Wireless synchronization system for electronic article surveillance system
First Claim
1. An electronic article surveillance system comprising transmitting means for producing in an interrogation zone periodic interrogation signals having bursts of RF followed by quiescent intervals, receiving means for detecting during said quiescent intervals a signal generated by a marker in response to said interrogation signals, and means responsive to radiated electromagnetic energy for synchronizing the production of bursts of RF by said transmitting means with bursts of RF from another like system, thereby preventing bursts of RF from said transmitting means from occurring during quiescent intervals of the interrogation signals of said another system so that such bursts cannot produce a false alarm or shut down a system as a result of being detected by the receiving means of said another system.
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Abstract
Operation of similar electronic article surveillance (EAS) systems in proximity to each other may result in false alarms or system "shut-downs" as a result of signals transmitted from one system being detected in the receiver circuits of the other systems. This may especially occur with EAS systems in which the receivers are only activated during quiescent intervals between transmitted bursts, such that if the systems are unsychronized, the transmitted bursts of the one system may occur during the quiescent intervals of the other system. In the present invention, synchronization is effected by responding to RF detected during the quiescent intervals and preventing the transmitted bursts from occurring during the quiescent intervals of the other system.
37 Citations
9 Claims
- 1. An electronic article surveillance system comprising transmitting means for producing in an interrogation zone periodic interrogation signals having bursts of RF followed by quiescent intervals, receiving means for detecting during said quiescent intervals a signal generated by a marker in response to said interrogation signals, and means responsive to radiated electromagnetic energy for synchronizing the production of bursts of RF by said transmitting means with bursts of RF from another like system, thereby preventing bursts of RF from said transmitting means from occurring during quiescent intervals of the interrogation signals of said another system so that such bursts cannot produce a false alarm or shut down a system as a result of being detected by the receiving means of said another system.
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9. A circuit for synchronizing an electronic article surveillance system with other like systems, each of which produces in a respective interrogation zone periodic interrogation signals having bursts of RF followed by quiescent intervals during which marker created signals are detected, and which bursts if present during a quiescent interval of another system could be detected as a marker created signal and either shut down the system or result in a false alarm, said circuit comprising
first means for detecting energy during a first time window occurring relatively late in each quiescent interval and during which no signals produced by resonating marker circuits would likely be present, second means for detecting energy during a second time window also occurring relatively later in each quiescent period but which is different from the first zone, comparator means for comparing the amplitude of outputs from said first and second means and for providing a timing control signal in the event the difference in amplitude exceeds a predetermined level, and synchronization means responsive to the timing control signal for incrementally adjusting the periodicity of the interrogation signals of said system to cause said periodicity to change so that it matches the periodicity of said other systems.
Specification