Intrusion alarm system
AssigneeTri-Century Industries
InventorLouis H. La Forge, Jr.
Life of this patent
Estimating the term…
Abstract
An intrusion detection apparatus employing a pressure differential sensor for sensing an entry into a room, building or other enclosure. A fan maintains a pressure differential between the enclosure and the external environment and causes air flow through the sensor. Opening of doors and windows or other intrusions into the enclosure causes changes in sensor air flow and the generation of an electrical signal highly sensitive to the changes. A signal processor processes the signal based upon direction, amplitude and time-period of change to distinguish between intrusion-caused and non-intrusion-caused changes.
Claims24
An intrusion detection apparatus for detecting intrusions into an enclosure wherein a pressure differential in a medium is maintained between the enclosure and the external environment, the improvement comprising:
- sensor means connected between the enclosure and the external environment for providing an electrical signal which varies over a plurality of values within the extreme values of a range as a function of changes in the differential pressure between the enclosure and the external environment,
- signal processing means for detecting predetermined properties in said electrical signal to distinguish between intrusion-caused changes and non-intrusion-caused changes in said differential pressure.
An intrusion detection apparatus for detecting intrusions into an enclosure wherein a differential pressure in a medium is maintained between the enclosure and the external environment comprising:
- sensor means connected to conduct a medium between the enclosure and the external environment with a rate of flow which is a function of said differential pressure, said sensor means including a movable vane urged in one direction by a restoring force and urged in the opposite direction by the flow of said medium whereby the movement of said vane from an equilibrium position is a function of said rate of flow, including electrical means for providing detection signals as a function of said movement, said electrical means including integrator means for integrating said detection signals to form an integrated signal having an amplitude proportional to changes in position of said vane, said integrator means including means for discharging said integrator at an exponential rate and means for limiting integration unilaterally with respect to a predetermined amplitude level,
- signal processing means including means for producing a threshold signal when the amplitude of said integrated signal exceeds a predetermined amplitude, including means for generating a time window for a predetermined duration commencing a predetermined time after a change in position of said vane, and including means for producing an alarm signal when said threshold signal occurs during said time window in order to indicate an intrusion-caused change in said differential pressure.
Dependencies are inferred from the claim text.