Pressure change intrusion detector

Abstract

Apparatus utilizing change in pressure condition in an area to be protected to indicate intrusion or change in conditions of the area by using a pressure detection device to detect pressure waves at low and infrasonic frequencies which includes a pressure transducer sensitive to change in pressure to provide an output signal. In some instances an amplifier is provided to amplify the output signal, a signal conditioning circuit is provided to delay a portion of the signal, and a detector device is provided to detect the signal with a comparator provided to compare the signal with the delayed signal and actuate an alarm. .Iadd.Additionally, a device producing signals responsive to pressure waves and selected sonic frequencies is taught. If the signals are coincidently received at a coincidence detector, an alarm is activated. Further, the signals can be stretched and/or delayed before receipt at the coincidence detector. .Iaddend.

The invention claimed is: 
     
       1. A signalling device to detect coincidence of first and second selected conditions in a selected area .[.where.]. .Iadd.wherein .Iaddend. the first selected condition is infrasonic air pressure waves having frequencies below 20 cycles per second and the second selected condition is selected sonic frequency waves, said device comprising;   a pressure sensitive transducer means responsive to said infrasonic air pressure waves to provide an alternating electrical signal;   an amplifier means to selectively amplify said alternating electrical signal to provide an amplified alternating output signal;   a rectifier means to rectify said amplified alternating output signal to provide a first .Iadd.rectified .Iaddend.signal;   a sonic frequency transducer means responsive to selected frequencies to provide a second alternating electrical signal;   a second amplifier means to selectively amplify said second alternating electrical signal to provide a second amplified alternating output signal;   a second rectifier means to rectify said second amplified alternating output signal to provide a second rectified signal;   a switch means, including a coincidence detector responsive to the first and second rectified signals, which activates an alarm in response to coincident receipt of the first and second rectified signals.   
     
     
       2. A signalling device according to claim 1 including .[.first.]. delay means to delay transmission of said first .Iadd.rectified .Iaddend.signal to said switch means for a selected period of time. 
     
     
       3. A signalling device according to claim 1 including .[.second.]. delay means to delay transmission of said second .Iadd.rectified .Iaddend.signal to said switch means for a selected period of time. .Iadd. 
     
     
       4.  A signalling device according to claim 1, including a stretch means to cause said first rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said second rectified signal and said first rectified signal having said increased pulse duration. .Iaddend. .Iadd. 
     
     
       5.  A signalling device according to claim 4, including a second stretch means to cause said second rectified signal to have a second increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal having first-recited increased pulse duration and said second rectified signal having said second increased pulse duration. .Iaddend. .Iadd. 
     
     
       6.  A signalling device according to claim 1, including a stretch means to cause said second rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said firsts rectified signal and said second rectified signal having said increased pulse duration. .Iaddend. .Iadd. 
     
     
       7.  A signalling device according to claim 2, including a second delay means to delay transmission of said second rectified signal to said switch means for a second selected period of time. .Iaddend. .Iadd.8. A signalling device according to claim 7, wherein said second selected period of time is greater than said first-recited selected period of time. 
     
     
        .Iaddend. .Iadd.9.  A signalling device according to claim 8, including a stretch means to cause said first rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said second rectified signal and said first rectified signal having said increased pulse duration. .Iaddend. 
     
     
        .Iadd.     A signalling device according to claim 9, including a second stretch means to cause said second rectified signal to have a second increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal having said first-recited increased pulse duration and said second rectified signal 
     
     
        having said second increased pulse duration. .Iaddend. .Iadd.11.  A signalling device according to claim 8, including a stretch means to cause said second rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said second rectified signal and said second rectified signal having said 
     
     
        increased pulse duration. .Iaddend. .Iadd.12.  A signalling device according to claim 7, including a stretch means to cause said first rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said second rectified signal and said first rectified signal having said increased 
     
     
        pulse duration. .Iaddend. .Iadd.13.  A signalling device according to claim 12, including a second stretch means to cause said second rectified signal to have a second increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal having said first-recited increased pulse duration and said second rectified signal having said second increased pulse duration. 
     
     
        .Iaddend. .Iadd.14.  A signalling device according to claim 7, including a stretch means to cause said second rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal and said second rectified signal having said increased pulse duration. .Iaddend. 
     
     
        .Iadd.     A signalling device according to claim 2, including a stretch means to cause said first rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said second rectified signal and said first rectified signal having said increased pulse duration. .Iaddend. 
     
     
        .Iadd.     A signalling device according to claim 15, including a second stretch means to cause said second rectified signal to have a second increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal having said first-recited increased pulse duration and said second rectified signal 
     
     
        having said second increased pulse duration. .Iaddend. .Iadd.17.  A signalling device according to claim 2, including a stretch means to cause said second rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal and said second rectified signal having said 
     
     
        increased pulse duration. .Iaddend. .Iadd.18.  A signalling device according to claim 3, including a stretch means to cause said first rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said second rectified signal and said first rectified signal having said increased 
     
     
        pulse duration. .Iaddend. .Iadd.19.  A signalling device according to claim 18, including a second stretch means to cause said second rectified signal to have a second increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal having first-recited increased pulse duration and said second rectified signal having said second increased pulse duration. 
     
     
        .Iaddend. .Iadd.20.  A signalling device according to claim 3, including a stretch means to cause said second rectified signal to have an increased pulse duration, wherein said switch means activates said alarm during any coincident receipt of said first rectified signal and said second rectified signal having said increased pulse duration. .Iaddend.