Digital fluid analyzer using capacitive sensing

Claim 1

Apparatus for determining the amount of contamination in a fluid, comprising: a test cell sensor for receiving fluid samples, said test cell sensor including a capacitive element between whose plates a fluid sample is located when one of said samples is in said test cell; a voltage controlled RC oscillator circuit, said capacitive element in said sensor forming the capacitive portion of said RC oscillator circuit; a phase lock loop circuit producing an output signal which is a measure of the dielectric constant of the fluid sample in said test cell; and comparing means connected to said phase lock loop circuit for comparing said phase lock loop output signals to provide a measure of the difference in dielectric constants of the tested fluids, said difference being an indication of the degree of contamination of one of said fluids; said comparing means including sample and hold circuitry for storing a signal representing a measure of the dielectric constant of the first tested fluid.