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EP0094279B1 - Method of protecting a telemonitoring system against sabotage and system carrying out this method - Google Patents

Method of protecting a telemonitoring system against sabotage and system carrying out this method Download PDF

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Publication number
EP0094279B1
EP0094279B1 EP83400810A EP83400810A EP0094279B1 EP 0094279 B1 EP0094279 B1 EP 0094279B1 EP 83400810 A EP83400810 A EP 83400810A EP 83400810 A EP83400810 A EP 83400810A EP 0094279 B1 EP0094279 B1 EP 0094279B1
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EP
European Patent Office
Prior art keywords
sensor
central station
signal
sensors
output
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German (de)
French (fr)
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EP0094279A1 (en
Inventor
Marc Tonello
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EUROPEENNE DE TELETRANSMISSION C E T T Cie
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EUROPEENNE DE TELETRANSMISSION C E T T Cie
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    • 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
    • G08B29/02—Monitoring continuously signalling or alarm systems
    • G08B29/06—Monitoring of the line circuits, e.g. signalling of line faults
    • G08B29/08—Signalling of tampering with the line circuit
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B26/00—Alarm systems in which substations are interrogated in succession by a central station
    • G08B26/001—Alarm systems in which substations are interrogated in succession by a central station with individual interrogation of substations connected in parallel
    • G08B26/002—Alarm systems in which substations are interrogated in succession by a central station with individual interrogation of substations connected in parallel only replying the state of the sensor

Definitions

  • the invention relates to the protection of a telemonitoring system against sabotage intended to neutralize it, that is to say to render it inoperative while keeping it apparently functioning normally.
  • a remote monitoring system intended to detect an intrusion into a room is deactivated if someone modifies the system in such a way that the sensors give a normal response when in fact they should report an intrusion.
  • each sensor of a conventional telemonitoring system is connected to the central station of the system by a line comprising four conductors: two constituting a protection loop to detect sabotage of the line, and two constituting a loaded detection loop to convey alarm information.
  • This line may be supplemented by other conductors to perform a remote test of the sensors. It is known to detect sabotage of such a line by detecting a variation in current, voltage, or impedance. These processes are simple and easily neutralizable for those who have a little time and a minimum of technical knowledge. On the other hand, several sensors are generally connected on the same line and it is not possible to distinguish which sensor transmits alarm information.
  • German patent DE-B-1 259 230 describes a remote monitoring device, consisting of a central station and a plurality of satellite stations to which sensors are connected, and where each satellite station is interrogated by sending on a first line of negative pulses whose number designates a satellite station and positive pulses whose number designates one of the sensors of this satellite station, and where the interrogated satellite station responds by sending a pulse of fixed amplitude on a second line , for each sensor detecting an anomaly.
  • This device makes it possible to individually locate each sensor detecting an anomaly, while requiring only two transmission lines, and makes it possible to detect a fault affecting these two lines.
  • it is quite vulnerable to sabotage because it is relatively easy to observe and then simulate the signals traveling on the second line; these signals being simple, in particular because they are pulses whose amplitude, frequency and duration are constant.
  • the object of the method according to the invention is to remedy these drawbacks by simple means.
  • the remote monitoring system shown in fig. 1 consists of a central station 6 and sensors n ° 1, n ° 2, n ° 3, ... each having an input terminal 2 connected to a bus line 4 and an output terminal 3 connected to a bus line 5, bus lines 4 and 5 being connected to the central station 6.
  • each sensor is connected to a switch 1 for which it is responsible for transmitting the state when the central station 6 interrogates the sensors.
  • This switch 1 makes it possible to detect, for example, the opening of a door.
  • the system can have up to 16 sensors. To detect the change of state of a switch 1, or an abnormal functioning of a sensor, each sensor is tested cyclically by interrogating it periodically from the central station 6.
  • the central station 6 comprises a signal generator 8, a separator 7 of synchronization signals and clock signals, a binary counter 9, a read only memory 10, a digital-analog converter 11, and an analog comparator 12.
  • the generator signal 8 provides a periodic binary signal Vi which is shown in FIG. 2a.
  • the signal generator 8 supplies a synchronization pulse 22 between instants t; and t o , then 256 periodic pulses, of period much less than the duration tAo.
  • the output of signal generator 8 is connected to the bus line 4 and therefore supplies this signal to the input terminal 2 of each sensor.
  • Fig. 2b represents the signal V 2 supplied on the bus line 5 by all of the outputs of the system sensors.
  • the sensor n ° 1 supplies a variable voltage 19 consisting of a succession of constant levels. During this time, the output of the other sensors does not provide any voltage and has a high impedance.
  • the output of the sensor n ° 2 provides on the bus line 5 another signal 20 don t the voltage is variable, while the outputs of all the other sensors have a high impedance .
  • the output of sensor no During the time interval (t z , t 3 ) the output of sensor no.
  • each sensor provides a variable voltage 21, having a shape different from the previous two, while the outputs of the other sensors have a high impedance.
  • Each sensor in turn provides a signal on the bus line 5 during a time interval corresponding to 16 periodic pulses from the signal generator 8.
  • the signal transmitted by each sensor has a complex shape, different for each of the sensors. If the switch 1 connected to a sensor changes state, the shape of the signal transmitted by this sensor is modified to transmit this information. For example, the response signal V 2 can be replaced by a signal of zero value.
  • Fig. 3 represents the block diagram of an exemplary embodiment of a sensor, such as sensor n ° 1.
  • the sensor comprises a separator 13 of synchronization signals and clock signals, a binary counter 14, a read only memory 15, a digital-analog converter 16 and an analog gate 17.
  • the input terminal 2 is connected to an input of the separator 13 which provides a logic signal on a first output when the central station sends a signal to the input terminal 2 synchronization characterized by its duration t i -t e , and which provides on a second output a clock signal constituted by the periodic pulses which follow the synchronization signal sent by the central station 6 on the bus line 4.
  • These signals are applied respectively to a reset input and to a clock input of the binary counter 14.
  • This counter 14 comprises eight stages, the outputs of which are connected to eight address inputs of the read-only memory 15.
  • the read-only memory 15 comprises eight data outputs, seven of which are connected to seven inputs of the digital-to-analog converter 16, and one eighth of which is connected to a first control input of the analog gate 17.
  • An output of the digital-to-analog converter 16 provides an analog value to a input of door 17.
  • the output of door 17 is connected to the output terminal 3 of the sensor.
  • the input terminal 2 first receives a synchronization pulse, which is transmitted by the separator 13 to the binary counter 14 to reset it, then 256 clock pulses which are transmitted to the binary counter 14 so that it successively supplies 256 address values to the memory 15.
  • the memory 15 provides on its eighth output a logic signal of value 1 for 16 consecutive address values corresponding to 16 clock pulses consecutive and thus validates the analog gate 17.
  • the analog gate 17 is validated during the time interval (t o , ti).
  • the other seven outputs of the memory 15 successively supply 16 binary words of 7 bits to the digital-analog converter 16 which thus synthesizes a waveform composed of 16 steps whose amplitude can take 128 values.
  • the signals transmitted successively by sensors n ° 1, n ° 2, n ° 3, ... are transmitted by the bus line 5 to the central station 6 where they are authenticated to verify that there is no fraud and change of state of one of the switches 1.
  • the output of the signal generator 8 is connected to an input of the separator 7 of synchronization signals and clock signals, identical to the separator 13 of the sensors.
  • the separator 7 provides a reset signal and a clock signal to the binary counter 9, identical to the counter 14 of the sensors.
  • the binary counter 9 has eight outputs which supply, during each interrogation cycle, 256 8-bit binary words to the address input of the read-only memory 10 which stores all the data stored in the read-only memories 15 of the sensors.
  • the output of the read-only memory 10 supplies 256 7-bit binary words to the inputs of the digital-analog converter 11, one output of which is connected to a first input of the comparator 12.
  • a second input of the comparator 12 is connected to the bus line 5, and an output of this comparator constitutes the output terminal 18 of the central station.
  • the output of the digital-analog converter 11 provides an analog signal whose waveform is made up of the series of waveforms of the signals expected as a response from the sensors.
  • the comparator 12 compares the series of waveforms supplied by the analog-converter 11 and the series of waveforms transmitted by the sensors and generates an alarm signal on the output terminal 18 if these two series of forms d are not identical. This case occurs when there is a change in the state of a switch 1 or when there is sabotage of a sensor or one of the bus lines.
  • the interrogation mode described below has the advantage of great simplicity since a single bus line is sufficient to transmit addressing information, synchronization information, and a clock signal. It is possible to make the addressing more complex, to make it even more difficult to neutralize the system, for example by generating the addresses in a pseudo-random order.
  • the waveforms transmitted in response by the sensors can be very complex, and are therefore difficult to simulate, neutralizing the system is therefore practically impossible to achieve.
  • the sensors include simple logic means which it is easy to integrate into a compact hybrid circuit, which can be located in the immediate vicinity of switches 1 or other means generating an alarm to be transmitted.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Alarm Systems (AREA)

Description

Linvention concerne la protection d'un système de télésurveillance contre un sabotage destiné à le neutraliser, c'est-à-dire à le rendre inopérant en lui conservant un fonctionnement apparemment normal. Par exemple, un système de télésurveillance destiné à détecter une intrusion dans un local est neutralisé si quelqu'un modifie le système de telle façon que les capteurs donnent une réponse normale alors qu'en fait ils devraient signaler une intrusion.The invention relates to the protection of a telemonitoring system against sabotage intended to neutralize it, that is to say to render it inoperative while keeping it apparently functioning normally. For example, a remote monitoring system intended to detect an intrusion into a room is deactivated if someone modifies the system in such a way that the sensors give a normal response when in fact they should report an intrusion.

Pour éviter un sabotage, chaque capteur d'un système de télésurveillance classique est relié au poste centrale du système par une ligne comportant quatre conducteurs: deux constituant une boucle de protection pour détecter un sabotage de la ligne, et deux constituant une boucle de détection chargée de véhiculer l'information d'alarme. Cette ligne est éventuellement complétée par d'autres conducteurs pour réaliser un test à distance des capteurs. Il est connu de déceler un sabotage d'une telle ligne en détectant une variation de courant, de tension, ou d'impédance. Ces procédés sont simples et aisément neutralisables pour qui dispose d'un peu de temps et d'un minimum de connaissances techniques. D'autre part, plusieurs capteurs sont reliés en général sur une même ligne et il n'est pas possible de distinguer quel capteur transmet une information d'alarme.To avoid sabotage, each sensor of a conventional telemonitoring system is connected to the central station of the system by a line comprising four conductors: two constituting a protection loop to detect sabotage of the line, and two constituting a loaded detection loop to convey alarm information. This line may be supplemented by other conductors to perform a remote test of the sensors. It is known to detect sabotage of such a line by detecting a variation in current, voltage, or impedance. These processes are simple and easily neutralizable for those who have a little time and a minimum of technical knowledge. On the other hand, several sensors are generally connected on the same line and it is not possible to distinguish which sensor transmits alarm information.

Pour remédier aux inconvénients de ces procédés classiques, il est connu d'associer à chaque capteur un circuit résonnant série ou parallèle relié à une ligne bus, d'envoyer successivement sur cette ligne des signaux périodiques de fréquence croissante, et de détecter les variations d'impédance correspondant à la résonance de chacun des circuits résonnants. Dans un tel procédé la neutralisation du système est beaucoup plus difficile à réaliser et la réponse de chaque capteur est individualisée puisqu'elle correspond à une valeur de fréquence différente pour chacun. La mise en oeuvre de ce procédé est toutefois délicate car la sélectivité des circuits résonnants et leur fréquence d'accord sont affectées par les caractéristiques de la ligne, ce qui limite le nombre des capteurs utilisables sur une même ligne. D'autre part, pour que les circuits d'analyse de la réponse des capteurs soient simples il est nécessaire de réaliser des réglages fins sur le site.To overcome the drawbacks of these conventional methods, it is known to associate with each sensor a series or parallel resonant circuit connected to a bus line, to send successive periodic signals on this line of increasing frequency, and to detect the variations d impedance corresponding to the resonance of each of the resonant circuits. In such a process, the neutralization of the system is much more difficult to achieve and the response of each sensor is individualized since it corresponds to a different frequency value for each. The implementation of this method is however delicate because the selectivity of the resonant circuits and their tuning frequency are affected by the characteristics of the line, which limits the number of sensors that can be used on the same line. On the other hand, in order for the sensor response analysis circuits to be simple, it is necessary to make fine adjustments on site.

Par ailleurs, le brevet allemand DE-B-1 259 230 décrit un dispositif de télésurveillance, constitué d'un poste central et d'une pluralité de postes satellites auxquels sont reliés des capteurs, et où chaque poste satellite est interrogé en envoyant sur une première ligne des impulsions négatives dont le nombre désigne un poste satellite et des impulsions positives dont le nombre désigne l'un des capteurs de ce poste satellite, et où le poste satellite interrogé répond en envoyant sur une seconde ligne une impulsion, d'amplitude fixée, pour chaque capteur détectant une anomalie..Ce dispositif permet de localiser individuellement chaque capteur détectant une anomalie, tout en ne nécessitant que deux lignes de transmission, et permet de détecter un défaut affectant ces deux lignes. Par contre il est assez vulnérable au sabotage car il est relativement facile d'observer puis de simuler les signaux transitant sur la seconde ligne; ces signaux étant simples, en particulier parce que ce sont des impulsions dont l'amplitude, la fréquence, et la durée sont constantes.Furthermore, German patent DE-B-1 259 230 describes a remote monitoring device, consisting of a central station and a plurality of satellite stations to which sensors are connected, and where each satellite station is interrogated by sending on a first line of negative pulses whose number designates a satellite station and positive pulses whose number designates one of the sensors of this satellite station, and where the interrogated satellite station responds by sending a pulse of fixed amplitude on a second line , for each sensor detecting an anomaly. This device makes it possible to individually locate each sensor detecting an anomaly, while requiring only two transmission lines, and makes it possible to detect a fault affecting these two lines. On the other hand, it is quite vulnerable to sabotage because it is relatively easy to observe and then simulate the signals traveling on the second line; these signals being simple, in particular because they are pulses whose amplitude, frequency and duration are constant.

Le procédé selon l'invention a pour objet de remédier à ces inconvénients par des moyens simples.The object of the method according to the invention is to remedy these drawbacks by simple means.

Linvention se rapporte donc à un procédé de protection d'un système de télésurveillance contre un sabotage, ce système étant constitué d'un poste central et d'une pluralité de capteurs, chaque capteur successivement transmettant, vers le poste central sur une même ligne, un signal traduisant l'état de ce capteur, procédé du type selon lequel on teste l'état de chaque capteur, on transmet d'un capteur testé vers le poste central du système un signal traduisant l'état de ce capteur, et l'on authentifie ce signal quand il arrive au poste central, et il est caractérisé en ce qu'il consiste:

  • - à transmettre d'un capteur testé vers le poste central du système d'un signal d'amplitude variable en fonction du temps, constitué d'une forme d'onde synthétisée à partir de données stockées dans une mémoire morte située dans le capteur,
  • - à authentifier ce signal quand il arrive au poste central en l'échantillonnant et en comparant la valeur de chaque échantillon avec une valeur de référence.
The invention therefore relates to a method of protecting a remote surveillance system against sabotage, this system consisting of a central station and a plurality of sensors, each sensor successively transmitting, to the central station on the same line, a signal translating the state of this sensor, a process of the type according to which the state of each sensor is tested, a signal translating the state of this sensor is transmitted from a tested sensor to the central station, and the this signal is authenticated when it arrives at the central station, and it is characterized in that it consists:
  • to transmit a signal of variable amplitude as a function of time from a tested sensor to the central station of the system, consisting of a waveform synthesized from data stored in a read-only memory located in the sensor,
  • - to authenticate this signal when it arrives at the central station by sampling it and comparing the value of each sample with a reference value.

Linvention sera miex comprise et d'autres caractéristiques apparaîtront à l'aide de la description ci-dessous et des figures l'accompagant:

  • la fig. 1 représente le schéma synoptique d'un exemple de réalisation d'un système de télésurveillance;
  • les figg. 2a et 2b représentent les chronogrammes d'un exemple de signaux échangés entre les capteurs et le poste central de ce système de télésurveillance;
  • la fig. 3 représente le schéma synoptique d'un exemple de réalisation d'un capteur.
The invention will be understood and other characteristics will appear from the description below and the accompanying figures:
  • fig. 1 represents the block diagram of an exemplary embodiment of a remote monitoring system;
  • figg. 2a and 2b represent the timing diagrams of an example of signals exchanged between the sensors and the central station of this remote monitoring system;
  • fig. 3 shows the block diagram of an exemplary embodiment of a sensor.

Le système de télésurveillance représenté sur la fig. 1 est constitué d'un poste central 6 et de capteurs n° 1, n° 2, n° 3, ... ayant chacun une borne d'entrée 2 reliée à une ligne bus 4 et une borne de sortie 3 reliée à une ligne bus 5, les lignes bus 4 et 5 étant reliées au poste central 6. Dans cet exemple chaque capteur est relié à un interrupteur 1 dont il est chargé de transmettre l'état lorsque le poste central 6 interroge les capteurs. Cet interrupteur 1 permet de détecter, par exemple, l'ouverture d'une porte. Dans cet exemple, le système peut comporter jusqu'à 16 capteurs. Pour détecter le changement d'état d'un interrupteur 1, ou un fonctionnement anormal d'un capteur, chaque capteur est testé cycliquement en l'interrogeant périodiquement à partir du poste central 6.The remote monitoring system shown in fig. 1 consists of a central station 6 and sensors n ° 1, n ° 2, n ° 3, ... each having an input terminal 2 connected to a bus line 4 and an output terminal 3 connected to a bus line 5, bus lines 4 and 5 being connected to the central station 6. In this example each sensor is connected to a switch 1 for which it is responsible for transmitting the state when the central station 6 interrogates the sensors. This switch 1 makes it possible to detect, for example, the opening of a door. In this example, the system can have up to 16 sensors. To detect the change of state of a switch 1, or an abnormal functioning of a sensor, each sensor is tested cyclically by interrogating it periodically from the central station 6.

Le poste central 6 comporte un générateur de signal 8, un séparateur 7 de signaux de synchronisation et de signaux d'horloge, un compteur binaire 9, une mémoire morte 10, un convertisseur numérique-analogique 11, et un comparateur analogique 12. Le générateur de signal 8 fournit un signal binaire périodique Vi qui est représenté sur la fig. 2a. Pour scruter l'ensemble des capteurs du système le générateur de signal 8 fournit une impulsion de synchronisation 22 entre des instants t; et to, puis 256 impulsions périodiques, de période très inférieure à la durée tAo. La sortie du générateur de signal 8 est reliée à la ligne bus 4 et fournit donc ce signal à la borne d'entrée 2 de chaque capteur. La fig. 2b représente le signal V2 fourni sur la ligne bus 5 par l'ensemble des sorties des capteurs de système. Pendant l'intervalle de temps (ti, te) la tension présente sur la ligne 5 est nulle, puis pendant un intervalle de temps (to, ti) le capteur n° 1 fournit une tension variable 19 constituée d'une succession de niveaux constants. Pendant ce temps la sortie des autres capteurs ne fournit pas de tension et présente une haute impédance. Pendant l'intervalle de temps (t1, t2) la sortie du capteur n° 2 fournit sur la ligne bus 5 un autre signal 20 don t la tension est variable, alors que les sorties de tous les autres capteurs présentent une haute impédance. Pendant l'intervalle de temps (tz, t3) la sortie du capteur n° 3 fournit une tension variable 21, ayant une forme différente des deux précédentes, cependant que les sorties des autres capteur présentent une haute impédance. Tour à tour chaque capteur fournit un signal sur la ligne bus 5 pendant un intervalle de temps correspondant à 16 impulsions périodiques du générateur de signal 8. Ainsi 16 capteurs peuvent répondre pendant chaque cycle d'interrogation de l'ensemble des capteurs. Le signal transmis par chaque capteur a une forme complexe, différente pour chacun des capteurs. Si l'interrupteur 1 relié à un capteur change d'état, la forme du signal transmis par ce capteur est modifié pour transmettre cette information. Par exemple, le signal de réponse V2 peut être remplacé par un signal de valeur nulle.The central station 6 comprises a signal generator 8, a separator 7 of synchronization signals and clock signals, a binary counter 9, a read only memory 10, a digital-analog converter 11, and an analog comparator 12. The generator signal 8 provides a periodic binary signal Vi which is shown in FIG. 2a. To scan all the sensors of the system, the signal generator 8 supplies a synchronization pulse 22 between instants t; and t o , then 256 periodic pulses, of period much less than the duration tAo. The output of signal generator 8 is connected to the bus line 4 and therefore supplies this signal to the input terminal 2 of each sensor. Fig. 2b represents the signal V 2 supplied on the bus line 5 by all of the outputs of the system sensors. During the time interval (t i , t e ) the voltage present on line 5 is zero, then during a time interval (t o , t i ) the sensor n ° 1 supplies a variable voltage 19 consisting of a succession of constant levels. During this time, the output of the other sensors does not provide any voltage and has a high impedance. During the time interval (t 1 , t 2 ) the output of the sensor n ° 2 provides on the bus line 5 another signal 20 don t the voltage is variable, while the outputs of all the other sensors have a high impedance . During the time interval (t z , t 3 ) the output of sensor no. 3 provides a variable voltage 21, having a shape different from the previous two, while the outputs of the other sensors have a high impedance. Each sensor in turn provides a signal on the bus line 5 during a time interval corresponding to 16 periodic pulses from the signal generator 8. Thus 16 sensors can respond during each interrogation cycle of all the sensors. The signal transmitted by each sensor has a complex shape, different for each of the sensors. If the switch 1 connected to a sensor changes state, the shape of the signal transmitted by this sensor is modified to transmit this information. For example, the response signal V 2 can be replaced by a signal of zero value.

La fig. 3 représente le schéma synoptique d'un exemple de réalisation d'un capteur, tel le capteur n° 1. Le capteur comporte un séparateur 13 de signaux de synchronisation et de signaux d'horloge, un compteur binaire 14, une mémoire morte 15, un convertisseur numérique-analogique 16 et une porte analogique 17. La borne d'entrée 2 est reliée à une entrée du séparateur 13 qui fournit sur une première sortie un signal logique quand le poste centrale envoie sur la borne d'entrée 2 un signal de synchronisation caractérisé par sa durée ti-te, et qui fournit sur une deuxième sortie un signal d'horloge constitué par les impulsions périodiques qui suivent le signal de synchronisation envoyé par le poste central 6 sur la ligne bus 4. Ces signaux sont appliqués respectivement à une entrée de remise à zéro et à une entrée d'horloge du compteur binaire 14. Ce compteur 14 comporte huit étages dont les sorties sont reliées à huit entrées d'adresse de la mémoire morte 15. La mémoire morte 15 comporte huit sorties de données, dont sept sont reliées à sept entrées du convertisseur numérique-analogique 16, et dont une huitième est reliée à une première entrée de commande de la porte analogique 17. Une sortie du convertisseur numérique-analogique 16 fournit une valeur analogique à une entrée de la porte 17. La sortie de la porte 17 est reliée à la borne de sortie 3 du capteur.Fig. 3 represents the block diagram of an exemplary embodiment of a sensor, such as sensor n ° 1. The sensor comprises a separator 13 of synchronization signals and clock signals, a binary counter 14, a read only memory 15, a digital-analog converter 16 and an analog gate 17. The input terminal 2 is connected to an input of the separator 13 which provides a logic signal on a first output when the central station sends a signal to the input terminal 2 synchronization characterized by its duration t i -t e , and which provides on a second output a clock signal constituted by the periodic pulses which follow the synchronization signal sent by the central station 6 on the bus line 4. These signals are applied respectively to a reset input and to a clock input of the binary counter 14. This counter 14 comprises eight stages, the outputs of which are connected to eight address inputs of the read-only memory 15. The read-only memory 15 comprises eight data outputs, seven of which are connected to seven inputs of the digital-to-analog converter 16, and one eighth of which is connected to a first control input of the analog gate 17. An output of the digital-to-analog converter 16 provides an analog value to a input of door 17. The output of door 17 is connected to the output terminal 3 of the sensor.

A chaque cycle de scrutation de l'ensemble des capteurs la borne d'entrée 2 reçoit d'abord une impulsion de synchronisation, qui est transmise par le séparateur 13 au compteur binaire 14 pour le remettre à zéro, puis 256 impulsions d'horloge qui sont transmises au compteur binaire 14 pour qu'il fournisse successivement 256 valeurs d'adresse à la mémoire 15. La mémoire 15 fournit sur sa huitième sortie un signal logique de valeur 1 pour 16 valeurs d'adresses consécutives correspondant à 16 impulsions d'horloge consécutives et valide ainsi la porte analogique 17. Ainsi pour le capteur n° 1 la porte analogique 17 est validée pendant l'intervalle de temps (to, ti). Les sept autres sorties de la mémoire 15 fournissent successivement 16 mots binaires de 7 bits au convertisseur numérique-analogique 16 qui synthétise ainsi une forme d'onde composée de 16 paliers dont l'amplitude peut prendre 128 valeurs. Quand l'état de l'interrupteur 1 change, la porte 7 est bloquée, l'absence de réponse du capteur déclenche ainsi une alarme.At each scan cycle of all the sensors, the input terminal 2 first receives a synchronization pulse, which is transmitted by the separator 13 to the binary counter 14 to reset it, then 256 clock pulses which are transmitted to the binary counter 14 so that it successively supplies 256 address values to the memory 15. The memory 15 provides on its eighth output a logic signal of value 1 for 16 consecutive address values corresponding to 16 clock pulses consecutive and thus validates the analog gate 17. Thus for the sensor n ° 1 the analog gate 17 is validated during the time interval (t o , ti). The other seven outputs of the memory 15 successively supply 16 binary words of 7 bits to the digital-analog converter 16 which thus synthesizes a waveform composed of 16 steps whose amplitude can take 128 values. When the state of the switch 1 changes, the door 7 is blocked, the absence of response from the sensor thus triggers an alarm.

Les signaux émis successivement par les capteurs n° 1, n° 2, n° 3, ... sont transmis par la ligne bus 5 jusqu'au poste central 6 où ils sont authentifiés pour vérifier qu'il n'y a pas de fraude et de changement d'état d'un des interrupteurs 1. Dans le poste central 6 (fig. 1) la sortie du générateur de signal 8 est reliée à une entrée du séparateur 7 de signaux de synchronisation et de signaux d'horloge, identique au séparateur 13 des capteurs. Le séparateur 7 fournit un signal de remise à zéro et un signal d'horloge au compteur binaire 9, identique au compteur 14 des capteurs. Le compteur binaire 9 possède huit sorties qui fournissent, pendant chaque cycle d'interrogation, 256 mots binaire de 8 bits a l'entrée d'adresse de la mémoire morte 10qui stocke l'ensemble des données stockées dans les mémoires mortes 15 des capteurs. Ces données sont rangées à des adresses se suivant dans l'ordre d'interrogation des capteurs. La sortie de la mémoire morte 10 fournit 256 mots binaires de 7 bits aux entrées du convertisseur numérique-analogique 11 dont une sortie est reliée à une première entrée du comparateur 12. Une deuxième entrée du comparateur 12 est reliée à la ligne bus 5, et une sortie de ce comparateur constitue la borne de sortie 18 du poste centrale. La sortie du convertisseur numérique-analogique 11 fournit un signal analogique dont la forme d'onde est consituée de la suite des formes d'onde des signaux attendus comme réponse des capteurs. Le comparateur 12 compare la suite des formes d'onde fournie par le convertisseur-analogique 11 et la suite des formes d'onde transmise par les capteurs et génère un signal d'alarme sur la borne de sortie 18 si ces deux suites de formes d'onde ne sont pas identiques. Ce cas ce présente lorsqu'il y a modification de l'état d'un interrupteur 1 ou bien lorsqu'il y a sabotage d'un capteur ou d'une des lignes bus.The signals transmitted successively by sensors n ° 1, n ° 2, n ° 3, ... are transmitted by the bus line 5 to the central station 6 where they are authenticated to verify that there is no fraud and change of state of one of the switches 1. In the central station 6 (fig. 1) the output of the signal generator 8 is connected to an input of the separator 7 of synchronization signals and clock signals, identical to the separator 13 of the sensors. The separator 7 provides a reset signal and a clock signal to the binary counter 9, identical to the counter 14 of the sensors. The binary counter 9 has eight outputs which supply, during each interrogation cycle, 256 8-bit binary words to the address input of the read-only memory 10 which stores all the data stored in the read-only memories 15 of the sensors. These data are stored at addresses following each other in the order of interrogation of the sensors. The output of the read-only memory 10 supplies 256 7-bit binary words to the inputs of the digital-analog converter 11, one output of which is connected to a first input of the comparator 12. A second input of the comparator 12 is connected to the bus line 5, and an output of this comparator constitutes the output terminal 18 of the central station. The output of the digital-analog converter 11 provides an analog signal whose waveform is made up of the series of waveforms of the signals expected as a response from the sensors. The comparator 12 compares the series of waveforms supplied by the analog-converter 11 and the series of waveforms transmitted by the sensors and generates an alarm signal on the output terminal 18 if these two series of forms d are not identical. This case occurs when there is a change in the state of a switch 1 or when there is sabotage of a sensor or one of the bus lines.

Il est à la portée de l'homme de l'art de réaliser un dispositif complémentaire permettant de compter le nombre d'impulsions d'horloge générées entre l'instant de synchronisation et l'instant d'alarme afin d'identifier quel capteur a transmis une réponse différente de la réponse attendue, et d'effectuer une vérification de l'alarme sur plusieurs cycles d'interrogation avant de fournir un signal d'alarme sur la borne de sortie 18. D'autre part il est à la portée de l'homme de l'art d'augmenter le nombre de capteurs utilisables en augmentant le nombre d'impulsions d'horloge transmises pendant chaque cycle d'interrogation, ou de modifier le nombre des niveaux d'amplitude des paliers de la forme d'onde synthétisée. Il est possible aussi de réaliser différemment l'adressage d'interrogation individuelle de chaque capteur, par exemple en remplaçant la ligne bus 4 par un bus à plusieurs conducteurs transmettant un mot binaire sous forme parallèle.It is within the reach of ordinary skill in the art to make a complementary device making it possible to count the number of clock pulses generated between the synchronization instant and the alarm instant in order to identify which sensor has transmitted a response different from the expected response, and to carry out an alarm check on several interrogation cycles before providing an alarm signal on the output terminal 18. On the other hand it is within the range of those skilled in the art to increase the number of sensors that can be used by increasing the number of clock pulses transmitted during each interrogation cycle, or to modify the number of amplitude levels of the bearings in the form of synthesized wave. It is also possible to carry out interro addressing differently. individual gation of each sensor, for example by replacing bus line 4 with a bus with several conductors transmitting a binary word in parallel form.

Le mode d'interrogation décrit ci-dessous a pour avantage une grande simplicité puisqu'il suffit d'une seule ligne bus pour transmettre une information d'adressage, une information de synchronisation, et un signal d'horloge. Il est possible de rendre l'adressage plus complexe, pour rendre encore plus difficile le neutralisation du système, par exemple en générant les adresses dans un ordre pseudo-aléatoire.The interrogation mode described below has the advantage of great simplicity since a single bus line is sufficient to transmit addressing information, synchronization information, and a clock signal. It is possible to make the addressing more complex, to make it even more difficult to neutralize the system, for example by generating the addresses in a pseudo-random order.

Il est aussi possible de mettre en oeuvre le procédé selon l'invention dans un système de télésurveillance où les capteurs prennent l'initiative de transmettre des informations sans interrogation préalable par le poste central.It is also possible to implement the method according to the invention in a remote monitoring system where the sensors take the initiative to transmit information without prior interrogation by the central station.

Au lieu d'utiliser un comparateur analogique 12 il est possible aussi de numériser la forme d'onde reçue par le poste central 6 et de comparer les valeurs obtenues aux données stockées dans la mémoire 10.Instead of using an analog comparator 12, it is also possible to digitize the waveform received by the central station 6 and to compare the values obtained with the data stored in the memory 10.

Les formes d'onde transmises en réponse par les capteurs peuvent être très complexes, et sont ainsi difficiles à simuler, la neutralisation du système est donc pratiquement impossible à réaliser. Les capteurs comportent des moyens logiques simples qu'il est aisé d'intégrer dans un circuit hybride de faible encombrement, pouvant être situé à proximité immédiate des interrupteurs 1 ou autres moyens générateurs d'une alarme à transmettre.The waveforms transmitted in response by the sensors can be very complex, and are therefore difficult to simulate, neutralizing the system is therefore practically impossible to achieve. The sensors include simple logic means which it is easy to integrate into a compact hybrid circuit, which can be located in the immediate vicinity of switches 1 or other means generating an alarm to be transmitted.

Claims (6)

1. A process for protecting a remote monitoring system against sabotage, this system comprising a central station (6) and a plurality of sensors (n° 1, n° 2, n° 3, ...), each sensor successively transmitting to the central station (6) on a common line (5) a signal indicating the state of this sensor, consisting in testing the state of each sensor, in transmitting, from a tested sensor to the central station of the system, a signal indicating the state of this sensor, and in authenticating this signal when it arrives at the central station, characterized in that it consists:
- in transmitting, from a tested sensor (n° 1, n° 2, n° 3, ...) to the central station (6) of the system, a signal of variable amplitude (V2) with time, constituted by a waveform (19, 20, 21, ...) synthesized from data stored in a ROM (15) located in the sensor (n° 1, n° 2, n° 3, ...);
- in authenticating this signal (V2) when it arrives at the central station (6), by sampling it and comparing the value of each sample with a reference value.
2. A process according to claim 1, characterized in that it consists in synthesizing a waveform (19, 20, 21, ...) which is different for each sensor (n° 1, n° 2, n° 3, ...).
3. A porcess according to claim 1, in which N sensors are tested sequentially, characterized in that the test consists in transmitting, from the central station (6) to the N sensors, for each scanning cycle of the N sensors, an interrogation signal (Vi) formed by a synchronisation pulse (22) followed by a train of periodic pulses whose number P is at least equal to N, and that it consists in counting, in each sensor (n° 1, n° 2, n° 3, ...), the pulses following any synchronization pulse (22), and in triggering the transmission of a variable amplitude signal (V2), when the count has reached a predetemined value proper to each sensor (n° 1, nO 2, nO 3,...) and chosen from the integer numbers between 1 and P.
4. A device for protecting a remote monitoring system against sabotage, this system implementing the process according to claim 3 and comprising a central station (6) and a plurality of sensors (n° 1, n° 2, n° 3, ...), the device having means by which each sensor is enabled to transmit successively to the central station (6) on a common line (5) a signal indicating the state of the sensor, and means by which it is able to authenticate this signal when it arrives at the central station (6), characterized in that each sensor (n° 1, n° 2, n° 3, ...) comprises:
- an alarm input terminal,
- a separator (13) for separating said synchroni= zation signals (22) and said signals of the periodic pulse train, an input of the separator being connected to the central station (6) and a first and a second output of the separator delivering respectively one of the two signal types,
- a counter (14) having a reset input and a clock input connected respectively to the first and to the second output of the separator (13), and having outputs,
- a ROM (15) having address inputs connected respectively to the outputs of the counter (14) and having outputs for supplying data permitting the syn- thetization of a waveform (19, 20, 21, ...),
-a digital-analog converter (16) having inputs connected respectively to the outputs of the ROM (15) and having an output for supplying a time variable amplitude signal (V2),
- an analog gate (17) having an input connected to the output of the converter (16), a first control input connected to an output of the ROM (15), a second control input connected to the alarm input terminal, and an output connected to the central station (6), for transmitting the variable amplitude signal (V2) to the central station (6) when the sensor is interrogated and when there is no alarm to be transmitted.
5. A device for protecting a remote monitoring system according to claim 4, characterized in that the central station (6) comprises:
- a generator (8) for producing interrogation signals (Vi), having an output connected via a first line (4) to all the sensors (n° 1, n° 2, n° 3, ...),
- counting means (7 and 9) having an input connected to the output of the generator (8) and having outputs,
- a ROM (10) having address inputs connected respectively to the outputs of the counting means (7 and 9), und having outputs for delivering data characteristic of the succession of waveforms (19, 20, 21, ...) transmitted successively by all the sensors (n° 1, n° 2, n° 3, ...) of the system in the absence of an alarm,
- means (11 and 12) having inputs connected respectively to the outputs of the ROM (10), an input connected to all the sensors (n° 1, n° 2, nO 3, ...) via a second line (5), and an output for delivering an alarm signal when the succession of waveforms received by the central station (6) differs from the succession of waveforms (19, 20, 21, ...) transmitted successively by all the sensors of the system in the absence of an alarm.
EP83400810A 1982-04-30 1983-04-22 Method of protecting a telemonitoring system against sabotage and system carrying out this method Expired EP0094279B1 (en)

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FR8207523A FR2526190B1 (en) 1982-04-30 1982-04-30 METHOD FOR PROTECTING A REMOTE MONITORING SYSTEM AGAINST SABOTAGE AND SYSTEM IMPLEMENTING SAID METHOD
FR8207523 1982-04-30

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EP0094279B1 true EP0094279B1 (en) 1986-02-19

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EP0094279A1 (en) 1983-11-16
FR2526190B1 (en) 1985-11-08
FR2526190A1 (en) 1983-11-04
DE3362154D1 (en) 1986-03-27
US4536748A (en) 1985-08-20

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