negative electrode.

D. Use the multimeter to block the electricity and use the method of forward and reverse charging to the electrolytic capacitor. According to the magnitude of the pointer swinging to the right, the capacity of the electrolytic capacitor can be estimated.