Fail safe fluid level detection circuit

Details Fail safe fluid level detection circuit Fail safe fluid level detection circuit

1993-06-14

1995-08-01

Peng, John K.

Communications: electrical

Condition responsive indicating system

Specific condition

340603, 340612, 340618, 73290R, 73304R, 200190, G08B 2100

Patent

active

054383234

ABSTRACT:
A fail safe output stage for a tank fluid level detection circuit having power supply/output leads periodically places a shunt across the leads to periodically generate a LOW signal which alternates with a HIGH signal to indicate an underfilled condition. In a filled condition, a steady signal appears across the leads. The output stage of the detection circuit consists of a parallel connection of switching devices where the "on" impedance of any single switching device is insufficient to place the detection circuit output lead in a LOW logic state. Therefore, in a condition where one of the switching devices fails, the detection circuit output may continue to alternate, but the alternating output is not recognized as such by a disable circuit which does not detect a LOW logic condition on the output lead. Accordingly, the failed output is interpreted as an filled condition, resulting in a shutdown of the system.

REFERENCES:
patent: 4165509 (1979-08-01), Betts et al.
patent: 4224606 (1980-09-01), Bartles
patent: 4244385 (1981-01-01), Hotine
patent: 4280164 (1981-07-01), Kozek
patent: 4367462 (1983-01-01), Dressler
patent: 5287086 (1994-02-01), Gibb

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