Abstract:
Monitoring and/or alarm device and process including a central unit, at least one intrusion detection peripheral facility, signalling elements and radio link elements allowing radio links on several redundant channels between the central unit and at least one intrusion detection peripheral facility, via which channels this peripheral facility is able to transmit signals to this central unit and wherein elements check the capacity or availability of each of the link channels to transmit the expected signals, elements count the number of available channels and/or the number of unavailable channels and transmission elements transmit to the signalling elements a control signal corresponding to the number of available channels and/or to the number of unavailable channels so as to selectively activate these signalling elements as a function of the state of the control signal.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a monitoring and/or alarm device and process, in particular for the monitoring and protection of goods, premises or persons, comprising a central unit, at least one peripheral facility allowing the detection of an intrusion and alarm signalling means. 
     DESCRIPTION OF THE RELATED ART 
     Security systems are generally classified into two main categories, wire-based systems and systems comprising radio link means. The latter have numerous advantages as compared with the wire-based systems and in particular they allow easy installation of the peripheral facilities of the central unit even in locations which wire-based systems have difficulty in accessing, thus allowing better monitoring coverage and thereby better protection. 
     However, these wireless systems also possess drawbacks related to the use of radio channels which may intentionally or unintentionally be partially occupied, completely or partially preventing the transmission of information between the peripheral facility and the central unit. 
     To solve this problem, Patent EP-A-0 811 959 proposes that several radio link channels be implemented, that the availability of these channels be analysed and that the information be transmitted via the available channel. 
     Manufacturers of alarm equipment have moreover designed systems with several frequencies or radio channels which are relatively far apart, allowing the information emanating from the peripheral facilities to be transmitted to the central unit even if one of the frequencies is jammed by an outside signal. 
     However, in case of simultaneous jamming of all the frequencies, the link between the peripheral facilities and the central unit is no longer ensured, thereby rendering the alarm system inoperative if the loss of link is not detected or causing the alarm to trigger if the complete loss of link is detected. In either case, the alarm system does not fulfil its main function which is to signal the presence of an intruder in a monitored zone. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide an improvement to wireless monitoring and/or alarm systems taking account of the above drawbacks. 
     Accordingly, the present invention firstly proposes a monitoring and/or alarm device comprising a central unit, at least one intrusion detection peripheral facility, signalling means and radio link means allowing radio links on several redundant channels between the central unit, and at least one intrusion detection peripheral facility, via which channels this peripheral facility is able to transmit signals to this central unit which are expected by the latter. 
     According to the invention, the device comprises: 
     means for checking the capacity or availability of each of the said link channels to transmit the said expected signals, 
     means for counting the number of available channels and/or the number of unavailable channels, 
     and transmission means for transmitting to the said signalling means a control signal corresponding to the number of available channels and/or to the number of unavailable channels so as to selectively activate these signalling means as a function of the state of the said control signal. 
     According to the invention, the said signalling means preferably comprise means for being placed or activated according to at least two different modes of operation as a function of at least two states of the said control signal. 
     According to the invention, the said signalling means are preferably audible, luminous or electrical means. 
     According to the invention, the said means for checking the availability of each of the said link channels comprise means for measuring the noise level in each of the said channels and means for checking the presence of an expected signal originating from a peripheral facility. 
     According to the invention, the said transmission means preferably deliver the said control signal each time the number of available and/or unavailable channels is modified during at least one specified duration. 
     According to the invention, the said signalling means preferably comprise means for being placed or activated according to different modes of operation according to whether the said transmission means transmit the said control signal or a signal corresponding to an intrusion detection. 
     The present invention also proposes a monitoring and/or alarm process comprising a central unit, at least one intrusion detection peripheral facility, signalling means and radio link means allowing radio links on several redundant channels between the central unit and at least one intrusion detection peripheral facility, via which this facility is able to transmit signals to this central unit which are expected by the latter. 
     According to the invention, the process consists: 
     in checking the capacity or availability of each of the said link channels to transmit the said expected signals, 
     in counting the number of available channels and/or the number of unavailable channels, 
     and in transmitting to the said signalling means a control signal corresponding to the said number of available channels and/or to the said number of unavailable channels so as to selectively activate these signalling means as a function of the state of the said control signal. 
     According to the invention, the process preferably consists in placing or activating the said signalling means according to at least two different modes of operation as a function of at least two states of the said control signal. 
     According to the invention, the process preferably consists: 
     in measuring the noise level in each of the said channels 
     and in checking the presence of an expected signal originating from a peripheral facility. 
     According to the invention, the process preferably consists in delivering the said control signal each time the number of available and/or unavailable channels is modified during at least one specified duration. 
     According to the invention, the process preferably consists in placing or activating the said signalling means according to different modes of operation according to whether the said transmission means transmit the said control signal or a signal corresponding to an intrusion detection. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood by studying a monitoring and/or alarm device and its mode of operation, which are described by way of non-limiting examples illustrated by the drawing in which: 
     FIG. 1 represents a general diagram of a monitoring and/or alarm device according to the invention; 
     and FIG. 2 represents a detailed view of a central unit of this device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, represented therein is a monitoring and/or alarm device  100  which comprises three intrusion detection peripheral facilities  1 ,  2  and  3  consisting preferably of volumetric detectors or pointwise detectors, communicating with a central unit  4  on four independent radio link channels f1, f2, f3 and f4. 
     The central unit  4  communicates via a radio link  5   a  with a siren  5  and via a wire path  6   a  with a telephone transmitter  6 . 
     The peripheral detection facility  1  comprises, like the other facilities  2  and  3 , a processing unit  7  linked to a transmit circuit  8  and to at least one sensor  9 , as well as an antenna  10  connected to the output of the transmit circuit  8 . 
     According to a preferred mode of execution known per se, this peripheral facility  1  operates in the following manner. 
     The processing unit  7  processes the data emanating from the sensor or sensors  9  and orders the despatch to the central unit  4  by way of the transmit circuit  8  and of the antenna  10  of a message or signal corresponding to the data emanating from the sensors. 
     This message may be an intrusion signalling message or autoprotection signalling message in the case in particular of an attempt to open the housing of the peripheral facility but also a message indicating a state of this facility, in particular a fault with its electrical power supply. 
     The message despatched by each peripheral facility to the central unit  4  can also comprise an identity code for this peripheral facility, in such a way that the central unit  4  which stores all the codes of the peripheral detection facilities in a memory accepts only the messages of peripheral facilities for which it is programmed. 
     In a manner known per se, the transmit circuit  8  of the peripheral facilities mainly comprises oscillators for generating various carrier frequencies each corresponding to a radio link channel. Each carrier frequency is mixed in a mixer comprising an input for the carrier frequency and an input for the message to be transmitted to the central unit  4 . 
     For each peripheral facility  1 ,  2  and  3 , the various carrier frequencies are thus modulated by the same message so as to obtain at the output of their transmit circuit a redundant message on the number of chosen channels. The modulation, known per se, is preferably an amplitude modulation. 
     In the device of FIG. 1, the message to be transmitted is mixed with four carrier frequencies so as to achieve the transmission of signals preferably centred on the frequencies of 433.20, 434.32, 868.30 and 869 MHz. 
     Referring to FIG. 2, represented therein is a detailed view of the central unit  4  including a superheterodyne receiver  11  comprising a local oscillator  12 , this oscillator comprising a stopper circuit  13  consisting of a choke  14  arranged in parallel with an arrangement of capacitors. 
     In a manner known per se, the frequency of oscillation of the local oscillator  12  is determined mainly by the characteristics of the stopper circuit  13 . In order to be able to vary this frequency of oscillation, the arrangement of capacitors comprises a voltage-controlled variable-capacitance capacitor  15 . 
     The superheterodyne receiver  11  also comprises a mixer  16  whose two inputs are linked to the local oscillator  12  and to a reception antenna  17  by way of an input amplifier  18  and an output linked to a signal amplifier  19 . 
     The central unit also comprises an electronic signal processing and drive unit  20 . 
     The electronic unit  20  comprises an input  21  to which is wired the line  22  emanating from an analog/digital converter  23  whose input is linked to the output of the amplifier  19 , as well as an input  24  to which is wired the output line  25  emanating from a comparator  26 , one input of which is linked to the output of the amplifier  19  and the other input to a reference signal S constituting a threshold S. 
     The electronic unit  20  furthermore comprises an output  27  to which is wired a line  28  connected to the input of a digital/analogue converter  29  whose output is linked to the variable-capacitance capacitor  15 . 
     Referring to FIGS. 1 and 2, the superheterodyne receiver  11  and the electronic unit  20  operate in the following preferred manner. 
     The electronic unit  20  is programmed to deliver via drive signal unit  35  and the line  28  a drive signal to the digital/analogue converter  29  whose output imposes a specified voltage on the capacitor  15 , thus fixing a frequency of oscillation of the local oscillator  12 . This controlled frequency of oscillation allows the superheterodyne receiver to receive an outside signal on a first reception channel which corresponds to a transmit channel of one of the peripheral facilities  1 ,  2  and  3 . 
     At programmed intervals, the electronic unit  20  thus delivers different drive signals in such a way as to modify the frequency of oscillation of the local oscillator  12  so as to investigate various link channels corresponding to the various transmit channels of the peripheral facilities  1 ,  2  and  3 . 
     According to a preferred embodiment, the manner of operation during the reception by the central unit  4  of an expected signal transmitted by a peripheral facility  1 ,  2  or  3  is as follows. 
     The signal transmitted by a peripheral facility on one of the four channels is received by the antenna  17 . It is mixed with the signal at the corresponding frequency of oscillation originating from the local oscillator  12 , in the mixer  16 , in such a way as to demodulate the signal received and to retrieve the message transmitted by the peripheral facility in question. 
     The signal obtained at the output of the mixer  16  is amplified by the amplifier  19  and the signal obtained at the output of this amplifier is digitized through the converter  23  then directed via the line  22  to the input  21  of the electronic unit. This input  21  is linked to a saturation level unit  30  of this electronic unit. 
     The signal obtained at the output of the amplifier  19  is compared with the threshold S in the comparator  26 . The result of this comparison is introduced, via its input  24  into a decoding unit  31  of the electronic unit  20 . This decoding unit analyses the signal emanating from the comparator  26 . 
     Once the entire expected signal transmitted by the peripheral facility in question has been received by the receiver  11 , the electronic unit  20  again delivers drive signals so that the receiver  11  successively investigates the other link channels. 
     Following reception of the said expected signal, the electronic unit  20  generates one or more instruction signals dependent on the result of the content of the signal received, which corresponds to the expected message transmitted by the corresponding peripheral facility. These instruction signals may contain alarm triggering commands directed to the siren  5  and/or to the telephone transmitter  6  or warning commands relating to the state of the peripheral facility. 
     According to a preferred embodiment, the manner of operation during the reception of a spurious or saturation signal is as follows. 
     Depending on the nature of the signal which it receives, the decoding unit  31  can detect the fact that the said received signal is not an expected signal transmitted by one of the peripheral facilities  1 ,  2  or  3  but a spurious or saturating signal. This observation may result in particular from an analysis of the format of the signal received if the latter for example is longer than a signal originating from a peripheral facility, of the actual content of the message, in particular of the absence of an identification code built into the message. 
     In this case, the decoding unit  31  generates a first information signal SI 1  indicating that the signal received on the receiving channel analysed is a spurious signal. 
     When the saturation unit  30  observes that the level of the signal received is greater than a predetermined, possibly variable, threshold Ss, this unit generates a second information signal SI 2 . 
     Insofar as the information signal SI 1  and the information signal SI 2  are present at the input of a counter  32  which the electronic unit  20  contains, this counter  32  records the fact that the receiving channel analysed is not available. 
     The counter  32  therefore records the link channels, between the peripheral facilities  1 ,  2  and  3  and the central unit  4  which are unavailable and increments itself by one unit when a channel becomes unavailable and decrements itself by one unit when a channel becomes reavailable. 
     Of course, once the decoding unit  31  detects that the signal received by the antenna  17  is a spurious or saturating signal, the electronic unit  20  again delivers drive signals so that the receiver  11  again begins to investigate the various reception channels. 
     When the number of unavailable channels varies, the central unit  4  is programmed to transmit, by radio to the siren  5  and by wire to the telephone transmitter  6 , a control signal Sc whose content corresponds to the number of unavailable channels and/or available channels which are recorded in the counter  32 . 
     The siren  5  comprises an electronic circuit  33  in which the control signal Sc received thereby is compared with reference signals of a register, each of these signals corresponding to a particular mode of operation, that is to say to a particular audible signal to be transmitted. 
     Thus, in a manner predetermined by programming, the siren  5  may possibly be activated, according to audible modes of operation which are adapted as a function of the number of link channels available or unavailable between the detection facilities  1 ,  2  and  3  and the central unit  4 . 
     In an exemplary embodiment, if no, one or two link channels are unavailable, the audible facility  34  of the siren  5  is not activated. If three transmission channels are unavailable at the same time, the electronic circuit  33  orders the audible facility  34  to emit spaced warning beeps for a specified duration. If the four transmission channels are unavailable at the same time, then the electronic circuit  33  orders the audible facility  34  to emit a louder sound constituting an alarm. 
     In an equivalent manner, the telephone transmitter  6  can comprise an electronic circuit designed and programmed in such a way as to generate control and telephone information signals adapted to the control signal Sc which it receives. 
     In a variant, the electronic unit  20  records in the counter  32  that a link channel is unavailable only when this channel receives a saturating signal or only when the level of saturation of the channel is greater than a threshold for a number of investigatory cycles corresponding to a specified duration. 
     In a variant, the central unit  4  can comprise as many receivers as channels to be investigated enabling the state of saturation of each channel to be ascertained simultaneously. 
     In a variant, the electronic unit  20 , at least as regards its part for monitoring the availability of the link channels could be built into the signalling means such as the siren  5  or the telephone transmitter  6 , by for example being physically linked or built into the electronic circuit  33  of the siren  5 . 
     In a variant, the structure of the receiver used of the central unit  4  may be different. It is in fact conceivable to use other types of receivers and in particular receivers of super-regenerative or homodyne type. 
     In a variant, each peripheral facility could exhibit its own link channels different from those of the others. 
     The present invention is not limited to the embodiments described above. It extends to all variants coming within the scope of the appended claims.