Ultrasonic Level Switch

Ultrasonic switches use piezoelectric crystals to transform electrical energy into mechanical motion (sound). The Transmit Crystal sends a pulse of sound through the space between the crystals, to the Receive Crystal. If the space is filled with air, gas or vacuum, the Receive Crystal does not detect the sound pulse. However, if the space is filled with liquid, any liquid, the pulse is detected by the receive crystal, and the switch output changes.