Frank Dennis Poag
Engineers at Russeff Fld Ln, Richmond, TX

4720997, Jan 26, 1988

Dec 1, 1986

6/936701

Roni K. Doak - Houston TX
Frank Poag - Rosenberg TX

G01F 2322

23295

The electronic monitor includes a level-sensing circuit, a reference circuit, a comparator circuit, and a logic circuit. The level sensing-circuit includes at least one level sensor positioned within the reservoir adjacent to and below a predetermined level. The reference circuit includes a reference sensor positioned in the air adjacent to the maximum allowed level for the material. A current source applies current to all the sensors. The comparator circuit compares the voltage across the reference sensor and the voltage across the level sensor and provides a difference voltage to a logic circuit that activates selective signaling devices depended upon the level of the monitored material. The sensors are preferably negative-coefficient thermistors.