The invention relates to a protective cover (4) for protecting a sensor (2) for determining the thickness of a plastic film (3). The protective cover (4) (81 82 8,) for receiving and positioning the sensor (2) with a contact surface (41) comprises a sensor section of the protective cover (4) and the contact surface (41) is such to the protective cover (4) provided that in the operational state by means of the sensor (2) the thickness of the plastic film (3) through at least a part of the contact surface (41) therethrough can be determined. According to the invention comprises the contact surface (41) of an electrically insulating the measuring surface (411) and an electrically conductive deflection surface (412), wherein the measurement surface (411) covers at least a portion of the sensor section (8, 81, 82). Furthermore, the invention comprises a measuring device 1, a protective cover 4 and a sensor. 2