Piezo Element quality identification: A mechanical multimeter can easily detect whether the piezoelectric element is good or bad. The method is as follows: Set the multimeter to 25V, gently pinch the two sides of the piezoelectric plate with your left thumb and index finger, and hold two test pens in your right hand. Press it down, then relax, and the piezo element will generate two voltage signals with opposite polarities successively, so that the pointer swings to the right - back to zero - left - back to zero, with a swing of about 0.1~0.15V. If you re-test after changing the position of the test leads, the sequence of pointer swing is left swing - zero return - right swing - zero return. Under the same pressure, the larger the pointer swing, the higher the sensitivity of the piezoelectric element. If the pointer does not move, it means that the acoustic element is leaking or damaged. The appearance should be free of scratches and fingerprints. The ceramic sheet is not eccentric. The ceramic sheet and the substrate are bonded perfectly without overflowing glue,