Detection Methods Of Capacitor

By Author: Rachel Anne
Total Articles: 2
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A capacitor is a device that holds electric charges. It is one of the electronic components that are widely used in electronic equipment, and widely used in circuits such as direct communication, coupling, bypassing, filtering, tuning loop, energy conversion, control, etc. Regarding the detection of capacitors, there are three main categories: fixed capacitors, electrolytic capacitors, variable capacitors.

一、Detection of fixed capacitor
1.When detecting small capacitors below 10pF, the fixed capacitors below 10pF are too small, so you can only use a multimeter to qualitatively check for leakage, internal short circuit or breakdown. When measuring, you can choose a multimeter R × 10k block, and then use two test leads to connect the two pins of the capacitor at will. At this time, the resistance value should reach infinity. If the measured resistance value (the pointer swings to the right) is zero, it means that the capacitor leakage is damaged or internal breakdown.
2.First check whether the fixed capacitor of 10PF ～ 0.01μF is charged, and then judge whether it is good or bad. The multimeter uses R ...
... × 1k gear. The β values of the two transistors are more than 100, and the penetrating current can be a composite tube composed of silicon transistors such as 3DG6. 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 capacitor under test is enlarged, and the multimeter pointer pendulum is enlarged, which is convenient for observation. It should be noted that, during the test operation, especially when measuring a small-capacitance capacitor, it is necessary to repeatedly swap the two points of the tested capacitor pin A and B to see the swing of the multimeter pointer clearly.
3.For fixed capacitors above 0.01μF, the R × 10k block of the multimeter can be used to directly test the capacitor for charging process and internal short-circuit or leakage, and the capacitor capacity can be estimated according to the amplitude of the pointer swinging to the right.

二、Detection of electrolytic capacitor
1.Because the capacity of electrolytic capacitors is much larger than that of general fixed capacitors, when measuring, you should choose a suitable range for different capacities. According to experience, in general, the capacitance between 1 ~ 47μF can be measured with R × 1k block, and the capacitor larger than 47μF can be measured with R × 100 block.
2.The multimeter's red test lead is connected to the negative electrode and the black test lead to the positive electrode. At the moment of contact, the multimeter pointer is deflected to the right by a large degree of deflection (for the same electrical block, the larger the capacity, the larger the swing), and then gradually turn left until it stops at a certain position. 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 more than a few hundred kΩ, otherwise, it will not work properly. In the test, if there is no charging in the forward and reverse directions, the hands do not move, which also indicates that the capacity disappears or the internal circuit is broken; If the measured resistance is small or zero, it means that the capacitor has a large leakage current or has been damaged by breakdown and cannot be used again.
3.For electrolytic capacitors with unknown positive and negative markings, the above method of measuring leakage resistance can be used to judge. So 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 was the positive connection method, that is, the black test lead was connected to the positive electrode, and the red test lead was connected to the negative electrode.
4.A multimeter is used to block electricity, and the electrolytic capacitor is charged in the forward and reverse directions. The capacity of the electrolytic capacitor can be estimated according to the magnitude of the swing of the pointer to the right.

三、Detection of variable Capacitor
1.Gently to rotate the shaft with your hand, it should feel very smooth, and it should not feel tight or sometimes stuck when loose. When the load axis is pushed forward, backward, up, down, left, right and other directions, the shaft should not be loose.
2.To rotate the shaft with one hand, and touch the outer edge of the film group with the other hand, and you should not feel any looseness. Variable capacitors with poor contact between the rotating shaft and the moving blade can no longer be used.
3.Setting the multimeter to the R × 10k position. With one hand, connect the two test leads to the lead-out ends of the moving and fixed pieces of the variable capacitor, and slowly rotate the shaft a few times back and forth with the other hand. The multimeter pointer should not move at the infinite position. In the process of rotating the shaft, if the pointer sometimes points to zero, there is a short-circuit point between the moving piece and the fixed piece; If you encounter a certain angle, the multimeter reading is not infinite but shows a certain resistance value, indicating that there is a leakage phenomenon between the variable capacitor moving piece and the fixed piece.

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An editor working in electron industry.