When measuring, you can choose to use a multimeter R× 10k, and use two probes to connect the two pins of the capacitor at will, and the resistance value should be infinite.
If the measured resistance (the pointer swings to the right) is zero, it means that the capacitor is damaged due to leakage or internal breakdown.
2. Check whether the fixed safety capacitor of 10pf ~ 00 1μ f is charged, and then judge its quality.
Select R× 1k range for multimeter.
The β values of both transistors are above 100, and the penetration current is very small.
Silicon triodes of 3DG6 and other models can be selected to form composite pipes.
The red and black probes of the multimeter are respectively connected with the emitter E and the collector C of the composite pipe.
Due to the amplification of the compound triode, the charging and discharging process of the measured capacitor is amplified, which makes the pointer swing of the multimeter larger and easier to observe.
It should be noted that when testing * operation, especially when testing a small-capacity safety capacitor, it is necessary to change the contact points A and B of the measured capacitor repeatedly to clearly see the swing of the multimeter pointer.
C For the safety capacitor above 00 1μF, you can directly test whether the capacitor has charging process, internal short circuit or leakage with R× 10k of multimeter, and estimate the capacitance according to the amplitude of the pointer swinging to the right.
Two: detect CG safety capacitor 1. Because the capacity of electrolytic capacitor is much larger than that of ordinary fixed capacitor, when measuring CG safety capacitor, the appropriate range should be selected according to different capacities.
According to experience, in general, the capacitance between 1 ~ 47μF can be measured by R× 1k, and the capacitance greater than 47μF can be measured by R× 100.
2. Connect the red probe of the multimeter to the negative electrode and the black probe to the positive electrode. At the moment of contact, the pointer of the multimeter deflects to the right by a large deviation (for the same electric hoist, the larger the capacity, the larger the swing), and then gradually turns to the left until it stops at a certain position.
The resistance at this time is the forward leakage resistance of electrolytic capacitor, which is slightly larger than the reverse leakage resistance.
Practical experience shows that the leakage resistance of electrolytic capacitor should be above several hundred kω, otherwise it will not work normally.
In the test, if there is no charging phenomenon in the forward direction and the reverse direction, that is, the watch hand does not move, it means that the capacity disappears or the internal circuit is open; If the measured resistance is small or zero, it means that the capacitor has a large leakage or has been broken down and cannot be used any more.
3. Electrolytic capacitors with unknown sign can be distinguished by the above method of measuring leakage resistance.
In other words, measure the leakage resistance at will, remember its size, and then exchange pens to measure a resistance.
In the two measurements, the one with high resistance is connected with the positive electrode, that is, the black contact pin is connected with the positive electrode and the red contact pin is connected with the negative electrode.
D. Charge the electrolytic capacitor forward and backward with a multimeter, and estimate the capacity of the electrolytic capacitor according to the amplitude of the pointer swinging to the right.
Three: routine safety capacitance detection 1, gently rotate the shaft by hand, it should feel smooth, and it should not feel loose or tight or even stuck.
When the load shaft is pushed forward, backward, up, down, left and right, the rotating shaft should not be loose.
2. Turn the rotating shaft with one hand and lightly touch the outer edge of the rotor set with the other hand, so as not to feel any looseness.
The variable capacitor with poor contact between the rotating shaft and the rotor cannot be used again.
3. Put the multimeter in the R× 10k file. One hand connects the two probes to the lead-out ends of the moving plate and stator of the variable capacitor, and the other hand slowly rotates the shaft several times. The pointer of multimeter should be in infinite position.
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 rotor and the stator; If a certain angle is encountered, the multimeter reading is not infinite, but a certain resistance value appears, indicating that there is leakage between the moving plate and the stator of the variable capacitor.