April 1st 2020
1. Test of Fixed Safety Capacitors
1.1 Test Small Capacitors Below 10pF
The capacity of fixed safety capacitor below 10pF is too small, so if using a multimeter to measure it, you can only qualitatively check whether it has leakage, internal short circuit or breakdown. When measuring, you can use a multimeter R × 10k block. Use two test leads to connect the two pins of the capacitor. The resistance should be infinite. If the measured resistance value (the pointer swings to the right) is zero, it means that the capacitor leakage is damaged or internal breakdown.
1.2 Test 10PF ～ 0 01μF Fixed Safety Capacitor
Test whether 10PF ～ 01 μF fixed safety capacitor has charging phenomenon, and then judge whether it is good or bad.
It should be noted that during testing, especially when testing small-capacity safety capacitors, it is necessary to repeatedly switch the two points of the capacitor under test to contact A and B to clearly see the multimeter pointer swing.
C For safety capacitors above 0 01 μF, the R × 10k range of the multimeter can be used to directly test the capacitor for charging process and 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.
2. Testing of Safety Capacitors
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, that is, the hands are not moving.
This means 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. It Can no longer be used.
(3) For electrolytic capacitors with unknown positive and negative markings, the above method of measuring leakage resistance can be used to judge. That means, first measure the leakage resistance arbitrarily, remember its size, and then exchange the test leads to measure a resistance value. The one with a large resistance value in the two measurements was the positive connection method.
To be more specific, the black test lead was connected to the positive electrode, and the red test lead was connected to the negative electrode. Then using multimeter resistance file and the positive and negative charging methods for the electrolytic capacitor, according to the magnitude of the swing of the pointer to the right, the capacity of the electrolytic capacitor can be estimated.
3. Conventional Safety Capacitance Test
(1) Gently rotate the shaft with your hand, it should feel very smooth, and it should not feel tight or sometimes stuck at times. When the load axis is pushed forward, backward, up, down, left, right, etc., the shaft should not be loose.
(2) 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.
In the process of rotating the 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 it encounters an angle, the multimeter reading is not infinite but a certain resistance value appears, indicating that the variable capacitor moves. There is a leakage phenomenon between the sheet and the fixed sheet.
4. What tests are performed on safety capacitors before leaving the factory? What are the differences from ordinary capacitors?
(1) Safety capacitors need to do a lot of testing and inspection certification. The main difference is that the outer case is a plastic case. With ABS material or TPB material, the flame retardant effect may be better. From the perspective of materials, they are no different.
(3) Safety capacitors are mainly used to suppress interference, and are divided into X and Y types.