How to use a pointer multimeter to measure the quality of a capacitor?

Without special instruments and instruments, the quality of capacitors can be detected and judged by the resistance of pointer multimeter. Large capacity (1 μ F and above) can use the resistance scale (R) of the multimeter × 1000) Measure the two electrodes of the capacitor, and the meter needle should swing in the direction of low resistance, and then slowly swing back to near ∞. Then exchange the test rod and try again. Check the swing of the meter needle. The greater the swing, the greater the capacitance of the capacitor. If the test bar keeps touching the capacitor lead, the pointer should be near ∞, otherwise, it indicates that the capacitor has leakage. The smaller the resistance is, the greater the leakage is, and the capacitor quality is poor; If the meter pin does not move at all during measurement, it indicates that the capacitor has failed or is open circuit; If the meter needle swings but cannot return to the starting point, it indicates that the leakage of the capacitor is large and its quality is poor.

For capacitors with small capacity, the needle swing can not be seen when measuring with a multimeter. At this time, you can use an external DC voltage and a multimeter DC voltage range to measure. The method is to adjust the multimeter to the corresponding DC voltage range. The negative (black) test bar is connected to the negative pole of the DC power supply, the positive (red) test bar is connected to one end of the capacitor to be measured, 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 multimeter should have a large swing; The greater the capacity of the capacitor, the greater the swing of the meter needle. After the swing, the meter needle can gradually return to the zero position. If the pointer of the multimeter does not swing when the capacitor is switched on, it indicates that the capacitor is invalid or open circuit; If the meter needle always indicates the power supply voltage without swinging, it indicates that the capacitor has been broken down and short circuited; If the meter needle swings normally but does not return to zero, it indicates 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 measured capacitor, so as to avoid the breakdown damage of the capacitor due to measurement. In order to accurately measure the capacity of the capacitor, it is necessary to use a capacitive bridge or a Q meter. The above simple detection method can only roughly judge the quality of the pressure gauge capacitor.

Experience in measuring capacitors with pointer multimeter

1. Check the quality of electrolytic capacitor with multimeter resistance

The two leads of the electrolytic capacitor are positive and negative. When checking its quality, the resistance of the electrolytic capacitor with low withstand voltage (6V or 10V) should be placed at R × 100 or R × In gear 1K, connect the red probe to the negative terminal of the capacitor and the black probe to the positive terminal. At this time, the pointer of the multimeter will swing and then return to zero or near zero. Such electrolytic capacitors are good. The larger the capacity of the electrolytic capacitor is, the longer the charging time is, and the slower the pointer swings.

2. Use multimeter to judge the positive and negative leads of electrolytic capacitor

For some electrolytic capacitors with low withstand voltage, if the positive and negative leads are not clearly marked, it can be judged according to the characteristics of small leakage current (large resistance value) during positive connection and large leakage current during reverse connection. The specific method is: contact the two leads of the capacitor with red and black probes, remember the size of the leakage current (resistance value) (the resistance value indicated when the pointer swings back and stops), then short circuit the positive and negative leads of the capacitor, exchange the red and black probes, and then measure the leakage current. Judging by the indication of small leakage current, the lead that contacts the black probe is the positive end of the electrolytic capacitor. This method is difficult to distinguish the polarity of electrolytic capacitors with small leakage current.

3. Check the variable capacitor with a multimeter

The variable capacitor has a set of fixed pieces and a set of moving pieces. The resistance gear of the multimeter can be used to check whether there is a collision between the moving and fixed pieces. The red and black probe can be used to connect the moving and fixed pieces respectively. The shaft handle can be rotated and the pointer of the meter can not move, indicating that there is no short circuit (collision) between the moving and fixed pieces; If the pointer swings, it indicates that there is a short circuit in the capacitor.

4. Roughly identify the capacitance above 5000PF with multimeter resistance

The resistance of the multimeter can be used to roughly identify whether the capacitor above 5000PF is good or not (those below 5000PF can only judge whether the capacitor is broken down). During the inspection, the resistance range is set at the high range value, and the two probes respectively contact the two ends of the capacitor. At this time, the pointer quickly swings and then recovers. The reverse connection makes the swing amplitude larger than the first time, and then recovers. Such capacitors are good. The larger the capacity of the capacitor, the greater the swing of the meter pointer during measurement, and the longer the pointer recovery time. We can compare the capacity of the two capacitors according to the swing of the meter pointer.