Digital multimeter to measure the quality of capacitors_Multimeter to detect the quality of capacitors
1) Judgment of good and bad
Step 1: Select the gear. Turn the conversion switch of the digital multimeter to the gear marked with the "Ω" symbol and select the range gear of "diode with buzzer".
Step 2: Check the operation. The two probes do not distinguish between positive and negative, and touch the two pins of the capacitor separately. At this point, the number displayed on the LCD screen quickly flashes and immediately shows the starting symbol (or "overflow symbol") "1", then swap the probes and measure again. At this point, a negative sign "~" appears in front of the number displayed on the LCD screen, followed by a rapid flashing of the number and the appearance of the starting symbol "1". The above situation indicates that the positive and negative charging processes of the tested capacitor are normal and good. If the number displayed on the LCD screen cannot show "1" after rapid flashing during the above testing process, and there is an unstable resistance reading, it indicates that the tested capacitor is leaking electricity; If in both tests of exchanging probes, the LCD screen displays "0" (or close to "0") and the buzzer keeps ringing, it indicates that the tested capacitor has short circuited; If only the overflow symbol "1" is displayed without a flashing process of numbers, it indicates that the tested capacitor is open circuit.
Attention: For capacitors with larger capacity, when the two probes touch the pins on both ends of the capacitor, the buzzer will have a brief beeping process. The larger the capacity of the capacitor, the longer the beeping process of the buzzer. This is because at the beginning of charging a large capacity capacitor, a large amount of heterogeneous charges in the circuit move and accumulate towards the two plates of the capacitor, resulting in a higher current and lower impedance in the circuit. Therefore, when testing capacitors with larger capacities, the time for the probe to contact the capacitor pin should not be too short, otherwise it may cause erroneous judgments.
Step 3: Detection and judgment of whether there is leakage.
When the second step of the above detection is completed and the digital flicker process on the digital multimeter LCD screen ends, only the overflow symbol "1" is displayed and no longer changes, it indicates that the charging process of the tested capacitor has ended, and there is already an energy storage voltage of about 2.6V at both ends (this voltage is the voltage between the two probes of the digital multimeter when using the diode mode). At this point, remove the probes from the pins of the capacitor, then turn the conversion switch of the digital multimeter to the DC voltage measurement range marked with the "V -" symbol, select the 20V range, and then touch the two probes separately to the two pins of the capacitor to detect the energy storage voltage at both ends. By observing the speed at which the voltage value on the LCD screen decreases, it can be determined whether the tested capacitor is leaking. If the voltage reading gradually decreases at an extremely slow rate, it indicates that the stored energy of the capacitor is slowly released through the "internal resistance" of the meter, indicating that there is no leakage phenomenon in the tested capacitor; If the voltage reading drops rapidly and quickly drops to 0, it indicates that the tested capacitor has leakage and cannot continue to be used in the circuit.
