Polarity identification and quality inspection of electrolytic capacitors are crucial to electronic engineering. A common method is to use a multimeter's electrical barrier to measure its polarity.
First, it is necessary to clarify the positive and negative poles of the electrolytic capacitor. The positive terminal should be connected to the positive terminal of the power supply (usually the black test lead), and the negative terminal should be connected to the negative terminal of the power supply (usually the red test lead). Only in this configuration, the leakage current of the electrolytic capacitor is small and the leakage resistance is large. On the contrary, if the connection method is wrong, the leakage current of the electrolytic capacitor will increase and the leakage resistance will decrease.
When measuring, first assume that a certain pole is a "+" pole, connect the black test lead to that pole, and the red test lead to the other pole, and record the scale position where the needle stops (usually to the left, indicating large resistance). Then, discharge the capacitor (that is, short-circuit the two leads), then reverse the positions of the two test leads and measure again. In the two measurements, the time the meter needle finally stopped at the left position, the black meter lead was connected to the positive electrode of the electrolytic capacitor.
When measuring, it is recommended to select the R*100 or R*1K gear. This method is suitable for electrolytic capacitors of different capacities. Judge the quality of the capacitor by observing the deflection of the needle. If the meter needle swings rapidly to the right and then slowly returns to its original position, it usually indicates that the capacitor is good. If the needle does not return after swinging, it indicates that the capacitor has broken down. If the hands of the watch gradually return to a certain position after swinging and stay there, it indicates that the capacitor has leaked electricity. If the needle does not move at all, it means that the capacitor's electrolyte has dried up and its capacity has seriously decreased.
However, some leaky capacitors may not be easy to accurately determine. In this case, you can use the reverse charging method and use the R×10K gear. Connect the black test lead to the negative terminal of the capacitor and the red test lead to the positive terminal, and observe the behavior of the needles. If the needle swings quickly and then stabilizes somewhere, it means the capacitor is good. If the needle is unstable at a certain position or gradually moves to the right, it means that the capacitor has a leakage problem and needs to be replaced. Generally, if the meter needle stays and is stable within the 50 to 200K scale range, it indicates that the capacitor is of good quality. This method has high accuracy and is especially suitable for applications that require high capacitor quality.