Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1990-01-16
1991-07-23
Swann III, Glen R.
Communications: electrical
Condition responsive indicating system
Specific condition
331 65, G08B 1326
Patent
active
050347225
ABSTRACT:
A capacitance sensing security system in which comparison/reference and sensing oscillator are coupled together to operate in substantial frequency synchronism, each of the oscillators includes an amplifier having input and output terminals and a feedback circuit including a capacitor connected to the input terminals, the feedback circuit connected to the sensing oscillator exhibiting a low capacitive reactance, the input terminals of the sensing oscillator being connected to one or more objects to be secured so that extraneous transient signals appearing at or on the objects do not affect the phase/frequency of the sensing oscillator, the resistive component being substantially greater than the resistance of the input terminals and is provided either by adjusting the value of the capacitive component in the feedback circuit and/or disposing a resistor in series therewith. An automatic tuner is provided to initially provide frequency synchronism between the reference/comparison and sensing amplifiers, and thereafter, a predetermined phase difference between the two amplifiers is provided by a suitable offset biasing supply for the sensing oscillator and the reference/comparison oscillator. Improved intruder detection includes controlled clocks and selectively operable registers to actuate an alarm condition indicator.
REFERENCES:
patent: 3222664 (1965-12-01), Premack
patent: 3293631 (1966-12-01), Premack
patent: 4103252 (1978-07-01), Bobick
patent: 4169260 (1979-09-01), Bayer
patent: 4222045 (1980-09-01), Cholin
patent: 4240528 (1980-12-01), Kraus
patent: 4366473 (1982-12-01), Inoue et al.
Mullen Jr. Thomas J.
Sturm Warren A.
Swann III Glen R.
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