Ultrasonic thru-beam sensors are always comprised of two separate components: the emitter and the receiver. The evaluation and switching output electronics are located in the receiver.
The emitter and receiver are mounted directly opposite one another. As soon as an object interrupts the sound beam between the emitter and the receiver, the sensor switching output activates.
The receiver sensitivity can be adjusted for different distances between the emitter and receiver, and/or for different object sizes, via Teach-in or a potentiometer.