The round sheets are taken off from the sheet stack with the blue coloured vacuum suckers/ cups and pressed against the sensors. As magnetic steel sheets and also non magnetic (stainles-) steel sheets are destacked , 2 singlesided sensors are fixed closed together: One for the magnetic steel sheets and the other for the non-magnetic sheets. Each sensor is connected to its own amplifier. The both output contact of these amplifiers are connected together and stop the sheet destacke when double sheets are detected.