How can the quality of capacitors be assessed using a multimeter?
Depending on the capacity of the electrolytic capacitor, the R value of the multimeter is usually selected × 10. R × 100, R × 1 K gear for testing and judgment. The red and black probes are connected to the positive and negative poles of the capacitor respectively (before each test, the capacitor needs to be discharged), and the quality of the capacitor is judged by the deviation of the meter needle. If the watch needle quickly swings to the right and then slowly returns to its original position to the left, a capacitor is generally good. If the watch needle does not rotate after swinging, it indicates that the capacitor has broken down. If the watch needle gradually returns to a certain position after swinging, it indicates that the capacitor has leaked electricity. If the watch needle cannot swing, it indicates that the electrolyte of the capacitor has dried up and lost its capacity.
It is difficult to accurately determine the quality of capacitors with leakage using the above methods. When the withstand voltage value of the capacitor is greater than the battery voltage value in the multimeter, according to the characteristics of the electrolytic capacitor, which has a small leakage current during forward charging and a large leakage current during reverse charging, R can be used × At 10K gear, charge the capacitor in reverse and observe whether the meter needle remains stable (i.e. whether the reverse leakage current is constant), in order to determine the quality of the capacitor with high accuracy. The black lead is connected to the negative pole of the capacitor, and the red lead is connected to the positive pole of the capacitor. The watch needle quickly swings up and then gradually retreats to a certain position without moving, indicating that the capacitor is good. If the watch needle is unstable at a certain position or gradually moves to the right after stopping, the capacitor has leaked electricity and cannot be used anymore. The watch needle generally stays and stabilizes within the scale range of 50-200 K.
How to use a multimeter to determine the quality of piezoelectric ceramics?
Piezoelectric ceramics are artificially synthesized piezoelectric materials. When subjected to external pressure, charges are generated on both sides, and the amount of charge is proportional to the pressure. This phenomenon is called the piezoelectric effect. Piezoelectric ceramics have a piezoelectric effect, which means that they will deform under the action of an external electric field. Therefore, piezoelectric ceramic sheets can be used as sound emitting components.
By utilizing the piezoelectric effect of piezoelectric ceramic sheets, a multimeter can be used to determine their quality.
Lead out two wires from the two poles of the piezoelectric ceramic plate, then place the ceramic plate flat on the table, connect the two wires to the two probes of the multimeter, set the multimeter to the minimum current position, and then gently press the ceramic plate with a pencil eraser. If the pointer of the multimeter swings significantly, it indicates that the ceramic plate is in good condition, otherwise it indicates that it has been damaged.
