Dual operating control circuits for intrusion detection systems

• US 4,074,248 A
• Filed: 11/22/1976
• Issued: 02/14/1978
• Est. Priority Date: 11/22/1976
• Status: Expired due to Term

• Current Assignee: Napco Security Systems Incorporated
• Original Assignee: Napco Security Systems Incorporated
• Inventors: Stockdale, Roy
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US05/743,539
• Time in Patent Office: 449 Days
• Field of Search: 340/256, 340/276, 340/274 R, 340/421
• US Class Current: 340/528
• CPC Class Codes: G08B 13/22 Electrical actuation
• CPC Class Codes: G08B 17/00 Fire alarms; Alarms responsive to explosion

Abstract

A series loop is in series with a control relay coil which has a first and a second contact. The first contact is coupled to an alarm and the second contact is coupled to one end of the loop. A control arm of the relay is operated by the coil to coact with said first contact when the coil is not energized and to coact with the second contact when the coil is energized to cause said second contact to latch said relay when the series loop is closed. Power is selectively applied to the control arm of the relay and a unidirectional current conducting circuit is coupled between the control arm of the relay and the second contact. The circuit supplies energizing current to the coil in the loop for the application of power to the control arm. This causes the relay to operate and therefore to latch if the loop is closed upon application of power to the control arm. The system user also is afforded a predetermined time to break the loop for purposes of leaving the premises and due to the nature of the unidirectional circuit, is assured that the intrusion system will be placed in a secured mode after the loop is broken.

Claims

1. An intrusion detection system comprising:

(a) a series loop including a plurality of intrusion sensing devices operative in a first closed position to indicate a secured condition and a second opened position to indicate an intrusion,

(b) control means adapted when energized to operate in a first position and in a second position when deenergized, said control means including a current activated actuator to operate said control means to said first position when a current flows through said actuator and means for coupling said actuator in series with said loop,

(c) an alarm coupled to said control means and responsive to said control means operative in said second position to indicate an alarm condition,

(d) means for providing a biasing current of a predetermined duration to said loop and hence, said actuator, in a first mode, to cause said actuator to operate said control means to said first position and

(e) means responsive to said control means operative in said first position for providing a second current to said loop, wherein if said loop is opened and closed during said predetermined duration, said means for providing a biasing current will again operate said actuator, and thereafter said actuator is biased by said means responsive to said control means.

2. The intrusion detection system according to claim 1 wherein said control means includes a relay having a current actuated coil, a first and second contact for access by a control arm which coacts with said first contact when current flows in said coil and said second contact when deenergized, said coil coupled in series with said loop with said first contact coupled to said loop.

3. The intrusion detection system according to claim 2 wherein said means for providing a biasing current to said loop comprises a capacitor in series with a unidirectional current device and coupled between said control arm of said relay and said first contact to supply for said predetermined duration said biasing current to said coil when said second contact is accessed.

4. The intrusion detection system according to claim 3 further comprising a resistor having one terminal coupled to the juncture between said capacitor and said current device and the other terminal coupled to a point of reference potential.

5. In an intrusion system of the type employing a series loop of normally closed sensing devices for indicating a secured situation, in series with a control relay coil having a first and a second contact, with said first contact coupled to an alarm means and said second contact coupled to one end of said loop, a control arm operative by said coil to a first position to access said first contact for energizing said alarm and to a second position for accessing said second contact to energize said loop and hence, said relay, to latch said relay in said second position when said loop is secured, a key switch coupled to said control arm and operative in a first position to apply operating potential to said control arm and in a second position to remove potential from said control arm, whereby when said key switch is in said first position and said series loop is secured, said relay coil is energized via said second contact and when said loop is open during said first position of said key switch, said coil is deenergized to cause said first contact to energize said alarm through said control arm, the improvement therein of apparatus for automatically activating said relay upon operation of said key switch in said first position, comprising:

unidirectional current conducting means coupled between said control arm and said series loop and operative to supply a predetermined current for a given duration to said loop when said key switch is operated to said first position, said predetermined duration selected according to a desired exit delay time.

6. The intrusion system according to claim 5 wherein said unidirectional current conducting means includes a capacitor having a first terminal coupled to said control arm and a second terminal, a unidirectional current conducting device having a first terminal coupled to said second contact of said relay and a second terminal coupled to said second terminal of said capacitor, a resistor coupled between said second terminal of said capacitor and a point of reference potential and selected in magnitude with respect to said capacitor to provide said given duration.

7. An intrusion detection system, comprising in combination:

(a) a series loop positioned about an area to be monitored and providing a low impedance series path when said area is secured and a high impedance path when said area is intruded upon,

(b) switching means having a current controllable actuator and a first and second contact, a control arm adapted to coact with said first contact when a current flows through said actuator and to coact with said second contact during the absence of a current through said actuator;

said controllable actuator coupled in series with said loop, with said first contact coupled to one end of said loop,

(c) a unidirectional current conducting means coupled between said first contact and said control arm,

(d) alarm means coupled to said second contact,

(e) means for selectively applying a bias potential to said control arm to cause said unidirectional means to conduct to thereby cause a current to flow through said first contact and said loop and therefore through said actuator, to cause said control arm to coact with said first contact thus directing said bias pontential to said loop when said area is secured and for directing said bias potential to said alarm means when said loop is opened due to said control arm accessing said second contact.

8. The intrusion system according to claim 7 wherein said switching means is a relay having a current controllable coil in series with said loop and a control arm adapted to coact with said first contact when said coil is energized and said second contact when said coil is deenergized.

9. The intrusion system according to claim 7 wherein said unidirectional current conducting means includes a time delay circuit operative to cause said unidirectional circuit to conduct for only a predetermined duration indicative of an exit delay to supply operating current to said actuator to allow opening and closing of said loop during said duration.

10. The system according to claim 9 wherein said time delay circuit is adjustable to provide a range of predetermined delays.