Testing the Quality of Capacitors with a Digital Multimeter
Judgment of Quality
The first step: Selection of the gear. Turn the changeover switch of the digital multimeter to the gear marked with the symbol "Ω" and select the range gear of "diode with buzzer".
The second step: Detection operation. The two test leads have no positive and negative distinction. Touch the two pins of the capacitor respectively. At this time, the number displayed on the liquid crystal display (LCD) screen flashes rapidly and then immediately shows the starting symbol (or "overflow symbol") "1". Then, exchange the test leads and measure again. At this time, a minus sign "～" appears in front of the number displayed on the LCD screen first, and then the number flashes rapidly and the starting symbol "1" appears. The above situation indicates that the forward and reverse charging processes of the measured capacitor are normal, and the capacitor is in good condition. If during the above testing process, the number displayed on the LCD screen cannot show "1" after flashing rapidly and there is always an unstable resistance value reading, it indicates that the measured capacitor is leaking electricity. If during the two measurements with the exchanged test leads, the LCD screen shows "0" (or close to "0") both times and the buzzer keeps sounding, it indicates that the measured capacitor is short-circuited. If only the overflow symbol "1" is displayed and there is no number flashing process, it indicates that the measured capacitor is open-circuited.
Judgment of Whether the Capacitance Has Changed
The first step: Use a soldering iron to lengthen the pins at both ends of the capacitor with wires to facilitate inserting them into the capacitor measurement jacks of the digital multimeter.
The second step: Operation of capacitance detection. Turn the changeover switch of the digital multimeter to the range of the capacitor capacitance measurement gear marked with the letter "F", and then select an appropriate range gear according to the nominal capacitance of the measured capacitor. Then, touch the lengthened pins of the capacitor against each other several times for discharging. After the discharging operation, insert the two pins into the two strip-shaped jacks marked with "cx" respectively. Since these two strip-shaped jacks have positive and negative polarities, when inserting the pins of the capacitor, the positive and negative polarities of the measured electrolytic capacitor should be aligned with the "+" and "－" symbols marked on the jacks respectively to ensure the accuracy of the measurement.
The third step: Judgment according to the reading.
When the reading displayed on the LCD screen stabilizes after a short period of change, the quality of the capacitor can be judged according to the difference between the nominal capacitance and the reading. Since the allowable error range of niobium and tantalum electrolytic capacitors is ±10%, if the displayed reading remains stable within the allowable error range, it indicates that the measured capacitor is in good condition. If the reading is much smaller than the nominal capacitance, it indicates that the capacitance of the capacitor has changed and it cannot be used continuously. If the LCD screen shows the overflow symbol "1" from the beginning and no longer changes, it indicates that the capacitor is internally open-circuited and damaged or the electrolyte has dried up and the capacitor has completely lost its capacitance. If the reading shows "0" or is close to "0" and the buzzer keeps sounding, it indicates that the measured capacitor is internally short-circuited.
