GB2060953A - Automatic synchronizing of time- pieces, e.g. time switches, by radio - Google Patents

Abstract

A time switch includes a free- running clock (31) having a timing source of its own e.g. AC mains or crystal oscillator, and switches (33, 34, 35) operated at preset times by the clock (31). A radio receiver (10-25) receives and decodes accurate time of day signals transmitted from a remote transmitter and these are used to correct or update the time of day indication of the clock (31). Switching instructions or preset switching times may also be transmitted to the receiver to programme the time clock remotely. The system is useful for controlling the switching of electrical equipment so as to use off- peak electricity. <IMAGE>

Description

SPECIFICATION Radio-controlled time switch The present invention relates to a radio-controlled time switch. Time switches are already known having a free-running clock, either mechanical or electronic, and operating to open and'or close one or more switch contacts at certain preset times. The accuracy of the switching performed by such time switches is dependent upon the accuracy of the free-running clock. Further, once the switching times have been set up in any particular time switch a special manual operation is normally required to alter these preset times. A particular application of time switches is the automatic switching of mains electricity supply, for example for a domestic consumer to operate night storage heaters from offpeak electricity.There are other potential or actual uses for such automatic timed switching of electric supply, such as switching on and off street lighting.

Although the radio-controlled time switch of the present invention is particularly applicable to the automatic timed switching of electricity supplies, it is also applicable to the switching of any other medium.

According to the present invention a radiocontrolled time switch comprises free running time clock means operative to provide an output indicative of time in a 24 hour cycle, time-set switching means responsive to the output of the clock means to effect operation of a switch when the time indicated by said output corresponds to a preset time, radio time signal receiving means for receiving and decoding transmitted time signals from a remote radio transmitter and means responsive to said decoded time signals to adjust or correct the freerunning time clock means so that its output indicates substantially the same time as said time signals.

With this arrangement any inherent inaccuracy in the free-running time clock is corrected automatically in response to the radio time signals. Furthermore, on changes from one time standard to another, e.g.

from Greenwich Mean Time to British Summer Time, the free running time clock is corrected automatically since it can be assumed that the radio time signals will reflect the change of time standard.

Particularly, with the electricity supply industry, the change between time standards is extremely important because the times of peak electricity demand do move with the time change. The time switches are frequently used to switch on certain domestic supplies, e.g. night storage heaters, as the evening demand peak is beginning to decline so as to flatten out this decline. It is difficult and expensive for the electricity supply to handle a relatively fast decline in supply demand after peak. If the time switches controlling these "off-peak" supplies do not change with changes in time standard, then at certain times of year a dip in demand can be experienced following the evening-peak before the "off-peak" supplies are switched on.

It will be appreciated that the free running time clocks used hitherto have in fact commonly been of the sort which operate in response to the frequency of the mains supply and depend for their accuracy on this frequency. The term " free running" when used herein should be construed to include such mains frequency driven clocks. With such mains clocks used hitherto for time switches, it is important to ensure that the clock does not stop if there is an interruption of the mains supply and thus battery or mechanical back-up is usually provided. However, with the radio-controlled time switch of the present invention, such back-up is not necessary.It does not matter if the free-running time clock means stops during an interruption in the mains supply, becuase on resumption of the supply the clock means is soon corrected to the right time in response to the received time signals.

Normally said switching means is responsive to effect operation of the switch into both on and off conditions at respective said preset times. Furthermore, commonly said switching means is responsive to effect said on an off operation of a plurality of switches at respective said preset times. Thus, when the time switch is used for switching the mains electricity supply to a domestic consumer, it may be arranged to switch on supplies at different times to different consumer appliances. For example, the night storage heaters may be switched on for a period of say seven hours during the period of night time off-peak demand, and the domestic water heating may be switched on for a shorter period also during the night.

Preferably, said receiving means is adapted to receive and decode also data, other than said time signals, transmitted from the remote transmitter, said data including coded instructions for effecting operation of the switch or at least one of the switches, and there is provided means responsive to said coded instructions to effect said switch operation overriding the time-set switching means. With this arrangment, actual switching commands can be sent to the time switch via the radio transmission to operate a particular set of switch contacts. This may be particularly desirable to the electricity supply authority since it will enable the control of electricity demand by switching on and off selected consumer circuits from a central point.

In a preferred embodiment, said means responsive to said decoded time signals includes time signal consistency check means comprising means for generating on receipt of each time signal a difference signal representing the difference in the time indicated by the output of the free-running clock means and the time signal, means for storing said difference signal until receipt of the next time signal, means for comparing said stored difference signal with said difference for said next time signal and providing an indication of an inconsisitency between said differences, and means responsive to said inconsistency indication to inhibit adjustment or correction of the free-running clock means in response to said time signals.It will be apparent that if two successive time signals have been correctly transmitted and decoded, then any difference between the time indicated by the signals and time output of the free-running time clock means should be substantially constant for each of the two time signals, because the time clock means should have moved on by an amount of time corresponding to the difference in time between the successive time signals. However, if there is an error in one or both of the time signals, then the differences for the two successive time signals will be inconsistent with one another and, as a result, any adjustment or correction of the free-running clock means is inhibited until consistent time signals are received. This arrangement prevents the free-running clock means from being altered in response to erroneous received time signals.

Conveniently, said free-running time clock means, said time-set switching means, and at least said means responsive to said decoded time signals are together embodied in suitable programed microcomputer system. The computer system may also include that part of the radio time signal receiving means which decodes the received data and performs any appropriate error checking operations on this data. Futhermore, the micro-computer system may be arranged to decode also said data including coded instructions for effecting operation of the switch, and may then embody said means responsive to these coded instructions to effect said switch operation overriding the time-set switching means.

Still further, the micro-computer system may embody the time signal consistency check means.

With a micro-computer system, said preset switching means may include one or more store locations in the micro-computer system containing data defining the or each preset switching time and said receiving means may be adapted to receive and decode also data transmitted from the remote transmitter, said data defining desired preset switching times and comprising instructions for loading said transmitted times data in the store location or locations, and further the micro-computer system may be operative on receipt of said data to load said transmitted times data, whereby the preset switching times can be set remotely via the radio transmission.This feature gives an added flexibility to the radio-controlled time switch since the preset switching times can be set up from a remote central point and can subsequently be altered remotely in a manner to suit the electricity generation requirements of the supply authority.

An example of a radio-controlled remotely operable supply switching means which incorporates the radio-controlled time switch embodying the present invention will now be described with reference to the accompanying drawing which is a block diagram of the apparatus.

The described example of the present invention employs time and data signals transmitted as phase modulation of the BBC Broadcast Transmission at 200 kilohertz from the Droitwich Transmitter. The phase modulated Data Transmission System proposed by the BBC is expected to have negligible effect on the audio signal which is amplitude moldulated on the Droitwich Transmission. It is proposed that the BBC Phase Modulation System will employ biphase level coding which is well known per se so as to avoid any overall phase effect on the transmitted carrier signal.Although the outlined features of the receiving and decoding circuitry for receiving and decoding data, including time signals, carried by phase modulation on the BBC Transmission will now be described, it should be understood that the particulartechnique of transmitting time signals and other data forms no part of the present invention. It is only necessary that the technique employed should enable the transmitted time signals and data to be received by the radio-controlled time switch which may typically be located inside a building.

Thus, the long wave transmissions from the Droitwich Transmitter are preferred since they are less susceptible to the screening effects of any intervening building walls etc. Further, the transmission system used must be capable of providing a sufficient data rate to enable at least the time signals to be transmitted at reasonable intervals. However, data rate requirements of the present example of this invention are very modest. With the proposed system using biphase level coded phase modulation of the BBC Transmission, a data rate to the phase modulator at the transmitter of 50 baud is quite sufficient. It will be appreciated that with biphase level coding, 50 baud represents 25 baud of actual usable data.

Referring to the drawing, the transmitted longwave signal, at 200 kilohertz, is intially picked up by the radio-controlled time switch at a ferrite aerial 10 which is conveniently located inside the time switch box. The ferrite aerial 10 feeds a pre-amplifier 11 which in turn supplies the received signal via a band-pass filter 12 to a radio frequency amplifier 13.

The output of the amplifier 13, which comprises substantially only the frequencies associated with the 200 kilohertz broadcast, are fed to a mixer 14 where they are mixed with the output of a local oscillator 15 to produce an intermediate frequency signal which is supplied via an IFfilter 16 to a quadrature detector 17. The IF filter 16 is designed with a linear phase/frequency relationship over the bandwidth occupied by the phase modulated data signal and is centred on the intermediate frequency.

In order to be sufficient only to pass the phase modulated data signal, the bandwidth of the filter 16 can be very much less than the bandwidth complete with sidebands of the amplitude molulated IF signal, so that the depth of amplitude modulation of the signal appearing at the output of the filter 16 is considerably restricted. Quadrature detectors 17 are well known and commonly used as frequency demodulators. The fact that the quadrature detector 17 provides frequency demodulation, whereas the input signal is phase modulated, is corrected for subsequently by an integrator 18. A further top cut filter 19 is provided before the integrator 18 to remove unwanted components of the output of the detector 17 which may arise due to noise and the inherent undesirable AM to PM conversion of the speech and music frequencies of the broadcast programme.

The output of the integrator 18 is the base-band data signal which should ideally correspond to the phase modulation applied to the 200 kilohertz carrier.

In practice, in order to avoid high frequency components in the phase modulation applied to the carrier at the transmitter, the logic pulses are first rounded before being phase modulated onto the carrier. Thus, the base band data signal from the integrator 18 similarly comprises rounded pulse signals. To reconstitute relatively square pulses, the output of the integrator 18 is fed to a slicer 20 which has substantially square wave output corresponding to the transmitted data signal.

In order to handle this pulse stream from the slicer 20, a data clock recovery circuit 21 monitors the incoming pulse stream and generates a regular clock pulses corresponding to the periodicity of the incoming data so that the successive bits of the incoming data stream can be identified.

In the BBC proposal, the data to be transmitted on the 200 kilohertz transmission will be transmitted as successive frames of a predetermined number of bits, e.g. 100. Each frame begins with a certain Frame Alignment Word (FAW). As mentioned previously, the data is transmitted using biphase level code according to which a logic level "0" in the source data is transmitted as a sequential pair of bits " 01 ", and a logic " 1 " is transmitted as "10". Thus, in the bit stream of the data proper from the slicer 20 there should never be more than two successive 0's or 1's. The frame alignment word is arranged to break this rule and may comprise for example (10001110).A frame alignment detector 22 is arranged to look for and identify the frame alignment words in the bit stream from the data slicer 20 by recognising this characteristic feature. Once the frame alignment word is identified in the unit 22, the remainder of the bits in each frame can be identified for decoding. Following the identification of each frame in the alignment unit 22, the data bits in each frame (other than the FAW) are checked for any errors in the biphase level coding in a biphase code checking unit 23. The data in each frame is then further given a cyclic redundancy check (CRC) by a further checking unit 24. For this purpose, each frame of data contains a number of bits which comprise a CRC word. This CRC word is calculated at the radio transmitter by performing a mathematical operation on the message data to be sent in the particular frame.Thus, at the receiver, in unit 24, a check can be peformed on the message data in the frame by peforming the same mathematical operation on this data and checking that the resulting word produced is the same as the CRC word contained in the frame.

In a preferred arrangement with the present example of the present invention, the CRC word is generated at the transmitter using not only the message data contained in the particular frame containing the CRC word but also a proportion of the data contained in the preceding frame. Thus, at the receiver, an error occurring in that part of a message data which is used to make up the CRC word not only of its own frame but also the following frame will produce a failure of the cyclic redundancy check on both the two frames. On the other hand an error occurring in the remaining part of the message data will produce a failure of the cyclic redundance check only on its own frame. Thus it can be determined whether an error is in one part of the message data orthe remaining part.For the purposes of the example of the present invention, the part of the message data in each frame which is used to make up two successive CRC words is that part which contains all the data used in controlling the radio controlled time switch.

The use and operation of cyclic redundancy checking is described in an article called "Cyclic codes for error detection" by Peterson and Brown in Proceedings of the l.R.E. Volume 49 No. 1, pages 228 to 235.

There is also an article by Cavell entitled "Implementation of Cyclic Redundancy Check Circuits" in Electronic Engineering, February 1977, pages 51 to 55.

If the biphase level error checking unit 23 detects a biphase level error in the message data of a particular frame it can be expected that the cyclic redundancy check will also indicate a failure. It is proposed to employ this double checking system in an error correction technique whereby appropriate bits in the message data are successively reversed to correct the biphase level error, until by trial and error a bit correction is discovered which cures the cyclic redundancy check failure. This procedure may succeed in correcting some simple logic errors in the message data received.

The message data of each frame passes after the cyclic redundancy check to a unit 25 which decodes the message data. The decoded data in the present example comprises time signals on a line 26, data for the special purposes of the Broadcasting Authority (the BBC in this instance) on a line 27, data defining switching instructions for the radio-controlled time switch, identified as E.S.I. data, on a line 28 and finally a flag on a line 29 which is generated if there is no usable data available.

The time signals on the line 26 may comprise logic words identifying a particular time of day on a 24 hour clock. These signals are transmitted at intervals which are generally irregular and depend on demands on the available space in the data transmission channel made by other message data. However, on receipt of a time signal a unit 30 compares the time indicated by the signal on the line 26 with the time indicated by the output of a free-running real time clock 31. Stored in the unit 30 is also an indication of the difference between the last received time signal and the time indicated by the clock 31 at that time. Before the difference between the latest time signal and the clock output is employed to up-date or correct the clock 31, this difference is checked against the previously measured difference to ensure that the difference values are consistent.If the clock 31 is operating reasonably accurately, when free-running, then there should not be an excessive variation in the measured error in the clock output on receipt of two successive time signals. If there is a sudden significant variation in this error, it is probable that there is an error in the time signal on the line 26. On changing between standard times, e.g. from Greenwich Mean Time to British Summer Time, there will be a sudden jump of one hour in the time indicated by the received time signals on the line 26. The consistency checking unit 30 then will not correct the clock on receipt of the first time signal in the new time standard. However on receipt of the second time signal at the new standard, there will then be a consistent error indicated so that the free-running time clock 31 will then be suitably corrected to the new standard.

Thus, if the incoming time signal on the line 26 passes the consistency check it is supplied to a correction unit 32 to up-data or correct the clock 31.

A master control unit 33 is connected to operate a number of, typically three, latching contactors 34.

One or more of the contactors 34 may be designated for operation at certain specified times of day, for example so that the contactor is closed to supply electrical power only during certain hours of the night. Forthis purpose, the preset times of operation of the or each contactor are stored at 35. A comparison unit 36 compares the time output from the real time clock with these stored preset times and delivers a signal to the master control 33 when the clock output corresponds with one of the preset times. The signal on the line 37 is sufficieht to indicate to the master control 33 which of the contactors 34 is to be operated and whether the operation should close the contacts or open them.

Apart from operating the contactors 34 at the preset times, the master control 33 may be arranged also to operate one or more of the contactors in response to predetermined instruction codes received on the line 28. A store 37 contains predetermined codes respectively representing closing and opening of the various contactors. The master control 33 compares any incoming code instructions on the line 28 with the stored codes and operates the contactors 34 appropriately. One or more of the contactors 34 may be operable both by commands from the comparison unit 36 at preset times and in response to specific instruction codes received on the line 28 via the radio transmission.

It can be seen that this structure of a radiocontrolled time switch has considerable advantages to the electricity supply autority. As a time switch, thetiming accuracyofthe unit can be maintained and also changes of time standard can be easily accounted for. Furthermore, specific switching instructions can be sent by the authority over the radio transmission link to operate selected sets of contactors thereby enabling direct control over the electricity power demand.

In an alternative arrangement, it may be arranged that the preset times for operating the contactors 34 can be loaded into the store 35 by the master control 33 in response to appropriate instructions and data received on the line 28. Thus, the electricity supply authority could alter the preset switch timing by sending over the radio transmission link instructions and data defining the new switching times. The master control will then respond to this data by inserting the new switching times into the store 35.

The master control 33 responds also to the flag on the line 29 indicating that no identifiable data is being received. Further, the control 33 responds to a time signal consistency failure flag from the consistency checking unit 30 by ensuring that the clock 31 is not updated or corrected by received time signals.

On receiving either one or both of these flags, the control 33 ensures that the switching operation of the contactors is determined only in accordance with the preset times in the store 35 as indicated by the output of the time clock 31, until such time as both are cleared and a further time signal or switching instruction is received. A further flag is applied to the control 33 from a unit 38 on restoration of the mains power supply after a failure, to ensure an orderly restart to the operation of the time switch.

The radio-controlled time switch has been described in the above with reference to the accompanying drawing in terms of a number of separate units identified as blocks in the drawing. However, it is to be understood that substantially all the operations of the time switch subsequent to the receiving and preparation of data in the form of a logic stream, can be embodied as a suitably programmed microcomputer connected to receive the output of the data slicer 20 and the data clock recovery unit 21 and to provide switching currents to operate the contactors 34. The free-running real time clock may be a crystal controlled pulse generator with suitable dividers and counters to provide an indication of the time.When embodied as a micro-computer system, the blocks illustrated in the accompanying drawings should be interpreted as representing the functional flow of the programme rather than discreet items of hardware in the system. Furthermore, the stores 35 and 37 are then embodied as specified locations in random access memory.

The radio-controlled time switch described herein can be operated in various ways providing considerable flexibility to the electricity authority in the control of electricity power demand. Arrangements can be made for sending in advance specific instruction data for operating predetermined sets of contactors at some later specified time in the day. This can be done simply by arranging for any of the contactors to be operated in response to commands from the preset time comparison unit 36 and arranging also for the store 35 to be loaded with appropriate time codes in response to the instruction data received on the line 28 by the control 33. Typically, a 24 hour cycle of time switching instructions transmitted over the radio link would remain in the store 35 until overridden by further transmitted data.Such an arrangement would be particularly useful for the control of for example street lighting where the operational cycle has to be changed occasionally with increasing and decreasing daylight hours.

The arrangements described would typically be used as radio controlled time switches in domestic.

premises and any one instruction sent over the radio link would be received simultaneously by all the installed time switches. Variations in the coding of the instructions can be used if it is desired that only certain groups of time switches respond to particular instructions. This can give a more precise control over the electricity demand in different areas. Furthermore, it would be possible to modify the described arrangement so that time switches are individually addressable by the transmitted instruction data. This would allow the electricity supply authority to vary remotely the operation of the time switch in the premises of a particular consumer. Then if a consumer changed from one tarrif to another, his time switch times could be remotely altered appropriately without the need of a visit to the premises.

The free-running clock in the timeswitch must provide an unambiguous indication of the time in any 24 hour period. However, it may also provide an indication of the date. It is intended that the time signals to be transmitted on the B.B.C. 200 kilohertz transmission will include date information, and then the timeswitch can be pre-programmed with pre-set switching times for an entire year.

Claims (8)

1. A radio-controlled time switch comprising free-running time clock means operative to provide an output indicative of time in a twenty-four hour cycle, timeset switching means responsive to the output of the clock means to effect operation of a switch when the time indicated by said output corresponds to a preset time, radio time signal receiving means for receiving and decoding transmitted time signals from a remote radio transmitter and means responsive to said decoded time signals to adjust or correct the free-running time clock means so that its output indicates substantially the same time as said time signals.

2. Atime switch as claimed in claim 1 wherein said switching means is reponsive to effect operation of the switch into both on and off conditions at respective said preset times.

3. A time switch as claimed in claim 2 wherein said switching means is responsive to effect said on and off operation of a plurality of switches at respective said preset times.

4. A time switch as claimed in any preceding claim, wherein said receiving means is adapted to receive and decode also data, other than said time signals, transmitted from the remote transmitter, said data including coded instructions for effecting operation of the switch or at least one of the switches, and there is provided means responsive to said coded instructions to effect said switch operation overriding the time-set switching means.

5. Atime switch as claimed in any preceding claim wherein said means responsive to said decoded time signals includes time signal consistency check means means for generating on receipt of each time signal a difference signal representing the difference in the time indicated by the output of the free-running clock means and the time signal, means for storing said difference signal until receipt of the next time signal, means for comparing said stored difference signal with said difference for said next time signal and providing an indication of an inconsistency between said differences, and means responsive to said inconsistency indication to inhibit adjustment or correction of the free-running clock means in response to said time signals.

6. A time switch as claimed in any preceding claim wherein said free-running time clock means, said time-set switching means, and at least said means responsive to said decoded tirne signals are together embodied in a suitably programmed microcomputer system.

7. A time switch as claimed in claim 6 wherein said preset switching means includes one or more store locations in the micro-computer system containing data defining the or each preset switching time and said receiving means is adapted to receive and decode also data transmitted from the remote transmitter, said data defining desired preset switching times and comprising instructions for loading said transmitted times data in the store location or locations, and further the micro-computer system is operative on receipt of said data to load said transmitted times data, whereby the preset swot( hing times can be set remotely via the radio transmission.

8. Atime switch substantially as hereinbefore described with reference to the accompanying drawing.