Ultrasonic proximity sensors use a transducer to send and receive high frequency ( 20
kHz - 1 GHz) sound signals. When a target enters the beam the sound is reflected back to
the switch, causing it to energise or de-energise the output circuit.
A piezoelectric ceramic disk is mounted in the sensor surface. It can transmit and receive
high-frequency pulses. A high frequency voltage is applied to the disk, causing it to
vibrate at the same frequency. The vibrating disk produces high-frequency sound waves.
When transmitted pulses strike a sound-reflecting object, echoes are produced. The
duration of the reflected pulse is evaluated at the transducer. When the target enters the
preset operating range, the output of the switch changes state. When the target leaves the
preset operating range, the output returns to its original state.