How to measure the quality of capacitance with a multimeter
1. Detect small capacitance below 10pF
Because the capacitance of the fixed capacitor below 10pF is too small, it can only be checked qualitatively if there is leakage, internal short circuit or breakdown phenomenon by using a multimeter to measure it.
When measuring, you can choose the R×10k block of the multimeter, and use the two test leads to connect the two pins of the capacitor arbitrarily, and the resistance 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.
2. Detect fixed capacitors from 10PF to 0.01μF
Detect whether the fixed capacitor of 10PF ~ 0.01μF is charged, and then judge whether it is good or bad. The multimeter can choose R×1k gear, and the β values of the two triodes are both above 100, and the penetration current should be small.
3DG6 and other types of silicon transistors can be used to form composite tubes. 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 measured capacitor is amplified, and the pendulum of the pointer of the multimeter is increased, which is convenient for observation.
Note: During the test operation, especially when measuring a capacitor with a small capacity, it is necessary to repeatedly switch the pins of the capacitor under test to touch points A and B, so that the pointer of the multimeter can visibly swing.
3. Detect fixed capacitance above 0.01μF
To detect fixed capacitance 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 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.
Steps to test the quality of capacitors with a digital multimeter:
1. To determine the polarity, first adjust the multimeter to the 100 or 1K ohm range. Assume that one pole is positive, connect the black test lead to it, and connect the red test lead to the other pole. Write down the resistance value, and then discharge the capacitor, that is, let the two poles Contact, and then change the test lead to measure the resistance. The black test lead with a large resistance value is connected to the positive electrode of the capacitor.
2. Adjust the multimeter to the appropriate gear of the ohm range. The principle of gear selection is: 1μF capacitors use 20K gears, 1-100μF capacitors use 2K gears, and capacitors larger than 100, μF use 200 gears.
3. Then use the red pen of the multimeter to connect the positive pole of the capacitor, and the black pen to the negative pole of the capacitor. If the display increases slowly from 0, and finally displays the overflow symbol 1, the capacitor is normal. If it always shows 0, the capacitor is short-circuited internally. If 1 is displayed, the capacitor is internally disconnected.
