Combined fluid condition monitor and fluid level sensor

The present invention relates to transducers of the type employed for providing a continuous electrical indication in real time of the chemical/contaminate condition of a fluid such as hydraulic fluids and for additive depletion, acidity and other types of degradation of lubricants employed in internal combustion engines and power transmission devices. An example of such a device employing impedance spectroscopy techniques for fluid monitoring is that shown and described in co-pending application Ser. No. 220,556, filed Dec. 23, 1998 entitled "Fluid Condition Monitor", now U.S. Pat. No. 6,278,281, and assigned to the Assignee of the present application. The aforesaid device utilizes a probe having interdigitated elements immersed in the fluid and excited by an alternating current signal sequentially at a low frequency and at a higher frequency. The resulting voltage is measured during excitation at both frequencies and the impedance is computed and the difference in impedance between the high and low frequency utilized as an indication of the fluid condition which can be determined from a look-up table of differential impedance measurements taken of fluids having a known condition. The sensing device or transducer has heretofore employed a probe having a pair of electrodes disposed in closely spaced generally parallel arrangement and immersed in the fluid with electrical connections made thereto such that one electrode is excited by the alternating voltage sequentially at the selected frequencies; and, the sensed or output current from which the impedance determinations are made flows through and is detected in the remaining electrode. A combination fluid condition monitor and fluid level sensor having an excitation electrode divided into two segments disposed closely spaced and parallel to current sensing electrode. For the fluid condition monitoring mode function both segments of the excitation electrode are commonly excited sequentially at high and low frequencies and the currents sensed in the sensing electrode employed to compute the difference in impedance for determining the fluid condition. For the level sensing mode function a mode switching circuit grounds one of the excitation electrode segments and excites the other then grounds the other segment and excites the one segment and the resultant currents ratioed to determine the amount of electrode immersed in fluid and hence the fluid level.