Communications: electrical – Condition responsive indicating system – With particular system function
Patent
1987-11-23
1989-02-14
Crosland, Donnie L.
Communications: electrical
Condition responsive indicating system
With particular system function
340506, 340507, 340508, 340511, G08B 2900
Patent
active
048049425
ABSTRACT:
An intrusion detection loop employing an end-of-line resistor that operates with a voltage window. As the voltage window is increased, the sensitivity of the system decreases. As the window is decreased, the sensitivity of the system increases. By utilizing two comparators each having one input coupled to the loop, one can specify one voltage window when the system is disarmed and hence place the system at maximum sensitivity thereby detecting any borderline problem. In any event, the same two comparators operate to provide a different voltage window when the system is armed and hence desensitizing the loop and therefore reducing alarm probability. In this manner one can determine during the disarmed condition that the loop is operating with a borderline resistance and still employ the system in the armed condition to assure that there will be a reduced alarm probability in view of an undesirable change of the loop resistance.
REFERENCES:
patent: 4523183 (1985-06-01), Frick
patent: 4651138 (1987-03-01), Morrison
patent: 4751498 (1988-06-01), Shalvi et al.
Crosland Donnie L.
Napco Security Systems, Inc.
Plevy Arthur L.
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