Abstract: The invention refers to a centrifugal separator comprising a stationary casing defining an inner space, a spindle and a rotating member, which is attached to the spindle and arranged to rotate around an axis of rotation with a rotary speed. The rotating member comprises a number of separating discs which are provided in the inner space. A drive member drives the spindle and the rotating member with said rotary speed. A sensor device senses the rotation of the rotating member in relation to the casing. The sensor device comprises at least one transmitter element which is provided in the inner space on the rotating member and a receiver element which is provided at the casing and arranged to sense the transmitter element. The receiver element is provided on the casing outside the inner space.