Communications: electrical – Systems – Call station
Patent
1973-11-16
1976-07-06
Caldwell, John W.
Communications: electrical
Systems
Call station
109 39, 340236, G08B 2100
Patent
active
039684822
ABSTRACT:
A monitoring system for detecting changes in the fluidic impedance or volume of the boundary or bounded regions of an enclosure, including detecting entry into, as well as certain movements within, a substantially sealed enclosure by means of non-synchronous or synchronous detection of a modulated pressure induced within the enclosure. The air pressure within the enclosure is modulated at a predetermined amplitude and frequency, and means tuned that that frequency produce electrical signals indicative of the amplitude and possibly phase, whereby entry into the enclosure, blockage or unblockage of passageways within the enclosure, or movement of certain objects within the enclosure vary the amplitude and/or phase of the modulated pressure in one or more bounded regions of the enclosure, thereby causing the electrical signal or signals to vary sufficiently to actuate an alarm. The means which produce the electrical signals may include sensor means constructed to cooperate with boundary regions of the enclosure to provide a chamber normally substantially closed with respect to the enclosure in which pressure variations are adapted to be induced, whereby movement of the sensor means away from the cooperating boundary region will open the normally closed chamber to the induced pressure variation thereby actuating the alarm. The sensor means, which may be part of a portable sensor-transmitter unit, may alternatively be located within furniture constructed to form such a normally closed chamber, whereby movement or opening of the furniture causes an alarm to be transmitted. A motor driven reversible pitch fan and a motor driven oscillating door are alternative means disclosed for inducing inverse pressure variations on opposite sides of an internal wall to facilitate cancellation of spurious pneumatic effects such as wind while providing the predetermined pressure modulation.
REFERENCES:
patent: 3513463 (1970-05-01), Stevenson, Jr. et al.
Caldwell John W.
Myer Daniel
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