Multimeter to test the quality of chip capacitors
1. Also adjust the multimeter to the appropriate gear of the ohm range. The principle of gear selection is: 1μF capacitor uses 20K gear, 1-100μF capacitor uses 2K gear, greater than 100, and μF uses 200 gear.
2. To determine the polarity, first adjust the multimeter to the 100 or 1K ohm range. Assuming that one pole is positive, connect the black test lead to it, and the red test lead to the other pole, write down the resistance value, and then discharge the capacitor. That is, let the two poles touch, 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.
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.
How to judge the quality of chip capacitors with a digital multimeter?
Detection of Fixed Capacitors
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 whether the 10PF～0.01μF fixed capacitor is charged, and then judge whether it is good or bad. The multimeter selects the R×1k block. 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. It should be noted that 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 swing of the pointer of the multimeter can be clearly seen.
3. For fixed capacitance above 0.01μF, use the R×10k block of the multimeter 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.
Detection of electrolytic capacitors
1. Because the capacity of electrolytic capacitors is much larger than that of ordinary fixed capacitors, when measuring, you should choose a suitable range for different capacities. According to experience, in general, the capacitance between 1 and 47μF can be measured with R×1k gear, and the capacitance larger than 47μF can be measured with R×100 gear.
2. Connect the red test lead of the multimeter to the negative pole, and the black test lead to the positive pole. At the moment of first contact, the pointer of the multimeter will deflect to the right by a large degree (for the same electric resistance, the larger the capacity, the larger the swing), and then gradually to the left Turn around 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 use experience shows that the leakage resistance of electrolytic capacitors should generally be above several hundred kΩ, otherwise, it will not work normally. In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the hands of the watch do not move, it means that the capacity has disappeared or the internal circuit is broken; if the measured resistance value is very small or zero, it means that the capacitor has a large leakage or has been broken down. Can no longer be used.
3. For electrolytic capacitors with unknown positive and negative signs, the above method of measuring leakage resistance can be used to identify them. That is, first randomly measure the leakage resistance, 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 positive connection method, that is, the black test lead is connected to the positive pole, and the red test lead is connected to the negative pole. D? Use a multimeter to block electricity, use the method of positive and negative charging to the electrolytic capacitor, and estimate the capacity of the electrolytic capacitor according to the size of the pointer swinging to the right.
Detection of Variable Capacitors
1. Gently rotate the rotating shaft by hand, it should feel very smooth, and it should not feel loose or tight or even stuck. When the loading shaft is pushed forward, backward, up, down, left, right, etc., the shaft should not be loose.
2. Use one hand to rotate the rotating shaft, and the other hand to lightly touch the outer edge of the moving piece group, and there should be no loosening. A variable capacitor with poor contact between the rotating shaft and the moving piece cannot be used any longer.
3. Put the multimeter in the R×10k gear, connect the two test leads to the leading end of the moving piece and the fixed piece of the variable capacitor with one hand, and slowly rotate the shaft a few times with the other hand. Should not move at infinity. 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 a certain angle, the reading of the multimeter is not infinite but a certain resistance value appears, indicating that the variable capacitor is moving. There is a leakage phenomenon between the sheet and the fixed sheet.
