Multiplexed radio frequency linear position sensor system

Reference Number: N 01-03

Inventors: Bitar, Ali A.

Owner: NISTAC

USPTO Link: 5150060

Invention Summary

In one aspect of the present invention an apparatus for detecting the linear extensions of a plurality of hydraulic cylinders is provided. Each hydraulic cylinder includes a piston, a piston rod, and a housing. The piston, piston rod, and housing form a variable length coaxial resonant cavity. The linear extension of each cylinder is defined by the position of each piston and piston rod relative to the corresponding housing. The apparatus includes a transmitting section for generating an RF signal having a predetermined frequency varying between preselected minimum and maximum values. A multiplexer selectively delivers the RF signal into the coaxial resonant cavity of one of the hydraulic cylinders and receives a first electromagnetic wave signal from within the coaxial resonant cavity. A receiving section compares the magnitude of the first electromagnetic wave signal to a first predetermined threshold value and responsively produces a first resonant signal. A controller determines the linear extension of the hydraulic cylinder as a function of the resonant signal and the frequency of the transmitted RF signal.

In a second aspect of the present invention a method for detecting the linear extensions of a plurality of hydraulic cylinders is provided. Each hydraulic cylinder includes a piston, a piston rod, and a housing. The piston, piston rod, and housing form a variable length coaxial resonant cavity. The linear extension of each cylinder is defined by the position of each piston and piston rod relative to the corresponding housing. The method includes the steps of producing a cylinder signal indicative of a desired cylinder position and generating an RF signal having a predetermined frequency varying between preselected minimum and maximum values. The generated RF signal is delivered into the coaxial cavity of one of the hydraulic cylinders. Electromagnetic wave signals are received from within the coaxial cavity and the linear position of the hydraulic cylinder is determined as a function of the electromagnetic wave signals.