How to judge the quality of capacitor with multimeter?
Answer: Depending on the capacity of electrolytic capacitor, R×10, R×100 and R×1 K blocks of multimeter are usually selected for testing and judgment. The red and black probes are respectively connected to the positive and negative poles of the capacitor (the capacitor needs to be discharged before each test), and the quality of the capacitor is judged by the deflection of the probe. Generally speaking, a capacitor is good if the hands swing to the right quickly and then slowly return to the original position to the left. If the hands do not rotate after swinging, the capacitor has broken down. If the hands swing back to a certain position and stop, it means that the capacitor has leaked electricity. If the hands can't swing, it means that the capacitor electrolyte has dried up and lost its capacity.
It is not easy to accurately judge the quality of the capacitor with leakage by the above method. When the withstand voltage value of the capacitor is greater than the battery voltage value in the multimeter, according to the characteristics that the leakage current of the electrolytic capacitor is small when charging in the forward direction and large when charging in the reverse direction, R×10 K gear can be used to charge the capacitor in the reverse direction, and whether the hand stays stable (that is, whether the reverse leakage current is constant) can be observed, thus judging the quality of the capacitor with high accuracy. The black stylus is connected to the negative pole of the capacitor, and the red stylus is connected to the positive pole of the capacitor. When the hands swing up quickly, and then gradually retreat to a certain place to stay still, it means that the capacitor is good. Any capacitor whose hands stay in a certain position unsteadily or gradually move to the right after staying has leakage, so it cannot be used any more. The hands of the watch generally stay and stabilize in the scale range of 50 ~ 200 K.
How to judge the quality of piezoelectric ceramics with multimeter?
A: Piezoelectric ceramics is a synthetic piezoelectric material. When subjected to external pressure, charges will be generated on both sides, and the amount of charge is directly proportional to the pressure. This phenomenon is called piezoelectric effect. Piezoelectric ceramics have piezoelectric effect, that is, under the action of external electric field, they will be deformed, so piezoelectric ceramic sheets can be used as sound generating elements.
Using the piezoelectric effect of piezoelectric ceramics, it can be judged by multimeter.
Lead out two wires from the two poles of the piezoelectric ceramic piece, then put the ceramic piece flat on the table, connect the two wires to the two probes of the multimeter respectively, set the multimeter to the minimum current stop, and then gently press the ceramic piece with the pencil rubber head. If the pointer of the multimeter swings obviously, it means that the ceramic piece is intact, otherwise, it means that it has been damaged.
