A sensor device for measuring a magnetic field in the region of a primary part of a permanently excited electrical machine or a corresponding primary part having teeth includes a sensor metal plate for conducting a magnetic field, a spacer, and a sensor for measuring a magnetic field. A distance between the sensor metal plate and a flank of a tooth of the primary part can be created by the spacer. The sensor may be a Hall sensor and is arranged in a region of the sensor metal plate between the sensor metal plate and the primary part.