Testing the condition of a capacitor with a digital multimeter.
1. Direct Detection Using the Capacitance Range
Some digital multimeters are equipped with the function of measuring capacitance, and their measurement ranges are divided into five levels: 2000p, 20n, 200n, 2μ, and 20μ. When measuring, you can directly insert the two leads of the discharged capacitor into the Cx jack on the meter panel. After selecting an appropriate range, you can read the displayed data.
The 2000p range is suitable for measuring capacitors with a capacitance less than 2000 pF.
The 20n range is appropriate for measuring capacitors with a capacitance between 2000 pF and 20 nF.
The 200n range is good for measuring capacitors with a capacitance between 20 nF and 200 nF.
The 2μ range is used to measure capacitors with a capacitance between 200 nF and 2 μF.
The 20μ range is for measuring capacitors with a capacitance between 2 μF and 20 μF.
Experience has shown that some models of digital multimeters (such as DT890B+) have relatively large errors when measuring small - capacity capacitors below 50 pF, and measuring capacitors below 20 pF has little reference value. In this case, the series method can be used to measure small - value capacitors.
The method is as follows: First, find a capacitor of about 220 pF and measure its actual capacitance C1 with a digital multimeter. Then, connect the small capacitor to be measured in parallel with it and measure the total capacitance C2. The difference between the two (C2 - C1) is the capacitance of the small capacitor to be measured. This method is very accurate for measuring small - capacity capacitors ranging from 1 pF to 20 pF.
2. Detection Using the Resistance Range
Practice has proven that a digital multimeter can also be used to observe the charging process of a capacitor. In fact, this reflects the change in the charging voltage in discrete digital values. Suppose the measurement rate of the digital multimeter is n times per second. During the observation of the capacitor's charging process, you can see n independent and successively increasing readings every second. Based on this display characteristic of the digital multimeter, you can detect the condition of the capacitor and estimate its capacitance.
The following is the method of detecting a capacitor using the resistance range of a digital multimeter, which is very useful for meters without a capacitance range. This method is applicable to measuring large - capacity capacitors ranging from 0.1 μF to several thousand microfarads.
