Methods of Measuring the Quality of an Air Conditioner Capacitor with a Digital Multimeter
Capacitors are one of the most commonly used electronic components. The appearance and circuit symbol of a capacitor are shown in the figure. The universal letter symbol for a capacitor is "C". A capacitor is mainly composed of metal electrodes, a dielectric layer, and electrode leads, and the two electrodes are insulated from each other. Therefore, it has the basic performance of "blocking direct current and allowing alternating current to pass through".
Some digital multimeters have the function of measuring capacitance, and their ranges are divided into five gears: 2000p, 20n, 200n, 2μ, and 20μ. When measuring, the two pins of the discharged capacitor can be directly inserted into the Cx jack on the meter panel. After selecting an appropriate range, the displayed data can be read.
The 2000p range is suitable for measuring capacitors with a capacitance less than 2000pF; the 20n range is suitable for measuring capacitors with a capacitance between 2000pF and 20nF; the 200n range is suitable for measuring capacitors with a capacitance between 20nF and 200nF; the 2μ range is suitable for measuring capacitors with a capacitance between 200nF and 2μF; the 20μ range is suitable for measuring capacitors with a capacitance between 2μF and 20μF.
Experience has shown that some models of digital multimeters (such as DT890B+) have relatively large errors when measuring small-capacity capacitors below 50pF, and measuring capacitors below 20pF has almost no reference value. At this time, the series connection method can be used to measure small-value capacitors. The method is as follows: First, find a capacitor of about 220pF 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 (C1 - C2) is the capacitance of the small capacitor to be measured. This method is very accurate for measuring small-capacity capacitors in the range of 1 to 20pF.
Detection with the Resistance Range
Practice has proved that a digital multimeter can also be used to observe the charging process of a capacitor. In fact, this reflects the change of the charging voltage with discrete digital quantities. Suppose the measurement rate of the digital multimeter is n times per second. Then, during the observation of the capacitor's charging process, n independent and sequentially increasing readings can be seen every second. Based on this display characteristic of the digital multimeter, the quality of the capacitor can be detected and the magnitude of the capacitance can be estimated. The following is the method of using the resistance range of a digital multimeter to detect capacitors, which is of great practical value for meters without a capacitance range. This method is suitable for measuring large-capacity capacitors ranging from 0.1μF to several thousand microfarads.
