CODED TONE MULTIPLEXED ALARM TRANSMISSION SYSTEM

• US 3,792,470 A
• Filed: 07/17/1972
• Issued: 02/12/1974
• Est. Priority Date: 07/17/1972
• Status: Expired due to Term

• Current Assignee: Johnson Controls International BV (Johnson Controls International plc)
• Original Assignee: Carl F. Klein, John C. Donovan, Lawrence B. Korta, Ramesh Krishnaiyer
• Inventors: Donovan, John C., Klein, Carl F., Korta, Lawrence B., Krishnaiyer, Ramesh
• Primary Examiner(s): Habecker, Thomas B.
• Application Number:
  US05/272,542
• Time in Patent Office: 575 Days
• Field of Search: 340/409
• US Class Current: 340/509
• CPC Class Codes: G08B 25/00 Alarm systems in which the location of the alarm condition is signalled to a central station, e.g. fire or police telegraphic systems
• CPC Class Codes: G08B 26/00 Alarm systems in which substations are interrogated in succession by a central station

Abstract

A frequency multiplexed alarm transmission system for transmitting alarm information provided by a plurality of intrusion detectors to a central monitor includes a plurality of alarm detector circuits, each individually associated with one of the intrusion detectors and each selectively operable in an access or a secure mode to provide a line supervision code comprised of a selected sequence of tone signals of a first or a second pair of frequencies, respectively, and a control circuit controlled by the corresponding intrusion detector to modify the tone sequence being provided by the associated alarm detector to indicate an intrusion of a corresponding protected area, different alarm detector circuits providing tone sequences having signals of different frequencies to enable simultaneous transmission of the line supervision codes to the central monitor over a common transmission line, line monitoring circuits at the central monitor include an individual tone detector for each alarm detector circuit for receiving the line supervision code sequences provided by the associated alarm detector circuit, the tone detectors being responsive to a modified line supervision code of the first pair of frequencies to indicate the detection of an authorized intrusion of the corresponding protected area and responsive to a modified line supervision code of the second pair of frequencies to indicate the detection of an unauthorized intrusion of the corresponding protected area.

Claims

1. In an alarm transmission system including a transmission line for carrying alarm information from a plurality of protected areas to a central monitor that is remote from the protected areas, alarm detecting means for each of said protected areas, each of said alarm detecting means including output means for continuously generating a line supervisory code comprised of a selected sequence of tone signals of predetermined frequencies, different output means being operable to provide supervisory code sequences having signals of different frequencies to enable simultaneous transmission over said transmission line of the supervisory code tone sequences provided by all of the output means, and separate control means for each output means for controlling an associated output means to modify the supervisory code tone sequence to indicate an alarm for a corresponding protected area, and line monitoring means at said central monitor, including an individual tone detecting means for each of said alarm detecting means including receiver means for receiving the supervisory code tone sequences provided by an associated alarm detecting means and alarm output means responsive to a modified supervisory code tone sequence provided by the associated alarm detecting means to provide an alarm indication at said central monitor.

2. An alarm transmission system as set forth in claim 1 wherein each said output means includes signal generating means for generating tone signals of first and second frequencies in said selected sequence, said signal generating means being controlled by said control means to provide a continuous tone output of one of said frequencies to indicate an alarm.

3. An alarm transmission system as set forth in claim 1 wherein said output means includes code generating means for generating a supervisory code comprised of a selected sequence of coded logic level bits, and tone generating means responsive to the bits of the supervisory code sequence to normally provide tone signals of predetermined frequencies in a sequence coded to represent the bits of the monitor code, and wherein each of said receiver means at said central monitor includes tone converter means for converting the received tone sequence into a sequence of logic level bits, reference code generating means for generating a reference code comprised of a sequence of logic level bits in which each bit is normally identical with a corresponding bit of the supervisory code at any given time, and each of said alarm output means includes comparator means for comparing each bit of the supervisory code with the coresponding bit of the reference code and means for providing an indication whenever the corresponding bits are different.

4. An alarm transmission system as set forth in claim 3 wherein each of said control means includes gating means normally enabled to pass tHe bits of the supervisory code unaltered to the corresponding output means to effect the generation of the supervisory code tone sequence, said control means further including alarm sensor means operable to provide an alarm output signal indicating an alarm condition in the corresponding protected area, said gating means being responsive to an alarm output signal provided by an associated alarm sensor means to invert each bit of the supervisory code as the bits are passed to the tone generating means to thereby effect the generation of said modified supervisory code tone sequence.

5. In an alarm transmission system including a transmission line for carrying alarm information from a plurality of protected areas to a central monitor that is remote from the protected areas, alarm detecting means for each of said protected areas, each of said alarm detecting means including code generating means for continuously generating a line supervisory code comprised of a selected sequence of logic level coded bits, tone generating means responsive to the bits of the supervisory code sequence to normally provide tone signals of at least first and second frequencies in a sequence coded to represent the bits of the supervisory code, and separate control means for each alarm generating means for controlling an associated tone generating means to modify the tone sequence to indicate an alarm for the corresponding protected area, different tone generating means being operable to provide tone signals of different frequencies to enable simultaneous transmission over said transmission line of the tone sequences provided by all of the tone generating means, and line monitoring means at said central monitor, including an individual tone detecting means for each of said alarm detecting means for receiving the tone sequences provided by an associated tone generating means, each of said tone detecting means including tone converter means for converting the received tone sequence into a sequence of logic level bits, reference code generating means for generating a reference code comprised of a sequence of logic level bits in which each bit is normally identical with a corresponding bit of the supervisory code at any given time, and comparator means for comparing each bit of the supervisory code with the corresponding bit of the reference code and providing an indication whenever any of the corresponding bits of the two sequences are different.

6. An alarm transmission system as set forth in claim 5 wherein said line monitoring means further includes clock signal generating means for providing clock signals of a predetermined frequency for transmission over said transmission line to the code generating means of all of said alarm detecting means and to the reference code generating means of all of said tone detecting means to synchronize the operation of said code generating means with the operation of said reference code generating means.

7. An alarm transmission system as set forth in claim 5 wherein said line monitoring means includes separation filter means connected between said transmission line and said tone detecting means including means for passing the tone sequence provided by each tone generator means to an associated tone detecting means.

8. An alarm transmission system as set forth in claim 6 wherein said comparator means includes first and second bit storage means, said clock signals being extended to said first and second bit storage means to gate the bits of the received line supervisory code into said first bit storage means a bit at a time and to gate corresponding bits of the reference code into said second bit storage means a bit at a time, and gating means for comparing the bits stored in the first and second bit storage means and providing an output signal whenever the stored bits are different.

9. An alarm transmission system as set forth in claim 8 wherein said tone detecting means includes alarm output means enabled by each output signal provided by the gating means to pRovide an alarm indication at the central monitor.

10. An alarm transmission system as set forth in claim 5 wherein said control means includes intrusion detector means operable to provide an alarm output signal in response to an unauthorized entry of the corresponding protected area, and gating means normally enabled to pass the bits of the supervisory code to the tone generating means to effect the generation of the supervisory code tone sequence, said gating means being responsive to each alarm output signal to inhibit the passage of the bits of the supervisory code to the tone generating means whereby the tone generating means provides a continuous tone of one of the predetermined frequencies.

11. An alarm transmission system as set forth in claim 5 wherein said alarm detecting means includes status means for controlling said tone generating means to be operable in a first mode to generate a tone sequence having signals of a first pair of frequencies and to be operable in a second mode to generate a tone sequence having signals of a second pair of frequencies, each of said tone detecting means including status detecting means responsive to a sequence of signals of said first pair of frequencies to provide an indication that intrusions of the protected area are authorized and responsive to a sequence of signals of said second pair of frequencies to provide a further indication that intrusions of said protected area are unauthorized.

12. In an alarm transmission system including a transmission line for carrying alarm information from at least one protected area to a central monitor that is remote from the protected area, an intrusion detector at said protected area operable to provide an alarm output in response to an intrusion of the protected area, alarm detecting means including code continuously generating means for generating a line supervisory code comprised of a known sequence of coded bits, tone generating means normally controlled by the bits of said line supervisory code to generate tones of first and second frequencies in a sequence coded to represent the bits of said supervisory code for transmission over said transmission line to said central monitor, and means responsive to each alarm output for controlling said tone generating means to provide a continuous tone output of one of said frequencies, and line monitoring means at the central monitor including means for detecting the tone sequence provided by said alarm detecting means and means responsive to a continuous tone output provided in response to an intrusion of the protected area to provide an alarm indication at said central monitor.

13. In a security system including a transmission line for carrying alarm information from at least one protected area to a central monitor that is remote from the protected area, intrusion detector means at said protected area operable to provide an alarm output in response to an intrusion of said protected area, alarm detecting means including means for continuously generating a line supervisory code comprised of a known sequence of coded bits, tone generating means responsive to the bits of the supervisory code to provide tone signals of predetermined frequencies in a sequence coded to represent the bits of the supervisory code for transmission over said transmission line to said central monitor, status means for selectively controlling said tone generating means to generate a first tone sequence having signals of a first pair of frequencies to indicate that instrusions of the protected area are authorized and to generate a second tone sequence having signals of a second pair of frequencies to indicate that intrusions of the protected area are unauthorized, and control means responsive to each alarm output provided by said intrusion detector means for controlling said tone generating means to modify the tone sequence being provided by said tone generating means to indicate the detection of an intrusion of the protected area, and line monitoring means at said central monitor including tone detecting means for receiving the tone sequence provided by said alarm detecting means, first means enabled by said tone detecting means whenever a modified tone sequence is provided by said tone generating means to provide an output indicating an intrusion of the protected area and second means enabled by said tone detecting means for indicating whether the intrusion is authorized or unauthorized.

14. An alarm transmission system as set forth in claim 13 wherein said tone generating means includes trilevel oscillator means operable in a first mode to provide signals of first and second frequencies and operable in a second mode to provide signals of said second frequency and a third frequency.

15. An alarm transmission system as set forth in claim 14 wherein said tone generating means further includes bias supply means responsive to the bits of said supervisory code to provide control signals for said oscillator means, said status means including switch means for selectively controlling said bias supply means to provide control signals at first and second levels for said oscillator means to render said oscillator means operable in said first mode and control signals at third and fourth levels for said oscillator means to render said oscillator means operable in said second mode.

16. An alarm transmission system as set forth in claim 15 wherein said tone detecting means includes means responsive to the supervisory code sequence of said first and second frequencies to provide a first sequence of output signals having first and second voltage levels and responsive to the supervisory code sequence of said second and third frequencies to provide a second sequence of output signals having third and fourth voltage levels.

17. An alarm transmission system as set forth in claim 15 wherein said second means includes bistable switching means responsive to an output signal at said first voltage level to provide an output indicating that intrusions of the protected area are authorized and responsive to an output signal at said fourth voltage level to provide an output indicating that intrusions of the protected area are unauthorized.

18. An alarm transmission system as set forth in claim 14 wherein said status switch means further includes tamper switch means for normally connecting the output of said oscillator means to said transmission line and operable responsive to tampering with said status switch means to disconnect the output of said oscillator means from said transmission line thereby interrupting the transmission of said supervisory code tone sequence to said central monitor.

19. In an alarm transmission system including a transmission line for carrying alarm information from at least one protected area to a central monitor that is remote from the protected area, intrusion detector means at said protected area operable to provide an alarm output in response to an intrusion of said protected area, alarm detecting means associated with said intrusion detector means including output means operable in a first mode to continuously provide a supervisory code comprised of signals of a first pair of frequencies in a predetermined sequence for transmission over said transmission line to said central monitor and operable in a second mode to provide a supervisory code comprised of signals of a second pair of frequencies in a predetermined sequence for transmission over said transmission line to said central monitor, status means for selecting the mode of operation of said output means and means responsive to each alarm output provided by said intrusion detector means to modify the sequence of frequency signals being provided by said output means to indicate the detection of an intrusion of the protected area, and line monitoring means at said central monitor including signal detecting means for receiving the sequence of coded frequency signals provided by said output means, status detecting means controlled by said signal detecting means tO provide an indication that intrusions of the protected area are authorized whenever a sequence of signals of said first pair of frequencies is being received and to provide a further indication that intrusions of the protected area are unauthorized whenever a sequence of signals of said second pair of frequencies is being received, and alarm indicating means enabled whenever a modified sequence of frequency signals is received to provide an output indicating the detection of an intrusion of the protected area.

20. In an alarm transmission system including a transmission line for carrying alarm information from at least one protected area to a central monitor that is remote from the protected area, alarm source means including intrusion detector means at said protected area operable to provide an alarm output in response to the detection of movement of an intruder within the protected area, alarm source monitoring means including alarm detecting means having output means for continuously generating a line supervisory code comprised of a selected sequence of tone signals of predetermined frequencies and control means responsive to each alarm output for controlling said output means to supervisory code tone sequence to indicate the detection of movement of an intruder within the protected area, and line monitoring means at said central monitor including means responsive to a modified supervisory code tone sequence to provide an alarm indication at said central monitor, and test signal generating means operable to provide a test signal for transmission over said transmission line to said alarm source monitoring means, said alarm source monitoring means further including test signal detecting means for detecting said test signal and motion simulator means enabled by said test signal detecting means whenever a test signal is received to enable said intrusion detecting means to provide an alarm output for enabling a modified supervisory code tone sequence to be provided for transmission to said central monitor.

21. An alarm transmission system as set forth in claim 20 wherein said intrusion detector means includes microwave motion detection means having means operable to produce Doppler alarm signals of frequencies within a predetermined range whenever a human intruder is moving within the protected area and alarm signal detecting means responsive to each of said Doppler alarm signals to provide an alarm output, said motion simulator means being operable when enabled to produce signals of a frequency within said predetermined range to enable said motion detection means to provide an alarm output.

22. In an alarm transmission system including a transmission line for carrying alarm information from a plurality of protected areas to a central monitor that is remote from the protected areas, an individual alarm detecting means for each of said protected areas, each of said alarm detecting means including code generating means for continuously generating a line supervisory code comprised of a known sequence of coded bits, tone generating means normally controlled by the bits of said supervisory code to generate tones of at least first and second frequencies in a sequence coded to represent the bits of the supervisory code for transmission over said transmission line to the central monitor, means for controlling said tone generating means to provide a continuous tone output of one of said frequencies to indicate an alarm for the corresponding protected area, the tone generating means of different alarm detecting means providing continuously tone sequences having signals of different frequencies to enable simultaneous transmission of the tone sequences provided by all of said tone generating means to said central monitor over the transmission line, and coupling means for coupling the tone sequences provided by all of said tone generating means to said transmission line, and line monitoring means at said central monitor including a separate tone detecting means for each of sAid alarm detecting means and filter means for extending the tone sequences provided by the tone generating means of each alarm detecting means to a corresponding tone detecting means, each of said tone detecting means including reference code generating means for generating a reference code comprised of a sequence of bits in which each bit is normally identical with corresponding bits of the supervisory code sequence provided by the code generating means of the corresponding alarm detecting means, code comparator means for comparing the bits of the reference code with corresponding bits of the supervisory code, and means controlled by the code comparator means for providing an alarm indication whenever any of the corresponding bits of the two sequences are different.

23. An alarm transmission system as set forth in claim 22 wherein said coupling means comprises summing amplifier means having a plurality of inputs, each individually connected to the output of one of said tone generating means, and an output connected to said transmission line.

24. An alarm transmission system as set forth in claim 22 wherein said filter means comprises a plurality of bandpass filters each individually connected between said transmission line and one of said tone detecting means, different ones of said bandpass filters being tuned to pass signals of the first and second frequencies provided by the associated alarm detecting means.

25. In an alarm transmission system including a transmission line for carrying alarm information from a plurality of protected areas to a central monitor that is remote from the protected areas, alarm source means including an individual alarm sensor for each of said protected areas, alarm source monitoring means including at least one code generating means for continuously generating a line supervisory code comprised of a known sequence of coded bits, a plurality of tone generators and a plurality of gating means, each of said gating means being individually associated with one of said tone generators and normally operable to extend the bits of the supervisory code to an associated tone generator, each of said tone generators being responsive to the bits of the supervisory code extended thereto to provide tone signals of at least first and second frequencies in a sequence coded to represent the bits of the supervisory code, different ones of said tone generators being operable to provide tone signals of different frequencies to enable simultaneous transmission over said transmission line of the tone sequences provided by all of said tone generating means, each of said gating means being individually connected to one of said alarm sensors and controlled by an associated alarm sensor to inhibit the passage of the bits of the supervisory code to the associated tone generator to thereby modify the tone sequence to indicate an alarm condition for the corresponding protected area, and line monitoring means at said central monitor including a separate tone detector corresponding to each of said tone generators for receiving the tone sequence provided by an associated tone generator, at least one reference code generating means for generating a reference code comprised of a selected sequence of coded bits, each bit of which is normally identical with corresponding bits of the supervisory code sequence at any given time, and a plurality of code comparator circuits each operable to compare the supervisory code received by an associated one of the tone detectors with the reference code and provide an indication whenever the codes are different.

26. In an alarm transmission system including a transmission line for carrying alarm information from at least one protected area to a central monitor that is remote from the protected area, supervisory code generating means at said protected area for continuously generating a line supervisory code comprising a selected sequence of code bits for transmission over the transmission line from said protected area to said central monitor, normally closed contact means interposed between said supervisory code generating means and said transmission line for interrupting the transmission of said supervisory code sequence whenever said contact means are operated to indicate an alarm, reference code generating means at said central monitor for generating a reference code comprised of a selected sequence of code bits that is normally identical to said supervisory code sequence, means for comparing said supervisory code with said reference code, and means for providing an alarm indication whenever the codes are different or the transmission of said supervisory code sequence is interrupted.