EP0448290A2 - Eindringmeldeanlage und Schaltungsanordnung zur Signalverarbeitung hierfür - Google Patents

Eindringmeldeanlage und Schaltungsanordnung zur Signalverarbeitung hierfür Download PDF

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Publication number
EP0448290A2
EP0448290A2 EP91302176A EP91302176A EP0448290A2 EP 0448290 A2 EP0448290 A2 EP 0448290A2 EP 91302176 A EP91302176 A EP 91302176A EP 91302176 A EP91302176 A EP 91302176A EP 0448290 A2 EP0448290 A2 EP 0448290A2
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EP
European Patent Office
Prior art keywords
signal processing
signal
output
circuit according
sensor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP91302176A
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English (en)
French (fr)
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EP0448290A3 (en
Inventor
Ian C/O Geoquip Limited Macalindin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Geoquip Ltd
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Geoquip Ltd
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Filing date
Publication date
Application filed by Geoquip Ltd filed Critical Geoquip Ltd
Publication of EP0448290A2 publication Critical patent/EP0448290A2/de
Publication of EP0448290A3 publication Critical patent/EP0448290A3/en
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/16—Actuation by interference with mechanical vibrations in air or other fluid
    • G08B13/1654—Actuation by interference with mechanical vibrations in air or other fluid using passive vibration detection systems
    • G08B13/169—Actuation by interference with mechanical vibrations in air or other fluid using passive vibration detection systems using cable transducer means

Definitions

  • the present invention relates to an intrusion detection system and in particular to signal processing circuitry therefor.
  • suitable processing circuitry is not without its difficulties if the circuitry is to maintain an adequate degree of sensitivity on the one hand while avoiding an excessive false alarm rate on the other. Difficulties arise from a number of sources, for example, wind noise being picked up by the transducer and the fact that the noise picked up for a given mechanical stimulus of the fence varies with the fabric of the fence. Further, different methods of attempted intrusion result in transducer output signals having different time signatures. A contributory factor to the false alarm rates of existing systems is the need for the processing circuitry to attempt to distinguish signals which genuinely reflect an attempted intrusion from those that do not.
  • an intrusion detection system incorporating an intrusion sensor comprising one or more microphonic mechanical to electrical transducers, signal processing circuitry for monitoring the output of the sensor and signalling an alarm condition on detection of mechanical stimulation of the transducer corresponding to an attempted intrusion, the signal processing circuitry having a number of parallel signal processing channels each adapted to monitor the transducer output signal and to respond to a set of predefined characteristics of the signal indicative of the type of mechanical stimulus of the transducer.
  • the transducer is a sensor cable in accordance with our above reference British patent, a commercial form of this cable being marketed by the Geoquip Limited under the name Guardwire GW300k.
  • the cable may be taken to be threaded through the links of a chain-link fence, and so will produce signals in response to vibrations caused by the mechanical disturbance an intruder induces in the fence or barriers as he climbs over or cuts through the barrier.
  • a cut-through type of attack where tools such as wire cutters, bolt croppers, hacksaws, files, etc, may be used to physically breach the fence
  • a climb-over type of attack where the intruder actually scales the fence and defeats the barrier in that way.
  • Each type of attack normally produces a distinctly different signature in respect of the signals produced by the sensor cable.
  • a cut-through attack will usually produce a series of impulses caused as the intruder cuts each strand of the fence wire to make a hole large enough to crawl through. Each impulse is characterised by a sudden change in the background noise level which most fences make anyway.
  • a climb-over type of attack is usually characterised by a protracted high-level signal caused as the intruder scrambles up to the top of the fence.
  • circuitry of figure 1 is intended to address the particular requirements of each type of attack signature so that we should be able to set the system controls to more accurately respond to a particular situation.
  • the system therefore has two separate channels, each dedicated to the task of responding only to that particular mode of attack.
  • the sensor cable 1 is connected to a high-gain low-noise front end stage as indicated at 2 in figure 1.
  • the sensor cable now employs an end-of-line resistor 3 to offer enhanced monitoring of the integrity of the sensor cable (by monitoring its electrical continuity).
  • the front end stage 2 may comprise an amplifier 2A transformer-coupled at 2B to the cable to achieve a high immunity to the effects of electrostatic discharges (ESD) close to the sensor cable compared with traditional co-axial systems where the front-end amplifier is directly coupled to the sensor cable.
  • ESD electrostatic discharges
  • Transformer coupling between the sensor and the signal processor also makes the system much more tolerant to the effects of radio frequency interference (RFI) by virtue of the common-mode rejection of the input transformer.
  • RFID radio frequency interference
  • the output of the front-end stage is effectively an audio signal which is fed to a notch filter 4, after which it is split into two separate signal processing paths 5A, 5B as shown in figure 1 which act as "cut” and "climb” channel filters, respectively.
  • the purpose of the notch filter is to remove any interference which may be induced into the sensor cable from 50 Hz (in the UK, 60 Hz in the USA) power sources in close proximity to the sensor cable.
  • the screen of the sensor cable 10 is formed from aluminium tape and, being non-ferrous, does not provided screening against the effects of stray magnetic fields which may be associated with 50 Hz power sources.
  • the audio signal from the notch filter 4 is fed to a filter board carrying the channels 5A, 5B via a multi-pin connector on the main board where it is split into two separate filter channels.
  • Each filter channel comprises a quad operational amplifier configured as a Sallen/Key equal component value filter 6A, 6B, each stage of which can be produced as either a high-pass or a low-pass section.
  • One set of filter parameters which has been found effective in practice is as follows:
  • Cut channel filter 6A 6th order high-pass section following a 2nd order low pass section.
  • Climb channel filter 6B 6th order low-pass section.
  • cut detection information is extracted from the audio signal content above 723 Hz and below 1.6 kHz while climb information is extracted from the audio signal content below 159 Hz, and the respective signals from the outputs of filters 6A, 6B have these spectra.
  • the filtered signals are passed to switchable gain stages 7A, 7B with control settings independently adjustable for each channel on a scale of 0 to 9.
  • Switchable gain stages may be preferable to continuously variable controls in that they permit repeatability in setting thereby easing the task of system optimisation.
  • the filtered signals from each channel are subject to different gain ranges to compensate for the difference in energy levels of the signals coming from the filter stages.
  • the energy content of a particular band of frequencies is a function of the bandwidth selected as well as the response of the fence fabric to a particular stimulus.
  • the AC signals are rectified and smoothed to an extent by the peak detectors 8A, 8B so that the unidirectional analogue voltage resulting form this stage tends to follow the 'envelope' of the applied AC signal.
  • the time constants of the precision rectifiers in the peak detectors should be carefully chosen to allow the resulting voltage to faithfully track the outline of the applied AC signal.
  • the unidirectional analogue voltages then pass into the analyser circuits 9A, 9B designed to respond only to:
  • Signals resulting from a combination of a) and b) are detected by the OR-ing together of the two channels 5A and 5B.
  • Each analyser circuit 9 is entirely different in design since the two types of stimuli exhibit entirely different characteristics.
  • the circuitry in the upper channel 5 dedicated to the cut detection relies on the signal from the filter satisfying 3 key characteristics in a certain order before it is classed as an 'event'.
  • the signals extracted from the audio signal by the low-pass filter circuit are fed into a peak detection circuit which generates an 'envelope' waveform, the outline of which tracks the peak levels of the low-pass filter output.
  • This 'envelope' waveform is integrated by a simple R-C circuit, the output of which is fed to a voltage comparator. If the 'envelope' waveform from the peak detector remains at a high level for a long enough period of time, the integrator output will rise at a rate determined by the R-C values until the threshold level of the voltage comparator is exceeded. When the threshold level is exceeded, the alarm circuit of the analyser is triggered, irrespective of any of the control settings associated with the 'cut' section of the analyser system.
  • the integrator output decays at the same rate as it rises since the same R-C components also control the decay of the voltage.
  • the circuit will therefore take longer to respond to an intruder climbing up the fence than it would to an intruder using a tool such as a disc cutter to hack a hole through the fence, where the signals generated would be at a consistently high level for a reasonable length of time.
  • the R-C components chosen for the integrator require the signals to be present for at least 1.5 seconds.
  • the cut analyser classes such an occurrence as an 'event' and the analyser 9A produces an output pulse which is counted by an events counter 10.
  • an 'event' occurs it can, taken alone, indicate an alarm condition.
  • the 'events' control 11 on the processor card must be set to position 1.
  • the setting of a timer switch 12 has no effect on the operation of the circuitry. If more than 1 'event' is selected, then that number of 'events' must occur within the time window set by timer circuitry 13 for the alarm to be operated.
  • the time window is initiated on receipt of the first 'event' and continues to operate until either the alarm is operated or until any 'events' accumulated in the system memory are decremented to zero which will occur after the time period equal to the number of stored 'events' multiplied by the 'timer' interval selected had elapsed.
  • Each increment on the 'timer' control switch suitably corresponds to a 30 second time interval.
  • the above described system offers two separate sensitivity controls each of which can be set independently of the other to enable the user to 'tailor' the system more closely to his needs.
  • Some users have, in fact, a requirement to respond only to one particular mode of attack - usually cut-through - so if they have the option to effectively turn off the other channel be reducing its sensitivity to a low level, he immediately gains the advantage of eliminating all the potential false alarms caused by this section of the circuitry. In such an application, this would result in a considerable increase in system performance when compared to the more traditional single-channel systems currently available.
  • the processing circuitry can be constructed in a manner which addresses some of the problems introduced by the wide variation of perimeter fence types by allocating separate plug-in analog filters to each processing channel thereby allowing a degree of optimisation of the system response to the various introduced by the response of different fence fabrics to similar stimuli.
  • the above described embodiment relates to a single zone system for outdoor perimeter fence protection and which can be adapted for building fabric protection.
  • the system may also be adapted to offer dual zone protection within a single box, and to systems in which analogue signals are sent back from remotely sited sensor cables and interface units to a central processing unit which determines the system response to the signals received.
  • the invention has been described by reference to its application to perimeter fences and cut and climb intrusions, it is not limited to that application, not those methods of intrusion.
  • the invention is also applicable to the protection of buildings from intrusion by breaches of the main fabric of their structure, ie, roof and walls.
  • the two commonest intrusion methods are impact intrusion (eg, by use of a hammer and chisel) which produces a series of short sharp bursts of information which, because of the rapid rate of rise of the signals, pass easily through the differentiation circuitry of the analyser, and sustained attack (eg, by use of an electrical drill or disc cutter).
  • the sustained mode of attack can be processed in the same way as the climb signals in the above fence application.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Burglar Alarm Systems (AREA)
EP19910302176 1990-03-14 1991-03-14 Intrusion detection system and signal processing circuitry therefor Withdrawn EP0448290A3 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB909005751A GB9005751D0 (en) 1990-03-14 1990-03-14 Intrusion detection system and signal processing circuitry therefor
GB9005751 1990-03-14

Publications (2)

Publication Number Publication Date
EP0448290A2 true EP0448290A2 (de) 1991-09-25
EP0448290A3 EP0448290A3 (en) 1992-09-30

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19910302176 Withdrawn EP0448290A3 (en) 1990-03-14 1991-03-14 Intrusion detection system and signal processing circuitry therefor

Country Status (2)

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EP (1) EP0448290A3 (de)
GB (2) GB9005751D0 (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0612047A1 (de) * 1993-02-19 1994-08-24 GEUTEBRÜCK GmbH Verfahren zur Auswertung elektroakustischer Signale
WO1994020937A1 (en) * 1991-09-09 1994-09-15 Hitek-Protek Systems Incorporated Intrusion detection apparatus
GB2290614A (en) * 1993-03-10 1996-01-03 Hitek Protek Systems Inc Intrusion detection apparatus
US7881882B2 (en) * 2006-09-25 2011-02-01 Ut-Battelle, Llc Apparatus and method for detecting tampering in flexible structures

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2045494A (en) * 1979-02-23 1980-10-29 Elliott Brothers London Ltd Intruder alarm system
US4365239A (en) * 1980-11-20 1982-12-21 Stellar Systems, Inc. Intrusion warning system

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4023156A (en) * 1975-01-30 1977-05-10 American District Telegraph Company Alarm system for detecting disturbance of a solid medium
US4845464A (en) * 1988-08-09 1989-07-04 Clifford Electronics, Inc. Programmable sensor apparatus
GB2221990B (en) * 1988-08-17 1992-04-08 Shorrock Ltd Intrusion detection system

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2045494A (en) * 1979-02-23 1980-10-29 Elliott Brothers London Ltd Intruder alarm system
US4365239A (en) * 1980-11-20 1982-12-21 Stellar Systems, Inc. Intrusion warning system

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1994020937A1 (en) * 1991-09-09 1994-09-15 Hitek-Protek Systems Incorporated Intrusion detection apparatus
EP0612047A1 (de) * 1993-02-19 1994-08-24 GEUTEBRÜCK GmbH Verfahren zur Auswertung elektroakustischer Signale
GB2290614A (en) * 1993-03-10 1996-01-03 Hitek Protek Systems Inc Intrusion detection apparatus
US7881882B2 (en) * 2006-09-25 2011-02-01 Ut-Battelle, Llc Apparatus and method for detecting tampering in flexible structures

Also Published As

Publication number Publication date
GB9105419D0 (en) 1991-05-01
GB2242745A (en) 1991-10-09
GB9005751D0 (en) 1990-05-09
EP0448290A3 (en) 1992-09-30

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