Abstract: In order to obtain a reliable position determination in a hydraulic cylinder optionally exposed to hard frost, it is suggested to mount a magnetically sensitive component in the form of a Hall-effect transducer in a bore in the cylinder wall and placed between a permanent annular magnet (17) and a magnetically conducting sheet (14). In the middle of the bore a magnetically conducting post (16) is placed and towards the inner side of the cylinder the bore is sealed by a non-magnetic material (19) e.g. brass. The Hall-effect transducer (15) forms thus part of a closed magnetic circuit comprising the permanent magnet (17), the magnetically conducting post (16), the magnetically conducting disc (14) and the hydraulic cylinder wall surrounding the bore. When the piston in the hydraulic cylinder opposes the sensor, a second closed magnetically conducting circuit is formed comprising the permanent magnet, the magnetically conducting post, the piston, and the steel wall of the cylinder.