System for monitoring changes in the fluidic impedance or volume

Details System for monitoring changes in the fluidic impedance or volume System for monitoring changes in the fluidic impedance or volume

1974-12-10

1976-11-02

Caldwell, John W.

Communications: electrical

Systems

Call station

109 43, G08B 2100

Patent

active

039900630

ABSTRACT:
A monitoring system for detecting changes in the fluidic impedance of the boundary regions or volume of an enclosure, including detecting entry into, as well as certain movements within, a substantially sealed enclosure by means of synchronous detection of a modulated pressure signal within the enclosure. The air pressure within the enclosure is modulated at a predetermined amplitude and at a frequency which is sufficiently low to substantially avoid reverberation and wave interference effects, and means tuned to that frequency produce electrical signals indicative of the amplitude and phase, whereby entry into or exit from the enclosure, opening of a chamber within the enclosure, or blockage or unblockage of passageways within the enclosure vary the amplitude and/or phase of the modulated pressure, thereby causing an electrical signal to vary sufficiently to actuate an alarm.

REFERENCES:
patent: 3513463 (1970-05-01), Stevenson, Jr. et al.

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