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　　In line aluminum Electrolytic capacitorIt is one of the Electrolytic capacitor, also called plug-in capacitance, lead capacitance. The in-line Electrolytic capacitor uses a metal foil (aluminum) as the positive electrode, and the insulating oxide layer (aluminum oxide) of the metal foil as the dielectric. The negative electrode of in-line aluminum Electrolytic capacitor is composed of thin paper soaked with electrolyte (liquid electrolyte).

Usually, the performance parameters of capacitors need to be tested using specialized testing equipment. In limited conditions, we can use a multimeter instead to quickly read and perform simple tests.

1、 Correct selection of resistance range for a multimeter

Since the capacity of the Electrolytic capacitor is much larger than that of the general fixed capacitor, the appropriate range should be selected for different capacities. Based on experience, in general, capacitance between 1-47UF can be measured in R * 1K gear, while capacitance greater than 47UF can be measured in R * 100 gear.

2、 Measure leakage resistance

Connect the red lead of the multimeter to the negative electrode and the black lead to the positive electrode. At the moment of first contact, the multimeter pointer will deflect to the right by a significant amount (for the same electrical barrier, the larger the capacity, the greater the swing), and then gradually rotate to the left until it stops at a certain position. Then, switch the red and black pens, and the multimeter pointer will repeat the above oscillation phenomenon. However, the measured resistance is the reverse leakage resistance of the Electrolytic capacitor, which is slightly less than the forward leakage resistance.

The reverse leakage current is greater than the forward leakage current. The practical use experience shows that the leakage resistance of Electrolytic capacitor should generally be more than several hundred K ohms, otherwise, it will not work normally.

In the test, if there is no charging phenomenon in both forward and reverse directions, that is, the pointer does not move, it means that the capacity has disappeared or there is an internal short circuit. If the measured resistance value is very small or zero, it means that the capacitance has a large leakage or has been broken down and damaged, and can no longer be used.

3、 Polarity discrimination

For Electrolytic capacitor with unknown signs of positive and negative poles, the above method of measuring leakage resistance can be used for discrimination. First, arbitrarily measure the leakage resistance, remember its size, and then exchange the probes to measure a resistance value. The one with the same resistance value between the two measurements is the forward connection method, where the black lead is connected to the positive electrode and the red lead is connected to the negative electrode.