Fluid measurement of dielectric property change in hydraulic fluid

Reference Number: N 01-03

Inventors: Morgan, Dennis E.; Hangartner, Eric J.; Collum, Jerry

Owner: NISTAC

USPTO Link: 5994906

Invention Summary

Variations in the dielectric properties of a hydraulic fluid are compensated by providing a combined oscillator and resonant cavity element wherein a resonance is produced in a sample of the hydraulic fluid, the variations in the frequency of which correlate with changes in the dielectric properties of the hydraulic fluid.

The principle of the invention involves a reference oscillator the frequency of which is correlated with the dielectric properties of the hydraulic fluid. A standing wave is generated in a resonant cavity having a fixed dimension, so that any changes in the resonant frequency from a calibration reference frequency can be assumed to result from changes in the dielectric properties of the fluid.

There is a central conductor in the resonant cavity with inductive coupling into the resonance at one point along the resonant cavity and at a separated point along the resonant cavity there is capacitive coupling into the resonance. The changes in output frequency of the oscillator produce a measurement indicative of dielectric changes in the hydraulic fluid. Where the apparatus is a piston position sensor the correction factor is applied to the piston position location determined by the sensor to increase accuracy of the location.