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: 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.