In the absence of special instrumentation, the quality and quality of the capacitor can be detected and judged with the resistance gear of the pointer multimeter. For fixed capacitors with large capacity (above 1μF), the resistance gear (R×1000) of the multimeter can be used to measure the two electrodes of the capacitor. Then exchange the test rod and try again to see the swing of the needle. The larger the swing, the greater the capacitance of the capacitor. If the test rod has been touching the lead of the capacitor, the pointer should point near ∞, otherwise, it indicates that the capacitor has leakage. The smaller the resistance value, the greater the leakage, and the quality of the capacitor is poor; indicating that the capacitor has failed or is open circuit; if the needle swings, but cannot return to the starting point, it indicates that the capacitor has a large leakage and is of poor quality.
For capacitors with small capacity, it is often impossible to see the needle swing when measuring with a multimeter. At this time, you can use an external DC voltage and use the multimeter to measure the DC voltage. The method is to adjust the multimeter to the corresponding DC voltage. The (black) test rod is connected to the negative pole of the DC power supply, the positive (red) test rod is connected to one end of the capacitor under test, and the other end is connected to the positive pole of the power supply.
When a capacitor with good performance is connected to the power supply, the needle of the pointer type multimeter should have a larger swing; the larger the capacity of the capacitor, the greater the swing of the needle. After the swing, the needle can gradually return to zero. If the pointer of the multimeter does not swing at the moment when the capacitor is turned on, it means that the capacitor fails or is broken; if the pointer keeps indicating the power supply voltage without swinging, it indicates that the capacitor has been broken down and short-circuited; if the pointer swings normally, but does not return to zero , indicating that the capacitor has leakage, the higher the indicated voltage value, the greater the leakage.
It should be pointed out that the auxiliary DC voltage used to measure the capacitor with small capacity cannot exceed the withstand voltage of the capacitor under test, so as to avoid the breakdown and damage of the capacitor caused by the measurement. To accurately measure the capacity of a capacitor, a capacitive bridge or a Q meter is required. The above simple detection method can only roughly judge the quality of the pressure gauge capacitor.
Experience with measuring capacitors with an analog multimeter
1. Use the resistance gear of the multimeter to check the quality of the electrolytic capacitor
The two leads of the electrolytic capacitor are divided into positive and negative. When checking whether it is good or bad, for electrolytic capacitors with lower withstand voltage (6V or 10V), the resistance should be placed in the R×100 or R×1K gear. The red test lead is connected to the negative end of the capacitor, and the black test lead is connected to the positive end. At this time, the multimeter pointer will swing and then return to zero or near zero. Such electrolytic capacitors are good. The larger the capacity of the electrolytic capacitor, the longer the charging time and the slower the pointer swings.
2. Use a multimeter to judge the positive and negative leads of the electrolytic capacitor
For some electrolytic capacitors with low withstand voltage, if the positive and negative lead marks are not clear, it can be judged according to the characteristics of its small leakage current (large resistance value) when it is connected positively and large leakage current when it is connected reversely. The specific method is: touch the two leads of the capacitor with red and black test pens, remember the magnitude of the leakage current (resistance value) (the resistance value indicated when the pointer swings back and stops), and then short the positive and negative leads of the capacitor. Next, switch the red and black test pens before measuring the leakage current. Judgment is based on the indication value of the small leakage current. The lead that is in contact with the black test lead is the positive end of the electrolytic capacitor. This method is more difficult to distinguish the polarity of electrolytic capacitors with small leakage current.
3. Check the variable capacitor with a multimeter
Variable capacitors have a set of fixed plates and a set of moving plates. Use the resistance gear of the multimeter to check whether there is any contact between the moving and fixed pieces. Use red and black test pens to connect the moving piece and the fixed piece respectively, and rotate the shaft handle. The pointer of the meter does not move, indicating that there is no short circuit between the moving and fixed pieces
