G - Physics – 08 – B
Patent
G - Physics
08
B
349/30
G08B 13/16 (2006.01) G08B 1/00 (2006.01) G08B 23/00 (2006.01)
Patent
CA 1098611
ABSTRACT An alarm system in which local transmitters emit sub- stantially pure acoustic signals for at least a predetermined minimum interval. The receiver includes a microphone and amplifier for transducing the acoustic signals into electrical signals. These electrical signals pass through two bandpass stages, the second being a phase locked loop circuit. An RC timing network is connected to the second bandpass circuit. After about 7500 cycles of the electrical signal have been received an "alarm received" signal occurs. The "alarm received" signal is applied to the triggering input of a free- running pulse generator which supplies pulse trains to a counter and is itself halted when the counter reaches a first intermediate state. A second "alarm received" signal is required to restart the free-running puIse generator and thus advance the counter beyond said first intermediate state. Thereafter, when the counter reaches a second intermediate state, the occurrence of the corresponding second intermedi- ate state signal actuates a suitable alarm signal to warn of intrusion or some other hazardous condition.
311898
Johnson & Hicks
Meyer Michael M.
LandOfFree
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