Claims
- 1. Apparatus for detecting intrusion of a partition, comprising:
- a detector means, attachable to the partition to be protected, for detecting vibrations of the partition and for providing a signal corresponding thereto;
- first circuit means for receiving and amplifying said signal from said detector means, said first circuit means including an amplifier for amplifying said signal and a variable gain switch, connected to an output of said amplifier, for selectively adjusting the level of the signal produced by said detector means to a predetermined level;
- second circuit means for selection of a predetermined frequency band for the partition being monitored, said second circuit means including band pass filter means, connected to receive an output signal from said variable gain switch, for filtering said output signal from said variable gain switch with at least two different pass bands, AM detector means for detecting the peaks of a filtered output signal from said filter means, and means for selectively causing an output signal from said second circuit means corresponding to an output signal from said AM detector means in only one of said pass bands; and
- third circuit means for processing the output signal from said second circuit means to provide an alarm indicating the detection of vibrations representative of an intrusion attempt of the partition.
- 2. Apparatus as defined in claim 1 further comprising LED bar display means for monitoring and displaying the output signal from said second circuit means.
- 3. Apparatus as defined in claim 1 wherein: said band pass fliter means includes at least firt and second band pass filters, each of said band pass filters having a different one of said pass bands at least two to cover a desired total band width, and with each of said band pass filters receiving said output signal from said variable gain switch as an input signal; said AM detector means includes a respective AM detector connected to the output of each of said band pass filters; said third circuit means includes respective shaping circuits for shaping respective output signals from each said AM detector, and switch means for selectively enabling one of said shaping circuits; and said third circuit means is connected to the output of each of said shaping circuits.
- 4. Apparatus as defined in claim 3 wherein: said detector means comprises a length of shielded cable including at least one center conductor surrounded by a dielectric; and said first circuit means includes means, connected to one end of said cable, for sensing changes in the electric field signal generated by the stressing of said cable dielectric due to flexing of same by movement of the partition and for producing an electrical signal corresponding to the sensed electrical signal.
- 5. Apparatus as defined in claim 4 further comprising LED bar display circuit connected to the output of each of said shaping circuits.
- 6. Apparatus as defined in claim 4 wherein said third circuit means includes fourth circuit means for producing an output signal in response to the output signal of the enabled one of said shaping circuits having a duration less than a first predetermined short value, a counting circuit means for counting output signals produced by said fourth circuit means and for producing an output signal in response to said counting circuit means reaching a predetermined count within a preset period of time, and an alarm circuit for producing an alarm signal in response to said output signal from said counting circuit means, whereby protection against intrusion by breaking through the partition to be protected is provided.
- 7. Apparatus as defined in claim 6, wherein said third circuit means includes: fifth circuit means for providing an output signal whenever the output signal of the enabled one of said shaping circuits has a duration greater than said first predetermined value, and an additional circuit means responsive to the output signal from said fifth circuit means and being in communication with said alarm circuit such that said alarm circuit produces an alarm signal when said fifth circuit means produces an output signal for a predetermined portion of a preset time period, whereby intrusion by sustained activity events aimed at breaching the partition can be determined.
- 8. Apparatus as defined in claim 4 further comprising means for monitoring a dc voltage level on said cable and for producing a tamper alarm when said level differs by a preset amount from a reference value.
- 9. A method of selecting a frequency band using the apparatus of claim 5, the method comprising the steps of:
- (a) applying a predetermined stimulus to said cable;
- (b) observing the indication on said bar display while each of said shaping circuits is selectively enabled; and
- (c) selecting and enabling the one of said shaping circuits which produces the highest level output on the bar display; and
- (d) enabling the pass band associated with said selected and enabled shaping circuit, whereby said frequency band is selected.
- 10. The method as defined in claim 9 further comprising the step of setting said variable gain switch while observing said bar display to provide a predetermined gain.
CROSS-REFERENCE TO RELATED APPLICATION
This application is a Continuation-In-Part of Applicants' U.S. patent application Ser. No. 07/669,430, filed Mar. 15th, 1991, now abandoned.
US Referenced Citations (4)
Continuation in Parts (1)
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Number |
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669430 |
Mar 1991 |
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