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:
May. 18, 1993
Filed:
Aug. 26, 1991
Marc Thuillard, Mannedorf, CH;
Cerberus Ltd., Mannedorf, CH;
Abstract
A fire alarm system having increased immunity to false alarms comprises control and indicating means (6) and a plurality of ionization smoke detectors (7) connected through signal lines (8, 9, 14) with the control and indicating means (6), each ionization smoke detector (7) comprising an ionization measurement chamber (1) for producing an electrical signal having a characteristic indicative of a monitored condition, a radioactive source (10) to ionize the air in the ionization measurement chamber (1), and an evaluation circuit comprising an amplifier element (3) to amplify the electrical signal from the ionization measurement chamber (1), threshold detection means (15, 16) for comparing the electrical signal characteristic to minimum and maximum limits and for producing an alarm or trouble signal, and electronic means (5, 11) by which the chamber voltage (UK) of the ionization measurement chamber (1) is increased as far as possible to the saturation range of the ionization chamber (1) if the ionization current in the ionization chamber (1) is reduced. From the current which flows at increased chamber voltage (UK2) it can be determined whether the saturation current (Is) of the ionization chamber (1) has fallen compared with given predetermined values. If the saturation current (Is) of the ionization chamber (1) has fallen compared with given predetermined values, a malfunction has occurred, for example, due to the covering of the radioactive source (10); if not, then an alarm signal is transmitted.