How to detect capacitors?

Testing technology occupies an important position in all walks of life. Through testing, we can guarantee product quality to a certain extent. In this article, the editor will introduce the capacitor detection technology in detail, mainly including three aspects: 1. Variable capacitor detection, 2. Electrolytic capacitor detection, 3. Fixed capacitor detection.

1. Detection of variable capacitors

A Gently rotate the shaft by hand, it should feel very smooth, it should not feel loose and tight or even stuck. When the carrier shaft is pushed forward, backward, up, down, left, right, etc., 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, you should not feel any looseness. A variable capacitor with poor contact between the rotating shaft and the moving plate cannot be used any longer.

C Put the multimeter in the R&TImes; 10k block, connect the two test leads to the moving plate and the fixed plate of the variable capacitor with one hand, and slowly rotate the shaft with the other hand. Do not move at infinity. In the process of rotating the rotating shaft, if the pointer sometimes points to zero, 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 certain resistance value, indicating that the variable capacitor is moving. There is a leakage phenomenon between the plate and the stator.

2. Detection of fixed capacitors

A. Detecting small capacitors below 10pF Because the capacity of fixed capacitors below 10pF is too small, measuring with a multimeter can only qualitatively check whether there is leakage, internal short circuit or breakdown. When measuring, you can use the multimeter R&TImes; 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 zero, it means that the capacitor is damaged by leakage or internal breakdown.

B. Detect whether the 10PF～0.01μF fixed capacitor is charged, and then judge whether it is good or bad. Use the R&TImes;1k block for the multimeter. The β values ​​of the two triodes are both above 100, and the penetration 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 connected to the emitter e and collector c of the composite tube, respectively. Due to the amplifying 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 during the test operation, especially when measuring small-capacity capacitors, it is necessary to repeatedly exchange the contacts A and B of the tested capacitor pins, so that the swing of the multimeter pointer can be clearly seen.

C. For fixed capacitors above 0.01μF, the R&TImes; 10k block of the multimeter 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 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 greater 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 greater the capacity, the greater 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 above several 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 has disappeared or the internal circuit is open; Can no longer 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.

Summarized by Easybom.