US4196423A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Acoustic emission intrusion detector
Assignee: United States Department of Energy
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Filing: 1978-08-09
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Granted: 1980-04-01
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Expires: 1998-08-09
Abstract
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.
Inventors
- 👤 Donald W. Carver
- 👤 Jerry W. Whittaker
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-24 06:40
CPC Classifications
G; G08; G08B; G08B13/00; G08B13/16; G08B13/1654; G08B13/1672
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
211 words
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.
Claim 2
Dependent Claim
211 words
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.
Claim 3
Dependent Claim
136 words
The intrusion detector as set forth in claim 1 wherein said signal amplitude discriminating means includes an operational amplifier having an inverting input, a non-inverting input and an output, said non-inverting input of said operational amplifier being connected to the output of said preamplifier, a resistor connected between said inverting input and ground potential, a selectable resistance feedback network connected between the output and the inverting input of said operational amplifier for providing a selectable range of feedback resistance corresponding to a desired gain so that gain adjustmemt may be made for specific installations, and a Schmitt trigger circuit connected to the ouput of said operational amplifier and having a preselected threshold triggering level corresponding to said preselected amplitude threshold level for generating said timing pulses when the signal input thereto exceeds said threshold triggering level.
Claim 4
Dependent Claim
99 words
The intrusion detector as set forth in claim 2 wherein said timing circuit means includes a gate having a first input connected to the output of said Schmitt trigger circuit, a one-shot connected between the output of said Schmitt trigger circuit and a second input of said gate, said one-shot having a preselected period corresponding to a selected maximum time period between said first and second timing pulses so that only transducer signals having a period less than said preselected period activate said gate, and an alarm driver connected between the output of said gate and said alarm means.
Claim 5
Dependent Claim
37 words
The intrusion detector as set forth in claim 3 wherein said preamplifier circuit means includes a filter circuit means for providing a low frequency cutoff for transducer signals below about 800 Hz, thereby further minimizing false alarms.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1983-04-01 | 1983-10-01 | 1984-04-01 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1987-04-01 | 1987-10-01 | 1988-04-01 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1991-04-01 | 1991-10-01 | 1992-04-01 | $7700.00 | Window Closed / Lapsed |