Ultrasonic Distance Sensor

An ultrasonic sensor measures distance by emitting a burst of high-frequency sound (40-400 kHz, above the range of human hearing) and measuring the time it takes for the echo to return from a target surface. Since the speed of sound in air is approximately 343 m/s, the round-trip time divided by two gives the distance: distance = (time × speed_of_sound) / 2.

The sensor has a blind zone — a minimum distance near the face where the echo returns before the transmitter has switched to receive mode. Typical blind zones are 30-300 mm depending on the model. Targets closer than the blind zone are not detected reliably.

The beam width is another key specification. Wide beams average the return from a larger area, which can give misleading readings when a target has an irregular or angled surface. Narrow-beam models (pencil-beam) are used for precise measurement of irregular objects.

Output options include 4-20 mA (proportional to distance), 0-10 V, or discrete switching (when the target enters a set window). Most modern sensors also offer IO-Link for digital configuration without changing the wiring.

Temperature affects the speed of sound (it increases with temperature by about 0.6 m/s per °C). Premium sensors include a temperature compensation circuit; budget models require an ambient temperature correction factor in the PLC scaling.