Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1986-06-02
1987-09-08
Crosland, Donnie L.
Communications: electrical
Condition responsive indicating system
Specific condition
340587, 340589, 340501, 340506, 340511, 340514, 340628, 340630, 34087017, 250574, G08B 1700, G08B 2300
Patent
active
046927506
ABSTRACT:
An improved fire alarm system utilizes receiver and fire detecting terminals connected thereto through a signal transmission line comprising two wires. The fire detecting terminal operates on two mode, one being a contact-closure mode of transmitting to the receiver a level signal whether or not a significantly higher fire-indicative quantity is detected, and the other being intelligent mode of transmitting a digital signal indicative of the sensed quantity in the form of a superimposed signal upon the level signal in answer to the instruction from the receiver for precise and convenient analysis thereof in determining fire presence on the side of the receiver. The fire detecting terminal includes a comparator having its own threshold with which the value of the sensed analog quantity is compared for providing the level-shifted signal when the sensed analog quantity has a level higher than the threshold, notifying fire presence independently of the intelligent mode. The threshold level can be selected independently of a criterion utilized in determining first presence based upon the digital signal on the receiver, so that the above two modes can have the same sensitivity against possible fires. Accordingly, the contact-closure mode can well stand for a back-up fire detection without reduction in sensitivity.
REFERENCES:
patent: 4489312 (1984-12-01), Yoshizaki
patent: 4518952 (1985-05-01), Tanaka et al.
patent: 4556873 (1985-12-01), Yamada et al.
Murakami Kazumasa
Terada Motoharu
Crosland Donnie L.
Matsushita Electric & Works Ltd.
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