System monitor with innate line security ability

• US 4,044,351 A
• Filed: 05/03/1976
• Issued: 08/23/1977
• Est. Priority Date: 06/24/1974
• Status: Expired due to Term

• Current Assignee: Lefrebure Corporation Cedar Rapids Iowa
• Original Assignee: Walter Kidde & Company Incorporated
• Inventors: Everson, Evan Philip
• Primary Examiner(s): Caldwell, John W.
• Assistant Examiner(s): Groody, James J.
• Application Number:
  US05/682,382
• Time in Patent Office: 477 Days
• Field of Search: 340/408, 340/409, 340/214, 340/213.2, 340/226, 340/213.1, 340/152 T, 340/151, 340/152 R, 343/6.5 R, 343/6.5 SS, 179/5 R, 179/2 A, 179/2 E, 179/2 TC, 325/64
• US Class Current: 340/505
• CPC Class Codes: G08B 26/002 only replying the state of the sensor
• CPC Class Codes: G08B 29/06 Monitoring of the line circuits, e.g. signalling of line faults
• CPC Class Codes: G08B 29/123 of line circuits
• CPC Class Codes: H04M 11/04 with alarm systems, e.g. fire, police or burglar alarm systems

Abstract

A system for monitoring a protected premises from a central station over telephone lines employs different audio tones sent back and forth over the lines. A random succession of audio tones from the central station interrogates the protected premises and is returned as a like succession of different tones to the central station where the latter tones are compared with the first to indicate a normal or a trouble condition at the protected premises or on the lines. When an alarm condition exists at the protected premises, still different tones are sent over the lines to cause an alarm alert at the central station. The entire system can be tested from the protected premises, including operation of the trouble and alarm circuits, without producing a trouble or an alarm alert at the central station.

Claims

1. A system for monitoring a protected premises from a central station including apparatus for location at the protected premises and apparatus for location at the central station and for interconnection by electrical lines, the central apparatus comprising generating means for generating first pulses at random time intervals, first transmitter means responsive to said first pulses for generating first tones having a first frequency at sequential intervals substantially contemporaneous with those of said first pulses and of substantially like durations and for transmitting said first tones over the lines to the premises apparatus;

the premises apparatus comprising premises logic means, first receiver means for receiving said first tones and providing second pulses to said premises logic means at sequential intervals substantially contemporaneous with those of said first pulses and of substantially like durations, second transmitter means operatively connected to said first receiver means through said premises logic means and responsive to said second pulses for generating second tones having a second frequency different from that of said first tones but at sequential intervals substantially contemporaneous with those of said first pulses and of like durations and for transmitting said second tones over the lines to the central apparatus substantially simultaneously with the transmission thereover of said first tones;

the central apparatus further comprising second receiver means for receiving said second tones and providing third pulses at sequential intervals substantially contemporaenous with those of said first pulses and of substantially like durations, central logic means operatively connected to said generating means and said second receiver means for ascertaining the presence or not of both said first and said third pulses at the central apparatus at substantially contemporaneous times;

the premises apparatus still further comprising a first alarm circuit responsive to an alarm condition at the protected premises, the first alarm circuit including said premises logic means and third transmitter means for generating a third tone having a third frequency different from those of said first and second tones, said premises logic means operatively disconnecting said first receiving means from said second transmitting means and activating said third transmitter in the event of said condition, said third transmitter means transmitting said third tone over the lines to the central apparatus substantially simultaneously with the transmission thereover of said first tones to the premises apparatus;

the central apparatus still further comprising a second alarm circuit including third receiver means for receiving said third tone.

2. The system of claim 1 wherein said first, second and third transmitter means provide no signals on the lines except when activated as aforesaid.

3. The system of claim 2 wherein a trouble condition is defined by the presence at said central logic means of one of said first pulses but not contemporaneously one of said third pulses and causes a central logic means output change from normal to abnormal, and including a trouble circuit responsive to said change, said trouble circuit having a latch circuit operatively connected to said central logic means for maintaining said central logic means output change in the event of a trouble condition and an unlatch circuit operatively connected to said latch circuit and said generating means for returning said central logic means to normal upon disappearance of said trouble condition.

4. The system of claim 3 wherein said trouble circuit includes means responsive to said central logic means output change to provide indication thereof.

5. The system of claim 3 wherein said premises logic means includes first alarm switch means activated by an alarm condition at the protected premises, said first alarm switch means in one position providing said disconnection of said first receiver means from said second transmitter means and activation of said third transmitter means to provide said third tone, said third tone being a constant signal as long as said first alarm switch is in said position.

6. The system of claim 5 wherein said third receiver means in response to said third tone applies a constant signal to said central logic means and to said generating means to activate said first transmitter means and thereby also causes said central logic means output change from normal to abnormal, said second alarm circuit being responsive to said central logic means output change.

7. The system of claim 6 including an override circuit operatively connected with said third receiver means and said trouble circuit to override the aforesaid effect of said central logic means output change upon said trouble circuit in the event of an alarm condition.

8. The system of claim 7 wherein said second alarm circuit includes means responsive to said central logic means output change to provide indication thereof.

9. The system of claim 8 wherein the premises apparatus includes test switch means effective to activate said third transmitter means to provide said third tone without operatively disconnecting said first receiver means from said second transmitter means, said third receiver means applying said third tone to said central logic means and to said generating means to activate said first transmitter means and said first receiver means and thereby said second transmitter means and said second receiver means.

10. The system of claim 9 wherein the premises apparatus includes means to provide visual indication of said second pulses provided by said first receiver means.

11. The system of claim 3 wherein said generating means comprises random timer means providing pulses at random time intervals, and fixed timer means providing pulses at fixed time intervals, said random pulses and said fixed pulses being combined to provide uniform pulses of equal durations at random time intervals but at least at intervals equal to those of said fixed pulses, said uniform pulses constituting said first pulses.

12. The system of claim 11 where the central apparatus includes backup timer means effective to provide backup pulses at greater intervals than those of said first pulses, said backup timer means being operatively connected to said trouble circuit and to said second receiver means to receiver said third pulses from said second receiver means, said backup timer means providing said backup pulses to said trouble circuit in the event none of said third pulses are received by said backup timer means from said second receiver means.