The device is an ultrasonic detector for detecting duplicate cardboard sheets. The sensor produces a signal at the output (NO connection variant) when there is one sheet in the sensor area on which it is set. If there is no object (sheet) or if there are two objects (leaves), the signal is dropped. The electrical connection allows selection of the type (PNP or NPN) and selection of the function of the NO / NC output. The active state of the output is indicated by the ‘O’ LED and eventual overloading by the ‘S’ LED. The presence of bargraph for the signal level and the function keys facilitate setup. When switched on, the sensor takes up to 90 seconds of diagnosis, which is indicated by blinking of the yellow LED ‘T’.