Solid-State Automotive liquid level Sensing System

Accurate remote sensing or control of liquid levels is of interest in a variety of applications. A method capable of distinguishing between the presence and absence of liquid at a discrete level by monitoring the rate of heat transfer from a solid-state sensing element is discussed; a detailed description is given of the silicon sensor and the associated electronic circuitry. Small size (0.50 × 0.50 × 0.15mm³) and low thermal conductance mounting of the active element assure precise level determination and rapid response, while an auto-referencing scheme used in the circuit permits reliable operation over a wide temperature range. Three versions of the system are described, each suited for different types of level sensing applications. Suggested among the possible uses are a number of automotive applications such as crankcase, transmission, and brake fluid measurements.