GB2180381A - Communication systems for use with AC power lines - Google Patents

Abstract

Electronic switches (7) are switched on and off in response to coded signals generated by a transmitter (5) which feeds the signals to AC power lines (1,2,3 and 4) of a three-phase power supply. The signal intended for any one electronic switch is fed only to the power line associated with that switch and starts with a phase identifier characteristic of that particular power line. Signals fed to the power lines are received by receivers (6) which are individually associated with the power lines and control associated electronic switches. Each receiver can respond only to a signal starting with the associated phase identifier. This avoids errors from echoes or vestiges of signals that tend to occur on the other power lines. Each of the receivers associated with any one of the power lines has a different address, and responds only to a signal including its own address. Each signal also includes an instruction which causes the addressed receiver to operate the associated electronic switch in a predetermined manner. A supervisor is described for programming the transmitter. <IMAGE>

Description

SPECIFICATION Communication systems for use with AC power lines This invention relates to communication systems for use with AC power lines.

The invention has been developed in relation to communication systems for transmitting signals from a central transmitting location in a building to a plurality of spaced receiver locations in the building, and although much of the description that follows relates to systems for that purpose it must be understood that the invention is of more general application than that.

Where there is a requirement for the remote control of devices such as switches and valves, for example, a central transmitter may be used to send appropriate instructions to receivers adjacent to the devices, those receivers acting on receipt of the instructions to cause the operation of the devices. In order to avoid the need to provide special wiring extending from the transmitter to the receivers various systems have been proposed for transmitting signals incorporating the instructions along AC power lines. While some of those systems may be satisfactory when they employ single-phase AC power supplies, they are often unsatisfactory or may even be inapplicable when used with AC power lines handling more than one phase.One reason for this is that when a signal is applied to a line carrying a current of one phase, an echo or vestige of that signal tends to appear at a slightly later time on a line carrying a current of another phase, because the lines carrying currents of different phases are usually coupled together at a transformer, and the signal is transmitted from one line to the other by way of that transformer.

An object of the present invention is to provide a system such as to enable that problem to be overcome.

From one aspect the present invention consists in a communication system for use with AC power lines and comprising a transmitter and a plurality of receivers, the transmitter being operative to apply to an AC power line of any one phase a signal including a phase identifier, which is characteristic of the phase of that line, at least one of the receivers being capable of receiving a signal from that power line and having phase identifying means operative to respond to the phase identifier characteristic of said line and thereby to render the receiver responsive additionally to at least part of the remainder of the signal.

From another aspect the present invention consists in a method of communication for use with AC power lines, in which method a transmitter applies to an AC power line of any one phase a signal including a phase identifier, which is characteristic of the phase of that line, and a receiver associated with the line receives that signal, responds to the phase identifier as being characteristic of the line and thereby renders the receiver responsive additionally to at least part of the remainder of the signal.

The transmitter is preferably operative to apply signals to each of a plurality of AC power lines of different phases, each signal including a phase identifier which is characteristic of the phase of the line to which it is applied, and a plurality of receivers such that each line has at least one receiver individually associated with it and having phase identifying means operative to respond to the phase identifier characteristic of its associated line and thereby to render the receiver responsive additionally to at least part of the remainder of the signal. Thus, there may be two or three AC power lines of different phases each having individually associated with it one or more receivers.

When such a system is in use and the transmitter supplies to any one of the lines a signal for a receiver associated with that line, the signal includes a phase identifier characteristic of that line. The receiver concerned has phase identifying means which enables it to respond to the phase identifier, and in particular to enable the receiver to respond additionally to at least part of the remainder of the signal. Any echo or vestige of the signal which is transmitted to another power line, supplied with a different phase, may be picked up by a receiver associated with that other power line but this causes no response in that receiver as the phase identifying means of the receiver is not responsive to the phase identifier of the echo or vestige signal.

It is normally necessary, or at least highly desirable, for the transmitter to operate in such a manner that it applies each signal incorporating a phase identifier only to the AC power line associated with that phase identifier. The reason for this can be understood by considering what would be likely to occur if, on the contrary, the transmitter applied a signal both to the AC power line associated with the phase identifier of that signal and also to one or more AC power lines not associated with that phase identifier. In that case, the signal applied to a non-associated power line could well lead to the production of an echo or vestige in the associated power line itself.

That echo or vestige would be superimposed on the signal that had been applied directly to the line and, as any echo or vestige is normally delayed, could corrupt the directly applied signal.

When there are two or more receivers associated with an AC power line, the transmitter is preferably operative to transmit a signal which includes not only a phase identifier associated with that line but also an address, each of those receivers incorporating address identifying means characteristic of that receiver and operative on receipt of the associated address to render the receiver responsive to at least part of the remainder of the signal.

In addition the signal preferably comprises an instruction. In use a receiver is capable of responding to that instruction only when its phase identifying means has identified the phase identifier of the signal as being the phase identifier associated with the receiver and its address identifying means has identified the address as being the receiver's own address.

In each signal the instruction is preferably transmitted subsequent to the phase identifier and the address. If the signal were not of that preferred form it would be necessary to provide some form of decoder at each receiver in order to prevent the receiver carrying out the instruction until the phase identifier and address had both been checked and found to be appropriate for the receiver concerned.

Each signal preferably includes a check code, which is based in a predetermined manner on at least part of the remainder of the signal, and preferably on the whole of the remainder of the signal, and each receiver preferably has checking means operative to compare a check code, actually received as part of a signal, with a check value derived by the receiver from the remainder of the signal actually received, the arrangement being such that the receiver is inhibited from carrying out the instruction of the signal unless the comparison is favourable.Each receiver preferably includes reply means operative to apply to its associated power line an acknowledgement signal when said comparison between the check code and the derived check value is favourable; and there is sensing means, preferably in the transmitter or associated with the transmitter, operative to sense whether an acknowledgement signal is received after the transmitter has supplied a signal addressed to a receiver that is operational in the system.

Moreover, the reply means may be operative to apply to its associated power line a reject signal when the signal received is correctly addressed to the receiver concerned but the check code that forms part of the signal received does not favourably compare with the check value derived by the checking means from the remainder of the signal received. At least in normal circumstances a reject signal will be applied to the line only when there is a fault in the system. The transmitter may incorporate repeat means operative to repeat a signal if a reject signal is received or if no acknowledgement signal is received by the sensing means in reply to a signal sent by the transmitter. Moreover there may be warning means, preferably in or associated with the transmitter, operative to give rise to a warning if a reject signal is received or if a sequence of successive reject signals is received.Alternatively, or in addition, the warning means may be operative to give rise to a warning if no acknowledgement signal is received in reply to a signal sent by the transmitter. There may be recording means, preferably in or associated with the transmitter, operative to record the occurrence of reject signals and/or the absence of acknowledgement signals.

In each of the arrangements outlined above it is assumed that the signal includes an instruction. In fact it is not always necessary or appropriate for the signal to include an instruction, provided that the receivers include reply means of the kind described. The system can then be used merely to monitor the presence and correct functioning of the receivers. For example the system may be used in an intruderalarm. In such a system, should a receiver be disconnected or rendered inoperative when a door or window adjacent to that receiver was opened, the sensing means would receive no reply to a signal addressed to that receiver and the warning means would give rise to an appropriate alarm.That alarm might be a general alarm but would preferably be such as to indicate which receiver was not replying or at least which group of receivers it is that contains the receiver which is not replying (the receivers being divided into groups for that purpose).

While the system described above is designed for use in avoiding problems that may occur when transmittiing signals over multiphase AC power lines, it will be understood that if desired the system could equally well be used with a single-phase AC power line.

The use of phase identification would be superfluous but would not interfere with the operation of the system. The system is therefore of general application and can be used with multi-phase or single-phase AC power lines as may be desired.

A communication system in accordance with the present invention may be operative to prevent selected electric lamps being switched on at other than selected on times, each of the lamps or groups of lamps concerned being connected to an electricity supply by way of a mechanical switch and an electronic switch in series with the mechanical switch, the electronic switch being operated by an associated one of said receivers, the arrangement being such that only when the electronic switch is on can the associated mechanical switch be used to switch on and off the associated lamp or group of lamps. ( The system may, for example, be used in licensed premises for preventing wasteful use of electricity. In a typical arrangement for achieving this, the system operates to prevent selected electric lamps being switched on in bars within the premises at other than selected on times. Each of the lamps concerned is connected to a mains electricity supply by way of a manually-operable mechanical switch and an electronic switch in series with the mechanical switch; only when the electronic switch is on can the associated mechanical switch be used to switch on and off the associated lamp. The system embodying the invention is used to control the electronic switches.

In the accompanying drawings: Figure 1 is a block diagram of a system embodying the present invention, Figure 2 is a wave form of a kind employed in signalling when the system is in use, and Figure 3 is a schematic elevation of a controller and associated devices for use in conjunction with the system.

In Figure 1 the lines of a three-phase AC electric power supply are indicated by the lines 1, 2, 3 and 4, 1 being a neutral line and 2, 3 and 4 being live lines of three different phases. Typically the rms voltage between each live line and neutral is 240 volts, the frequency is 50 Hz and there is a 1 2or phasedifference between each phase and each of the other phases.

A communication system in accordance with the invention comprises a transmitter 5 and a number of receivers 6, only a few of which are shown. The transmitter 5 is connected to all of the lines 1, 2, 3 and 4, but each of the receivers 6 is connected to the neutral line and to an associated one only of the live lines 2, 3 and 4.

The system may be used in the manner outlined above to permit the use of certain lamps in the bars of licensed premises during certain on periods (which may include licensing hours) but normally to prevent the use of those lamps during the remaining off periods.

When the system is used for this purpose a timer is incorporated in the transmitter, while each receiver 6 is connected to at least one associated electronic switch 7 which is in series with a mechanical switch 8 controlling the supply of electricity to one or more of the lamps referred to.

The transmitter 5 includes a microprocessor and associated electronic components programmed and connected so as to constitute transmitting means, repeat means, sensing means, warning means and recording means.

Likewise each of the receivers 6 includes a microprocessor and associated electronic components programmed and connected so as to constitute phase identifying means, address identifying means, checking means and reply means.

In use the transmitter 5 generates a sequence of signals for the receivers 6. Each of those signals is addressed to a different one of the receivers 6, and a complete sequence of signals, one addressed to each receiver in turn, is repeated unceasingly. Each signal is applied by the transmitter between the neutral line 1 and whichever one of the live lines 2, 3 and 4 is connected to the receiver for which that signal is intended. It is not applied to either of the other live lines.

The basis of the signal is a carrier wave of low radio frequency, for example of 125 Khz, and this is modulated either by amplitude modulation or by frequency modulation to provide a binary, digital signal with a baud rate of about 1000 bits per second. The RMS voltage of the signal may be between 100 and 1000 mv. The digital signal is of a kind such that a square wave comprising a succession of cycles of uniform amplitude and uniform period represents a series of 'ones'. In fact, each change in value of the signal represents a 'one'. A 'zero' is represented by the absence of any change in the signal at a time when such a change would have occurred had the 'zero' concerned been replaced by a 'one'.

This is illustrated in Figure 2, which represents a typical signal. Marks 10 on a time scale 11 represent moments of time spaced at uniform intervals. Any changes that occur in the signal occur only at those moments 10. Any changes in the signal, such as those indicated by the reference numeral 12, represent 'ones', while those moments, such as those indicated at 13, where no changes occur, represent 'zeros'.

When the system is in operation a continuous train of 'ones' is initially applied to one of the live power supply lines and this is then intermittently modulated to transmit signals to the receivers associated with that line. The initial train of 'ones' enables the receivers to become synchronised with the transmitter so that they are ready to receive the subsequent signals. While this occurs, no signal whatsoever is applied to the other power supply lines. After signals have been sent to all the relevant receivers associated with one line, the transmission of signals is transferred to another live line, the arrangement being such that signals are similarly applied to each of the three live lines in turn. The signal intended for each receiver comprises a data packet made up from about ten or eleven 8-bit bytes and a check code. Each byte starts with a 'zero' and ends with a 'one'.

The signal intended for each receiver comprises four components: a phase identifier, an address, an instruction and a check code.

Each component consists of a predetermined number of bytes. The phase identifier is one of three phase identifiers employed in the system and is characteristic of the phase of the live line to which it is applied by the transmitter. The address is one of a relatively large number of addresses that are or that can be employed in the system, there being a different address associated with each receiver.

The instruction is one of a range of instructions that can be sent to the receivers to cause them to react in any desired ways. The check code is a code calculated at the transmitter in a predetermined manner from the preceding components of the signal and serves to assist in reducing any errors that might arise in the system.

Between each signal and the next there is a pause of predetermined duration. This is intended to allow time for the transmission of an acknowledgement signal by the reply means of a receiver and its receipt by the sensing means, as described below.

Each receiver 6 operates continuously and its phase identifying means picks up and analyses the phase identifier of each signal it receives. If it finds that the phase identifier of a particular signal is not that associated with its own power line it takes no further action until the next phase identifier is received. If, on the other hand it finds that the phase identifier of a particular signal is indeed that associated with the phase of its own power line its address identifying means becomes operative to discover whether the address component of the signal is or is not its own address. Only if the address is correct is the receiver able to respond to the instruction component of the signal.Before it responds, however, its checking means calculates a check value in a predetermined manner from the preceding components of the signal and compares that value with the check code of the signal. Provided that comparison between the check value and the check code is favourable-that is the value and check are equal or are related in some other predetermined manner-the receiver acts on the instruction. The checking means of the receiver also applies to its associated power line an acknowledgement signal which is transmitted along that line during the pause following the end of the signal. This acknowledgement signal is picked up by the sensing means of the transmitter and enables the transmitter to continue transmitting the sequence of signals. In this way each receiver is instructed in turn.

In the event of the comparison between the check code and the check value being unfavourable, an occurrence that could result from a failure of an electrical or electronic component or from an unexpected fluctuation in the power supplied by the power line, the receiver concerned does not respond to the instruction, and instead of sending an acknowledge ment signal may send a reject signal to the transmitter. On receipt of a reject signal the sensing means of the transmitter may take any of a number of different actions. These may extend from continuing operation, as if an acknowledgment signal had been received, to causing a warning to be issued and stopping all further operation of the transmitter. In a preferred arrangement, however, the repeat means is brought into operation and repeats the signal that led to the reject signal.If that too leads to a reject signal the signal is re peated again. Only if a third successive reject signal is received is a warning signal gener ated. The transmitter nevertheless can continue to send signals to the other receivers as before. If desired, the occurrence of reject signals may be recorded by the recording means so as to enable a user at any appropriate time to assess the operation of the system and to assist the user in correcting any errors in the system.

If a receiver is faulty or becomes disconnected so that it sends neither an acknowledgement signal nor a reject signal, the sensing means may again take any of a number of different actions, much as it can its response to receipt of a reject signal. In general, however, it is preferable for the sensing means to take more stringent action when receiving no signal at all from a receiver than when receiving a reject signal from a receiver. It will be understood that while it is preferred to arrange for the receivers to generate both acknowledgement and reject signals, the system may be modified in such a manner that only one of those signals or neither of those signals is employed. When the receivers are arranged to generate neither acknowledgement nor reject signals, it is of course unnecessary for there to be repeat means, sensing means, warning means and recording means.

During normal operation of the system the timer instructs the transmitter to transmit to the receivers instructions appropriate for the time of day. For example, during an off period the transmitter may transmit signals to all of the receivers such that their associated triacs are rendered nonconductive and their associated mechanical switches cannot be used to switch their lamps on. During an on period, the timer may instruct all the receivers to render their associated triacs conductive. During yet other periods, before and after on periods, some only of the triacs are rendered conductive.

Each receiver is preferably powered from the power line to which it is connected. The voltage requirements of a receiver, however, are normally much lower than the voltage of the power lines, and may for example be 15 volts. It is therefore necessary for the receiver to incorporate voltage-reducing means. This may comprise a transformer, but the use of a transformer may be unsatisfactory as transformers are relatively bulky and expensive. It is therefore generally preferred for the voltagereducing means to comprise circuit components not including a transformer. The use of resistors would normally result in the generation of excessive amounts of heat, so it is preferred to employ a capacitative coupling from one of the power lines.

It is to be understood that numerous alteta- tions can be made in the system without de parting from the scope of the present invention. For example, the timer, the sensing means, the warning means and the recording means may be physically separate from the transmitter.

In another modification the address of a receiver connected to a power line of one phase may be the same as that of a receiver connected to a power line of another phase; the phase identifier alone is then used to distinguish one of those receivers from the other.

As indicated above, one application of systems embodying the present invention is to the control of lighting circuits in licensed premises.

Certain areas or zones of licensed premises, such as bars, restaurants and the like, are used by members of the public only during certain access periods. In order to avoid or at least reduce a wasteful use of electricity it is desirable to control the supply of electricity to most of the electric lamps in those areas or zones in such a manner that the lamps can be switched on only during predetermined on periods, those on periods usually including the access periods referred to. To this end it is proposed to provide manually operable mechanical switches for the lamps and also to provide electronic switches in series with the mechanical switches, the arrangement being such that the mechanical switches can be used to switch the lamps on only when the electronic switches are on.The electronic switches are operated by a common controller which incorporates a transmitter of the kind described above and a timer. There may well be a requirement for different groups of electronic switches to have different on periods and for those on periods to overlap one another; in consequence the controller may have a relatively complex function to perform and will need to be programmed to carry out those functions. As the requirements of one premises are likely to differ from those of other premises it is envisaged that it will be necessary for each controller to be individually programmed to perform its particular function.

Moreover it is likely that the switching requirements will change from time to time and as a result it will be necessary to reprogramme the controller whenever this occurs.

To enable this to be done, use may be made of a control system comprising a controller, incorporating a transmitter of the kind described above and capable of controlling a plurality of receivers of the kind described above, the controller being capable of being programmed to enable it to control the receivers in a predetermined manner, a carrier, capable of carrying a program for the controller, and a supervisor, it being possible to interconnect the controller, the carrier and the supervisor, to manipulate the supervisor so that a program carried by the carrier is introduced into the carrier, and to disconnect the controller the carrier the supervisor again.

It is to be understood that the term program is used herein to include (inter alia) a complete sequence of steps necessary for the operation of the controller, or merely data for use in performing a complete sequence of steps necessary for the operation of the con troller.

The controller preferably incorporates a timer and is operative, in accordance with a program with which it has been programmed, to control the receivers at predetermined times.

The controller preferably incorporates dis play means operative to provide a visual indi cation of at least one of the following: the time as determined by a timer incorporated in the controller, the identity of any program with which the controller is currently pro grammed, and contents of any program with which the controller is currently programmed.

The carrier preferably incorporates solid state electronic means operative to carry a program for the controller. That electronic means is preferably reprogrammable to enable the carrier to be used to carry different pro grams on different occasions.

The supervisor preferably has user-operable insertion switch means operative to bring about the insertion into the controller of a program from the carrier. The supervisor pre ferably has user-operable programming switch means operative, when the supervisor is con nected to the controller, to enable a user to alter a program with which the controller is currently programmed.

The controller may be provided with over ride means, which can be brought into effect by a user even in the absence of the supervi sor and carrier, the override means being op erative, when brought into effect, to override a program with which the controller is cur rently programmed. The controller may also incorporate recording means operative to re cord those occasions on which the override means is brought into effect. In that case the supervisor is preferably capable, when con nected to the controller, of interrogating the controller in such a manner as to enable a user to determine the extent to which the override means has been employed, as re corded by the recording means.Where the controller incorporates display means, the ar rangement is preferably such that results of any interrogation of the recording means are displayed on the display means.

The arrangement is preferably such that the carrier can be connected to and disconnected from the supervisor, the connection not ex tending through the controller and that the su pervisor can be connected to and discon nected from the controller, that connection not extending through the carrier. With that ar rangement, disconnection of the supervisor from the controller necessarily disconnects the carrier from the controller (if there is a carrier present).

An embodiment of the control system will now be described in more detail, by way of example, with reference to Figure 3.

Figure 3 shows a controller 14 which incorporates a transmitter of the kind described above. The controller is fixed to a wall, and the operative parts of the controller are housed in a metal box with a locked door so that no unauthorised person can obtain access to the interior of the box. The operative parts of the controller also include an electronic clock, which serves as a timer. The controller also includes a display 15 which may take the form of a liquid crystal display mounted behind a window in the door of the box. In normal conditions the time, as measured by the clock, is displayed by the display 15.

The operative parts of the controller also include one or more RAMs in which a program can be stored. In normal use, the program serves to bring about operation of the transmitter in such a manner that different groups of receivers to cause the electronic switches to be switched on and off at different times.

When a system of this kind is first installed a schedule is prepared of the times at which the different groups of electronic switches are to be switched on and off. The schedule is then taken to a factory or other centre where it is used as the basis for a program to be inserted into the RAM or RAMs in the controller. A suitably programmed computer at the centre may be used in preparing the program for the controller. In using that computer an operator may be able to enter from the schedule particulars of the electronic switches td be operated and the times at which they are to be switched on and off. The resultant program can then be loaded at the centre into a RAM or RAMs in a carrier 16 which can, for this purpose, be temporarily attached to the computer.

The carrier 16 is then disconnected from the computer and taken to the premises where it is connected to a supervisor 17. For this purpose there is a multi-pin plug-andsocket connection between the carrier 16 and the supervisor 17. Both the carrier 16 and the supervisor 17 are of a size such as to be readily portable. The appearance of the supervisor is similar to that of an electronic calculator in that it is provided with rows of buttons 18 which can be depressed by a user to operate associated electrical switches in the supervisor. Unlike a conventional calculator, however, the supervisor also has a flexible lead 19 terminating in a jack-plug 20 which can be inserted into a complementary socket 21 in the box of the controller 14, thus bringing about a releasable connection between the supervisor and the controller.

When the carrier 16 is plugged into the supervisor 17 and the supervisor's jack-plug 20 is inserted into the socket 21, so that the carrier supervisor and controller are interconnected, the user can manipulate one or more of the buttons 18, which constitutes or together constitute user-operable insertion switch means, and thus bring about the insertion into the controller of the program previously stored in the carrier. The program is stored in RAMs inside the box of the controller. When the insertion of the program has been completed an associated message (which may comprise a symbol or symbols) appears on the display 15. The user can then unplug the jack-plug 20 to disconnect the supervisor from the controller. This necessarily disconnects the carrier 16 from the controller.At some later time the carrier can be disconnected from the supervisor and returned to the factory or other centre for reprogramming with a program which may be for use with a different controller elsewhere.

The controller 14 can now operate in accordance with the program it contains. Without a supervisor the licensee is unable to alter that program or to reprogram the controller.

Nevertheless the system is provided with override means enabling the licensee (or anyone else) to override the program to some extent. The override means includes an override switch 22 on the box of the controller.

When the override switch is operated, an on period for at least one of the groups of switches controlled by the controller is extended either for up to a predetermined extension period or for an indefinite extension period, the extension period in either case coming to an end when the override switch 22 is switched off. Use of the override switch 22 may enable lamps in a particular part of the licensed premises to be switched on for a period beyond the usual licensing hours, something that may be desirable when, as occasionally happens, an extension of the normal licensing hours is granted. However, the controller includes logging means, conveniently in the form of a solid-state electronic device incorporating one or more RAMs, which operates to log the date and time when the override switch is used and the duration for which it is used. That information can be obtained from the logging means with the aid of the supervisor. To this end the supervisor's jackplug 20 is plugged into the socket 21 and one or more of the buttons 18 depressed.

The logged information is then displayed on the display 15. If desired the information may be transferred to recording means in the supervisor or in a carrier plugged into the supervisor.

In addition, or alternatively, the controller 14 may be wired to a panic button or panic buttons (not shown) located in one or more suitable locations, the arrangement being such that when the panic button or one of the panic buttons is depressed all the electronic switches are switched on. The purpose of a panic button is to enable the licensee to switch on whatever lamps he wishes in an emergency. A panic button may be located in the licensee's bedroom to enable him to operate it in the event of his hearing a burglar during the night. It will be appreciated that the panic button or each panic button also constitutes override means.

It is intended that the supervisor 17 should remain in the possession of someone such as an area manager who would visit the premises only from time to time.

It may happen that alterations in the premises or in the use of certain parts of the premises may make it necessary or desirable for a relatively minor modification to be made to the program stored in the controller. An appropriate alteration in the program can be made in either of two ways. In one method the carrier 16 (or a similar carrier) is programmed at the factory or other centre and its new program if substituted for the original program in the controller. In the other method no carrier is used and the alterations are made entirely with the aid of the supervisor 17. To enable this to be done the supervisor's jackplug 20 is plugged into the socket 21 and an appropriate sequence of buttons 18 is depressed to enable program alteration to be effected and then to bring about the desired alteration. Each stage of the operation is displayed on the display 15. The arrangement is preferably such that the carrier 16 plays no part in this process so that it makes no difference whether the carrier is or is not plugged into the supervisor during program-alteration.

Appropriate manipulation of the buttons 18, while the supervisor 17 is connected to the controller also enables the identity of a program stored in the controller to be displayed on the display 15 and the contents of the program to be sequentially displayed on the display.

Claims (20)

1. A communication system for use with AC power lines and comprising a transmitter and a plurality of receivers, the transmitter being operative to apply to an AC power line of any one phase a signal including a phase identifier, which is characteristic of the phase of that line, at least one of the receivers being capable of receiving a signal from that power line and having phase identifying means operative to respond to the phase identifier characteristic of said line and thereby to render the receiver responsive additionally to at least part of the remainder of the signal.

2. A communication system according to claim 1 in which the transmitter is operative to apply signals to each of a plurality of AC power lines of different phases, each signal including a phase identifier which is characteristic of the phase of the line to which it is applied, and a plurality of receivers such that each line has at least one receiver individually associated with it and having phase identifying means operative to respond to the phase identifier characteristic of its associated line and thereby to render the receiver responsive additionally to at least part of the remainder of the signal.

3. A communication system according to claim 2 in which the transmitter is operative to apply each signal incorporating a phase identifier only to the AC power line associated with that phase identifier.

4. A communication system according to either of claims 2 and 3 in which there is a plurality of receivers associated with an AC power line and the transmitter is operative to transmit a signal which includes not only a phase identifier associated with that line but also an address, each of those receivers incorporating address identifying means characteristic of that receiver and operative on receipt of the associated address to render the receiver responsive to at least part of the remainder of the signal.

5. A communication system according to claim 4 in which the transmitting means is operative to transmit a signal including an instruction, a receiver being capable of responding to that instruction only when its phase identifying means has identified the phase identifier of the signal as being the phase identifier associated with the receiver and its address identifying means has identified the address as being the receiver's own address.

6. A communication system according to claim 5 in which the transmitter is operative to transmit a signal in which the instruction is subsequent to the phase identifier and the address.

7. A communication system according to either of claims 5 and 6 in which the transmitter is operative to transmit a signal that includes a check code, which is based in a predetermined manner on at least part of the remainder of the signal, and each receiver has checking means operative to compare a check code, actually received as part of a signal, with a check value derived by the receiver from the remainder of the signal actually received, the arrangement being such that the receiver is inhibited from carrying out the instruction of the signal unless the comparison is favourable.

8. A communication system according to claim 7 in which each receiver includes reply means operative to apply to its associated power line an acknowledgement signal when said comparison between the check code and the derived check value is favourable, and there is sensing means operative to sense whether an acknowledgement signal is received after the transmitter has supplied a signal addressed to a receiver that is operational in the system.

9. A communication system according to claim 8 in which the transmitter incorporates repeat means operative to repeat a signal if no acknowledgement signal is received by the sensing means in reply to a signal sent by the transmitter.

10. A communication system according to any one of claims 7 to 9 in which the reply means is operative to apply to its associated power line a reject signal when the signal received is correctly addressed to the receiver concerned but the check code that forms part of the signal received does not favourably compare with the check value derived by the checking means from the remainder of the signal received.

11. A communication system according to claim 10 in which the transmitter incorporates repeat means operative to repeat a signal if a reject signal is received by the sensing means in reply to a signal sent by the transmitter.

12. A communication system according to any one of the preceding claims operative to prevent selected electric lamps being switched on at other than selected on times, each of the lamps or groups of lamps concerned being connected to an electricity supply by way of a mechanical switch and an electronic switch in series with the mechanical switch, the electronic switch being operated by an associated one of said receivers, the arrangement being such that only when the electronic switch is on can the associated mechanical switch be used to switch on and off the associated lamp or group of lamps.

13. A communication system substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

14. A communication system according to any one of the preceding claims comprising a controller, incorporating said transmitter and capable of controlling a plurality of said receivers, the controller being capable of being programmed to enable it to control the receivers in a predetermined manner, a carrier, capable of carrying a program for the controller, and a supervisor, it being possible to interconnect the controller, the carrier and the supervisor, to manipulate the supervisor so that a program carried by the carrier is introduced into the carrier, and to disconnect the controller the carrier the supervisor again.

15. A communication system according to claim 14 in which the controller incorporates a timer and is operative, in accordance with a program with which it has been programmed, to control the receivers at predetermined times.

16. A communication system according to either of claims 14 and 15 incorporating display means operative to provide a visual indication of at least one of the foilowing: the time as determined by a timer incorporated in the controller, the identity of any program with which the controller is currently programmed, and contents of any program with which the controller is currently programmed.

17. A communication system according to any one of claims 14 to 16 in which the carrier incorporates solid-state electronic means operative to carry a program for the controller, the electronic means being reprogrammable to enable the carrier to be used to carry different programs on different occasions.

18. A communication system according to any one of claims 14 to 17 having user-operable programming switch means operative, when the supervisor is connected to the controller, to enable a user to alter a program with which the controller is currently programmed.

19. A communication system according to any one of claims 14 to 18 in which there is override means, which can be brought into effect by a user even in the absence of the supervisor and carrier, the override means being operative, when brought into effect, to override a program with which the controller is currently programmed.

20. A communication system according to any one of the preceding claims and incorpo- rating a controller, a supervisor and a carrier substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.