Abstract: A hydraulic positioning drive with a physically separated work cylinder which is connected via pressure oil lines, comprises a follow-up cylinder mounted at the positioning drive or in the immediate vicinity thereof, of the same type and the same volume as the work cylinder, which is hydraulically connected in series with the latter, so that its piston moves synchronously with that of the work cylinder. The piston position of the follow-up cylinder is sensed electrically and used as the positioner position. For synchronizing, both cylinders are connected in parallel from time to time and their pistons are run into the end positions.

Abstract: In a filling level measuring installation with a radioactive radiator, which can be rotated within a lead shield from a peripheral operating position opposite the measuring receiver into a central safety position, a second radiation detector is arranged on a rearward extension of the measuring path in such a manner that in the safety position, its distance from the radiator is smaller than in its operating position, so that the output signal of the second detector can serve for monitoring the radiator position.