The combined sensor package is usually installed on the display board itself or under the platform roof. In both cases, the ultrasonic sensor is directed at the outer edge of the train roof diagonally from above. It emits short ultrasonic pulses and detects the echoes that are reflected from the object—in this case the train. Distance from the sensor widens the detection range, which is often referred to as the sound beam. The shape of the sound beam can be adapted to the application. The sensors used by HNC have a detection range of four or six meters. Their sound beams have a particularly large diameter so they can scan a correspondingly large area of the outer surface of the train. This ensures that varying train contours are reliably covered by the detection range and the sensor can still detect the stationary train if it is focused on a coupling gap between two cars.
"Even a buildup of dirt on the sensor itself is not a problem for signal transmission," states Wolfgang Fischer of Pepperl+Fuchs. He supports HNC with any questions relating to ultrasound. "The membrane that generates the sound vibrates, preventing any significant buildup of dirt on the area that is essential for sending and receiving pulses. This means that the sensor requires neither maintenance nor cleaning."