How to detect electrolytic capacitors with a digital multimeter
(1) Directly detect with capacitor mode
Some digital multimeters have the function of measuring capacitance, and the UT51 has two ranges of 200 μ and 20 μ.
When measuring, first connect the red probe to the current terminal hole and the black probe to the COM terminal hole. Select the capacitor mode for the function mode, and then connect the red and black probes to the two pins of the discharged capacitor (pay attention to polarity). After selecting the appropriate range, the display data can be read.
200 μ F range, suitable for measuring capacitance between 20uF and 200 μ F; 20 μ F is suitable for measuring capacitance between 2 μ F and 20 μ F.
(2) Preliminary judgment of the quality of capacitors using buzzing mode
By using the buzzer mode of a digital multimeter, the quality of electrolytic capacitors can be checked at high speed. Set the digital multimeter to buzzer mode and use two probes to distinguish the contact between the two pins of the tested capacitor Cx. Next, swap the two probes and measure again. The buzzer should sound, indicating that the measured electrolytic capacitor is basically normal. At this point, you can switch to the high resistance range of 20M Ω or 200M Ω and measure the leakage resistance of the capacitor to determine its quality.
During testing, it is assumed that the buzzer keeps sounding, indicating that there has been a short circuit inside the electrolytic capacitor; If the buzzer does not sound and the instrument always displays "1" after repeatedly adjusting the probe measurement, it indicates that the tested capacitor has an internal open circuit or capacity loss. Use a digital multimeter to measure capacitance greater than 20 μ F, and note that this method is very practical.
(3) Preliminary detection of capacitance using resistance mode
It has been proven that the charging process of capacitors can also be observed using a digital multimeter, which in practice reflects the changes in charging voltage based on the digital quantity on the screen. The following is a method of using a digital multimeter to detect capacitors in resistance mode, which is of great practical value for instruments without capacitor mode configuration. This method is suitable for measuring large capacity capacitors ranging from 0.1 μ F to several thousand microfarads.
Set the digital multimeter to the appropriate resistance range, and distinguish between the red and black probes that touch the two poles of the tested capacitor Cx. At this point, the displayed value will gradually increase from "000" until the overflow symbol "1" is displayed. If "000" is continuously displayed, it indicates an internal short circuit in the capacitor; If overflow is continuously displayed, it can cause an open circuit between the internal poles of the capacitor, or it can cause the selected resistance range to be inappropriate. When inspecting electrolytic capacitors, it is important to note that the red probe (positively charged) should be connected to the positive terminal of the capacitor, and the black probe should be connected to the negative terminal of the capacitor.
