Abstract: The identification of and compensation for changes in the dielectric properties of a hydraulic fluid in hydraulic apparatus is achieved by continuously sampling a hydraulic fluid in a resonant chamber with a central conductor that is both inductively and capacitively coupled to an oscillator. The output frequency changes of the oscillator is an indicator of changes of the dielectric properties of the hydraulic fluid and their magnitude. The invention is of particular value in hydraulic cylinder piston position determining systems.

Abstract: A piston position sensing system with improved accuracy and reliability is achieved by electromagnetic wave coupling using the combination of: a mechanical structure that in addition to supporting the rod, provides an extension of the resonance cavity, supports the electromagnetic wave couplers and a hydraulic fluid input-output port into the extended cavity and a piston travel stop; an electronic circuitry shielded package having a high frequency section with coaxial shielded input and output conductors on opposing package sides and a lower frequency counting section having a piston position output shielded conductor and a fluid dielectric property change monitor input conductor separated from the high frequency section conductors; and, the positioning of the electronic package on the mechanical structure with the coaxial shielded input and output conductors respectively adjacent to the input and output couplers and with the hydraulic fluid input-output port positioned elsewhere around the periphery of the c

Abstract: The ability to be able to identify, distinguish and verify a lock onto harmonic frequency signals in the oil of a hydraulic cylinder using a ratio between consecutively detected harmonics. The identification is useful in providing early and reliable harmonic resonance "lock on" and the ability to "lock on" to a particular order harmonic resonance.