Sensor device

The device has a flat camera (3) e.g. red, green, blue flat camera, with a matrix sensor (4) attached to a print substrate web. Sections (6.1-6.5) of pressure control strips are projected onto a print substrate (2) through an optical unit, and are successive in a direction of main expansion of the strips, where the optical unit is pre-arranged to the flat camera and has mirrors (5.S) or prisms. The unit is shared across the print substrate width along an optical axis (8) of the camera at regular intervals. The device is activated during shrinking of the strips in a lamellar detection area.