The aim of the invention is to create an inexpensive sensor system for a movable electric machine in order to determine positions, the sensor signal featuring zero crossings. Said aim is achieved by a sensor device (1) comprising a U-shaped yoke (3) and a sensor (10) which is disposed in/on the yoke (3) to detect a magnetic variable, for example. Magnets (6 to 9) that are or can be inversely magnetized are arranged at a free end of the yoke (3). Opposite magnetic fluxes that can be detected by the sensor (10) can be generated in the yoke (3) in accordance with the position of the magnets (6 to 9) relative to one of the pole teeth (11, 12, 13) of a machine component. Approximately sinusoidal sensor signals can be generated therefrom without having to use several measuring sensors, e.g. in order to regulate a linear motor.