AU712697B2 - System for data transmission, remote sensing, remote controls, remote readings and the like, particularly suitable for the electric power distribution lines - Google Patents

Description

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION The present invention relates in general to a data transmission and communication system, which includes means for transmitting data to and receiving data from a plurality of electronic units over a conventional power distribution network.

Communication systems, which utilise the existing electrical power distribution network as thetransmission medium, are traditionally used for transmitting data, remote sensing, remote controlling and remote reading.

e• For example, US 4,429,299 discloses a central processing unit, which polls a plurality of room -control units, placed in each room or designated area 0 0 of a hotel, hospital or building complex; the central 0* 0 processing unit conducts this polling sequence by 00 periodically transmitting, over the neutral and o o ground lines of the power distribution network, an interrogation signal having an address portion and a data portion. Each room control unit is arranged to receive the interrogation signal and to compare the address portion of this signal with an address previously programmed into the unit.

This power line communication system is suitable for being used in combination with a room status indicating system to monitor the status of each room in buildings such as a hotel, motel or hospital complex, to monitor the condition of a smoke detector located in each room of the complex, to remotely control the operation of the heating and cooling equipment in each room of the complex, to convey message-waiting information to each room and to perform an automatic wake-up.

i However, the wide and capillary expansion of the road network and distribution networks has created a bar to the implementation of data transmission and communication systems of the previously described *o type in the extra-urban and urban areas.

In fact, Power Line Carrier (PLC) systems are usually used for these purposes, but they have serious drawbacks, such as the limited propagation and the possible radiofrequency radiation, which creates interference and noise over the adjacent lines or towards other systems; moreover, the data transmission of PLC. systems, which usually occurs between a neutral grounded line and three phases, linked by unpredictable loads and high power factor capacitors, actually develops a typical unbalanced dipole, i.e. a real transmitting antenna which itrradiates especially via the vertical supply conductors and the ground. Since they use modulated waves, they are highly susceptible to be affected by line disturbances and electric noise and thus they require complex management protocols, which are capable of recognising any data that can be lost and able to generate related message repetition; these drawbacks lead to greater complexity and relevant costs as well as to a reduced capacity of data transmission, with respect to the theoretical values, 9* in a fixed time.

Furthermore, it is necessary to check the passband and the group delay of each of the electric lines, in order to put them in synchronism with the frequency of the emission and the depth of the modulation.

Moreover, in view of the reduced capacity of propagation of the signals, owing to a lower capacitive reactance, due to the necessity of using high frequencies, it is not possible to reach the operating distances without the use of further amplifier means or signal repetition means.

Other known techniques involve considerable costs for the employment of the necessary apparatus and high maintenance costs, while systems which use radio units or dedicated telephone lines are exposed to the same problems as the accessory conductors.

^-7 The Dual Tone Multifrequency (DTMF) technique is a call-routing telephone system which employs two tones out of the eight available ones at a time and it is thus able to supply sixteen different values at one time; although this system presents advantages over the prior art, it still lacks the feature of being able to communicate data and any configuration of bytes and to send commands very quickly.

According to one aspect of the present invention there is provided a data transmission and communication system for transmitting data, remote sensing, remote controls, remote readings and the like, including a power delivery section, connected to an electric power supply and to a field section, said power delivery section having at least one control unit and said field section having at least one station unit, all said control and station units being powered and linked through said electric power supply and said data transmission and communication being performed over electric power supply lines or dedicated lines, said control unit 15 further including a first address counters section and a first logic section, clocked by a power supply signal and connected to said address counters section, said station unit also including a second address counters section and a second logic section, which distributes a clock signal to said second address counters section, said clock signal being produced by one oscillator section of said station unit for synchronising said transmitted and communicated data with the frequency of said power supply signal, wherein said first logic section is connected to a tone reception section and to a tone transmission section for processing said data, in order to transfer them from said field section towards said control unit by means of a set of un-modulated transmission frequencies or tones, which are synchronised with said power supply signal and are used for modulating said power supply signal.

According to a further aspect of the present invention there is provided a method for data transmitting and communicating, which is provided for a data transmission and communication system as claimed in claim 1, wherein either said control units and station units are capable of transmitting and receiving data, said transmitting data being transferred in a block, which contains a set of said un-modulated transmission frequencies, each of said frequencies being -6transmitted for at least a fraction of one period of said power supply signal and in synchronism with said signal, said power supply signal clocking all said control and station units, which are connected with said electric power supply, in order to maintain said synchronism between said control and station units, said power supply signal also clocking a sequence of transmission by said station units and an address position of said units in a predefined polling list addressed by said control units, each of said set of un-modulated transmission frequencies corresponding to one sequence of bits or a byte, so that each control unit is capable of reconstructing any binary content of a data communication provided by a respective station unit through a signal integration redundancy process and a communication management protocol of the token-passing synchronous type is provided with a predetermined sequence.

The system according to the present invention can be easily produced and installed thus obtaining a securer method of performance, with respect to the prior S15 art.

It may comprise a supervision centre, which controls a plurality of electronic units, intelligent and capable of transmitting and receiving data from a "plurality of field electronic units; more than one electronic unit may depend on the same supervision centre and may also operate independently and autonomously.

The field electronic units or stations may be capable of managing a plurality of transducers for remote sensing, remote control and the like, according to the various user demands; these stations, when are installed on a public lighting a• system, can also be in function when the lights are off, without booster batteries or other support systems.

The various sections of a station may be constrained in a sealed, thermostatic box, which can supply the voltages and currents required for the various types of the transducers that are to be used.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are employed to indicate like parts in the various views: t% DG C:\WINWORD')EULAHWORIC222g2CL.DOC 0 -7- Fig. 1 is a block diagram of a first example of a data transmission and communication system, according to the present invention, which is installable on a public lighting system, for the remote sensing and the remote control; Fig. 2 is a block diagram of a second example of a data transmission and communication system, according a p a a a a a a a a *a.

a.* p 8 to the present invention, for the remote readings; Fig. 3 is a block diagram of a data transmission and communication system, according to the present invention, which is connected to a single phase and neutral power distribution networks; Figs. 4A, 4B, 4C, 4D show the diagrams of the waveforms of a first communication code, which is used in a data transmission and communication system,, according to the present invention; Figs. 5A, 5B, 5C, 5D, 5E show the diagrams of the

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"waveforms of a second communication code, which is used in a data transmission and communication system, according to the present invention; Figs. 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 61, 6L, 6M show the diagrams of the waveforms of a third code, which is used for the transmission and the communication of data in the system according to the present invention; Fig 7 is a block diagram of an' electronic control unit, which is used in the data transmission and communication system, according to the present invention; Fig. 8 is a block diagram of a typical field unit, Which is used in the data transmission and communication system, according to the present 1101-1 '1 invention.

It should be noted that the electric circuits of the system, according to the present invention, will be described using discrete components, even though programmable Large-Scale-Integration (LSI) components (such as gate arrays, microprocessors or other similar components) can also be used.

Similarly, the present invention refers to a 220 Volt, 50 Hz electric circuit supply voltage, but all the relevant characteristics are also valid for use with other types of components and different voltage S. and frequency values.

Referring now to the drawings, Fig. 1 shows a block diagram of a data transmission and communication I S.

system, according to the present invention, which is intended for sensing and remote control and which can be installed onto a public lighting system (not shown in the Figs.); a power delivery point section 32 comprises an electronic control unit 5, while a field section 33 comprises a plurality of field units or stations 9.

An incoming three-phases R, S, T plus the neutral ground N of an electric line supply 1 (220 Volt, Hz) are connected to the power delivery section 32, while a power factor capacitor 2 is connected between the phase T and the neutral ground N.

A plurality of switches 3, which can be operated by radio communication, are capable of inserting a low voltage, 50 Hz power supply unit 4, in order to feed the stations 9 in case of failure of the primary electric line supply 1; the low voltage power supply unit 4 is not normally connected to the installed public lighting system and it is connected during the hours when the lights are switched off. In fact, the switches 3 are normally closed onto the electric line 0* supply 1, as in Fig. 1; upon the lack of said power line supply 1, the switches 3 automatically switch onto the stand-by contacts 3A and they are capable of S; connecting the low voltage power unit 4 to the stations 9 in order to feed their sensors and transducers.

The control unit 5 transmits its commands towards the field section 33 via the transmitter TX and the induction circuits 6, one for each supply phase, and collects the data coming from the field section 33 through a receiver RX connected to three induction circuits 7, one for each phase, which have no physical connection with the electric lines 7A; moreover, the control unit 5 can communicate with a supervision centre 8A via a data transmission line 8.

Fig. 1 shows only one station 9, which is provided with active and/or passive sensors and detection transducers 10 and remote control outputs 11 for the connection with actuators and/or display devices; the electric lines 12A, 12B, 12C, one for each phase, are capable of connecting the field section 33 with the other units, while it is clear from Fig. 1 that the sensor station 9 of the field section 33 is connected to the control unit 5 only via the electric line 12C.

Fig. 2 shows a block diagram of the data transmission o and communication system, according to the present invention, which is employed on phase to phase distribution networks; this type of connection also permits to translate the communication of data and commands between a secondary circuit and a primary :circuit of a transformer (at a medium voltage).

The diagram of Fig. 2, relating to the remote readings 35 as a field section, comprises an electric switchboard section 34, which includes an electronic control unit 14,. .while the field section includes a field unit constituted by the reading station By means of the two-phase power line supply 13 (220 Volt, 50 Hz)) of the electric switchboard section 34, the control unit 14 sends its commands to the remote readings 35 via two induction circuits 15 and two

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transmitters TX and receives the data via two detection circuits 16 and two receivers RX, in order to obtain a line synchronism at 50 Hz. It is important to note that the control unit 14 does not act directly on the electric line 24, but it is isolated by electrochemical deposition.

The remote readings 35 of the field section comprise a column of counters 18 and respective transducers 19 for their reading; the reading station 20 reads the values indicated by the transducers 19 via a demultiplexer 21 and keeps them in storage means, moreover it receives the commands emitted by the control unit 14 via the detection circuits 23 and the receivers RX and sends the data detected to the control unit 14 via the induction circuits 22 and the transmitters TX. The control unit 14 can be connected to a supervision centre 17.

For example, a comparison between the system of the present invention, which employs a 1,600 Hz unmodulated transmission frequency, and a PLC system, which employs a 80 kHz frequency to transmit on a phase-to-phase distribution circuit, is herewith provided.

SDue to the different communication protocols in the two systems (the system of the present invention uses 13 a synchronous protocol, while the PLC system uses an asynchronous protocol), the system according to the present invention can transfer much more data than a PLC system (at 1,200 byte per second communication speed), during a prefixed time period; moreover, the power that is necessary to transmit at distance over low voltage electric lines depends on the presence of power factor capacitors of the circuit.

o In fact, assuming the capacitor 2 has a nominal value

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of 8 gF and the overall capacitance is 800 pF (for each phase), the relationship relating to the 9 reactance will be as follows:

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1) PLC system (80 kHz): 1/ (2*7*80-10 3 -800-10 6 Q=0 .00252; 2) The system of the present invention (1,600 Hz): 600-800.10'-) =0.1252.

The dB attenuation ratio between the two systems is: -33.9 dB, that- is to say, in order to obtain an effective voltage (at least of 0.05 the following transmission induced currents (Ampere) are required: 1) PLC system (80 kHz): I' (0.050/0.0025) 20 A.; 2) The system of the present invention (1,600 Hz): I" (0.050/0.125) 0.4 A.

14 It follows that, if the system of the present invention employed the 20 A. induced current it would exceed by at least 5 times the propagation, which can be obtained by means of a PLC system; therefore, the system according to the present invention is capable of better performances, such as a better propagation and a greater transport of data, in a prefixed time, with respect to the PLC systems.

Fig. 3 shows a data transmission system according to the present invention, which is applied over a single phase and neutral power distribution network; the three-phase medium voltage power supply 25 is 9* connected to a three-phase medium/low voltage transformer 26 and to a receiver/transmitter induction circuit 27 of a control unit 28, while the receiver/transmitter induction circuit 30 of the station 29 is connected to the control unit 28 by means of the electric lines 36, 37 of the phases R, S, T and of the neutral ground N. The stray capacitance, which is distributed over the lines 36 towards the ground, is indicated with the number 31.

The attenuation of the signals over the lines 36, 37, caused by the stray capacitance 31, is represented by a value of capacitive reactance (the stray load), which can be measured as above.

For example, a comparison between the performance of a PLC system and a system according to the present invention is provided; assuming that the PLC system has the following characteristics: 1) V 2 Volt (effective transmission voltage); 2) V 0.01 Volt (effective receiving voltage); 3) Wx= 1 Watt (effective transmission power); 4) 72 kHz (transmission frequency), we have: S(effective transmission current)= 0.5 A.; X' (load capacitive reactance)= V,/I 4 C (value of each distributed capacitance 31)= l/(2*7*F 0.552 iF; A' (attenuation in dB between the effective voltage of the received signal V. and the effective voltage of the transmitted signal 20-Log(V/V,)= -46 dB.

a* aThe system of the present invention has a 1,600 Hz un-modulated transmission frequency and a load capacitive reactance of 180 Q.

The -attenuation ratio between the two systems (PLC system and the system according to the present invention) is represented by: 20-Log (4/180)= -33 dB.

Thus, due to the different attenuation, the system of the present invention is able to ensure a propagation more than 5 times greater than that of PLC systems.

16 Figs. 4A, 4B, 4C, 4D show the diagrams relative to the communication code waveforms of the data which are sent from the field sections 33, 35 towards the control units 5, 14, 28 by means of un-modulated transmission frequencies; the operating principle is based on the employment of the frequencies, which are synchronised with a sine wave at 50 Hz of the power supply-line current or half-sine wave groups in order to transfer 1 byte.

principle upon which the principle upon which the communication from the various field units 33, 35 to the control units 14, 28 is founded consists in the modulation of the current of a group of sine waves by means of unmodulated frequencies (tones), which are synchronously transmitted with the sine waves. Both the control units 5, 14, 28 and all the field units 33, 35 are connected to the sine wave at 50 Hz of the power supply line and are provided with 50 Hz counters, which are started and synchronised by an appropriate start signal emitted by a logic section (see Fig. 7) of the control units 5, 14, 28.

According to this start signal, the counters of the units 5, 14, 28 are simultaneously set to zero and they will start a step counting as from the same sine wave; if one group or all of the control units 5, 14, /4_S _TPA~e' 28 have been addressed, each unit 5, 14, 28 will transmit in turn, according to a sequential order that is established upon installation, i.e. when the Hz synchronous counting will correspond to the block of sine waves which are assigned as group sequence or stations array sequence.

In this case, the system is able to maintain the synchronism between the 50 Hz control counters and the field units counters; the control units 5, 14, 28 are capable of reconstructing the binary content of the communication operated by the corresponding field unit and thus of recognising their source, by means of the analysis of the sequence of the various sine waves blocks with an identical counting system of the stations 9, 20, 29 and by means of the recognition of the tones in the respective parts of each block.

Figs. 4B, 4C, 4D show three examples of various blocks, where the sign indicates the positive half sine-waves, the sign indicates the negative half sine waves and the letter R shows the result of the communication which is obtained according to the position of the tones (the un-modulated transmission frequencies) in the sine waves or half sine waves, while Fig. 4A shows the 50 Hz electric power supply line sine-waves.

In particular, Fig. 4B shows a first example in which each station 9, 20, 29 is assigned four sine waves to transmit one byte using four different tones: station 1 is assigned block 1, which comprises sine waves 1 to 4, station 2 is assigned block 2, which includes sine waves 5 to 8 and so on; in the diagrams of the figures 4B-4D the following values have been chosen for each pair of bits of a byte: 1) Tone is constituted by a "00" binary value; 2) Tone is constituted by a "01" binary value; 3) Tone is constituted by a "10" binary value; 4) Tone is constituted by a "11" binary value.

According to the binary value of each bit pair of the byte which is to be communicated, one of the four tones of reference is chosen and, by means of that "tone, the signal of the power line current is modulated for a period of one sine wave.

For example, the block 3 in Fig. 4B is composed of the 9 t h 10', 11' and 12 t sine wave of the Fig. 4A; however, the same result can be attained, for example, by employing only three tones and by associating the "00" binary value to the function "no-tone".

Fig. 4C shows how to use the method mentioned above in the event that a higher communication speed is 19 needed; in this case, the duration of the line current modulation is reduced to one half sine wave for each tone, thus obtaining the possibility of communicating one byte with two sine waves, two bytes with four sine waves and so on.

The three-tones method mentioned above and related to the block 3 and station 3 of the figure 4B is also applicable in this case.

Fig. 4D shows how to use the method in case of a slower communication, suitable, for example, for remote readings and the like; in this case it is possible to use tones of lower frequency and to enlarge the modulation of the power supply line current for two or more sine waves at 50 Hz, as better detailed in Figs. For the sake of clarity, the examples show that each

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control unit 5, 14, 28 transmits only one byte, but in general the system of the present invention is capable of transmitting any number of bytes, one after the other, until the necessary length of a message is reached; according to the -performance required and the frequencies which are chosen for the tones, the power line current can be modulated for the period of one half sine wave (or fraction of it) or of one sine wave (or multiple of it).

1 i An un-modulated transmission frequency or tone can be used according to a binary logic 1/0, so that its presence or absence in a block allows the sending and the receiving of the state of each bits of one byte; if one has more available elementary tones, it will be possible to associate a specific tone to each binary configuiration of bits, thereby obtaining increasingly faster communication techniques, as the value of increases, so that, at equal time, it will be possible to transfer increasingly greater parts of a byte. In this case, if is the value of bits, it will be necessary to have a number of elementary tones that is constituted by 2 N or 2"-1, if an information of "no-tone" (value of equal to 0) is also used.

SHaving for example one has 255 different

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elementary tones and it would be possible to transmit any value of a byte in one unit of time, while, having only one tone, eight time units will be needed to obtain the same transmission or communication.

The optimal choice will be made by balancing the desired performance and the basic complexity of the system.

Figs. 5A-5E show the waveforms of the method of communication depicted in the above mentioned Figs.

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4A-4D, particularly suitable for monitoring systems regarding phenomena which are characterised by low variation speed. In this case, the use of tones of appropriate frequency, associated to the presence of a tone for multiple sine waves, allows to obtain a communication which is free from disturbances, thanks to the signal integration redundancy that can be effected by the receiver.

In particular, Fig. 5A shows the signal waveforms of a 50 Hz electric power supply line, Fig. 5B shows the waveform of the frequency related to the tone (unmodulated transmission frequency) which prolongs for 10 sine waves, and a portion of the as frequency signal related to the tone Fig.

shows a signal waveform which constitutes the integration upon reception of the un-modulated transmission frequency Fig. 5D shows the beginning of the tone integration upon reception, while Fig. 5E shows a diagram identifying the intervals in which the tones are transmitted and received.

Figs. 6A-6M show the electric diagrams of the waveforms of a code formulated and emitted by the control units 5, -14, 28 which is used in order to control the field units or stations 9, 20, 29. In this case, it is to be noted that the current signal of a plurality of sine waves related to the power supply line is modulated to generate binary codes, which correspond to a start signal, encoded commands, an identification of addressed devices and any other code and/or data of said signals.

The 50 Hz power supply line signal (at low frequency) is converted into a brief and fast binary code which can be sent over the line in a way that is not dependent on the flow of data sent by the field units 9, 20, 29 to the control units 5, 14, 28.

o* The control unit 5, 14, 28 can generate over the line

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a powerful, complete and composite message, which is *o able to satisfy any data and command communication requirement, due to the number of the un-modulated So tones; the module that formulates the code is contained inside the control unit 5, 14, 28, which sends it via the induction circuits 6, 15, in order to insert the tone current synchronously with the power supply line sine waves. A start command which is emitted by a control unit is capable of synchronising only the field units 9, 20, 29 related to the application system that is controlled by them.

For example, Figs. 6A-6M show diagrams of a code, which is dimensioned for 16 commands and 64 addresses and uses a block of 12 sine waves configured as follows: a start signal at 2 bits, a command code at 4 bits, an address code at 6 bits.

In particular, Fig. 6A shows a 50 Hz power supply line current signal, Fig. 6B shows the command code signal, which is obtained by a direct modulation of the current signal and it is particularly suitable for stations 9, 20, 29 that are installed on public o S: lighting systems, while Fig. 6C shows the command code signal obtained by indirect modulation of the current signal, particularly suitable for the stations 9, 20, 29 which are installed over other o. *distribution networks.

e* In the Figs. 6A, 6B, 6C, the code starts with a start command which is formulated with the use of an un- .9 modulated transmission frequency in a "ON" sine wave, *5 while another frequency is correlated to a "OFF" sine wave; the code is followed by the command code and the address of the field units 33, 35 to which the command is addressed. Figs. 6A, 6B, 6C represent a command which is emitted by the control unit 5, 14, 28, while the Figs. 6D-6M show how said command is elaborated upon reception and how it is detected by the field units 33, The un-modulated transmission frequencies which are 24 used for the start signal can be different from the frequencies which are used for communicating data, commands and addresses.

In particular, Fig. 6D shows the result of an integration of the un-modulated frequencies; it shall be noted that the logic level is always high in the presence of the tone state) and it is low when the tone is missing ("OFF" state).

Fig. 6E shows a 50 Hz continuous clock signal which "i is reproduced locally and it is furnished by a local S. O• system that is in synchronism and in phase with the line sine waves.

*Fig. 6F shows a series of continuous pulses, which go are shifted in phase towards the end of each positive half-wave; each pulse is used to detect the presence of an un-modulated frequency (tone) in each halfwave. The code shown in the example relates only to the positive half-waves, however, it can relate even to the negative half-waves.

Fig. 6G shows an output signal which is emitted by a "AND" circuit (not shown) that compares the previous signal levels of the Figs. 6D, 6E, 6F.

Fig. 6H shows a result of the start command in a prefixed interval of time.

Fig. 61 shows a control signal relating to the communication cycle of the full code, command and address, which begins at the end of the start command of the Fig. 6H and which extends up to a pre-fixed sine wave relating to the Figs. 6A-6C.

Fig. 6L shows an output result signal of the command code in an assigned time interval (for example, 4 sine waves following the start command).

Fig. 6M shows an output result signal of the field units address code; the message is received by all the stations 9, 20, 29 which are operationally connected to the control unit 5, 14, 28 that has emitted the command code. All the stations 9, 20, 29 are enabled to receive the commands over a specific a r frequency, but only one or more addressed stations 9, 29 will execute it starting from the end of the communication cycle.

a* Fig. 7 shows the block diagram of a control unit 14, 28, which comprises four sections: an address counters section 41, a tone reception section 42, a tone transmission section 43 and a logic section 44.

The address counters section 41 counts the 50 Hz sine waves through the detection circuits 50, the circuit 51, which recognises the command code and collects and squares the 50 Hz synchronisation pulses supplied by the detection circuits 50, the 50 Hz pre-scaler circuit 52, the decimal counters 53, 54, 55 and the "AND" matrix 56, which determines the address of the station 9, 20, 29 that sends the data coming from the field sections 33, The tone reception section 42 separates and detects the received un-modulated transmission frequencies through a circuit 57, which collects and preamplifies the frequencies acquired by means of the detection circuits 50, a tone treatment and squaring circuit 58, a tone detector 59, a tone "B" detector 60, a tone detector 61, a tone "D" detector 62 and a de-multiplexer 63.

The logic section 44 manages all the units by means of a microprocessor or CPU 64 and a circuit 65, which supplies to the CPU 64 a 50 Hz synchronism pulse 9* signal that is collected from the detection circuits The transmission section 43 sends the commands to the stations 9, 20, 29 which are operationally connected to the control units 5, 14, 28 and comprises a first push-pull driver circuit 66, which transmits the tone of the command code, a second push-pull driver circuit 67, which transmits the tone of the command code at the opposite phase with respect to the first push-pull circuit 66, and an induction circuit 68 of the command code.

Practically, the CPU 64 picks up in the matrix 56 the address of the station 9, 20, 29, which sends the data from the field section 33, 35, by means of the Hz counters 53-55 and on the basis of the multiples of the sine waves which are established for each group of -sine waves or half-waves, as shown in the Figs. 4B, 4C, 4D.

The CPU 64 actuates the de-multiplexer 63 in synchronism with the 50 Hz power supply current signal, in order to locate the tone (the un-modulated transmission frequency) which is present in each sine-wave or half-wave of each group.

The CPU 64 is capable of reconstructing the binary content of the information which is sent by the a station 9, 20, 29 whose address is the address determined by the matrix 56, on the basis of the tones which are present in each wave of a group.

Moreover, the CPU 64 enables the push-pull current driver circuits 66, 67, in order to .transmit the commands and through the interface 69 the CPU 64 may also send the data towards a supervision centre via a line or coaxial cable.

Fig. 8 shows the block diagram of a typical field station 9, 20, 29, which comprises three sections: an 28 address counters section 45, an oscillator circuit 46 and a logic section 47.

The address counters section 45 counts the 50 Hz sine waves through a 50 Hz pre-scaler 71, three decimal counters 72, 73, 74 and a decoding "AND" matrix which stores the address numbers assigned to the stations 9, 20, 29 upon their installation.

The logic section 47 manages the control unit 5, 14, 28 through a microprocessor or CPU 76, a circuit 77, which supplies to the CPU 76 a 50 Hz synchronism *4 pulse signal and which detects the command code, a de-multiplexer 78, which selects and separates the tone that is to be transmitted, an "AND" circuit 79, 0 which transmits the communication tones, a transmitter 80, an induction circuit 81, a transducer 4* interface 82 and a driver circuit 83, which actuates the remote control outputs 11.

The oscillator circuit 46 supplies a clock signal to the CPU 76 and it generates the communication tones, by means of an oscillator 84, which is synchronised with the 50 Hz power supply sine waves, a first divider 85 for the tone a second divider 86 for the tone a third divider 87 for the tone and a fourth divider 88 for the tone The CPU 76 analyses the data of each transducer Riy, via the interface 82 and composes and stores in a memory the messages which are to be transmitted, while it picks up from the "AND" matrix 75 the transmission groups of sine waves or half waves which correspond to the received command.

The transmission can take place upon the termination of the command'if the control unit 5, 14, 28 has been addressed individually; alternatively, the transmission shall take place on the basis of the S" turn which is assigned to the control unit 5, 14, 28 as a group sequence or as a universe sequence, if the command has been addressed, respectively, to a specific group or to all the units 5, 14, 28 which are connected to the same control section.

When the transmission starts, the CPU 76 actuates the de-multiplexer 78 to select the tone which is to be used, as a function of the binary value of each pair of bits of the byte that is to be transmitted; moreover, the CPU 76 enables the "AND" circuit 79, in order to actuate the transmitter The CPU 76 is in synchronism with the 50 Hz power supply sine waves by means of the circuit 77, through which it also detects the command code, which is sent by the control unit 5, 14, 28, and it sets up for the requested -executions; if an external device is addressed by the command, it will act through the driver 83.

The system of the present invention substantially comprises two types of electronic units, a control unit 5, 14, 28 and a sensor station 9, 20, 29 for remote sensing, remote control and the like, which is to be installed in the field section 33, The transmission of control data and codes from the control unit 5, 14, 28 to the field units 9, 20, 29 is synchronous with the frequency of the power supply line; in particular, this method of transmission, which utilises un-modulated transmission frequencies or tones, is managed by the control units 5, 14, 28 and it uses the electric power supply line in order

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to obtain an extremely rugged and reliable communication system.

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The data and commands can be addressed both to one or more control units 5, 14, 28 or to all the various units, installed in a field section 33, 35, which use the same electric power supply line; said data and commands start, synchronise, stop and modify the technical parameters of the field units 9, 20, 29 and the data managed by said units 9, 20, 29. The system according to the present invention operates over any type of electric power supply lines; moreover, more than one system can exist over the same power supply line, for different purposes and without any limitations or interference.

The data and commands which are sent by the control unit 5, 14, 28 do not interrupt the stream of the data that are sent by the field units 9, 20, 29, in the meantime, to the control units 5, 14, 28.

The method of the data communication from the field Sunits 9, 20, 29 towards the control units 5, 14, 28 makes use of "tones", whose transmission frequencies are not modulated; the operating principle is based on the employment of the "tones", which are inserted .4« p and synchronised with a group of one or more electric power supply line sine waves or half waves, in order to transmit one byte.

The use of the un-modulated transmission frequencies po (starting from the audio frequency range), which are synchronous with the electric power supply line signal, according to the above mentioned method, allows extremely simple and efficient communication protocols to be implemented, as well as free from interference, thanks to the signal integration redundancy, which can be effected by the receiver in synchronism with the transmitter, thus avoiding the sending of bits of parity and/or the repetition of messages.

Thanks to the reliability in recognising the presence of a known frequency tone, it is possible to group and discriminate more tones at the same time, for example in a bandwidth of 4 kHz, in order to obtain a full duplex transmission channel.

The use of base tones at different frecuencies allows to have a large number of control units and various station arrays, each relating to the same system, over the same electric power supply line; moreover, i the control units can manage independently and concurrently.

With the system of the present invention, it is also possible to reduce the occupation of the available frequency range, because it is not necessary to •"introduce pauses between the sending of two ao successive data and every instant of time can be used to communicate data and commands.

Moreover, the system according to the present invention allows to implement a communication management protocol of the token-passing synchronous type with a pre-determined sequence, in case of scanning of a group or of all the control units.

The control unit and the stations connected to said unit can manage transparently the communication A4RA protocol, without occupying parts of the power supply line pass-band, which is thus entirely available for the communication of data and commands.

The above mentioned methods of transmission allows a bi-directional communication over the power supply lines and the control unit can always send to the field units anr data without interrupting or waiting for the end of the flow of the data which are transmitted to the control unit by the stations, .o because such unit uses tones other than those used by the stati6ns.

Furthermore, if the sensor stations are installed on a S. a public lighting system, they can operate when the lights are switched off and they have no need for an autonomous supply; in fact, a low operating voltage, which is capable of feeding the sensor stations, can be inserted over the power supply line in order to allow interventions of maintenance, but not to trigger the starters of the lamps.

Finally, the system of the °present invention allows to monitor and control a road network and power, gas and water distribution networks, using the existing electric power supply lines.

Claims (16)

1. A data transmission and communication system for transmitting data, remote sensing, remote controls, remote readings and the like, including a power delivery section, connected to an electric power supply and to a field section, said power delivery section having at least one control unit and said field section having at least one station unit, all said control and station units being powered and linked through said electric power supply and said data transmission and communication being performed over electric power supply lines or dedicated lines, said control unit further including a first address counters section and a first logic section, clocked by a power supply signal and connected to said address :counters section, said station unit also including a second address counters S* section and a second logic section, which distributes a clock signal to said second .e•:address counters section, said clock signal being produced by one oscillator section of said station unit for synchronising said transmitted and communicated data with the frequency of said power supply signal, wherein said first logic section is connected to a tone reception section and to a tone transmission section for processing said data, in order to transfer them from said field section towards said control unit by means of a set of un-modulated transmission 00 20 frequencies or tones, which are synchronised with said power supply signal and are used for modulating said power supply signal.

2. A method for data transmitting and communicating, which is provided for a data transmission and communication system as claimed in claim 1, wherein either said control units and station units are capable of transmitting and receiving data, said transmitting data being transferred in a block, which contains a set of said un-modulated transmission frequencies, each of said frequencies being transmitted for at least a fraction of one period of said power supply signal and in synchronism with said signal, said power supply signal clocking all said control and station units, which are connected with said electric power supply, in order to maintain said synchronism between said control and station units, said power supply signal also clocking a sequence of transmission AZ/ by said station units and an address position of said units in a predefined polling DG C:\WINWORD\DELILA"WORK22292CL.DOC list addressed by said control units, each of said set of un-modulated transmission frequencies corresponding to one sequence of bits or a byte, so that each control unit is capable of reconstructing any binary content of a data communication provided by a respective station unit through a signal integration redundancy process and a communication management protocol of the token-passing synchronous type is provided with a predetermined sequence.

3. A method for data transmitting and communicating as claimed in claim 2, wherein said power supply signal is constituted by a power supply current signal. 10 4. A method for data transmitting and communicating as claimed in claim 2, wherein each of said un-modulated transmission frequencies is S transmitted for at least one half a period of said power supply signal and in synchronism with said signal.

5. A method for data transmitting and communicating as claimed in claim 2, wherein each of said un-modulated transmission frequencies is transmitted for at least one period of said power supply signal and in synchronism with said signal.

6. A method for data transmitting and communicating as claimed in claim 2, wherein one predefined binary value is associated with an information 20 that no un-modulated transmission frequencies are provided in said block.

7. A data transmission and communication system as claimed in claim 1, wherein said un-modulated transmission frequencies are different from the frequencies which are used for communicating data, commands and addresses.

8. A data transmission and communication system as claimed in claim 1, wherein said first address counters section of said control unit is provided for counting waves of said power supply signal by means of detection circuits, a synchronisation circuit, which recognises a command code and collects and squares a plurality of synchronisation pulses supplied by said detection circuits, a pre-scaler circuit, decimal counters and a "AND" matrix, which determines addresses of said station units when said units send data coming from said field sections. DG C:\WINWORD\DELILAHKWORK\22292CL.DOC 36

9. A data transmission and communication system as claimed in claim 8, wherein said tone reception section of said control unit is provided for separating and detecting said received un-modulated transmission frequencies by means a pre-amplifier circuit, which collects frequencies acquired by said detection circuits, a tone treatment and squaring circuit, detecting circuits for detecting said un-modulated frequencies and a de-multiplexer connected to a logic section. A data transmission and communication system as claimed in claim 9, wherein said logic section of said control unit is provided for managing said control units by means of a microprocessor and a circuit, which supplies to said 0.OV, microprocessor a synchronism pulse signal that is collected from said detection S° circuits.

11. A data transmission and communication system as claimed in claim .0 10, wherein said tone transmission section of said control unit is capable of sending commands to said station units, which are operationally connected to said control units and comprises a first push-pull driver circuit, which transmits frequencies of a command code, a second push-pull driver circuit, which °l transmits frequencies of said command code at an opposite phase with respect to said first push-pull circuit, and an induction circuit of said command code. 20 12. A method for data transmitting and communicating as claimed in o claim 2, which is provided for a data transmission and communication system as claimed in claim 11, wherein said microprocessor picks up in said "AND" matrix an address of a station unit, which sends data from said field section, by means of said decimal counters and on the basis of said predefined fractions of periods of said power supply signal, said microprocessor further actuating said de- multiplexer in synchronism with said power supply current signal, in order to locate an un-modulated transmission frequency, which is present in each of said fractions of periods, reconstructing a binary content of data, which are sent by said station unit whose address is determined by said "AND" matrix, on the basis of un-modulated transmission frequencies which are present in each fraction of periods, and enabling said push-pull current driver circuits, in order to transmit S commands. DG C:\WINWORDDELILA-HWORK2292CL DOC -37-

13. A data transmission and communication system as claimed in claim 1, wherein said address counters section of said station unit is provided for counting waves of said power supply signal, by means of a pre-scaler, a plurality of decimal counters and a decoding "AND" matrix, which stores address numbers assigned to said station units upon their installation.

14. A data transmission and communication system as claimed in claim 13, wherein said logic section of said station unit is provided for managing said control unit, by means of a microprocessor, a synchronism circuit, which supplies to said microprocessor a synchronism pulse signal and which detects a command code, a de-multiplexer, which selects and separates said un-modulated transmission frequency that is to be transmitted, an "AND" circuit, which transmits a plurality of communication un-modulated frequencies, a transmitter, an o induction circuit, a transducer interface and a driver circuit, which actuate a S. 15 plurality of transducers and a plurality of remote control outputs.

15. A data transmission and communication system as claimed in claim 14, wherein said oscillator circuit is provided for supplying a clock signal to said microprocessor and for generating a plurality of un-modulated communication frequencies, by means of an oscillator, which is synchronised with said power supply signal, and a plurality of dividers for treating each of said un-modulated 20 transmission frequencies.

16. A method for data transmitting and communicating as claimed in claim 2, which is provided for a data transmission and communication system as claimed in claim 15, wherein said microprocessor analyses data of each of said transducer via said transducer interface and composes and stores in a memory a series of messages which are to be transmitted, while it picks up from said "AND" matrix said fractions of periods of said power supply signal which correspond to received commands.

17. A method for data transmitting and communicating as claimed in claim 16, wherein said transmission of messages takes place upon the termination of said commands, said control unit, being addressed individually.

18. A method for data transmitting and communicating as claimed in claim 16, wherein said transmission of messages takes place on the basis of a DG C:\WINWORD\DELILAKWORK\22292CL.DOC

38- turn which is assigned to said control unit as a group sequence or as a universe sequence, said command being addressed to a specific group or to all of said units which are connected to one control section. 19. A method for data transmitting and communicating as claimed in claim 16, wherein, when said transmission starts, said microprocessor actuates said de-multiplexer to select a transmission frequency which is to be used, as a function of a binary value of each pair of bits of a byte that is to be transmitted, said microprocessor enabling said "AND" circuit, in order to actuate said transmitter, and being in synchronism with said power supply signal by means of said synchronism circuit, through which said microprocessor also detects a command code, which is sent by said control unit, and sets up for executions. A data transmission and communication system as claimed in claim .ii 1, wherein said station units are constituted by sensor stations, in particular '0 stations which are installed on a public lighting system, said sensor stations operating when lights of said public lighting system are switched off and having no need for an autonomous supply, a lower operating voltage, which is capable of 000. feeding said sensor stations, being inserted over said power supply lines in order to allow interventions of maintenance, but not to trigger the starters of said lights. 21. A data transmission and communication system substantially as 00 S 20 hereinbefore described with reference to the accompanying drawings. 22. A method for data transmitting and communicating substantially as hereinbefore described with reference to the accompanying drawings. DATED: 25 August, 1999 PHILLIPS ORMONDE FITZPATRICK Attorneys for: CITYCOM S.p.A. DG C:\WINWORD\DELILAKAWORK\22292CL.DOC