Testing capacitors with a digital multimeter
A pointer multimeter can only detect the quality of capacitors (it is not suitable to judge the open circuit faults of small capacity capacitors) and roughly estimate the size of capacitors. It cannot accurately measure the capacitance size of capacitors. The capacitance of capacitors usually requires a capacitance meter, digital multimeter, and specialized capacitance measuring instruments to measure. When measuring the capacitance of a capacitor with a digital multimeter, it should be noted that not all capacitors can be measured and should be determined based on the measurement gear of the digital multimeter. Some digital multimeters have multiple capacitance measurement gears, which can measure 2nF~2; The capacitance of tF can be measured from ⒛ nF to ⒛ 0ctF, while some digital multimeters only have one ⒛ 0ptF capacitance measurement gear. When using a digital multimeter to measure the capacitance of a capacitor, place the digital multimeter in the capacitance range and select the appropriate range based on the capacitance. After the measured capacitor is fully discharged, directly plug it into the test hole or make direct contact between the two probes for measurement. The display screen of the digital multimeter will directly show the capacity of the capacitor to be tested.
If the displayed value is equal to or very close to the nominal capacity, it indicates that the capacitor is normal; If the displayed value of the tested capacitor is significantly different from the nominal capacity, check whether its nominal capacity is within the testing range of the multimeter. If it exceeds the measuring range of the multimeter, replace it with a multimeter with an appropriate range and measure again. If the difference is still too large after replacing the multimeter, it indicates that the tested capacitor has deteriorated and cannot be used anymore; If the displayed value of the tested capacitor is much smaller than the nominal capacity, it indicates that the tested capacitor has been damaged.
Note: (1) If the capacitance of the tested capacitor exceeds the measurement range of the multimeter, it cannot be measured with a digital multimeter.
(2) The method of connecting the probes of a digital multimeter is opposite to that of a pointer multimeter. The black probe of a pointer multimeter is connected to the positive terminal of the power supply inside the meter, which is the current outflow end of the meter; The red probe of the digital multimeter is connected to the positive terminal of the power supply inside the meter, which is the current outflow terminal inside the meter. After the capacitor is fully discharged, connect the red probe of the multimeter to the positive pole of the electrolytic capacitor and the black probe to the negative pole of the electrolytic capacitor to measure the positive insulation resistance. On the contrary, connecting the red probe of a multimeter to the negative electrode of an electrolytic capacitor and the black probe to the positive electrode of the electrolytic capacitor can measure the reverse insulation resistance.
