Multiplexed alarm system

Claim 2

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a zone containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair or wires; a bandpass filter for said tone signal; a synchronizing signal decoder responsive to tone signals from said bandpass filter; a precision oscillator; a programmable counter coupled to said oscillator and said decoder to count oscillations from said oscillator upon receipt of a decoded synchronizing signal; means for selectively programming said counter to produce an output at a predetermined count; means for generating an acknowledgment signal within a time slot after receiving said output of said counter; a current driver connected to said acknowledgment signal generating means for sending an acknowledgment signal on said pair of wires, said current driver having a high impedance to help minimize the loading on said pair of wires by said plurality of transponders; and means for preventing an acknowledgment signal from being sent if the contact connected to the transponder indicates that an opening is open; control means including means for sending said tone synchronizing signal to said zone of transponders and low impedance means connected to said pair of wires for receiving acknowledgment signals from said zone, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in said zone; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.

Claim 3

The alarm system of claim 1 wherein said control means includes means for causing an alarm if an acknowledgment signal is received at a time other than a time slot corresponding to a transponder in said zone.

Claim 4

The alarm system of claim 1 wherein said control means includes means for sending a troubleshooting synchronizing signal and each of said transponders sends an acknowledgment signal during the time slot corresponding to said transponder, regardless of the status of its respective contact.

Claim 5

The alarm system of claim 1 wherein each of said transponders includes latch means for storing a high signal if the respective contact is opened and means for resetting said latch means at the end of the time slot corresponding to said transponder if the respective contact has been closed.

Claim 6

The alarm system of claim 4, wherein each of said transponders further comprise redundancy counter means, connected between said reset means and said latch means, for preventing said latch means from being reset until a predetermined number of synchronizing signals are received after said latch means has been set to a high signal.

Claim 7

The alarm system of claim 1 wherein said memory means retains data identifying each transponder that fails to respond to a synchronizing signal.

Claim 8

The alarm system of claim 1 wherein one or more of said transponders is a designated exit transponder and said control means includes timer means for counting predetermined time period after said alarm system is armed so that an alarm is not caused if one of said exit transponders fails to respond to a synchronizing signal during said predetermined time period.

Claim 9

The alarm system of claim 1 wherein one or more of said transponders is designated an entry transponder and said control means includes timer means for counting a predetermined time period after one of said entry transponders fails to respond to a synchronizing signal so that an alarm is caused only if said alarm system is not disarmed before the end of said predetermined time period.

Claim 10

The alarm system of claim 1 wherein each of said transponders includes oscillator means for producing a narrow band tone signal frequency to be used to generate said acknowledgement signal.

Claim 11

The alarm system of claim 1 wherein said low impedance means for receiving acknowledgment signals comprises a balanced current transformer connected between said zone of transponders and said control means for attenuating the amount of common mode noise which is picked up by the pair of wires.

Claim 12

The alarm system of claim 1 wherein said display means further includes means for displaying which openings are presently open.

Claim 13

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a plurality of zones, each containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair of wires; a precision oscillator; a programmable counter coupled to said oscillator; means responsive to receipt of said synchronizing tone signal for initiating a count in said counter; means for selectively programming said counter to produce an output at a predetermined count; means for generating an acknowledgment signal within a time slot corresponding to the predetermined count of a particular transponder following the receipt of a synchronizing signal; a current driver connected to said acknowledgment signal generating means for sending an acknowledgment signal on said pair of wires, said current driver having a high impedance to help minimize the loading on said pair of wires by said plurality of transponders; and means for preventing an acknowledgment signal from being sent if the contact connected to the transponder indicates that an opening is open; control means including means for sending a synchronizing signal to each of said zones of transponders and low impedance means connected to the pair of wires in each of said zones for receiving acknowledgment signals from each of said zones, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in one of said zones; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.

Claim 14

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a plurality of zones, each containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair of wires; a precision oscillator; a programmable counter coupled to said oscillator; means responsive to receipt of said synchronizing tone signal for initiating a count in said counter; means for selectively programming said counter to produce an output at a predetermined count; means for generating an acknowledgment signal within a time slot corresponding to the predetermined count of a particular transponder following the receipt of a synchronizing signal; a current driver connected to said acknowledgment signal generating means for sending an acknowledgment signal on said pair of wires, said current driver having a high impedance to help minimize the loading on said pair of wires by said plurality of transponders; and means for preventing an acknowledgment signal from being sent if the contact connected to the transponder indicates that an opening is open; control means including means for sending a synchronizing signal to each of said zones of transponders and low impedance means connected to the pair of wires in each of said zones for receiving acknowledgment signals from each of said zones, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in one of said zones; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.

Claim 15

The alarm system of claim 12 wherein said control means includes means for causing an alarm if an acknowledgment signal is received at a time other than a time slot corresponding to a transponder in said zone.

Claim 16

The alarm system of claim 12 wherein said low impedance means for receiving acknowledgment signals comprises a plurality of balanced current transformers, each connected between one of said zones of transponders and said control means for attenuating the amount of common mode noise picked up by the respective pair of wires.

Claim 17

A multiplexing method for wired alarm systems comprising: sending a synchronizing tone signal; receiving said synchronizing tone signal in a plurality of transponders wired in parallel each connected to one of a plurality of contacts which indicate whether an opening is open or secured; counting a precision frequency in each of said transponders from the receipt of said synchronizing signal up to a preprogrammed count corresponding to the particular transponder; storing a high signal in a transponder if its respective contact indicates an opening that is open; resetting the high signal to a low signal at the end of a time slot following the completion of the preprogrammed count corresponding to the particular transponder if its respective contact is then secured; each of said transponders sending an acknowledgment signal upon completion of the preprogrammed count if it has a low signal stored; and causing an alarm if a transponder fails to send an acknowledgment signal at its preprogrammed count.

Claim 18

A multiplexing method for wired alarm systems comprising: sending a synchronizing tone signal; receiving said synchronizing tone signal in a plurality of transponders wired in parallel each connected to one of a plurality of contacts which indicate whether an opening is open or secured; counting a precision frequency in each of said transponders from the receipt of said synchronizing signal up to a preprogrammed count corresponding to the particular transponder; storing a high signal in a transponder if its respective contact indicates an opening that is open; resetting the high signal to a low signal at the end of a time slot following the completion of the preprogrammed count corresponding to the particular transponder if its respective contact is then secured; each of said transponders sending an acknowledgment signal upon completion of the preprogrammed count if it has a low signal stored; and causing an alarm if a transponder fails to send an acknowledgment signal at its preprogrammed count.

Claim 19

The multiplexing method of claim 15 further comprising: displaying an identification of the transponder(s) which caused an alarm.

Claim 20

The multiplexing method of claim 15 further comprising: causing an alarm if an acknowledgment signal is sensed at a time other than the end of a preprogrammed time delay corresponding to one of said transponders.

Claim 21

The multiplexing method of claim 15 further comprising: storing the identity of each transponder that fails to respond to a synchronizing signal.

Claim 22

The multiplexing method of claim 15 further comprising: counting a predetermined amount of time after said alarm system is armed so that an alarm is not caused if a designated exit transponder fails to respond to a synchronizing signal during said predetermined amount of time.

Claim 23

The multiplexing method of claim 15 further comprising: counting a predetermined amount of time after a designated entry transponder fails to respond to a synchronizing signal so that an alarm is caused only if said alarm system is not disarmed before the end of said predetermined amount of time.

Claim 24

The multiplexing method of claim 15 wherein said synchronizing signal is a sequence of tone bursts.

Claim 25

The multiplexing method of claim 15 wherein said acknowledgment signals comprise a sequence of tone bursts in the respective time slots of the transponders.

Claim 26

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a zone containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair of wires; a bandpass filter for said tone signals; a synchronizing signal decoder responsive to tone signals from said bandpass filter and including means for indicating receipt of a troubleshooting synchronizing signal; a precision oscillator; a programmable counter coupled to said oscillator and said decoder to count oscillations from said oscillator upon receipt of a decoded synchronizing signal; means for selectively programming said counter to produce an output at a predetermined count; means for sending an acknowledgment signal on said pair of wires within a time slot after receiving said output of said counter; and means for preventing an acknowledgment signal from being sent if the contact connected to the transponder indicates that an opening is open unless said signal decoder indicates receipt of a troubleshooting synchronizing signal; control means for sending said tone synchronizing signal to said zone of transponders and for receiving acknowledgment signals from said zone, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in said zone, said control means further including means for sending a troubleshooting synchronizing signal; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.

Claim 27

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a zone containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair of wires; a bandpass filter for said tone signals; a synchronizing signal decoder responsive to tone signals from said bandpass filter and including means for indicating receipt of a troubleshooting synchronizing signal; a precision oscillator; a programmable counter coupled to said oscillator and said decoder to count oscillations from said oscillator upon receipt of a decoded synchronizing signal; means for selectively programming said counter to produce an output at a predetermined count; means for sending an acknowledgment signal on said pair of wires within a time slot after receiving said output of said counter; and means for preventing an acknowledgment signal from being sent if the contact connected to the transponder indicates that an opening is open unless said signal decoder indicates receipt of a troubleshooting synchronizing signal; control means for sending said tone synchronizing signal to said zone of transponders and for receiving acknowledgment signals from said zone, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in said zone, said control means further including means for sending a troubleshooting synchronizing signal; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.

Claim 28

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a zone containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair of wires; a bandpass filter for said tone signal; a synchronizing signal decoder responsive to tone tone signals from said bandpass filter; a precision oscillator; a programmable counter coupled to said oscillator and said decoder to count oscillations from said oscillator upon receipt of a decoded synchronizing signal; means for selectively programming said counter to produce an output at a predetermined count; means for sending an acknowledgment signal on said pair of wires within a time slot after receiving said output of said counter; latch means for storing a high signal if the contact connected to said transponder is opened; means for resetting said latch means after the time slot corresponding to said transponder if the contact connected to said transponder has been closed; and means for preventing an acknowledgment signal from begin sent if said latch means is storing a high signal; control means for sending said tone synchronizing signal to said zone of transponders and for receiving acknowledgment signals from said zone, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in said zone; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.

Claim 29

A multiplexed alarm system for monitoring a plurality of openings comprising: a plurality of contact means each connected with one of said openings, for indicating whether its respective opening is open or secured; a zone containing a plurality of transponders connected in parallel by a pair of wires, each transponder being connected with one of said contact means and including: means for receiving a synchronizing tone signal over said pair of wires; a bandpass filter for said tone signal; a synchronizing signal decoder responsive to tone tone signals from said bandpass filter; a precision oscillator; a programmable counter coupled to said oscillator and said decoder to count oscillations from said oscillator upon receipt of a decoded synchronizing signal; means for selectively programming said counter to produce an output at a predetermined count; means for sending an acknowledgment signal on said pair of wires within a time slot after receiving said output of said counter; latch means for storing a high signal if the contact connected to said transponder is opened; means for resetting said latch means after the time slot corresponding to said transponder if the contact connected to said transponder has been closed; and means for preventing an acknowledgment signal from begin sent if said latch means is storing a high signal; control means for sending said tone synchronizing signal to said zone of transponders and for receiving acknowledgment signals from said zone, said control means including means for causing an alarm if an acknowledgment signal is not received within the time slot corresponding to a particular transponder in said zone; and display means connected with said control means for providing an identification of the transponder(s) which caused an alarm.