Claims
- 1. Apparatus for use in a multi-zone alarm system having a two-wire alarm loop, a plurality of alarm sensors in series with the loop, and a processor at a central location coupled to the loop and operative to indicate an alarm condition in response to alarm signals from any of said sensors, comprising:
- a current source serially connected to the alarm loop and operative to provide a predetermined current signal in the loop;
- a plurality of networks, each connected across a respective alarm sensor and operative in response to its sensor actuation and to a positive magnitude of said loop signal current to provide a signal pulse for transmission in the loop to the central location processor, the signal pulse having a detectable characteristic to denote the identity of the actuated sensor;
- circuit means at the central location processor operative in response to signal pulses from any one or more of the networks to provide a signal indication of the zone in which alarm actuation has occurred; and
- each of said networks includes an electronic switch in parallel with the associated alarm sensor; a resistor in shunt with the electronic switch and of a value representing the identity of an associated zone; a capacitor in shunt with said resistor and said electronic switch; the capacitor being operative to minimize radio frequency interference and switching transients from triggering the electronic switch.
- 2. The system of claim 1 further including a resistor in series with said electronic switch and said alarm sensor to limit the capacitor discharge current.
- 3. The system of claim 1, wherein said alarm sensors each include a pair of alarm switch contacts;
- and wherein said circuit means includes:
- means for providing timing signals to said current source to provide a repetitive staircase current signal to the alarm loop;
- demultiplexer means receiving timing signals from said timing means;
- means for coupling pulses received from any one or more of the networks to the demultiplexer means;
- a plurality of integrators each receiving a respective output from the demultiplexer means;
- gating means operative in response to any output signal from said integrators to provide a signal indication of an alarm condition; and
- annunciator means operative in response to the output signals from said integrators to provide respective signal indications of the zone in which alarm actuation has occurred.
Parent Case Info
This is a division of application Ser. No. 951,765, filed Oct. 16, 1978, now U.S. Pat. No. 4,359,721.
US Referenced Citations (5)
Foreign Referenced Citations (9)
Number |
Date |
Country |
989016 |
Apr 1965 |
GBX |
1096808 |
Dec 1967 |
GBX |
1266424 |
Mar 1972 |
GBX |
1429781 |
Mar 1973 |
GBX |
1347187 |
Feb 1974 |
GBX |
1424751 |
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1548526 |
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GBX |
Divisions (1)
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Number |
Date |
Country |
Parent |
951765 |
Oct 1978 |
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