AU635782B2 - Alarm system - Google Patents

Description

635782 COMMONWEALTH OF AUSTRALIA Patents Act 1952 SO S

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*.oS Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: AUTOMATION ENGINEERING LIMITED 227 Neilson Street, Onehunga, Auckland, NEW ZEALAND.

COLIN RICHARD DILLICAR.

GRANT ADAMS COMPANY Patent Trade Mark Attorneys Level 9 NATIONAL MUTUAL CENTRE 144 Edward Street BRISBANE QUEENSLAND 4000

AUSTRALIA.

FOR THE INVENTION ENTITLED: @505

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COMPLETE SPECIFICATION "ALARM SYSTEM" The following statement is a full description of the invention including the best method of performing it known to the applicant.

Nhl 2 THIS INVENTION relates to an alarm system for commercial, industrial, domestic, or other use, to monitor alarm conditions, including -the presence of intruders within the premises so monitored, heat or fire, or to monitor process conditions in a factory or the like.

Hitherto, remote alarm stations have relied upon a number of sensors installed in the premises, and connected to a telephone line, so that the alarm. unit would send a signal through the public telephone system, or a leased line, to a.

monitory station. Such systems are. dependent upon the presence of telephone lines, the cost of leased or public telephone services, and the ability of the telephone system to cope with 24 hour monitoring, of premises. Public telephone systems are prone to overloading, or physical and perhaps malicious damage to the telephone lines and thus are not as reliable as, they should be f or a 24 hour monitoring system.

There is a need for an improved system which does not rely on telephone lines to communicate with the monitoring station.

It is an object of this invention to provide an improved alarm system, or one which will at least provide the public with a useful choice.

In one aspect, the invention provides an alarm system including: a wireless monitoring station; q~nd a group of remote alarm stations, each alarm station containing a wireless receiver, means for monitoring 0: alarm conditions, and means to send, at predetermined time intervals, a wireless signal to said monitoring station, and wherein each alarm station includes means for receiving a clock signal, and each alarm station is programmed to send a status signal to the monitoring station within a defined transmission window occurring at a predetermined time synchronised by means of a received clock signal, said window being started and stopped by a clock means within the alarm station, the clock means in all the alarm stations being started simultaneously by said clock signal, and wherein the transmission window of each alarm station differ from 2a that of each other alarm station in the group, so that the monitoring station can distinguish between the identity of the alarm stations dependent upon the transmission window of each respective alarm station in the group.

In the interval is short enough this status signal could include an alarm condition. The interval will vary depending upon the application and number of alarm stations monitored. If an alarm station monitors a factory process, eg a chemical process or an r a -3industrial freel:,.er the intervals could be of the order of say 30 minutes whereas in the case of a security alarm intervals of no more than 60 seconds an preferably of the order of 30 seconds would be more appropriate.

Preferably the clock signal is provided by a broadcast signal capable of being received by all of the alarm stations of a particular group, so that the alarm stations each respond to a common clock signal.

Preferably the broadcast is in the form of a clock signal superimposed on a public transmission utility, eg ordinary radio, television, Teletext, datacasts, radio data system (RDS), direct broadcasting satellite, or other transmission means which is preferably available on a 24 hour basis. Alternatively, the public utility could broadcast a signal on some form of widespread transmission network such as cable TV (in some cases a computer network) or perhaps a clock signal transmitted along the electrical supply i: lines, or along telephone lines or links e.g. by derived channel means (a subsonic transmission) or other means.

Preferably the clock signal is transmitted by means of a radio or television broadcast, S" 20 and more preferably by means of a RDS, television or Teletext signal as this enables each alarm station to have a relatively low cost transponder capable of detecting such signals and transmitting to the monitoring station also by a radio frequency signal. The vertical blanking interval of a television signal may be used either as a countable event or to carry data (as is the case for the Teletext protocol, which uses several television 25 lines immediately following the blanking period).

:The above are examples of existing broadcast technology while other broadcasting techniques, mediums, or protocols may become available in the future for use as synchronisation means and perhaps also instruction-transmitting means with the system of this invention.

By this means each alarm station can send a status signal of defined duration within a defined transmission window, so that the monitoring station can distinguish between each alarm station on the basis of the time separation of each transmission after a clock signal. Preferably each alarm station will also send a unique identity code as part of its status transmission.

-4- Preferably each transmission window is less than 20 milliseconds, and may be of the order of 10 milliseconds. On the other hand, reception of larger amounts of data from a smaller number of sites within the same overall group timing frame may result in longer transmission windows sent from individual stations.

In the case of a large number of alarm stations sending to a single monitoring station, it is possible to distinguish between each station on the basis of the respective transmission windows, even if the status signal is not fully received. If for example an alarm station is disabled (as by an intruder) it will fail to send its status signal at the required time (perhaps once every 30 seconds at the outside), and thus the monitoring station will trigger an alarm and notify the appropriate personnel to investigate the status of that alarm station. Similarly, if the alarm station fails to receive its clock signal and detects an intruder or alarm condition, it can send an alarm signal to the monitoring station by radio, independently of its normal clock synchronising signal.

These and other aspects of this invention, which should be considered in all its novel aspects, will become apparent from the following description, which is given by way of example only, with reference to the accompanying drawings, in which: Figure 1: is a block diagram showing the transmission equipment which may be used as a source of synchronising signals.

25 Figure 2: is a block diagram showing an alarm transponder including the flow of information.

Figure 3: is a block diagram showing the operation of the receiving equipment at the monitoring station.

Figure 4: is a flow diagram of the decision path re transmission within the alarm transponder units.

PREFERRED EMBODIMENT A preferred form of the invention will now be described with reference to a radio-based monitoring system. In this description reference will be made to public broadcast facilities presently available in New Zealand, but the description should be read in the light of similar or equivalent services available in the country where the alarm system of this invention is to be installed.

A prototype of this invention is designed to cater for up to 2048 alarm stations (transponders); however this number is given by way of example only and is likely to change depending on the size of area serviced, the distribution of subscribers within that area, the available transmission frequency, and available transmission window.

Preferably each transponder unit or its equivalent would accept a number of parallel inputs from some standard alarm controller, or alternatively from a serial input from a suitable controller, eg the applicant's AE model universal controller/dialer. In our experience with earlier alarm systems we have found that eight parallel inputs is a i convenient number of inputs to monitor alarm conditions within a typical office/factory installation. Of course, different numbers of inputs can be specified for different applications.

Preferably the condition of these inputs, or the serial data equivalent, would be transmitted to the monitoring receiver at regular intervals, via a suitably modulated VHF (or UHF., radio link.

In order to ensure that each transponder can be individually identified, and moreover 25 that each transponder transmits at a different time, a suitable method of synchronising all the transponders is needed. It is preferred that each transponder unit would incorporate a radio receiver for this purpose and that a centralised transmitter would provide synchronising signals conveniently to all transponders within a prescribed area.

The synchronising signals would preferably need to be transmitted at regular intervals, and these intervals should preferably be gret. ;r than the length of time that it takes for each of the transponders to report, one after the other from the first to last.

-6- It is preferred that all transponders should be able to send their data to the monitoring receiver within approximately 95% of the synchronising interval, and each transponder should therefore preferably send its reply within: 1 (total number of transponders serviced) of this synchronising interval.

Preferably the uource for this synchronising signal would be an existing transmitted signal that could provide such synchronisation, and thereby conveniently avoid the need for obtaining approvals and installing special transmitter facilities for this purpose. Preferably the identified broadcasting signal would be generally available throughout the country, with preferably strong signal coverage and therefore preferably of a reasonably high transmitter power. Preferably this strong transmission source would overcome the need for bulky equipment for transmission and reception and therefore removing the burden on the public subscriber to have to pay large sums of money to benefit from this system.

Within New Zealand at present there are three convenient signal sources available, and these are given by way of an example only. Sinailar signal sources are available in Australia.

Firstly, the synchronisation could for example be related to the hourly time pips 25 broadcast in the AM band by the National Programme of Radio New Zealand.

S: Secondly, the synchronising signal could preferably be transmitted on part of the subcarrier of commercial FM radio stations. Radio New Zealand provides the basic transmission facilities throughout the New Zealand, and such a synchronising or clock signal would be transmitted on a 24 hour basis without interfering with the program content of the various radio transmissions. An ideal European protocol for such transmissions to be carried by FM stereo transmissions has been publicised under the name of RDS or Radio Data System.

An alternative convenient source of signal is the Teletext signal transmitted via television channels. As yet Teletext is not available in New Zealand on a 24 hour -7basis. However, It is envisaged that Teletext will in the near future be available on a 24 hour basis when the television stations begin to broadcast around the clock, Preferably a backup transmission facility would be available to accommodate for any measure of time when the Teletext signal was unavailable.

One possible development of this system is to employ RDS c~r Teletext as a data transrssion medium, for example to send messages that control lighting, heating, or fire control means at a particular site, or messages to disable those sites for which fees have not been received.

Figure 1: Block diagram showing the transmission equipment which may be used as a source of synchronising signals. Figure la shows the arrangement for broadcasting the series of I KHz time pulses or pips that may be received throughout New Zealand for purposes such as synchronising seismographs. The occurrence of the commencement of the last of these time pips constitutes the time signal; there is no other inherent information to be decoded.

Figure lb shows the arrangement for broadcasting RDS data over a Frequency Modulated (FM) radio transmitter; for which time information may be encoded according to a particular protocol and embedded in a substantial amount of unrelated data.

.o Figure lc shows the arrangement for broadcasting time information within Teletext 25 signals; again the time information may be carried along with other data.

The blocks labelled 'control information' may from time to time include control information to be sent to one or more specifically addressed transponder units to cause changes of mode, or heating or lighting (for example) to be controlled at that remote site. Such control information would preferably be transmitted via the modem to the collating equipment at the site where the public programme is generated.

Alternatively, other transmission sources may become available in the future, however the examples given do provide some idea of the costs involved where the transmission facilities already exist, the receiver technology is well known, and components are mass produced.

It is preferred that the synchronising signal source transmits its signal at regular intervals, and by way of example, we prefer to use a 30 second interval as the systemwide timing interval; the timing means of each transponder. This could be achieved by using the hourly time pips broadcast by the National Programme on its broadcasting network. The transponder can, after receiving two such consecutive signals derive its own 30 second synchronisation interval as a submultiple of the basic hourly rate.

Working prototypes prove that an ac,uracy of better than one part in four million is achievable and that this is adequate for reliable system operation.

It is also possible to achieve synchronisation using teletext by inserting a unique page number into the teletext transmission at 30 second intervals. However, we prefer to use the clock data (available at the top of every Teletext page) and derive a local synchronisation on the zero and 30 second period. This method could also be used with RDS where the second is defined as part of a minute, and the time transmitted accurate at the time of transmission but not necessarily a precise interval.

By dividing the time interval, 30 seconds [or more conveniently 30,000 milliseconds by the number of transponders or alarm stations we can find thi- nber of time 20 slots in milliseconds, available within approximately 95-100% of the synchronisation period. For example if we had 2048 transponders we can divide 30,000 ms by 2048 with the result that 2048 x 14 ms time slots will fit into 28.67 seconds or approximately 95% of the synchronisation period. Preferably if we allow some leeway we can expect to be able t ransmit transponder responses with a duration of approximately 10 ms.

This conveniently allows some guard band between each, antu time for the transponder to get its transmission under way. If for example we used a data rate of 4800 we could send three or four ASCII characters of information, or alternatively some other nonstandard and unique code.

-9- The code could incorporate digital data to represent the following: a) Transponder address or sub-address b) The alarm data at the transponder c) a coded representation of the authorised user opening or closing the premises d) Check code to ensure that the data sent was received correctly.

e) A special security code to ensure system integrity.

The security code is a digital data bit value which represents a combination of address data, and other transmitted data encrypted with the program code contained within the transponder microprocessor. This means that any apparatus constructed to duplicate the operation of the transponder must be an absolutely exact copy of and contain the identical software code, thus infringing copyright in the code, and making loning' more difficult. If the code is not identical the decoding system will pinpoint the unauthorised equipment.

The description of operation described above shows how each of the up to 2048 .transponders sends its current status to the receiving station based on the correlation between its assigned address and a corresponding time slot within the overall thirty second cycle. A variation of the transponder address selection mode allowed for alteraAon of response time of transponders as follows:- Assume that the total number of transponder addresses to be 1024 instead of 2048, and 25 that addresses 1025 to 2048 are re-allocated as duplicates of addresses 1 1024. TI allows each of the 1024 transponders to report at 15 sec'nd intervals instead of the otherwise 30 second intervals, with each reporting twice within a cycle. Or, 256 Transponders could ha-e a 7.5 second reporting time, while the remainder report once every 30 seconds, such arrangements being set up simp!ly by altering addresses.

Combinations could extend down to one report every 14 milliseconds. A mode selection switch on each transponder enables the appropriate selection to be made, and the corresponding decoding is selectable in the microprocessor associated with the Receiver system. In the other direction, reception of larger amounts of data from a smaller number of sites within the same overall group timing frame may result in longer transmission windows sent from individual stations. There is considerable inherent flexibility.

It is preferred that in the absence of synchronising signals, the transponders and the receivers at the monitoring stations would need to default to a transmission by exception system, relaying their changed status for a preset number of transmissions with random time intervals between each burst. Preferably transponder ID will also have to be sent in this instance and it may be convenient, although not absolutely necessary, to send ID in the normal mode.

Figure 2: Block diagram showing an alarm transponder including the flow of information.

Figure 2 is a block diagram showing electronics modules connected to two antennae (above) and a number of connections to sensing or control transducers (below). The synchronisation receiver block detects the timing pulses in the particular public broadcast radio signal chosen for the purpose. The master clock signal so derived is fed e to the microprocessor block which adjusts its continually operating clock counting and correction factors according to the observed deviation. This continual internal clock operation is used, in conjunction with the selected address which sets the •moment of transmission within the system-wide clock to send (as per Fig 4) a packet S 20 of data to the Radio Transmitter block at the top of Figure 2 and hence to the receiving equipment (Figure The alarm interface block simply accumulates serial or parallel event data arriving on the connections shown, together with preferably switchselectable user code data, and forms it into a coded string of bits preferably compatible with the ASCII code. In some embodiments this interface may be simulated 25 by microprocessor software and buffers form the only separate physical part for the alarm interface block. Otherwise this interface may for e.xample be part of the "applicant's AE model universal controller/dialer.

The synchronisation receiver block within each transponder will incorporate a commercial tuner for the appropriate public transmission service (whether Teletext RDS (FM) or AM tie pips, being cheap, mass produced and reliable, with a suitable associated hybrid or I.F. strip. The signal source, for example the Teletext signal, would preferably be extracted from the video signal and processed as simply as possible to detect either the teletext clock data or a particular page header signal code which is used as the synchronising clock signal. In the case of tie RDS service decoding circuitry would extract the time portion of the coded message, or it may extract data other than the time information and may decode it to implement local control at the site, such as contr( heating in a building or security lights in its surroundings.

It is envisaged that as an added advantage to the system, extraction of some data other than (for instance) the Teletext header could allow for some management facilities to be incorporated, eg additional code within the page would also allow a service provider company to switch "on" or "off" alarm stations if the monitoring company or any one of its customers had defaulted on payment.

It is preferred that the transponder incorporates a microprocessor to use the synchronisation signal and fit the transponder response into its addressed time slot.

The microprocessor would also preferably handle the parallel and serial inputs to the 15 device and generate the appropriate response codes.

r o The transponder would preferably use the radio trailsmitter block to transmit on a suitable VHF frequency, with preferably one frequency being assigned to each "client ogroup" (a client group typically being one monitoring company or security firm and its associated customers in a given locality). It is preferred that each transponder will have a peak output power of approximately 30 watts so even if the transponder is operating from its backup battery (preferably 12 volts) it will operate for a considerable time ""because individual transmissions are so short in duration.

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25 Preferably the transponder transmitter modulation mode would be suitable to allow for the fact that the transmitter should go from no output to full output substantially instan- 1 taneously. We prefer to send the information via a transmission system comprising frequency shift modulation, thus providing a very simple system to reliably transmit data at 4800 Bd.

Figure 3: Block diagram showing the operation of the receiving equipment at the monitoring station.

In this diagram two antennae are shown. The synchronisation receiver block is connected to an antenna adapted for reception of the appropriate public broadcast. The receiver block itself consists of amplifying means then time data decoding means (if I~ t KK:, 1 -12necessary) to extract time data from the information received and to pass it to the microprocessor decoder block A high-gain communications receiver block may be required to pick up the data from the transponder stations and pass digital data to the microprocessor decoder. The decoder, with the database computer checks the incoming stream of alarm data for normality, and causes advice of changed or abnormal data to be advised to operators either directly (not shown) or via an automatic dial-up modem and telephone lines to a human operator at a remote monitoring station.

Figure 4: Flow diagram showing the operation of the transmitter within the alarm transponder units. A similar procedure is used within the central monitoring, or receiving station.

This diagram amplifies the method by which the timing of the system is maintained.

Flow may conveniently be assumed to start at the top of the diagram, at 'WAIT FOR CLOCK PULSE'. Prior to the arrival of a first clock pulse from an internal or external reference source (the latter situation being for clock pulses derived from public ,.broadcasts) the system operates in a random mode and broadcasts its data to the central Po. 20 monitoring station at random time intervals. This is, however, an abnormal state and it is desirable to leave it as quickly as possible. On the arrival of a first clock pulse after that uninitialised state, the system enters the preferable and normal timed mode. If the decision to transmit now is 'yes' (based on present time and remaining data to send) the system continues to transmit its present alarm status. If the decision is 'no' the system tests whether or not it has done all the transmission required and either reverts to its waiting mode or gets another piece of data to transmit and sends it.

.i The above description is given by way of example only, and many other secure transmission systems exist, for example Spread Spectrum, Trellis Coding, Quadrature Modulation, etc.

A main transmitter/receiver may be associated with each broadcast site, although this is not necessary. We prefer that a high quality receiver is used to demodulate the incoming data at each site for each client group of 2048 transponders. As each alarm station will be transmitting within a very short transmission window, separated only by a very short time interval, it is preferred that a de-inultiplexer is associated with the -13receiver to separate the received data and pass the information relating to the transponder change of state data to the monitoring company's premises by a suitable route. Typically, this would be via a modem and a Telecom line, although this could also be by way of radio transmission, or alternatively, each monitoring station could have its own high quality receiver situated at its premises, but this would depend upon the spread of alarm stations and the geographical location of the monitoring station. It is also possible to equip mobile units with either complete receiving equipment, or to receive a relayed signal from a fixed receiver, so that personnel can respond quickly to a problem.

Variations on the alarm system as outlined in the above preferred embodiment could include systems in which communications are depending on means other than electromagnetic radiation (radio) such as lW' waves, or for more restricted group distributions, using signals carried through wi. such as the electric utility wiring or in 0 dedicated wiring, or using ultrasonic signals.

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The timing signals could be transmitted from the central monitoring station, especially if no reliable public broadcast reception is available in remote areas. Otherwise, it may 20 be possible to design a sufficiently accurate reference oscillator or clock for use in all units that the system may run without a group-wide synchronisation process for many :months or years.

0 0: Finally, it will be appreciated that various al terations or modifications may be made to a a" 25 the foregoing without departing from the scope of this invention as exemplified by the following claims.

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Claims (9)

1. An alarm system including: a wireless monitoring station, and a group of remote alarm stations, each alarm station containing a wireless receiver, means for monitoring alarm conditions, and means to send, at predetermined time intervals, a wireless signal to said monitoring station, and wherein each alarm station includes means for receiving a clock signal, and each alarm station is programmed to send a status signal to the monitoring station within a defined transmission window occurring at a predetermined time synchronised by means of a received clock signal, said window being started and stopped by a clock means within the alarm station, the clock means in all the alarm stations being started simultaneously by said clock signal, and wherein the transmission window of each alarm station differs from that of each other alarm station in the group, so that the monitoring station can distinguish between the identity of the alarm stations dependent upon the transmission window of each respective alarm station in the group.

2. An alarm system as claimed in claim 1, wherein the clock signal is provided by a broadcast signal capable of being received by all of the alarm stations in the group, so that the alarm stations each respond to a common clock signal. S 25

3. An alarm system as claimed in claim 2, wherein the broadcast signal is in the form of a clock signal superimposed on a public transmission utility. *l

4. An alarm system as caimed in any one of claims 1-3, wherein the clock signal is transmitted at a regular clock interval which is greater than the length of time required for all of the alarm stations in a particular group to report to the monitoring station one after the other from first to last.

An alarm system as claimed in claim 4, wherein the clock signal is chosen from the group comprising: hourly wireless time signals, television signals, telephone signals, Teletext data, ~c~~i datacasts, wireless data system time information, direct broadcasting satellite time signals.

6. An alarm system as claimed in any one of claims 1-5, wherein each transmission window is less than 20 milliseconds.

7. An alarm system as claimed in any one of claims 1-6, wherein means are provided to receive, decode, and cause the execution of control instructions at remote alarm stations.

8. An alarm system as claimed in any one of the preceding claims, wherein each alarm station has means to transmit a unique identity code as part of its status signal.

9. An alarm system substantially as hereinbefore described with reference to any one of the accompanying drawings. DATED this second day of February 1993. AUTOMATION ENGINEERING LIMITED, Sby its Patent Attorneys, GRANT ADAMS COMPANY. e# S