The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 01, 1995
Filed:
Jun. 14, 1993
Arthur W Shea, W. Somerville, MA (US);
Scully Signal Company, Wilmington, MA (US);
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.