Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1984-12-10
1987-01-06
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
340518, 340551, G08B 1324
Patent
active
046350411
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a theft protection system, particularly for a shop area, for recording the unauthorized removal of objects or goods to which a preferably passive protection device is affixed having a resonance circuit tuned to a given frequency, through one of a number of exit passages, each of which comprises an antenna system having a transmitting antenna for transmitting electro-magnetic interrogation signals of said given frequency and a receiving antenna for the reasonance signals generated by the unauthorized removal of an object or a good through the passage, an alarm device being connected to a receiver connected with said receiving antenna to generate an alarm in response to reception of said resonance signal.
In recent years theft protection systems of this kind which are used mainly for theft protection of shops have gained increased use and are known in different designs, for instance with the arrangement mentioned above by which the recording of the unauthorized removal of a good from the shop area depends on detection of the electro-magnetic signal when the resonance circuit in a protection device affixed to the good, for instance, in the form of a disc, is influenced by the transmitted electro-magnetic interrogation signals.
In the known systems an antenna system with associated transmitter and receiver is required for each passage to be surveyed, whereby installation of a theft protection system for a shop area having several exit passages will be very expensive.
In addition, the known systems will in many cases not warrant sufficient security against false alarm from an antenna system caused by irrelevant signals such as electrical disturbances or signals from separate antenna systems in other exit passages in the vicinity.
From EPE-A-0003178 a system is known in which a number of exit passages are surveyed by means of separate transmitting/receiving devices controlled according to a master-slave principle and actuated in succeeding time frames.
SUMMARY OF THE INVENTION
For a theft protection system of the kind mentioned the above-mentioned shortcomings are remedied according to the invention in that the antenna systems for the exit passages are connected to a common transmitter and a common receiver through a transmitting multiplexer and a receiving multiplexer and that a common control unit is connected to and controls said multiplexers, said transmitter and said receiver for sequential coupling of said antenna systems to the transmitter and the receiver in successive time frames for individual ones of said exit passages and actuation of said transmitter and said receiver in a sequence of transmitting and receiving intervals within each time frame, said control device being further connected to a number of separate alarm generators for each of said exit passages for actuating an alarm generator associated with a given exit passage in response to compliance with at least one alarm criterion associated with the transmitting and receiving intervals associated with the exit passage.
By connecting a number of antenna systems for several exit passages to a single common transmitting/receiving device with an associated control unit which may comprise a microprocessor, the installation costs for surveyance of several exit passages may be reduced considerably relative to the above-mentioned known systems. Thus, by the system according to the invention it is without difficulty possible to survey up to, for instance, thirty exit passages by means of a single transmitting/receiving device and a number of antenna systems and alarm devices corresponding to the number of passages, said antenna systems being actuated sequentially in succeeding time frames in the manner indicated.
Thereby, and through the distribution of the actuation of the individual antenna systems in time so that only one antenna system at a time is made operative, it is further made possible in an economic manageable way to use several alarm criteria for each exit passage, whereby a very high
REFERENCES:
patent: 3256517 (1966-06-01), Saltzberg et al.
patent: 3949396 (1976-04-01), Cantrell
patent: 4067008 (1978-01-01), Sprowls et al.
patent: 4135184 (1979-01-01), Pruzick
patent: 4257038 (1981-03-01), Rounds et al.
patent: 4535323 (1985-08-01), Eccleston
Maimann Mogens
Svendsen Bent
2 M Security Systems APS
Swann III Glen R.
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