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1. Measuring Capacitor Quality with a Pointer Multimeter
To measure the quality of a capacitor, it is best to use a pointer multimeter, which is more intuitive. Below, we will use the pointer multimeter as an example to explain how to measure the quality of a capacitor.
First, measure the capacitance value of the capacitor. For capacitance above one hundred microfarads, set the meter to the resistance range Rx100. For several thousand microfarads, set to Rx10. For several hundred microfarads, set to RxK. During measurement, use the two probes to measure across the capacitor terminals, and the pointer will exhibit the following movements:
a. The pointer swings quickly to the right (the larger the capacitance, the larger the swing angle), and then slowly returns. This indicates that the capacitor is good.
b. The pointer swings quickly to the right, reaches zero, and then stops moving, indicating that the capacitor has internally shorted or broken down. If the pointer does not move at all, it is also bad.
c. If the pointer swings to the right and then slowly returns to the middle, it indicates that the capacitor has internal leakage and is also bad.
d. If there is no multimeter, you can use a battery and a small light bulb to determine the quality. Connect the capacitor in series with the battery and the small bulb; if the bulb lights up, the capacitor is bad; if it does not light, it is good.
e. For capacitance in the thousands of microfarads, if the pointer does not move much, it is good; if it reaches full scale, it is bad.
2. Measuring Capacitor Quality with a Digital Multimeter
1. Most digital multimeters have a capacitance range (some have a capacitance testing socket, while others use probes). 2. If not, you can use the diode symbol range (if the probes are connected to the capacitor terminals and you hear a beep, then it stops, the display usually shows 1. If you reverse the probes and the same phenomenon occurs, the capacitor is good. If the probes connected to the capacitor terminals cause the meter to beep continuously, the capacitor has broken down). Note: During the time the meter beeps until it shows 1, the displayed number is continuously increasing. Method 2 only tests the capacitor’s quality, not its capacitance.
3. Summary of Methods for Testing Capacitors with a Multimeter
1. Directly measure using the capacitance range. Some digital multimeters have the capability to measure capacitance, with ranges of 2000p, 20n, 200n, 2μ, and 20μ. When measuring, the discharged capacitor’s two leads can be directly inserted into the Cx socket on the meter, and after selecting the appropriate range, the display data can be read. The 000p range is suitable for measuring capacitors less than 2000pF; the 20n range is suitable for measuring capacitors between 2000pF and 20nF; the 200n range is suitable for measuring capacitors between 20nF and 200nF; the 2μ range is suitable for measuring capacitors between 200nF and 2μF; the 20μ range is suitable for measuring capacitors between 2μF and 20μF. It has been verified that some models of digital multimeters (such as DT890B+) have significant errors when measuring small capacitors below 50pF, and measuring capacitors below 20pF has almost no reference value. In this case, the series method can be used to measure small capacitors. The method is as follows: first find a capacitor around 220pF, use the digital multimeter to measure its actual capacitance C1, then connect the capacitor to be tested in parallel and measure the total capacitance C2; the difference (C1-C2) is the capacitance of the capacitor to be tested. This method is very accurate for measuring small capacitors of 1 to 20pF.
2. Measuring with the resistance range. It has been proven that using a digital multimeter can also observe the charging process of the capacitor, which actually reflects the change in charging voltage in discrete digital quantities. If the measurement rate of the digital multimeter is n times per second, then during the observation of the capacitor’s charging process, you can see n independent and sequentially increasing readings each second. Based on this display feature of the digital multimeter, the quality of the capacitor can be detected and the capacitance size estimated. Below is a method for using a digital multimeter’s resistance range to detect capacitors, which is very practical for instruments without a capacitance range. This method is suitable for measuring large capacitors from 0.1μF to several thousand microfarads. Set the digital multimeter to the appropriate resistance range, and connect the red and black probes to the two terminals of the capacitor Cx. The displayed value will start from “000” and gradually increase until it shows the overflow symbol “1”. If it continuously shows “000”, it indicates that the capacitor is internally shorted; if it continuously shows overflow, it may indicate that the capacitor is internally open, or the selected resistance range is not suitable. When checking electrolytic capacitors, note that the red probe (positive) should connect to the positive terminal of the capacitor, and the black probe should connect to the negative terminal.
3. Measuring with the voltage range. Measuring with the voltage range is actually an indirect measurement method, which is the most accurate measurement method. Set the multimeter to the DC current range, connect the red and black probes to the capacitor, charge the capacitor, and then use a formula to calculate the capacitance. There are many methods for measuring capacitance with a multimeter, and the measurement principle utilizes the charging process of the capacitor. As the charge increases, when current flows, the changes in the readings on the multimeter reflect the capacitance size. The multimeter is a precision instrument, but some precautions must also be taken during use, such as ensuring the probes are connected correctly and the voltage/current ranges are not mismatched to avoid damage to the instrument.
Precautions for Using a Multimeter to Measure Capacitance: Always disconnect power and discharge before measuring. The discharging method is to find a metal object like a screwdriver, holding the insulated handle, touch the exposed metal parts of the capacitor’s two leads. For measuring capacitors with a digital multimeter, find the capacitance range, then discharge the capacitor and insert the two leads into the capacitor measurement socket. Wait for the LCD screen’s changing readings to stabilize; the displayed value is the capacitance of the capacitor being measured. If testing for leakage, you can use a pointer multimeter’s resistance range. When measuring small capacitors, the multimeter can be set to RX1K or RX100. When the probes touch the capacitor’s two leads, the pointer should deflect clockwise, and as the capacitor charges, the current ceases, the pointer should return counterclockwise towards infinity. The larger the angle of deflection, the larger the capacitance. During the deflection process, the pointer should swing uniformly and then return to infinity, initially indicating that the capacitor has no leakage. If at any point the pointer slows down or does not return, it indicates that the capacitor is leaking at that moment. If it ultimately shows infinity, it indicates no leakage; however, this can only be a rough judgment. To find precise values, a capacitance meter and a capacitance leakage tester or an oscilloscope should be used to observe characteristics, which is generally not possible for most individuals. Also, capacitors have voltage ratings; the voltage rating of electrolytic capacitors is usually marked on them, while some ceramic capacitors may not have markings, so be careful when selecting.
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Siemens Comprehensive + Portal + EPLAN Electrical Drawing Video Recordings Available for Sale at Low Package Prices!
Chuangkong Education Siemens Comprehensive Course Introduction
