Ultrasonic contact switches use a pair of piezoelectric crystals that are encapsulated in epoxy at the tip of the transducer for level measurement. The crystals are made of a ceramic material that vibrates at a given frequency when subjected to an applied voltage. The transmit crystal converts the applied voltage from the electronics into an ultrasonic signal. When liquid is present in the gap, the receive crystal senses the ultrasonic signal from the transmit crystal and converts it back to an electrical signal. This signal is sent to the electronics to indicate the presence of liquid in the transducer gap. When there is no liquid present, the ultrasonic signal is attenuated and is not detected by the receive crystal.
The ultrasonic transducer continuously monitors the gap to determine if the gap is wet or dry. When used as a high level switch, the electronics will immediately actuate a relay or shift a current when it detects a wet gap. When used as a low level switch, it continuously checks for a dry gap condition.