Two-wire multi-zone alarm system
AssigneeAmerican District Telegraph Company
InventorsAaron A. Galvin, Roy L. Harvey
Life of this patent
Estimating the term…
Abstract
A multi-zone alarm system operative with a two-wire alarm loop and having a simple network at each alarm sensor for providing a coded signal indicative of sensor identity and relatively simple circuitry at a central location for interrogation of the remote sensors and determination of those sensors providing an alarm signal.
Claims3
For use in a multi-zone alarm system having a two-wire alarm loop, a plurality of alarm sensors each including a pair of alarm switch contacts in series with the loop and the selective opening or closing of which is in response to and signifies an alarm condition, 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 switch contacts, the improvement comprising:
- a current source coupled to the two-wire alarm loop and operative to provide a predetermined current signal in the loop;
- a plurality of networks, each connected across a respective pair of alarm switch contacts and operative in response to its switch contact actuation to provide a signal for transmission in the loop to the central location, the signal having a detectable characteristic to denote the identity of the actuated sensor;
- circuit means at the central location operative in response to signals from any one or more of the networks to provide a signal indication of the zone in which alarm actuation has occurred;
- and wherein said networks each includes an electronic switch in parallel with the associated alarm switch contacts;
- and
- a serially connected resistor and capacitor in shunt with the electronic switch.
For use in a multi-zone alarm system having a two-wire alarm loop, a plurality of alarm sensors each including a pair of alarm switch contacts in series with the loop and the selective opening or closing of which is in response to and signifies an alarm condition, 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 switch contacts, the improvement comprising:
- a current source coupled to the two-wire alarm loop and operative to provide a predetermined current signal in the loop;
- a plurality of networks, each connected across a respective pair of alarm switch contacts and operative in response to its switch contact actuation to provide a signal for transmission in the loop to the central location, the signal having a detectable characteristic to denote the identity of the actuated sensor;
- circuit means at the central location operative in response to signals from any one or more of the networks to provide a signal indication of the zone in which alarm actuation has occurred;
- and wherein each of said networks includes an electronic switch in parallel with the associated alarm switch contacts, and a capacitor in shunt with the electronic switch and of a value representing the identity of a switch zone;
- and wherein said circuit means includes:
- counter means having a plurality of outputs;
- a function generator operative in response to the outputs from said counter means to drive said current source for providing a repetitive exponential current signal to the alarm loop;
- a plurality of sample and hold circuits each enabled by a respective output from said counter means and each operative to receive signals from any one or more of said networks;
- a plurality of integrators each receiving an output from respective ones of said sample and hold circuits;
- and
- a plurality of threshold circuits each receiving an output from respective ones of said integrator circuits and each operative to drive an associated indicator for a respective zone.
Dependencies are inferred from the claim text.