Abstract: A target or rotor blade clearance measurement device is disclosed for indicating an interaction of a measurement probe with a target or rotor blade. In a preferred embodiment, the measurement device comprises a measurement probe containing a coil, a frequency source arranged to apply an input alternating signal to the measurement probe, and a frequency regulator arranged to regulate the input alternating signal at a frequency below the resonance frequency of the measurement probe. A detector is arranged to detect an output signal from the measurement probe at a frequency of the frequency source which varies in amplitude with an admittance and resonance frequency of the measurement probe. A circuit is arranged to scale the amplitude of the output signal detected by the detector according to the amplitude of the input signal provided by the frequency source.

Abstract: A fluid pressure operated chuck is provided with a stationary slip ring mounted on an axially rotatable chuck body, and a resilient sealing ring is located in substantially opposed grooves in the slip ring and mounted therein by temporary deformation of the resilient sealing ring during fitting, in the absence of fluid pressure. The sealing ring may be of a squat "T" section with the flanges at the head of the T providing marginal edge parts for location in the opposed grooves and the broad base face of the stem of the T forming a sealing contact face. Valve means are also provided in the chuck body to control the fluid pressure which latter acts on an axially displaceable piston to operate the jaws of the chuck.