Communications: electrical – Condition responsive indicating system – With particular system function
Patent
1993-03-31
1995-08-29
Crosland, Donnie L.
Communications: electrical
Condition responsive indicating system
With particular system function
34082506, 34082507, 34031001, 340588, G08B 2600
Patent
active
054464439
ABSTRACT:
In a fire-alarm system in which a plurality of terminal units are connected to a fire receiver via a main signal line, the fire receiver polls each terminal unit, and the terminal unit called by the polling sends a current signal back to the fire receiver. A voltage signal receiving circuit having a DC signal component blocker is provided in each terminal unit for removing a DC signal component of a polling signal so as to detect only an AC signal component of the polling signal, and a current signal transmitting circuit having a constant-current circuit is provided so that the constant-current circuit is turned on/off to deliver the return signal. Therefore, a threshold used for signal discrimination in the voltage signal receiving circuit can be easily set. The current consumed by the terminal unit becomes constant regardless of the number of the terminal units connected when it is outputting the current signal, resulting in the terminal unit not wastefully consuming an extra current.
REFERENCES:
patent: 4825196 (1989-04-01), Morita
patent: 4899131 (1990-02-01), Wilk et al.
Crosland Donnie L.
Nohmi Bosai Ltd.
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