GB2196161A - Intruder detection - Google Patents

Abstract

In an intruder detection system for installation in a building equipped with mains wiring for power and/or lighting, communication between the intrusion sensors and the control box are effected by superimposing data signals on the existing mains wiring. <IMAGE>

Description

SPECIFICATION Intruder detection The present invention relates to intruder detection and seeks in particular to provide an intruder detection system that may be installed simply within a building.

When installing an intruder detection system in a building, it is necessary to provide communication between sensors of different types and a control box. Existing equipment falls into two sectors namely systems which use wireless communication and those in which dedicated wiring needs to be installed.

Wired systems are simple in design and construction but are expensive, troublesome and time-consuming to install. Wireless systems are complex in design and construction and as a result more expensive, but are less secure and not as reliable as the wired systems.

With a view to mitigating the above problems experienced in the prior art, the present invention provides an intruder detection system for installation in a building equipped with mains wiring for power and/or lighting, in which the communication between the intrusion sensors of the system and the control box are effected by superimposing data signals on the existing mains wiring.

The system of the present invention makes use of existing domestic, office or factory wiring which will afford the reliability of wired systems whilst reducing the time, trouble and expense of installation.

The system preferably uses the mains circuits in the building not only for communication but also as a source of power. As will be explained in further detail below, mains circuits are particularly suitable for this application. A reduction in the quantity of components incorporated in the system is achieved by utilising large scale integrated parts where practicable, and by not utilising radio communication.

In the preferred embodiment of the invention, use is made of microprocessors in key areas.

This enables the system to perform tasks using software instead of copious amounts of expensive hardware. Microprocessors also make possible the use of operator interfaces that are compact, respond intelligently and are easier to use.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block circuit diagram showing the whole of the intruder detection and alarm system, Figure 2 is a block diagram the controller shown in Figure 1, Figure 3 is a block circuit diagram of the user interface shown in Figure 1, Figure 4 is a block diagram of a detector shown in Figure 1, and Figure 5 is a block diagram of the sounder/beacon shown in Figure 1.

List of abbreviations used in the text, and definitions.

GDS General Design Specification IDAS Intruder Detection and Alarm System PIR Passive Infrared ROM Read Only Memory RAM Random Access Memory (read and/or write) sync abbreviation for synchronisation PIN personal identification number LED Light emitting diode LCD Liquid crystal display program a set of software statements submitted as a unit to a processor based system and used to direct its behaviour.

programme a list of instructions or operating strategy entered by an operator into a processor based system.

System Requirements.

Referring to the System Block Diagram of Figure 1, the system comprises the following functional units: i) Controller-continuously monitors the status of all installed Detectors, administers communication with the User Interface and issues a control signal to the Sounder/Beacon.

ii) User Interface-incorporates all facilities necessary for the user to monitor and control the system.

iii) Detector/s-Detectors can be connected either to the lighting main or the power (ring) main which they will use as a communication link and a source of power. The Detector contains a passive infrared sensor which is designed to respond only to changes in infrared radiation caused by movement of warm/hot bodies. The Detector also incorporates a panic switch for use in the instance of a personnel attack.

iv) Sounder/Beacon--the Sounder/Beacon is fixed to the building's external wall and provides both audible and visual annunciation of an alarm condition.

The system can monitor up to 33 detectors identified numerically as 0.1....32. Detector O is incorporated in the User Interface, therefore a minimum system will at least monitor the main point of entry to the building. Detectors are supplied with a pre-configured numeric identity which makes them unique in a given system. The concept of detection zones can be ignored if the user so wishes. If the user requires detection zones, the system can be configured with up to nine, comprising one detector in zone 0 and up to four detectors in each of zones 1 to 8.

The facilities offered by the system are provided by a combination of hardware and software.

The software construction is based on the use of a general purpose real-time multi-tasking executive-facility. Use of an executive ensures the system software design is modular and coherent, and subsequently ensures that the system will be more reliable, maintainable and extendible.

Controller.

With reference to the block diagram of Figure 2, the system Controller design is based on a microprocessor, providing for flexible operation, adaptation to differing requirements and a reduced parts count. All functions carried out by the hardware in the Controller are under the supervision of the software program configured into the program memory (ROM).

The operating software is conditioned by data contained in the data memory (RAM) which is updated as a result of programme control data input at the User Interface or the software in response to the detection of system events. The data memory also contains secondary data for the purpose of checking the validity of the primary data.

The Controller is self configuring, and will readily amend its configuration to accommodate system alterations provided the correct procedures are observed.

The Controller, at regular intervals, tests and verifies the validity of its software and data, and the hardware for correct operation.

Correct software operation is monitored by a 'Watch dog' circuit which will detect out-ofprogram errors caused by excessive noise interference. In such instances the 'Watch dog' will invoke a controlled automatic recovery to program control.

Allied to the microprocessor is a crystal controlled clock providing an accurate timing signal to the microprocessor, and also to the timer counters for the purpose of Detector signal validation, serial communication baud rate generation and software task timing.

The serial communication interface (SCI) is used to maintain contact with the User Interface in order to update the Controller's data base with respect to the handling of signals received from the Detectors. Communication through the SCI must observe a clearly defined protocol and are accompanied by error detection codes. It is not deemed necessary within the context of the present invention to provide a detailed description of the protocol and error detection method.

Signalling and communication are routed through a mains interface comprising an astable oscillator, signal detector, impedance matching device and mains blocking capacitor. The 'sync' circuit ensures that the processor can maintain correct synchronisation with the various phases of signalling and communication.

The Controller incorporates two 'clean-up' circuits that effectively terminate and isolate the signals on the lighting main from power (ring) main.

The alarm (Sounder/Beacon) is activated as a result of a valid discontinuity or degradation of mains power and/or the signal/s received from the Detector. This concept endows the system with the ability to be generally tamper proof. The Controller incorporates a tamper detection device which will generate an alarm in the event of an attempt to gain access to its internal structure.

A key operated switch is included to facilitate alarm inhibition.

User Interface With reference to the block diagram of Figure 3, the User Interface incorporates all the facilities necessary for the user to exact and maintain control of the system. The User Interface is designed around a microprocessor affording ease of use concomitant with pseudo-intelligence, flexibility, and reduced parts count.

All functions carried out by the hardware in the User Interface are under the supervision of the software program configured into the program memory (ROM).

The operating software is conditioned by control data contained in the data memory (RAM) which is updated as a result of user input via the keyboard or control data received from the Controller unit.

The data memory will also contain secondary data for the purpose of checking the validity of the primary data.

The User Interface incorporates a 'Watch dog' circuit for detection of out-of-program errors caused by excessive interference noise. In such circumstances the 'Watch dog' will invoke a controlled automatic recovery to program control.

Allied to the microprocessor is a crystal controlled clock providing an accurate timing signal to the microprocessor, and also to the timer counters for the purpose of serial communication baud rate generation, local sounder control and software task timing.

The serial communication interface (SCI) is used to maintain a dialogue with the Controller in order to update its data base with respect to the handling of signals received from the Detectors. Communication is routed through a mains interface comprising a signal detector, astable oscillator, impedance matching device and mains blocking capacitor. The 'sync' circuit will ensure that the processor can maintain correct synchronisation with the communication phase.

The keyboard, indicator panel and local sounder provide the operator with the means of setting and unsetting the system (or the required parts of it), and visual and audible indication of system status. These function blocks fall into the user facility category and are described in more detail below.

The User Interface incorporates a tamper detection device which will generate an alarm in the event of an attempt to gain access to its internal structure.

Detector/s With the aid of the block diagram of Figure 4, the function of the blocks comprising the Detector will now be described.

Infrared radiation incident upon the detector is focused on to a dual element passive infrared (PIR) sensor by a multi-element Fresnel lens. The PIR sensor is specially constructed to respond only to the differential of the infrared radiation incident at the elements. This property affords a high degree of immunity from response to variations in ambient infrared radiation levels.

A secondary benefit of using a PIR sensor for intruder detection is that it has a limited ability to detect fire, although, if fire detection is important, the use of a smoke detector is considered preferable.

The small signal generated by the PIR sensor is amplified by a gain circuit based on a high input impedance operational amplifier. Providing the amplified signal is changing rapidly enough it will then be fed to a comparator configured to respond only to signals that are above a set threshold level.

A 'panic' switch is incorporated for use in instances of personnel attack. Because lighting controls are sited near to points of room entry/exit and are readily accessible, the inclusion of -a panic switch is seen as being particularly beneficial. The Detector incorporates a tamper detection device which will generate an alarm in the event of an attempt to gain access to its internal structure.

The synchronisation (sync) circuit extracts one half cycle of the 50 Hz mains signal for use as a frame in which the Detector transmits its pulse encoded status information. The onset of the sync pulse triggers a delay circuit. The delay time constant is a pre-programmed function of the Detector identity number which is unique for a given system. The delay circuit signals its timeout to the differentiator by changing state. The output pulse from the differentiator gates (enables) an astable circuit set to oscillate at a super-sonic frequency. The pulse of super-sonic frequency is then fed to the impedance matching device.

Each Detector in the system will have a particular time slot, referenced to the on-set of the sync frame, in which to transmit its pulse sequence encoded status information to the Controller.

To reduce the need for wire runs Detectors are incorporated in special lighting switch housings which are fixed in place of the usual lighting switch for the room. In addition to using the mains circuit to communicate status information, Detectors will draw the small amount current necessary to power their circuitry.

As an alternative to Detectors fixed at lighting control points, and because this may not always be an ideal surveillance site in a room, Detectors can be supplied in forms suitable for connection to the power (ring) main via a 13 Amp plug or switched isolator. These Detectors are otherwise identical, internally, to the ones connected to the lighting main.

Status signals transmitted by Detectors connected to the lighting main are isolated from the status signals transmitted by Detectors connected to the power (ring) main by the 'clean-up' circuits in the Controller.

Sounder/Beacon This unit is fixed to an external wall affording the most conspicuous placement for alarm annunciation. Referring to the block diagram of Figure 5, the battery powered Sounder/Beacon is connected to the Controller by a two core cable. This inter-connecting cable serves two pur poses, namely to carry a trickle charge current to the battery and an alarm 'hold off' signal to the signal detector circuit.

Verification of the signal transmitted by the Controller are performed by the signal detector.

Should this signal deviate outside of prescribed limits, both the Sounder and Beacon circuits will be activated. The 'hold off' signal is interrupted by an enclosure tamper detector if an attempt is made to gain access to the Sounder/Beacon internals.

The Sounder circuit consists of a warble oscillator, an amplifier and a speaker. The Beacon circuitry is similar to that of the stroboscopic lamps used for road works warning. The Beacon flashes in sympathy with the warble tone.

User Facilities All user facilities are made available by a combination of hardware and software.

System Configuration The system can automatically configure or reconfigure itself for different numbers and mixes of Detectors. A Detector can be installed or removed at any time with minimal effort. Prior to removal the relevant Detector must be disabled. The system provides a default personal identifi cation number (PIN) for first time entry to the system program amendment mode. The users first action will be to create their own PIN for subsequent use. Once the user PIN has been created use of the default PIN will be prohibited.

System Programming All system programme amendments may be carried out by key depression sequences at the User Interface keyboard. Any alterations to the operating programme must be preceded by the entry of the user's 4 digit personal identification number (PIN).

The user will be able to make all necessary programme amendments subsequent to the entry of the PIN. The changes will be effected when the operator exits the programme amendment mode by depressing the ENTER key twice in succession. For security reasons the period between key depressions, whilst in the programme amendment mode, will be timed. If the time out is allowed to elapse the system will automatically exit this mode and no programme updating will be carried out. The system programme amendment facility will allow the user to amend the PIN should they so desire.

Temporary PIN The user can create a temporary PIN for use by, for example the baby sitter or the pet minder. Users of the temporary PIN will be restricted to setting/unsetting zones/detectors and resting alarms. The user will be able to delete the temporary PIN when it is no longer required.

Setting and Unsetting Detectors As previously stated Detectors can be grouped into zones. The keyboard offers facilities to set or unset individual Detectors or all installed Detectors in a zone. In addition the user will be able to set or unset all Detectors in the system.

System Test The user can verify that the system is in functional order. All indicators including the local sounder and the Sounder/Beacon will be exercised for approximately 30 seconds.

Alarm Resetting An alarm condition or pending alarm condition is cancelled upon exit from the programme amendment mode.

System Status Indication The system will indicate its status by both audible and visual means.

Visual Indications The status of any active remote Detectors will be indicated on a liquid crystal display (LCD) at the User Interface. The display will indicate: a) a target has been detected b) a target has been detected and an alarm is pending c) a target has been detected and an alarm has been issued d) the 'panic' switch has been depressed e) a tamper detector has been activated.

The User Interface is equipped with a fault and an alarm override indicator. The fault indicator shows that a system failure has been detected, and that it has not been possible to effect a recovery. The alarm override indicator will convey the state of the key operated manual override switch at the Controller (refer also to section 3.4).

Audible Indication.

Audible indication of system status is provided by the Sounder/Beacon unit and the local sounder at the User Interface. The Sounder/Beacon indicates a valid alarm condition resulting from detection of an intruder, or depression of a 'panic' switch or a power failure. The Sounder/Beacon will remain active for 20 minutes and then cease. The local sounder will indicate a pending alarm condition for a short time prior to activation of the Sounder/Beacon and will continue to operate until the user resets the system.

Manual Override A manual override facility is provided for the purpose of disabling the Sounder/Beacon. This facility is intended for use in the event of a legitimate circuit or power failure or during installation and commissioning.

Error Conditions There now follows a description in outline of the system's ability to cope with hardware, software and user errors. Where possible an automatic recovery will be attempted. Detector signalling errors caused by noise interference is averaged out by a majority vote acceptance process. Communication error handling is inherent in the protocol.

Hardware Errors.

In the event of a temporary hardware fault being detected, the software attempts to recover from it by re-initialisation. If re-initialisation fails then the software attempts to bring the error to the notice of the user by signalling a fault at the User Interface.

Software Errors.

In the event of a software crash owing to noise interference, the hardware 'watch dog' monitor will automatically invoke a re-start of the operating program.

User Errors.

User errors are expected to fall into one or more of the following categories, namely; (i) syntax errors-incorrect key sequence entries, (ii) security errors-improper attempts to gain access to the system or attempts to execute commands or programme changes without the requisite PIN security clearance, (iii) illegal programme amendments--attempts to amend the programme status of non-existent parts of the system.

The above categories will be expanded into error definitions, and methods of detection, recovery and reporting in the software requirement specification.

The system described above has a controller which is separate from the user interface but it is possible to combine the two functions within the same unit. It will be noted from the circuit diagrams given for the two units that they have many items of hardware in common and by combining the two units it is possible to avoid a certain amount of duplication.

In a combined controller and user interface unit, there need only be a single microprocessor, though the program will of necessity need to be modified to achieve the two separate functions described previously. It is unnecessary to isolate the signals on the power circuit from the signals on the lighting circuit and the two can be treated as one circuit thereby further simplifying the construction and avoiding duplication.

In the embodiment described by reference to the drawings, the need for separation of the signals on the lighting and power circuits arose chiefly because the communications between the controller and the user interface occupied half of the available time slots. As such communication is no longer necessary in a combined unit, these time slots are freed and this allows the same number of detectors to be used without isolating the signals on the the lighting circuit from those on the power circuit.

The connection between the controller and the sounder/beacon may be hard wired, but it is preferred that the main supply also be used for communications between these two units, so that the sounder/beacon may also be plugged into the nearest convenient power point. A hold off signal is transmitted to the sounder/beacon through a time slot on the main supply.

Enhancements and Developments.

The system will allow for future improvements and customer options by providing for microprocessor bus extension. This feature plus any additional software to be integrated with the basic software, will provide the means to extend the system by adding function boards. Alternatively, additional system tasks can be accommodated by the connection of new function units to the mains circuit.

Amongst the features which may be incorporated in the system, the following in particular are noted: (i) Incorporation of a calendar clock at the User Interface.

(ii) Incorporation of lighting dimmer controls at Detector sites. These could be either rotary control type or touch sensitive control type.

(iii) The facility to turn selected lights on for periods, giving the impression that the dwelling is occupied when it is not.

(iv) Incorporation of smoke detectors into the system.

(v) Incorporation of baby listeners into the system.

(vi) Incorporation of fridge/freezer fault detectors into the system.

(vii) Incorporation of heating control and economy monitoring providing for higher efficiency in homes and offices.

(viii) Incorporation of automatic dialling and forwarding of alarm notification utilising pre-configured synthesised speech messages.

(ix) Tailoring of the system to meet the needs and budget of people at risk, such as the aged and the disabled. This could also involve the forwarding of pre-configured synthesised speech messages for the purpose of alerting a service centre.

(x) Another application for synthesised speech message forwarding to a service centre is that of sub-post office, small building society branches and monetary exchange bureau. In this instance the message could be communicated silently whilst a crime is being perpetrated.

The list above although not exhaustive serves to illustrate some of the enhancements that could be made to this system. The ability to extend the system and its ability to communicate to function units linked to common mains circuits and sharing a common communication protocol, makes it both easy and economical to extend the system to incorporate new tasks.

The main advantage of the invention, as described above, resides in the ease of installation which results directly from the use of existing mains wiring for the communication between the individual modules which constitute the system. It is particularly convenient to include the detectors in light switches but because such switches may not be well positioned power sockets may be used as suitable sites for locating the detectors. As a further option, the detectors may be included in ceiling fittings such as light roses. The latter option has the advantage that the ceiling light is normally well positioned to "see" all parts of a room and offers easy access to both the live and the neutral side of the lighting main.

Claims (7)

1. An intruder detection system for installation in a building equipped with mains wiring for power and/or lighting, in which the communication between the intrusion sensors of the system and the control box are effected by superimposing data signals on the existing mains wiring.

2. An intruder detection system as claimed in claim 1, wherein the mains wiring in the building serves not only for communication but also as a source of power.

3. An intruder detection system as claimed in claim 1 or 2, wherein signalling between the detectors and the control box is synchronous, each detector having allocated thereto a time slot fixed in reiation to the phase of the mains supply.

4. An intruder detection system as claimed in any preceding claim, wherein the control box incorporates a microprocessor.

5. An intruder detection system as claimed in any preceding claim, wherein the system includes a sounder activated by the control box through a signal on the mains supply.

6. An intruder detection system as claimed in any preceding claim, wherein the detectors are formed integrally with a light switch, power socket or ceiling rose.

7. An intruder detection system constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

7. An intruder detection system as claimed in any preceding claim, wherein a device for issuing an alarm in instances of personnel attack is incorporated in the detector(s).