Abstract: A hydraulic cylinder (1) with a piston (5) made completely or partially of electrically conductive material comprises at least one opening (19, 20) for the mounting of an electric position indicator (21, 22). The openings (19, 20) are closed in a liquid and pressure-proof manner towards the interior of the cylinder (1) by means of circular plate-shaped bodies (17, 18) glued to the inner surface of the cylinder (1). As the plate-shaped bodies (17, 18) are made of a ceramic material, preferably steatite, they may allow passage of the magnetic field transmitted from the electric position indicators (21, 22). The openings (19, 20) are adapted in the end covers (2, 3) of the cylinder (1) for the determination of the end positions of the piston (5). Furthermore the cylinder may be provided with piston-braking means in the form of seal rings (12, 13).

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.