Apparatus and method for the measurement of electrical conductivity and dielectric constant of high impedance fluids

Abstract

A sensor, a system of direct measurement using that sensor, and a method of direct and simultaneous measurement of conductivity and dielectric constant of a fluid, particularly high impedance, hydrocarbon-based fluids. The sensor has a cell that holds the fluids to be measured between a single pair of coaxial, bare metal electrodes connected through interface circuitry to measurement circuitry preferably implemented in one or several IC's. The sensor has a mutually compatible electrode geometry that provides both the correct cell constant for measurement of conductivity of hydrocarbons fluids (typical range 0-100,000 pS/cm), and a bulk capacitance (for use in dielectric constant measurement) in the range of measure of readily available low cost commercial IC's (having a typical capacitance measurement span of <10 pF, with a total bulk capacitance at the chip of <20 pF). The cell conductivity constant for use with hydrocarbon-based oils having a conductivity in the range of 1 to 500,000 pS/M is preferably less than or equal to about 0.1. The cell bulk capacitance with hydrocarbon fluids inside the sensor results in a bulk capacitance of at least about 4 pF. In one embodiment, the electronic circuitry is a Microcontroller/DSP that both generates synchronous drive signals at various frequencies, for both conductivity and dielectric constant measurements while directly digitizing and numerically processing the sensor output.