The measurement method of digital multimeter to measure the quality of capacitance
Using the capacitance file of a digital multimeter can easily measure the quality of a capacitor. The specific measurement method is introduced below.
A 47μF electrolytic capacitor is measured with a digital multimeter capacitance file, and it is displayed as 45.17μF.
The method of judging whether the capacitor is good or bad
Adjust the range switch of the digital multimeter to the appropriate range of the capacitance range, and then insert the red and black test leads of the multimeter into the Cx jack and the COM jack of the multimeter respectively (for the convenience of taking pictures, the test leads with alligator clips are used here instead of the test leads), and then The red and black test leads respectively touch the two pins of the capacitor (if you measure the electrolytic capacitor, the polarity can be ignored), then if the value displayed by the multimeter is close to the nominal value of the capacitor (generally, 5% to 10% error is allowed) , it means that the capacitor is good.
The capacitance of the multimeter measures a 47μF electrolytic capacitor, the actual display capacity is 45.17μF, and the error is within the specified range, indicating that the capacitor is good.
The capacitance of the multimeter measures a good CBB capacitor with a nominal value of 0.1μF/630V, and the actual display capacity is 0.1037μF.
For capacitors damaged by breakdown, the resistance between the two pins is very small. At this time, the multimeter will display "1" when measuring with the capacitance gear of the multimeter, which means overflow. Therefore, when measuring the capacitance, if the multimeter range switch is not turned Wrong, but the meter displays "1", it means that the capacitor is likely to be broken down or the leakage is too large (at this time, you can measure its resistance value with the multimeter resistance file to confirm whether it is damaged).
For electrolytic capacitors placed for a long time, the internal electrolyte of some capacitors will gradually dry up, making the capacity smaller. Therefore, when measuring electrolytic capacitors, if the displayed capacity is significantly lower than its nominal value, the capacitor is generally not suitable for use. The picture above shows a 100μF electrolytic capacitor that has been placed for several years, and its measured capacity is only 54.08μF.
You can use a multimeter to identify good or bad capacitors. Three methods can be provided for your reference. The capacitor needs to be discharged before measurement, which will not be repeated below.
1. Direct measurement
If the measured capacitance is less than the maximum range of the multimeter, you can use the multimeter to measure it directly. If the capacitance is normal, the corresponding capacitance will be displayed on the display of the multimeter. The measured capacitance can be compared with the marked capacitance. If this If the two are equal or relatively close, it can be determined that the capacitor is good.
2. Diode file measurement
If the capacitance to be identified has exceeded the range of the multimeter, you need to use the diode file of the multimeter at this time, and also connect the test leads to both ends of the capacitor. If you can see that the number is increasing on the dial, and the capacitance is larger. The more obvious, then it can be concluded that the measured capacitance is also good.
3. Resistance file measurement
This method is very similar to the second method. It can be selected when the capacitance exceeds the range of the multimeter. First, turn the needle to the resistance position, and then connect the needle to both ends of the capacitor. If you can see the number on the dial of the multimeter Constantly increasing, the larger the capacitance, the slower the increase, then it can be judged that the capacitor is good, if the number 1 is always displayed on the dial, then the capacitor is broken.
