What is the principle behind ultrasonic retroreflective mode sensors? How do they work?
Retroreflective mode uses the same type of design as diffuse mode sensors, such that a single housing contains both the transducer and the evaluation electronics, allowing one sensor to operate as both an emitter and receiver. Much like diffuse mode sensors, retroreflective sensors emit a three-dimensional sound cone which creates a beam angle that defines the sensing range. However, instead of calculating the distance to a target object, retroreflective sensors are set to a specific constant value based on an unchanging distance to a reflective surface like a wall, plate, or conveyor belt. This distance between the sensor and the surface serves as a reference. The sensor measures the amount of time between the emission of a sound pulse and its return echo from the reflective surface. If there is a change in the amount of time or if the echo disappears entirely, this indicates that a target object is present.