Measurement of a 400 microfarad capacitor with a pointer multimeter
Firstly, a metal object should be used to short-circuit the capacitor pins and discharge them. The main purpose of doing this is to eliminate danger and reduce measurement errors, as some charged capacitors can be very dangerous when discharged, not only damaging the multimeter but also potentially injuring people. Even if there is only a small amount of charge that the human body cannot feel, it still has an impact on the measurement results.
The discharged capacitor can be measured with confidence. The first step in measuring is to select the gear of the watch. The principle of gear selection is that the maximum amplitude of pointer swing during measurement can be near the middle of the dial. For measuring a capacitance of 400 μ F using MF47, it is generally advisable to choose Rx10.
At the moment when a capacitor is connected to direct current, it will generate a charging current, and the larger the capacitance, the greater the current. If the Ω range of a pointer multimeter is used to measure capacitance, it is equivalent to charging the capacitor with the battery inside the meter. The larger the capacity, the greater the swing amplitude of the pointer.
But what exactly is the swing of 400 μ F? We need to find a new capacitor with a similar capacity for comparison, and we can choose a capacitor with a capacity of 470 μ F as the comparison scale. Different models of watches may have some differences, but as long as the pointer can swing to the middle for comparison, it's enough. According to this principle, some multimeters even indicate the capacitance scale and can be directly measured.
Another thing to note is that electrolytic capacitors have polarity, and the leakage current measured in reverse and forward directions will be different. Using a red probe to connect the negative terminal of a capacitor will result in less leakage, while conversely, the leakage will be greater. The closer the pointer swings back to its original position, the smaller the leakage. When simply measuring leakage, the Rx1K range can also be selected for a more detailed view. When the red probe is connected to the negative terminal, it should not be less than 1M Ω. The higher the withstand voltage, the smaller the leakage (the larger the resistance).
In addition, the capacitor should be discharged every time it is measured, otherwise it will seriously affect the accuracy.
Express the multimeter to the 100 Ω range (resistance range) and short-circuit the two meter pins to zero. Connect the two meter pins to the two legs of the capacitor separately. If the black meter pin is placed on the positive pole of the capacitor and the red meter pin is placed on the negative pole of the capacitor, this is called forward charging measurement; On the contrary, it is a reverse measurement. The swing amplitude of the positive measuring needle is very large, close to zero; The reverse measurement needle swing is too small. The method of measuring the quality of capacitance, whether measured in forward or reverse direction, involves a large swing of the pointer almost to the zero position, and then slowly swinging back until it approaches infinity, indicating that the capacitance is good. If the pointer directly reaches the zero position without retracting, it indicates that the capacitor has been broken down and damaged. If the needle does not retract to any position in the middle, it indicates that the capacitor has serious leakage and cannot be used. If the pointer remains motionless, it means that the capacitor has no capacity and cannot be used anymore. The above are the methods for measuring the quality of capacitance, and the measurement of other capacities is also similar.
