Acoustic emission intrusion detector
First Claim
1. An acoustic emission intrusion detector for monitoring a secured structure and generating an alarm upon detection of acoustical signals generated durng forcible entry into said structure while minimizing false alarms based on signal amplitude and frequency discrimination, comprising:
- an acoustic emission transducer mounted to sense vibrations generated in said structure and generating an a.c. signal at an output thereof in response to said vibrations;
a preamplifier circuit means responsive to the output of said transducer for providing preselected amplification of said a.c. signal;
signal amplitude discriminating means responsive to the output of said preamplifier for generating first and second successive timing pulses when the signal from said preamplifier exceeds a preselected amplitude threshold level, said first timing pulse being generated when the amplitude of a first cycle of said a.c. signal exceeds said threshold level and said second timing pulse being generated when the amplitude of a subsequent cycle of said a.c. signal exceeds said threshold level, thereby providing said amplitude discrimination; and
a timing circuit means for monitoring the time span between said first and second timing pulses and generating an alarm signal when the time span is less than a preselected value, thereby providing said frequency discrimination, and means responsive to said alarm signal for providing an alarm indication.
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Abstract
An intrusion detector is provided for detecting a forcible entry into a secured structure while minimizing false alarms. The detector uses a piezoelectric crystal transducer to sense acoustic emissions. The transducer output is amplified by a selectable gain amplifier to control the sensitivity. The rectified output of the amplifier is applied to a Schmitt trigger circuit having a preselected threshold level to provide amplitude discrimination. Timing circuitry is provided which is activated by successive pulses from the Schmitt trigger which lie within a selected time frame for frequency discrimination. Detected signals having proper amplitude and frequency trigger an alarm within the first complete cycle time of a detected acoustical disturbance signal.
20 Citations
4 Claims
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1. An acoustic emission intrusion detector for monitoring a secured structure and generating an alarm upon detection of acoustical signals generated durng forcible entry into said structure while minimizing false alarms based on signal amplitude and frequency discrimination, comprising:
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an acoustic emission transducer mounted to sense vibrations generated in said structure and generating an a.c. signal at an output thereof in response to said vibrations; a preamplifier circuit means responsive to the output of said transducer for providing preselected amplification of said a.c. signal; signal amplitude discriminating means responsive to the output of said preamplifier for generating first and second successive timing pulses when the signal from said preamplifier exceeds a preselected amplitude threshold level, said first timing pulse being generated when the amplitude of a first cycle of said a.c. signal exceeds said threshold level and said second timing pulse being generated when the amplitude of a subsequent cycle of said a.c. signal exceeds said threshold level, thereby providing said amplitude discrimination; and a timing circuit means for monitoring the time span between said first and second timing pulses and generating an alarm signal when the time span is less than a preselected value, thereby providing said frequency discrimination, and means responsive to said alarm signal for providing an alarm indication. - View Dependent Claims (2, 3, 4)
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Specification