Security polling transponder system

• US 3,952,285 A
• Filed: 04/21/1975
• Issued: 04/20/1976
• Est. Priority Date: 04/21/1975
• Status: Expired due to Term

• Current Assignee: Morse Products Manufacturing
• Original Assignee: Morse Products Manufacturing
• Inventors: Falck, Melvin S. Jr.
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Stellar, George G.
• Application Number:
  US05/570,094
• Time in Patent Office: 365 Days
• Field of Search: 340/152 R, 340/152 T, 340/157, 340/408
• US Class Current: 340/870.09
• CPC Class Codes: G08B 26/002 only replying the state of the sensor

Abstract

Transponder apparatus and a corresponding method for use in a security polling system having a central controller and a number of remotely located transponders which are polled sequentially to initiate transmission of status conditions, over telephone lines to the central controller for monitoring. The transponder detects polling signal bursts of a particular frequency from the central controller, and counts the bursts to determine its turn for response. Each response includes two sequential signal bursts of different frequencies, the durations of which define, with the frequency sequence, the status condition being transmitted. Control information is encoded into the lengths and spacings of the polling signal bursts, and is decoded by the transponder, to indicate transmission errors, transponder resetting commands, and remote control commands. Means are also provided at the transponder for transmitting a special alarm code when electrical power is first applied to the transponder, thus indicating the possible substitution of an unauthorized transponder at a protected site.

Claims

1. For use in a security polling system having a central controller and a plurality of remote transponders, a method of transmitting security status information from a transponder to the central controller, said method comprising the steps of:

detecting polling signals transmitted from the central controller;

determining whether each of the polling signals is intended to trigger transmission from this particular transponder; and

transmitting, in response to an affirmative decision in said determining step, a response signal indicative of at least one security status condition at the transponder site, the response signal including a plurality of sequential signal bursts, each of a preselected frequency and duration such that the response signal uniquely identifies the security status condition.

2. A method as set forth in claim 1, and further including the steps of:

monitoring the time of arrival of the next polling signal following said transmitting step;

determining from said monitoring step whether the status condition transmitted was correctly received at the central controller; and

retransmitting the status condition if necessary.

3. A method as set forth in claim 1, wherein:

said step of determining whether each of the polling signals is intended to trigger transmission from this particular transponder includes accumulating a count of polling signals detected by said detecting step, and comparing the accumulated count with a transponder number associated with this particular transponder; and

said method also includes the additional steps of detecting a reset signal from the central controller to initiate a scan of transponders, and resetting the accumulated count in response to said step of detecting a reset signal.

4. A method as set forth in claim 1, wherein said transmitting step includes:

selecting for transmission one of a possible plurality of status conditions at the transponder site;

generating transmission parameters corresponding to the selected status condition; and

controlling a plurality of oscillators in accordance with the generated parameters to produce the required sequence of signal bursts comprising the response signal.

5. A method as set forth in claim 4, and further including the steps of:

monitoring the time of arrival of the next polling signal following said transmitting step;

determining from said monitoring step whether the status condition transmitted was correctly received at the central controller; and

retransmitting the status condition if necessary.

6. A method as set forth in claim 4, wherein:

said step of determining whether each of the polling signals is intended to trigger transmission from this particular transponder includes accumulating a count of polling signals detected by said detecting step, and comparing the accumulated count with a transponder number associated with this particular transponder; and

said method also includes the additional steps of detecting a reset signal from the central controller to initiate a scan of transponders, and resetting the accumulated count in response to said step of detecting a reset signal.

7. For use in a security polling system having a central controller and a plurality of remote transponders, a method of transmitting security status information from a transponder to the central controller, said method comprising the steps of:

detecting the presence and absence of polling signals transmitted from the central controller as signal bursts of a first particular frequency;

timing the durations of the polling signals and the durations of the periods of silence therebetween;

generating transponder control signals in accordance with the nature of the received polling signals as determined by said detecting and timing steps;

resetting a transponder counter in response to a reset signal generated in said generating step on detection of a silence of predetermined duration;

comparing the contents of the transponder counter with a number associated with this particular transponder, on receipt of a polling signal;

advancing the transponder counter in response to a signal generated in said generating step on receipt of each polling signal; and

transmitting, in response to a successful comparing step, a response signal indicative of a status condition at the transponder site, the response signal including two sequential signal bursts having different frequencies chosen from second and third particular frequencies, such that the frequency sequence and durations of the two sequential signal bursts uniquely identify the status condition.

8. A method as set forth in claim 7, wherein said step of generating control signals includes generating an error signal to initiate retransmission if the polling signal received following said transmitting step is spaced more than a predetermined time from the previously detected polling signal.

9. A method as set forth in claim 7, wherein said transmitting step includes:

selecting for transmission one of a possible plurality of status conditions at the transponder site;

generating transmission parameters corresponding to the selected status condition; and

controlling two oscillators of the second and third particular frequencies in accordance with the generated parameters, to produce the required sequence of signal bursts comprising the response signal.

10. A method as set forth in claim 9, wherein said transmitting step further includes:

sensing the application of power to the transponder;

temporarily substituting a special set of transmission parameters in response to said sensing step, whereby application of power to the transponder may be indicative of unauthorized tampering.

11. A method as set forth in claim 9, wherein:

the transmission parameters includes a frequency sequence indicator, indicating the frequency of the first signal burst, a shift-frequency indicator, indicating the duration of the first signal burst, and a terminate-transmission indicator, indicating the total duration of the response; and

said step of controlling the oscillators includes comparing the shift-frequency indicator and the terminate-transmission indicator with the time since transmission was begun, and generating control signals when comparison is successful.

12. A method as set forth in claim 7, wherein said step of generating control signals includes generating a control signal indicative of possible tampering with equipment if a polling signal or an absence thereof persists for some predetermined minimum time.

13. A method as set forth in claim 7, wherein said step of generating control signals includes generating signals for the control of selected devices at the transponder site in response to polling signal bursts of particular predetermined durations, whereby the duration of the polling signal indicates a control function to be performed.

14. A method as set forth in claim 7, and further including the step of enabling the transponder in response to detection of an enabling polling signal of a particular preselected relatively long duration following said resetting step, whereby the long enabling polling signal will be easily distinguishable from possible noise signals present after the period of silence initiating said resetting step.

15. For use in a security polling system having a central controller and a plurality of remote transponders connected to the central controller by telephone lines, a method of transmitting security status information from a transponder to the central controller, said method comprising the steps of:

detecting the presence and absence of polling signals transmitted from the central controller as signal bursts of a first particular frequency;

timing the durations of the polling signals and the durations of the periods of silence therebetween;

generating transponder control signals in accordance with the durations of the detected polling signals and the periods of silence therebetween, the control signals including

a reset signal for resetting a counter in response to a silence of a predetermined duration,

an enable signal for enabling the transponder following a reset signal,

a counter-advancing signal in response to any received polling signal,

a coincidence signal indicating equality of the counter contents with a number associated with this transponder, and

a transmission error signal in response to detection of a period of silence of predetermined duration following transmission by the transponder;

resetting, enabling and advancing the counter under direction of the reset signals, enable signals and counter-advancing signals generated in said generating step;

transmitting, in response to the coincidence signal, a response signal indicative of a status condition at the transponder, the response signal including two sequential signal bursts having different frequencies chosen from second and third particular frequencies, such that the frequency sequence and durations of the two sequential signal bursts uniquely identify the status condition, said transmitting step including

selecting for transmission one of a possible plurality of status conditions at the transponder site,

generating transmission parameters corresponding to the selected status conditions, and

controlling two oscillators of the second and third particular frequencies in accordance with the generated parameters, to produce the required sequence of signal bursts comprising the response signals; and

retransmitting the same sequence of frequency

bursts, if necessary, in response to the transmission error signal, and when the transponder is next triggered to respond.

16. Transponder apparatus for use in a security polling system having a central controller and a plurality of transponders, said apparatus comprising:

means for detecting a polling signal from the central controller, including means for determining whether the polling signal is intended to trigger transmission from this particular transponder; and

transmitting means, responsive to said means for detecting a polling signal, for encoding and transmitting a security status condition at the transponder site as a plurality of sequential signal bursts, each of a preselected frequency and duration such that the response signal uniquely identifies the security status condition.

17. Apparatus as set forth in claim 16, and further including:

timing means for monitoring the time of arrival of the next polling signal after transmission of the response signal; and

means for initiating retransmission of the response signal if said timing means determines that the original transmission was not correctly received, whereby transmission errors in transmitted status conditions are indicated by the time of occurrence of the next following polling signal.

18. Apparatus as set forth in claim 16, wherein:

said means for determining whether the polling signal is intended to trigger transmission from this particular transponder includes counting means for accumulating a count of detected polling signals, and comparing means for comparing the count in said counting means with a transponder number associated with this particular transponder; and

said apparatus also includes means for detecting a reset signal from the central controller, and means for resetting said counting means in response thereto.

19. Apparatus as set forth in claim 16, wherein said transmitting means includes:

priority selection means, for selecting one of a possible plurality of status conditions at the transponder site;

status encoding means for generating response transmission parameters corresponding to the selected status condition; and

oscillator control means, for controlling a plurality of oscillators in accordance with the generated parameters to produce the required sequence of signal bursts comprising the response signal.

20. Apparatus as set forth in claim 19, and further including:

timing means for monitoring the time of arrival of the next polling signal after transmission of the response signal; and

mean for initiating retransmission of the response signal if said timing means determines that the original transmission was not correctly received, whereby transmission errors in transmitted status conditions are indicated by the time of occurrence of the next following polling signal.

21. Apparatus as set forth in claim 19, wherein:

said means for determining whether the polling signal is intended to trigger transmission from this particular transponder includes counting means for accumulating a count of detected polling signals, and comparing means for comparing the count in said counting means with a transponder number associated with this particular transponder; and

said apparatus also includes means for detecting a reset signal from the central controller, and means for resetting said counting means in response thereto.

22. Transponder apparatus for use in a security polling system having a central controller and a plurality of transponders, said apparatus comprising:

polling signal detection means, for detecting the presence and absence of polling signals received from the central controller as signal bursts of a first particular frequency;

timing means, for timing the durations of the polling signals and the periods of silence separating the polling signals;

control means connected with said timing means, for generating transponder control signals in accordance with the durations and spacings of the polling signals;

polling signal counting means, including coincidence means for comparing the count in said counting means with a transponder number associated with this particular transponder; and

transmitting means for encoding and transmitting a response signal indicative of a status condition at the transponder site, the response signal including two sequential signal bursts having different frequencies chosen from second and third particular frequencies, such that the frequency sequence and durations of the two sequential signal bursts uniquely identify the status condition.

23. Apparatus as set forth in claim 22, wherein said control means includes means for generating an error signal to initiate retransmission of the response signal if the polling signal detected following transmission is spaced more than a predetermined time from the previously detected polling signal.

24. Apparatus as set forth in claim 22, wherein said transmitting means includes:

priority selection means for selecting for transmission one of a possible plurality of status conditions at the transponder site;

status encoding means, for generating response transmission parameters corresponding to the selected status condition; and

oscillator control means, for controlling two oscillators of the second and third particular frequencies in accordance with the generated parameters, to produce the required sequence of signal bursts comprising the response signal.

25. Apparatus as set forth in claim 24, wherein said transmitting means further includes:

means for sensing the application of electrical power to the transponder;

logic means responsive to said sensing means, for temporarily substituting a special set of response transmission parameters, whereby application of power to the transponder is indicated to the central controller without delay since it may be indicative of an unauthorized substitute transponder.

26. Apparatus as set forth in claim 24, wherein:

said status encoding means includes means for generating a frequency sequence indicator, a shift-frequency indicator and a terminate-transmission indicator; and

said oscillator control means includes means for comparing the shift-frequency indicator and the terminate-transmission indicator with the time elapsed since transmission was begun, and means for generating oscillator control signals when comparison is successful.

27. Apparatus as set forth in claim 22, wherein said control means includes means for generating a control signal indicative of possible tampering with equipment if a polling signal or an absence thereof persists for some predetermined minimum time.

28. Apparatus as set forth in claim 22, wherein said control means includes means for generating signals for the control of selected devices at the transponder site in response to polling signal bursts of predetermined durations, whereby the duration of the polling signal indicates which control function to be performed.

29. Apparatus as set forth in claim 22, wherein said control means includes:

means for generating a reset signal in response to detection of a silence period of predetermined duration; and

means for generating an enabling signal in response to detection of a polling signal of predetermined and relatively long duration following a reset silence period, whereby the long enabling burst will be easily distinguishable from possible noise signals present after the reset silence period.

30. Apparats as set forth in claim 22, wherein said polling signal detection means includes:

zero-crossing detection means for producing a relatively short-duration pulse each time a received signal crosses a zero axis;

pulse timing means for measuring the times between zero crossings;

pulse counting means coupled with said pulse timing means to keep a running count indicative of the number or pulses derived from a received signal of the first particular frequency which occurred during a period defined by a preselected number of most recent pulse times; and

decision means coupled with said pulse counting means, for determining whether a polling signal is currently being received, whereby, if said pulse counting means has a capacity of n, its current contents indicates the number of pulses detected during the most recent n pulse times.

31. In a transponder for use with a security polling system having central controller and a plurality of transponders, apparatus comprising:

sensing means for sensing application of electrical power to the transponder;

gating means responsive to said sensing means, for inhibiting retransmission of a response signal indicative of a status condition to the central controller, and simultaneously enabling transmission of a special response signal indicative of the sensed condition; and

counting means for effecting transmission of the special response signal a predetermined number of times, said counting means being coupled to said gating means to permit normal transmission after the predetermined number of special response transmissions.

32. Apparatus as set forth in claim 31, and further including means for resetting said counting means in response to detection of an error signal indicative of an error in the transmission of the special response signal, whereby the special response signal will be retransmitted until no error signal is detected.

33. For use in a security polling system having a central controller and at least one remote transponder, a method for detecting an unauthorized transponder substitution, said method comprising the steps of:

sensing the application of electrical power to the transponder; and

, in response to said sensing step,

inhibiting transmission of a normal response signal; and

enabling transmission of a special response signal indicative of application of electrical power to the transponder.

34. A method as set forth in claim 33, and further including the steps of:

detecting a transmission error signal indicative of an error in transmission of the special response signal; and

enabling transmission of the special response signal if said detecting step determines that there was an error in transmission.