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Abstract

A method and apparatus for automatically detecting a lubricant type and the relative quantity of water present in a test sample of lubricating oil includes the use of an open grid capacitive sensor element that incorporates the lubricating oil as a dielectric medium. The sensor element grid is energized by a frequency variable oscillator that automatically responds to changes in the oil dielectric constant with corresponding frequency changes. As a reference, a sample of new or uncontaminated test oil is confined in wet surface contact with the energized, open grid sensor element. Oscillator frequency changes are measured and recorded, either continuously or at frequent intervals, over a standardized elapsed time interval to generate a reference characterization of the frequency-time relationship distinctive of the particular oil. The same is repeated for a sample of contaminated oil and a corresponding frequency-time relationship generated. Water affinity rate correlations between frequency change and respective states of moisture content are determined and data base recorded. The affinity rate correlations are applied to the respective frequency differentials between the contaminated oil and uncontaminated oil at the end of the test period. Data bases are also recorded of correlations between natural frequency and sample temperature changes that distinguish lubricants by type, use classification or quantity of additive content.

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