GB2051439A - Checking facility for data signalling systems - Google Patents
Checking facility for data signalling systems Download PDFInfo
- Publication number
- GB2051439A GB2051439A GB7919785A GB7919785A GB2051439A GB 2051439 A GB2051439 A GB 2051439A GB 7919785 A GB7919785 A GB 7919785A GB 7919785 A GB7919785 A GB 7919785A GB 2051439 A GB2051439 A GB 2051439A
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- GB
- United Kingdom
- Prior art keywords
- station
- signals
- duration
- central control
- data signalling
- 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.)
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Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
- G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
- G08B29/12—Checking intermittently signalling or alarm systems
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- Engineering & Computer Science (AREA)
- Computer Security & Cryptography (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Selective Calling Equipment (AREA)
Abstract
A checking facility for a data signalling system having a central control station and one or more remote out-stations connected by land line, comprises circuit means at the out-station to detect (16, 18) a received signal of duration greater than a fixed duration to light a lamp (28). The incoming signals may comprise the ordinary address signal comprising fixed duration bursts of fixed frequency pulses separated by fixed duration quiescent periods, and means is provided at the central station for increasing the duration of the otherwise fixed duration bursts of pulses for a particular out- station. <IMAGE>
Description
SPECIFICATION
Checking facility for data signalling systems
Field of invention
This invention concerns security alarm systems particularly multi-line security alarm systems where alarm signals are transmitted from different remote stations to a central control station. In particular the invention provides a device for checking and monitoring such a system from the central control station.
Background to the invention
In any data signalling system and particularly a multi-line security alarm system where alarm signals are transmitted from different remote stations to a central control station it is important that each line should be regularly monitored for line faults. It is also important that only genuine line faults are detected so that it is not possible for a third party wishing to break an alarm system to simulate a line fault. Were this to be readily done, the alarm system would be virtually useless since it would only be necessary for a third party to simulate a line fault on the appropriate circuit and thereafter little attention would be paid to signals arising from that part of the security alarm system at least until after the line fault had been cleared.
One method of continuously monitoring line faults in a multi-line security alarm system is described in British Patent Specifiction No.
1 391 905 and reference is made to that specifiction for general background to multi-line security alarm systems. However the system described in that specification involves the use of a line fault detector not only at the central control station but also at each of the remote stations or out-stations as they are often referred to.
Since in general each out-station will be connected to the central station via the normal telephone network, and since each out-station will normally comprise the premises of a business or private house or the like, a second telephone link can normally be established between the out-station and the central control station using the normal telephone facilities available at the two locations.
Furthermore in the event that a line fault or similar appears to arise during the security period (i.e. the period during which the premises are under surveillance from the central control station) then an alarm will normally be raised indicating that the premises are now at risk and personnel immediately despatched to watch the premises and alert the local police station etc. This step is taken not only because of the potential risk in the event that it is a genuine line fault but also in case the line fault turns out to have been a simulated line fault and the premises are in fact at that very time being interfered with.
Once the premises have been reached by the personnel sent thereto, the normal telephone link can be used to establish that the personnel have arrived and line checks can be established using the link between the personnel at the out-station and those left at central control station.
During the standby period (i.e. those hours during the 24-hour cycle and the weekly cycle during which the premises at the out-station are occupied and are consequently no longer under surveillance, there will be personnel available to answer the telephone so that in the event that a line fault appears at the central station indicating equipment indicating either that a genuine or a simulated fault has occurred on the lines feeding that out-station, a check can be made via the normal telephone link with personnel at the out-station and again checks can be made via that link to establish whether or not a genuine line fault has occurred.
With this in mind it is an object of the present invention to provide apparatus by which a check can be made on the incoming signals at a remote out-station to determine whether or not a line fault has occurred.
The invention
According to the present invention means for checking the condition of a line in a data signalling system having a central control station and one or more remote out-stations connected thereto by land line, comprises means at the out-station adapted to receive electrical signals transmitted thereto from the central control station, means for decoding the signals and producing control signals therefrom provided the duration of the incoming signals is greater than a given duration, and means responsive to the control signals for indicating the presence of such signals of said greater duration.
In a typical data signalling system, the central control station includes equipment which generates a so-called call signal for each of the out-stations in turn and this call signal which typically comprises a short fixed duration burst of electrical pulses of a given frequency, different frequencies applying to different out-stations, is received and decoded by one of the out-stations which recognises the signal as a call signal for that out-station and a transponder unit within the out-station, upon receipt of a decoded call signal, generates after a given period of time a reply or response signal comprising a further burst of electrical pulses on another frequency which when received by an appropriate receiver unit in the central control station will be recognised as having been received from that particular out-station.Clearly if there is a line fault or a breakdown at the out-station (or in any of the equipment in the central station) a re sponse signal of correct frequency and duration will not be received in response to the out-station's transmission of a call signal for a particular out-station and this absence of a response signal is used in the central control station to generate an alarm indicating that there is probably a line fault or equipment fault associated with that particular out-station.
In order to define the period of time during which the response signal must be received from a given out-station, a quiescent period is provided following each call signal and the system will be deemed to be functioning correctly if a response signal is received by the central control station within the quiescent period immediately following the appropriate call signal.
Since each call signal is itself of fixed duration, it will be seen that the invention can be incorporated into an existing system operating on such a basis by simply making provision at the central control station for extending the duration of the outgoing call signal to any particular out-station. By programming the equipment in the out-station so as to ignore call signals of normal duration but to respond to call signals of duration greater than the normal duration and provide an indication typically in the form of a flashing light at the out-station, so a check can be made independently of the normal pulses transmitted and received in a given circuit to determine whether or not the circuit is working correctly.
In practice it is simply achieved by establishing a telephone link with the given outstation and asking the personnel to watch the equipment whilst the pulses from the central control station are modified. The personnel at the out-station simply advise the personnel at the central control station whether or not the light (or other indicator) on the equipment in the out-station flashes during the test period and if it does then the personnel at the central control station can safely assume that there is no line fault between the central control station and the out-station and any failure on the part of the central control station to receive response signals presumably lies in the transponder unit at the out-station or in the receiver equipment in the central control station. An engineer can be despatched immediately to locate and mend the fault.
Alternatively if a line fault warning is generated for a given out-station at the central control station then an engineer in the field can be contacted and asked to check that outstation. On arrival the engineer can telephone the central station and ask the controller at the central control station to modify the call signals for that particular out-station thereby allowing the engineer to check very quickly whether or not there is a line fault between the central control station and the out-station or whether the fault lies in the equipment at the out-station.
From a servicing point of view this checking facility is of immense value and the fact that it is not operating continuously as is required in the system described in British Patent Specification 1391 905,represents no deficiency in practice since the check at the out-station end only has to be made in the event that a fault or fault condition is apparently detected at the central control station. Since an engineer will have to be sent to the out-station there is no actual disadvantage in arranging for the line and circuit test to be performed when the engineer arrives on the site as opposed to performing the test remotely from the central control station as is effectively provided by the more complicated system described in the prior published British Patent Specification 1391905.
In a central control system a cancel/test button is normally allocated to each out-station served by the central station equipment.
In order to obviate the need for further test buttons the existing cancel/test button may be used for producing the modified call signals to perform the test provided by the invention by incorporating a time delay circuit of for example 5 or 10 seconds between the switch and a circuit means initiating the modification of the call signals. The normal functions of the cancel/test button can be performed by rapid depression of the button and in any case if the button is held down for a longer period of time all that will happen is that the call signals for that particular out-station when transmitted will be a longer period than normal and all that will result is that the out-station test equipment will be rendered operational and the warning signal generated (typically a flashing light) in response to the receipt of the extended duration call signals. In this way additional equipment is minimised and existing central control station equipment utilised with minimum modification.
The invention will now be described by way of example with reference to the accompanying drawings.
In the drawings
Figure 1 is a graphical representation of call and response signals in a data signalling system showing how the call signal can be extended into the quiescent period to provide a test signal,
Figure 2 is a test circuit adapted to be fitted to a remote out-station receiver for detecting whether or not test signals are being received by the out-station, and
Figures 3(1), 3(2), and 3(3) illustrate different waveforms at different points in the circuit of Fig. 2.
Detailed descriptions of the drawings
Fig. 1 illustrates graphically the burst of oscillation corresponding to a call signal fol lowed by the corresponding burst of oscillation for a response signal in a data signalling system incorporating line and circuit check facilities. The call signal is of duration T1 seconds after which there is a quiescent period and providing the call signal has been received by the appropriate remote out-station and providing the transponder unit at that outstation is operating correcting, a transmitter unit in the out-station generates a response signal burst for transmission back to the central station originating the call signal. The latter is designated by reference numeral 10 and the response signal sent back by the outstation is designated by reference numeral 12.
Use is made by the invention of the quiescent period which is normally provided between the end of the call signal burst and the beginning of the response signal burst. By providing an appropriate control circuit for opening the gate which releases the call signal to the line so as to open the gate for a longer period of time (i.e. T2 seconds, see
Fig. 1) so the duration of the call signal can be increased from T1 to T2 without interfering with the overall operation of the system.This extended signal is transmitted instead of the original call signal of T1 duration and provided that T2 is not so great as to extend into the beginning of the response signal period 12, the system will operate quite normally, the transponder unit (not shown) at the outstation addressed by that call signal responding quite normally to the incoming call signal and generating the normal response signal for transmission back to the central station indicating that all the circuits are correctly functioning.
A line fault between the central control station and the particular out-station will of course mean that the call signal may not arrive at the out-station and/or the response signal will not return to the central control station. Consequently the central control station equipment will not receive the response signal 1 2 when it expects it and failure to receive this pulse in the allotted space of time will generate an alarm signal indicating that for some reason or another a line fault has developed or the circuits have been interfered with, for one particular out-station, and the appropriate steps can be taken to remedy the fault.
Clearly it is advantageous if it can be determined at an early stage whether the fault lies in the line or in the equipment at the remote out-station. Clearly since no response signals are being received it is not possible to say without a further check whether or not the out-station equipment is functioning correctly or not and the invention provides a device for checking whether or not the call signals are being received by the out-station equipment.
If they are then clearly the line is not at fault and the fault can be isolated to the equipment within the out-station and an appropriate engineer sent. (As a corollary, if signals are not being received by the call station equipment it can be assumed that even if there is an equipment fault there is also a line fault and a line engineer can be sent.)
Fig. 2 of the drawings shows a circuit which will respond only to extended call signal pulses and provide a visible indication that such pulses are being received.
The circuit is shown connected to the output of a receiver 14 forming part of a transponder of a out-station in a data signalling system. Output signals from the receiver are supplied to input signals to a timing circuit 1 6 which produces from the leading edge of any input pulse an output pulse of duration T3 where T3 is greater than T1 but less than T2.
The output pulses from the timing circuit 1 6 provide one input to a NAND gate 18 and the other input of this NAND gate 1 8 is supplied with signals from the output of the receiver direct via signal path 20.
The output of the NAND gate 1 8 is inverted by inverting amplifier 22 and the pulses so obtained converted into a direct current signal by means of a diode 24 and capacitor 26. An indicator lamp 28 is powered by the voltage across the capacitor 26 and a current limiting resistor 30 is provided where appropriate.
The operational circuit is such that the
NAND gate 18 is only satisfied when the receiver output is at least equal to T3 and this only occurs when the call signal has been increased in duration from T1 to T2 by d'prn- priate adjustment of the call signal generating circuit at the transmitter in the central control station.
When this occurs the NAND gate 18 will produce an output signal which after inversion by the inverting amplifier 22 will provide power for operating indicator lamp 28.
The indicator lamp can either be made to operate virtually continuously provided the repetition rate of the call signal 10 is sufficient as to maintain a series of pulses to the rectifying diode 24 and capacitor 26 so as to maintain the potential across the capacitor 26.
Alternatively the indicator lamp 28 can be made to flash in response to each of the incoming pulses of the call signal (when extended) by using a smaller capacitor 26 OF removing the capacitor altogether.
Waveforms at the points 1, 2 and 3 of Fig.
2 are shown in Fig. 3. The extended call signal is shown in dotted outline at 32 and the resulting output pulse from the NAND gate 1 8 is likewise shown in dotted outline at 34.
Although not shown buffer amplifier means may be located between the receiver 14 and timing circuit 16 and/or between the output of the inverting amplifier 22 and the input to the rectifying circuit 24, 26 etc.
The circuit for extending the call signal pulse duration is not shown but it will be appreciated that the ciruit will require some form of control signal which can be obtained by depressing a check or test button provided on the control equipment in the central control station. A separate button may be provided for initiating this extension of the call signal duration but in a preferred arrangement, an existing test button already provided on such equipment for testing the circuits associated with a particular out-station may be provided by combining with the switch a timing circuit for delaying control signal generation from the switch for a set period of time say five or ten seconds so that the push button switch may be used for normal functions which simply require the push button to be depressed momentarily whereas if a line test is required for the particular out-station the push button is depressed for longer than the set period of time and in fact is depressed for as long as the test is required i.e. 20 or 30 seconds.
Claims (9)
1. A data signalling system having a central control station and one or more remote out-stations connected thereto by land line, in which means for checking the condition of a line therein comprises means at the out-station adapted to receive electrical signals transmitted thereto from the central control station, means for decoding the signals and producing control signals therefrom provided the duration of the incoming signals is greater than a given duration, and means responsive to the control signals for indicating the presence of such signals of said greater duration.
2. A data signalling system as claimed in claim 1 in which the central control station includes equipment for generating a so-called call signal for each of the out-stations in turn, the call signal comprising a short fixed duration burst of electrical pulses of a given frequency, different frequencies applying to different out-stations.
3. A data signalling system as claimed in claim 2 in which each out-station contains circuit means for identifying signals of a particular frequency and a transponder unit for generating after a given period of time from the receipt of a decoded call signal, a reply or response signal, comprising a further burst of electrical pulses at another frequency for transmission to a receiver unit in the central control station.
4. A data signalling system as claimed in claim 3 further comprising circuit means in the central control station for generting an alarm signal in the event that a response signal of correct frequency and duration has not been received by the central control station receiver after transmission of a call signal for a particular out-station.
5. A data signalling system as claimed in claim 4 in which a quiescent period is provided following each call signal during which the response signal must be received from an addressed out-station if an alarm signal is not to be generated.
6. A data signalling system as claimed in any of claims 1 to 5 further comprising circuit means at the central control station for extending the duration of an outgoing call signal and the said means for decoding signals received by the out-station is adapted to ignore call signals of the extending duration only.
7. A data signalling system as claimed in claim 6 further comprising an electric lamp at the out-station and circuit means for supplying operating current thereto in response to the generation of control signals from the said decoding means.
8. A data signalling system as claimed in claim 6 or 7 further comprising a cancel-test button at the central station equipment for each of the out-stations served by the central station equipment, and a time delay device for introducing a delay between the operation of the button and the operation of the said means for extending the duration of an outgoing call signal so that the normal cancelling function of the button can be performed by a rapid depression of the button but in the event that the button is held down for a longer period of time, call signals for that particular out-station when transmitted will be of a longer period than normal so that the outstation test equipment will be rendered operational and the said control signals will be generated to activate the said means for indicating the presence of the greater duration signals.
9. Data signalling system constructed arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7919785A GB2051439B (en) | 1979-06-07 | 1979-06-07 | Checking facility for data signalling systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7919785A GB2051439B (en) | 1979-06-07 | 1979-06-07 | Checking facility for data signalling systems |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2051439A true GB2051439A (en) | 1981-01-14 |
| GB2051439B GB2051439B (en) | 1983-02-02 |
Family
ID=10505678
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7919785A Expired GB2051439B (en) | 1979-06-07 | 1979-06-07 | Checking facility for data signalling systems |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2051439B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2149547A (en) * | 1983-11-08 | 1985-06-12 | Nittan Co Ltd | Surveillance control apparatus for security system |
| GB2301465A (en) * | 1995-02-21 | 1996-12-04 | Ivan Martin Ginger | Apparatus with remotely operable units |
-
1979
- 1979-06-07 GB GB7919785A patent/GB2051439B/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2149547A (en) * | 1983-11-08 | 1985-06-12 | Nittan Co Ltd | Surveillance control apparatus for security system |
| GB2301465A (en) * | 1995-02-21 | 1996-12-04 | Ivan Martin Ginger | Apparatus with remotely operable units |
| GB2301465B (en) * | 1995-02-21 | 1998-09-23 | Ivan Martin Ginger | Apparatus with remotely operable units |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2051439B (en) | 1983-02-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |