Abstract: A piston position sensing system in which tabulated resonance width related information is stored in a form correlated with piston travel so that measured resonance width information can be compared with the stored information in determining piston position and compensation for the velocity of the piston is provided by correction for a time difference in serial sensing between the initial and the following extremes of a resonance signal as the piston moves. the compensation is developed from velocity information identified through previous and current processing cycles which assures reliability in detection of the subsequently sensed portion of the resonance signal envelope and enhanced sensitivity and accuracy through automatic application incrementally in a dynamic gain adjustment of the sensing system.

Abstract: Improvement of the ability to detect selected resonant frequencies associated with the position of the piston in a piston position sensing system using electromagnetic waves in the fluid in a hydraulic cylinder is achieved by positioning the electric signal input and output probes with 90 degree separation around the circumferential periphery of the cylinder to suppress coupling into unwanted modes that diminish detectability of particular resonant frequency signals, In a coaxial sensing system "dummy" probes at 90 degree separation to each other and 90 degree separation to the input and output probes operate to improve symmetry and resonance shape and to suppress unwanted modes.

Abstract: Dynamic gain adjustment in hydraulic piston position sensing that continuously accommodates for changes in signal level is provided by attenuating the gain of the sensing system through a comparison of a measured value with a stored value at each piston position.

Abstract: A contacting and sealing structure, for electrical continuity, noise reduction and leakage reduction between parts that move in relation to each other at the ends of the cavity within a hydraulic cylinder employing electromagnetic wave position sensing, is provided by employing two springs having garter and canted coil spring functions that are retained in side by side grooves in one of the parts so that the spring coils extend directly across the intersection of the parts.