Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1986-01-02
1988-01-19
Swann, III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
330207R, 333 19, 340551, G08B 1324
Patent
active
047207019
ABSTRACT:
An antipilferage system is provided with an improved signal processing system to prevent false alarms. This signal processing involves singly or in combination the improvements of a slew rate limited amplifier, which prevents impulse noise from ringing or being stretched by subsequent filters; a gain-controlled amplifier ahead of said slew rate limited amplifier, the gain of the gain-controlled amplifier being reduced as the noise and/or signal exceeds a minimum threshold level; a video detector which controls the gain-controlled amplifier and serves to maintain a minimum signal to noise ratio; a digital smoothing circuit which averages several "frames" of the entire signal such that random noise is averaged to zero while any signals which are synchronized with the modulation are added together; signal processing circuitry for the recognition of incoming signal pulse shape as compared to a predetermined pulse shape, the output of which is a trigger signal to an alarm. Moreover, blanking is employed to block any signals from passing through the system during specific portions of the modulation period and when no "tag" signals would normally be present in the system. A dead zone elimination circuit is also disclosed along with a power-up timed inhibit circuit to prevent false alarms when the system is turned on or when severe power line transients are present.
REFERENCES:
patent: 3500373 (1970-03-01), Minasy
patent: 4512000 (1985-04-01), Masuko
patent: 4539558 (1985-09-01), Fearon
patent: 4581524 (1986-04-01), Hoekman et al.
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