WO1996000399A1 - Metering systems - Google Patents

Abstract

One aspect of the invention provides a device for storing periodic data indicative of the consumption of a metered quantity, the device comprising: means for receiving periodic data; data storage means having a plurality of data storage locations; and control means for controlling storage of periodic data items indicative of consumption during respective first periods of time in respective data storage locations, the control means being arranged to determine when additional storage is required for new received periodic data and then to accumulate a plurality of periodic data items, including at least one stored data item, to produce a compressed data item for a second period, equal to the sum of the first periods to which the accumulated data items correspond, and to control storage of the compressed data item in a said data storage location. Compressed data may be generated from a plurality of stored data items for the first periods, thereby to free at least one data storage location for new data. The device may be a meter for generating the periodic data including timer means for monitoring the time while the data is being generated. The compression is preferably performed using a series of predefined time sets, each comprising a plurality of time set periods corresponding to respective predefined, finite periods of time. A given time set period may correspond to a period of time equal to the accumulated periods of a plurality of time set periods from other time sets.

Description

M TRRTNG SYSTEMS

The present invention relates generally to metering systems and provides various methods and apparatus which can be used in such systems to store or communicate metered data, ie. data indicative of the consumption of a metered quantity.

Various aspects of the invention will be particularly described herein with reference to electricity meters and associated equipment. However, it is to be appreciated that the invention can equally be applied to all types of metering systems including gas, water and other systems used to record metered data.

Currently a number of types of electricity meter exist for the recording of electricity consumption. Generally, two generic classes of meter exist. First, those which record a cumulative total and, second, those which record the consumption during a defined period (or record cumulative consumption at the start and/or end of a defined period). The first class of meter will be referred to herein as cumulative meters, and the second as periodic meters.

A meter may also exhibit functionality for both cumulative and periodic operation. In this case, it is a combined meter. Such a meter usually has registers to store cumulative data, and a memory to store periodic data usually as a profile with periods of constant duration, the periods following one another chronologically.

Figure 1 of the accompanying drawings illustrates the basic circuit required for a cumulative meter. A measurement circuit 1 of the meter is used to measure the desired properties such as current flow, voltage, gas flow etc. The measurement circuit 1 provides an output indicating the number of units measured. A register 2 is used to store the cumulative meter reading. The register value and units consumed (from the measurement circuit 1) are added by an adder 3 to form a new register value.

Alternatively, the measurement circuit may indicate when a single unit (or fractional unit) has been measured, and the register contents may be incremented accordingly. Here, the adder 3 can be replaced with an incxementer which is generally simpler to implement using digital logic and some forms of mechanical logic. This simple structure can be enhanced to provide cumulative data for specific times. Thus, a register A could record cumulative data during one period (say midnight to 0600 hours) and a register B could record data for all other periods. Figure 2 of the accompanying drawings shows the basic circuit for such a meter. In this meter, the register logic is replicated to provide sufficient registers, A and B. The output of the measurement circuit 1 is then directed to the currently "active" register by means of a timer control circuit 5 which monitors the time and controls a switch 6 to connect the output of the measurement circuit 1 to the appropriate register via the associated adder. The timer control 5 is programmed with the periods for which each register is required to accumulate measurements in.

In cumulative meters (Figures 1 and 2) the register value is never re-set or cleared. It is therefore a permanent record of the consumption. The period over which a register records consumption is undefined and is not fixed. Thus, the same register in different meters can represent the consumption during completely different periods depending on the age and use of the meter. If , as in Figure 2, a register is used to record data between, say, midnight and 0600 hours, then the register will record such data since it began operation. The recorded data will not represent the consumption during a period in any one day or a period in a defined number of days.

Periodic meters record consumption during specific periods of time. In a cumulative meter a register may record data during each and every day, so the duration of the associated measurement period is indefinite and theoretically infinite. In a periodic meter, however, the period of measurement is defined and finite. Thus a data value may be recorded for a single period of, say, midnight to 0600 hours on a particular day. Current periodic meters therefore record data during finite periods of continuous time. Figure 3 of the accompanying drawings illustrates the basic structure of a current periodic meter.

In the periodic meter, a register 7 is again used to accumulate data from the measurement circuit 1 via an adder during a period of time. However, timer control circuitry 8 controls the overall operation of the unit. At the end of the finite period, the timer control 8 causes the value held in the register 7 to be loaded to a location of a memory 9, the location being defined by an address control unit 10. The timer control 8 may then clear the register (depending on whether the recorded data is to indicate consumption during a period or the cumulative value at the end of the period) and increments the address control.

Each memory location is used to record the consumption data during a specific period. There are a number of ways to store the data. The options are:

1. location 0 is used to store the start time. Location 1 then stores the metered data for the first period, location 2 stores the meter data for the second period, and so on. Thus location i will store the metered data for period i;

2. metered data is stored in the current address and the memory acts as a cyclic buffer. hen the memory becomes full, recording begins again from location

0 overwriting the oldest data. If there are N memory locations then the memory will always contain the last N metered data values.

The arrangement shown in Figure 4 of the accompanying drawings enables method 2 to be implemented. Consumption values stored in the memory 12 are directly incremented with measured data from the measurement circuit 1 (or incremented via a register). An address counter 13 provides the address of the current metered data. When a period ends, the timer control 14 increments the address counter 13 to reference the address for the next period's metered data. However, the timer control and associated logic assumes that each period is only active once and therefore that periods of measurement are continuous. The address counter 13 can therefore be a simple counter which operates between 0 and N-l, where N is the number of memory locations available for periodic data. In this system, a mechanism is required to ensure a memory location is cleared prior to being re-used for a new period and therefore that the consumption value for a period starts from 0 and is incremented during the period to record the associated consumption.

An alternative way to achieve the system would be to record total cumulative consumption as a standard cumulative meter does, and then to store the cumulative meter reading in memory at the end of each period. Thus, the memory would not contain consumption values during individual periods but the cumulative reading at a defined point in the period. The system of Figure 3 is suitable for this type of application. In this situation, the register 7 would be used to record the total cumulative consumption (as per a cumulative meter) and the registers value would be stored in the memory 9 at the end of each period at the address defined by the address control 10.

It is desirable for meters to record consumption during defined finite periods. Current cumulative meters cannot do this unless the current meter reading is taken by some additional means at the beginning and/or end of the required period(s). Current periodic meters can do this, although, as explained above, they can only record data during finite periods of continuous time. This restricts the application and efficiency of such meters. Another problem with current periodic metering is that if a periodic meter has

N memory locations and records metered data for periods of P duration, then it can only record data for a duration of N x P. After this time an error condition exists or it must overwrite previous data or cease recording.

Currently, most meters are read by manual means (a person visits the meter location). However, various methods have been proposed for the electronic retrieval of metered data, using a communications system to retrieve metered data from a remote location (meter). If the meters are used to record periodic data, then the communications system can be used to retrieve data from a meter for a number of periods. However, care needs to be used to ensure that the data received by devices in the communications system does not exceed their data capacity. If a controller in the communications system requested periodic metered data from multiple meters and was then unable to forward the data a situation could occur where:

1. periodic metered data has been retrieved from meters and potentially deleted or overwritten in the meters; 2. the device in the communication systems reaches the limit of its capacity;

3. the communications device is unable to forward the periodic metered data which would have freed memory in the device;

4. the communications device receives further data or commands requiring additional storage.

In such a situation, the probable result would be loss or corruption of some data in the communications system.

The various aspects of the present invention relate to improvements in existing metering systems.

In accordance with one aspect of the present invention there is provided a device for storing periodic data as set forth in claim 1.

In accordance with another aspect of the invention there is provided a meter as set forth in claim 5.

In accordance with a further aspect of the invention there is provided a meter as set forth in claim 16. In embodiments of the aforementioned aspects of the invention, periodic data is accumulated when additional storage is required for new data to produce compressed periodic data for a longer period, thereby allowing storage of the new data. Devices in a metering system can therefore handle various situations without error or loss of data, only the resolution of the data being changed. Devices embodying these aspects of the invention may be meters themselves or other devices in the metering system, for example devices in a communication system for transferring metered data from meters to a remote control station.

The invention further proposes alternative means to obtain metered data from meters. Thus, in accordance a further aspect of the invention there is provided metering apparatus as set forth in claim 18. The transportable device may be a smart card. (It is to be understood that a "smart card" as referred to herein could be, for example, a card having a memory and appropriate communications interface or, for example, an intelligent smart card operating under microprocessor control, as appropriate). In systems using a transportable device a problem can exist when a meter transfers metered data to the transportable device and then deletes that data from memory. If the transportable device, such as a smart card, is subsequently lost or damaged, then the data is also lost. Accordingly, it is preferred that the control means is arranged to delete or allow over-writing of data stored in the first storage means in response to a command from the transportable device identifying the data to be deleted or overwritten. Thus, the data can be transferred to the transportable device which is then transported to a remote location where the data is read. When the transportable device is next connected to the meter, the transportable device generates the command indicating the data which can be safely deleted. The invention also provides a method for transferring data as set forth in claim 22. Problems may also occur where one device, eg. a meter, in a metering system transfers periodic data to another device, eg. a transportable device or a link or device in a communication system, if the data storage/transmission capacity of the second device is insufficient to accept the data to be transferred. Accordingly, another aspect of the invention provides apparatus as set forth in claim 23. In embodiments of this aspect, data is compressed on down-loading from a device to the next stage in a metering system, allowing greater flexibility in the operation of the system without loss of data due to insufficient data handling capacity.

The invention also provides for compression of data retrieved from multiple sources as may be required in a number of circumstances. Accordingly, an aspect of the invention provides a method for retrieving periodic data as set forth in claim 29. Another aspect of the invention provides apparatus for processing periodic data as set forth in claim 32. In embodiments of these aspects, data items indicative of consumption at a plurality of different predefined logical groups of said metering points may be accumulated to produce respective compressed data items for said different groups, which compressed data items are then stored. These aspects of the invention enable compression of data according to a variety of schemes such as customer identifier, geographical location or customer's supplier, as but a few examples. Data items can be accumulated according to the logical grouping by a transportable device which is used for meter-reading. Another aspect of the invention provides a meter as set forth in claim 35. Yet another aspect of the invention provides a device for recording periodic data items as set forth in claim 37. In accordance with these aspects of the invention, periodic data can be simultaneously recorded with different time resolutions, the higher resolution data items being accumulated to generate the lower resolution data items. As previously described, existing periodic meters can only record metered data for finite periods of continuous duration, and this substantially restricts the flexibility of metering systems employing these meters. In accordance with another aspect of the invention there is provided a method for storing data as set forth in claim 43.

Another aspect of the invention provides a meter as set forth in claim 47. Said predefined, finite periods of time for which data is stored may comprise a common time interval, so that data values are obtained for overlapping periods. Where a given period consists of two non-continuous time intervals for example, another period may include the intervening time interval, ie. periods may be interleaved with one another.

Existing meters are constructed to store data for specific time periods, so that if a change in the measurement system is required the meter must be changed or modified accordingly. A further aspect of the present invention provides a meter as set forth in claim 17. Meters embodying this aspect of the invention enable a metering system to be highly flexible since the measuring system employed by each meter can be set up as required for a particular situation, and may be altered as necessary when required. It will of course be appreciated that an apparatus or method may embody one or more of the various aspects of the present invention. Further, it is to be appreciated that, where features are described herein with reference to an apparatus embodying the invention, corresponding features may be provided in accordance with a method of the invention, and vice versa. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a schematic block diagram of a cumulative meter; Figure 2 is a schematic block diagram of a dual period cumulative meter; Figure 3 is a schematic block diagram of one form of periodic meter; Figure 4 is a schematic block diagram of another form of periodic meter;

Figure 5 is a schematic block diagram of one example of a periodic meter embodying the invention;

Figure 6 is a schematic block diagram of another example of a periodic meter embodying the invention; Figure 7 is a schematic block diagram of another form of meter embodying the invention; Figure 8 is a schematic block diagram illustrating the operation of another form of meter embodying the invention;

Figure 9 is a schematic block diagram illustrating the operation of a further form of meter embodying the invention; Figure 10 is a schematic block diagram of a further device embodying the invention;

Figure 11 is a flow diagram for use in explaining operation of another embodiment of the invention; and

Figure 12 is a schematic block diagram of a further embodiment of the invention.

Some of the embodiments of the present invention to be described below utilise a system of "time sets" for storing/processing periodic data. Prior to discussing the embodiments in detail, the principal of the proposed time sets will be described.

A number of time sets can be defined where t_j is the default. Each time set will contain a number of periods (time set periods). The i* period in t_j can be referred to as t_j(i), and similar the i^Λ period in t_B is .,(_). A series of time sets can be defined where t₂ is derived from t„ t₃ from tj, and so on. The rules when defining a time set t_B from t_B__j may be:

1. each t_B period must contain a finite integer number of t,_, periods; 2. each t.., period must be contained in one and only one t_B period.

Rule 2 is not essential to operation of embodiments of the invention but, if implemented, ensures that measurements using a time set collectively relate to a defined period of time without duplication.

The rules may be extended or modified to account for particular situations or requirements. The basic result of time sets is a set of periods of defined finite duration where a period in any time set corresponds to a finite integer number of periods from other time sets.

Meters embodying the invention can be designed to record periodic metered data using the proposed time sets. For example, if a meter is required to record data for periods t_B (a) to t_B (z), ie. data using time set t_B between periods a and z, then it can store each reading in a memory location. An embodiment using time sets as the basis for recording data could have a similar structure to that of periodic meters illustrated in Figure 3. However, a preferred embodiment of the invention is illustrated in Figure 5. The basic circuit structure involves a measurement circuit 1, adder 15, memory 16, and control means in the form of a timer control unit 17 and address logic/look-up unit 18 connected as shown. In the embodiment, the timer control 17 determines the current period of measurement. Unlike prior meters, the control means of Figure 5 can, if required, re- select a period for which some data has already been recorded. Thus, the recording periods for which data is stored in a given location of the memory 16 can consist of non-continuous time intervals, and can be interleaved with other periods. The timer control 17 monitors the time while data is being generated and determines the currently active recording period which is then indicated to the address logic 18. For example, the required recording period may be defined as a time set period t_B (i) which is indicated to the address logic. The address logic then converts the period into a memory address whereby generated data is accumulated in the associated memory location each time the recording period is active. Thus, the timer control 17 determines which period is active at any given time and this is translated into an address for that period wherein the data is accumulated. Alternatively, the contents of the memory location could be loaded to a register or working memory location for accumulation of new data for that period. Either way, as measurements are performed the current metered data value for that period is adjusted, and when the period ends the timer control will indicate the next period to the address logic. The current (final) value for the previous period's metered data is thus saved in its memory location and a new location selected for the new period. With the above structure, recording periods can be non-continuous periods.

Thus, a given recording period can be used to record data from time intervals in different days. For example, a recording period may be used to record data between predetermined times in successive days for a week. Whenever a given recording period is active, the associated memory location is selected and measurements added to the existing value. Therefore, when a memory location is selected during a recording period via the address logic, its contents are not cleared. A separate mechanism is therefore provided to clear the memory either (1) at the start of the recording or (2) when a period first starts (ie. when the associated memory location is first accessed). Option 1 can be performed by some overall control logic, for example implemented in software within a processor (not shown) managing the overall meter. In the embodiments shown, however, option 2 is implemented by the address logic 18 when a memory location is first accessed for a given recording period. Thus, when a given period is first active, the memory location will first be cleared before actual data is accumulated in the memory location. Of course, option 2 could equally be implemented under control of the timer control 17. Also, a register may be used to act as a temporary store for a given period's recorded value, and an embodiment illustrating such an implementation is illustrated in Figure 6.

In Figure 6, a measurement circuit 1, adder 20, register 21, and memory 22 are connected as shown with control means in the form of a timer control unit 23, address logic/look-up unit 24, and load control unit 25. Here, the timer control 23 again monitors the time and identifies which period is active, indicating this to the address logic 24 which accesses the associated memory location. When a memory location is first accessed, ie. at the start of a given period, the register contents are cleared by the load control unit 25 under control of the timer control unit 23. Accumulation of data for that period thus starts from 0. When the period becomes inactive again (eg. at the end of the first time interval of that period) this is indicated by the timer control 23 to the load control unit 25 whereupon the contents of the register 21 are loaded to the memory location indicated by the address logic 24 for that period. If and when that period next becomes active (at the start of the next time interval of that period if any, ie. where the period consists of non-continuous time intervals) the contents of the memory location are loaded via the load control 25 to the register 21 whereupon accumulation of data for that period continues in the register until the period next becomes inactive and the new data value is reloaded to the memory location.

The embodiments described above allow periodic data to be recorded for non- continuous time periods and also periods which are interleaved with one another. However, embodiments may be designed to provide these features with the additional option of more than one period to be active at any point in time, ie. with overlapping recording periods. Figure 7 illustrates a simple example of such an implementation using registers. Here, only two registers A and B are shown providing storage for data generated during two overlapping periods, though of course multiple registers can be provided to provide for multiple recording periods. In this simple example, the output of the measurement circuit 1 is supplied to a switching circuit 26 having 2 outputs connected to the respective registers A, B via associated adders 27. The switching circuit 26 can selectively connect the measurement circuit output to each of the adders 27 under control of the timer control unit 28. The timer control 28 determines when each of the two recording periods for which data is to be stored in the respective registers A, B is active, and controls the switching circuit 26 to make the connections accordingly. When the periods are both active, (ie. when the periods overlap) the measurement circuit output is supplied to both adders. When a period is first activated, the timer control 28 resets the corresponding register whereby accumulation of data for that period in the register starts from 0. When the same period is next activated, new data is added to the register value for that period.

In the embodiments of Figures 5 to 7, it should be noted that the control logic clears the memory location or register contents at the first enabling of a particular recording period. This being the case in Figures 5 and 6, the memory can be still be used as a cyclic buffer. Thus, if the memory contains N locations it can be used to record consumption for N periods even if some or all of those periods represent non- continuous time. When a new period is enabled for the first time the associated memory location will be selected. In Figure 6, the register contents will be cleared and subsequent consumption added to the registers value. When the timer control de¬ selects a period the current register value is written to the selected memory location. If a period is re-selected (as a result of being a non-continuous time period) the register contents are loaded from the existing value in the memory location associated with that period.

If period N+l is selected then the address logic will select a memory location which has previously been used (since the memory can only store N values). However, the register contents will be clear because N+l is a new period. When the period is de-selected the register contents will be stored in memory over-writing the old period's value. In this way, the memory acts as a cyclic buffer.

Unlike prior meters which are constrained by their construction to record metered data in a particular manner, meters embodying the present invention can be programmable to record periodic data using any required pattern of periods. Individual periods may be non-continuous and periods may be interleaved with each other as previously described. Also, periods may be of different durations. The control means of meters embodying the invention may be programmable in response to a programming command generated by the supplier for example. The programming command can be transmitted to the meter in any convenient manner, for example via a telecommunications system. Thus, in the embodiments of Figures 5 and 6, for example, the timer control 17 can be programmed with the required recording periods and the address logic programmed to allocate (and clear if necessary) memory space for these recording periods. Thus, when the meter receives the command to record periodic data according to a particular pattern of recording periods, the control means allocates memory for the data and sets up the timer control to commence recording according to the desired pattern. If a group of time sets as previously described is defined within the system, eg. predefined in the control means of the meter, then a command may program the control means to effect recording using particular time set periods as the recording periods. The required recording periods could be from different time sets or could even be different to the periods defined by the time sets. Thus, a highly flexible and efficient metering system can be provided.

Rather than using the memory, or part of the memory, as a cyclic buffer as described with reference to Figures 5 and 6, periodic data items representing recorded values for a period can be compressed to make some location free for further storage. Embodiments of the invention which make use of the time sets previously described and which provide for compression of periodic data will now be described.

As previously described, time sets can be defined such that a period in time set t_B contains several periods from time set t_B_j. Thus, if a meter is recording data and reaches the limit of its memory (or an allocated part of the memory), then it can convert existing data from one time set t_ to time set t_₊₁. Using rule 1 above for defining the time sets, a t_I+ι data value will represent the total of several t_x data values. Thus, several t_x data values can be combined to form one t_x+1 data value and in the process free some memory. The meter is therefore able to compress data and release memory for other purposes whilst still maintaining the existing data's validity.

If the meter reaches the point where storage is required for a new period but memory space is not available, then, in existing meters as previously described, an error condition would exist or data must be over-written or recording must cease. In embodiments of the present invention, the control means can be arranged to detect such a situation. For example, in the system previously described with reference to Figure 6, such a situation could be detected by the address logic 24 if it is required to access a location N+l where the memory contained N locations, or if required to access a location which had already been used to store a periodic data item. In such circumstances, the meter can compress recorded periodic data to make additional storage available so that data for new periods can be recorded. For example, in Figure 6 the address logic can be programmed to effect the necessary compression of recorded data in the memory and reallocation of memory space in accordance with the predefined algorithm. Alternatively, the address logic may be arranged to indicate the need for compression to a compression controller (not shown) which effects the necessary compression of data in the memory and instructs the address logic concerning the reallocation of memory space. In embodiments of the present invention, periodic data can be compressed in a number of ways. These are as follows:

1. where a time set period t_x(i) is defined and periodic metered data exists for a number of periods which collectively exactly correspond to the period of t_(i), then that periodic data can be combined to form a single value for t_x(i); 2. where a time set period t_x(i) is defined which contains sub-periods from time set t_x__j, then if periodic data exists for those sub-periods the periodic data can be combined (accumulated) to form a single value for t_(i);

3. where the meter has recorded periodic data for more than one period, then it can define a new period, not necessarily corresponding to any defined time set period, which is the combination of the recorded periodic data periods and can combine the recorded data for those periods to form a single value for the new combined period;

4. the last period (or any period for which periodic data already exists) could be extended to include new data.

When a unit requires additional storage for new data, it may perform the compression on all existing data or on selected values. One preferred method is to compress the oldest data values with the highest time resolution, and to compress sufficient as to provide free storage to meet the immediate needs.

For example, if a meter has 10 data storage locations for storing periodic data, then it could record 10 periodic values. If it initially recorded values using periods from time set t_j then the data storage locations would be allocated as follows:

t>(i) t,<2) t,<3) t_(4) tι(5) t,(6) t,(7) t,(8) t,(9) t,(_0)

A problem exists if and when the meter needs to store t,(ll). However, if time set t₂ is defined such that time set period t₂(n) corresponds to time set periods tι(2n-l) and t_j(2n) then existing data can be compressed in accordance with these time sets. In the above example, t₂(l) would represent t,(l) and t_j(2). These values can therefore be compressed to form a new, compressed value for t₂(l). The memory locations would then be used as follows:

ta ) t,(3) ,(4) t,(5) t,(6) t.(7) t,(8) t_.(9) 1,(10)

This provides the storage required to record t_j(ll). However, if the meter then needs to store a value for t_j(12) a storage problem again exists. The memory now contains values for both t_j and t₂. The t_j periods have the smallest resolution and are therefore compressed first. The oldest t_j values are t,(3) and t_j(4) which can be compressed to form t₂(2). After this compression, and storing of t,(12), the memory would look as follows:

t₂(i) t₂(2) t,(5) t>(6) t,(7) t,(8) t,<?) 1,(10) tι(H) t,(12) If this process continues, then eventually the memory will contain periodic data items corresponding solely to ^ periods as shown below:

φ) Φ) Φ) Φ) Φ) Φ) Φ) Φ) Φ) φO)

If further storage is required for new generated data, then data values corresponding to t₂ would have the smallest resolution and the oldest of these would be compressed first to form compressed data items for t₃ periods according to the same system. It will be appreciated that this process can continue indefinitely whilst suitable time sets are defined in the meter or whilst the meter can define new combined periods.

At any point in time in the above examples the memory contains data values corresponding to one or two time sets, where all values up to a point are using one time set and all values beyond that point use the second. The allocation of memory locations to time periods at a given time can be stored in the address logic or compression controller (if provided) and transferred with retrieved data when the memory is read, for example by means of a communication system or other medium to be described below. Alternatively, data indicative of the periods to which metered data values correspond may be stored in the memory itself, for example as part of a data word containing the data value.

While the above simple example illustrates the principal of the compression, the system can of course be enhanced so that more than two time sets are in use at any time, and each memory location could contain the metered data (consumption) value, time set identifier and time set period identifier. If a maximum of two time sets are used at any point in time, then only the following identifier data may be recorded: start time, start time set (A), start period identifier, the point (memory location) of transition between recording with time set A and time set B, second time set B, and possibly also the period identifier for time set B at the transition in recording. This information can be stored separately of the memory, eg. in the address logic. Clearly this system can be extended such that more time sets can be used simultaneously if required. Meters embodying the invention and utilising the compression techniques described above can be of significant advantage in a metering system. It may be desirable to have a single standard form of meter. However, in different situations the duration of measurement periods for periodic data may vary. This could require the use of different meters or direct programming of meters. Using the compression techniques described above, however, a meter can begin recording periodic data using a defined default time set or pattern of periods. For example, the meter could begin by recording periodic data for half-hour periods. Generally, the meter will have sufficient capacity to store such periodic data for a limited time. If the periodic data is read within that time, then memory can be freed and the operation may continue normally. However, if the meter is not read within the time limit provided by the meter's capacity, then the meter can automatically compress some or all periodic data. This allows it to continue operation without losing data (only changing the resolution of the data). This process can continue until the meter is read and memory freed. Thus, the frequency of reading a meter will indirectly determine the resolution of the data obtained. Using a single design of meter, half-hour data could be obtained if the meter is read daily, or perhaps every second day for example. Alternatively, reading the same meter monthly may result in weekly data values (depending on the definition of periods and the memory capacity of the meter). Further embodiments of the present invention provide meters which are able to record consumption with varying resolution to maximise the use of available memory. While it may be desirable to record periodic data with a high resolution (for example half-hourly), the storage capacity of a meter may not be sufficient to allow such recording for an extended period. The embodiments of the invention described above illustrate the principal of compression of periodic data, which can be performed on a gradual basis compressing the oldest values first. In further embodiments of the invention, memory can be used as a first-in-first-out (FIFO) type of buffer containing a given number of locations. As a new data value is added to the buffer, the oldest one is removed. Further locations could be used as a second buffer to store data with a different set of periods. Figure 8 illustrates the basic circuit for implementing one example of this system. Here, two buffers are shown, buffer A being used to record half-hourly periodic data values and having, for example, 336 data storage locations (equating to a total period of one week). Buffer B is for recording weekly periodic data values and has, for example, 510 locations for storing 51 weeks of weekly periodic data. In total, therefore, storage for a year's periodic consumption is provided.

The circuit includes adders 30 and 31, registers 32 and 33, the measurement circuit 1 and the timer control unit 34 connected as shown. In operation, the timer control 34 monitors the time and identifies the start of each new half-hourly period for which periodic data is required. During each period, the measurement circuit output is accumulated in the register 32 via adder 31 and at the end of the period the timer control loads the register value into buffer A. This process continues until buffer A contains one week of half-hourly data values. When the next half-hourly value is loaded to buffer A, the oldest half-hourly value is supplied via adder 31 to register 33. The process continues over the next week, buffer A always containing the most recent week's worth of half-hourly values, week old values being successfully accumulated in register 33 until register 33 contains the compressed (accumulated) consumption value for the previous week. The timer control 34 then loads this value from the register 33 to the buffer B and clears the register. As the process continues for successive weeks, successive weekly data values are recorded in buffer B.

In the above, buffer B simply contains a number of data values where each represents a week's recording. The system can be extended such that buffer B records data with any pattern of periods, for example using periods of a defined time set. If each of the periods is continuous then the circuit in figure 8 can be used and the timer control will be responsible for controlling when the register 33 contents are loaded to B. If periods can be interleaved with each other, and therefore individual periods can be non-continuous, then an address control is required as previously described. When a new period is started in B the address control will be responsible for allocating a memory location. Data can then be accumulated in the memory location or in the register 33 and then loaded to the memory location in B when the period is deselected. If the period is reselected, as a result of being non-continuous, then the memory location used for the period must be reselected and if necessary the existing value loaded to register 33 in order that further data values can be accumulated into it. This system assumes that the periods used to record data in B are combinations of the periods used in A. In Figure 8 address logic may also be associated with buffer A and register 32 if buffer A can be used to record data for interleaved periods.

Figure 9 illustrates the basic circuit for an alternative embodiment. Again, two buffers A and B are provided, for storing half-hourly and weekly periodic data values in this example. Again, two adders 35 and 36 are provided connected to the measurement circuit 1 and feeding two registers 37 and 38 which are controlled by a timer control unit 39. In this example, the output of the measurement circuit 1 is connected via the adders 35, 36 to both registers 37 and 38. The timer control 39 controls the register 37 to accumulate, and load into buffer A, half-hourly periodic values, buffer A having sufficient capacity for one week's worth of half-hourly periodic data. Thus, buffer A always contains the most recent week's worth of half- hourly data. Simultaneously, however, the timer control 39 controls register 38 to accumulate and load into buffer B weekly period data values. Buffer B has the capacity for, for example, one year's worth of weekly periodic data. In both Figures 8 and 9, when the meter is read the periodic data from both buffers A, B may be retrieved, or data may be read from buffer A or buffer B individually.

Figure 9 is suitable for recording with continuous periods. As previously described the system can be extended to enable non-continuous and/or interleaved periods to be used by providing address control logic for controlling buffer A and register 37, and/or buffer B and register 38. Figures 8 and 9 are simple examples to illustrates the basic principle involved, though in practice, of course, the system may involve recording for more than two sets of time periods. Also, while separate buffers A and B are illustrated in the above example, these may in fact be implemented as one or more sections of a memory or other storage used to record periodic data, with control means configured appropriately to access data storage locations as required to implement the functions described. Following the above example, 846 locations can be used to store a year's periodic consumption with 336 locations being used as a FIFO to record the most recent half- hour values for the last seven days, and the other 510 locations being used as a FIFO to record weekly values for the prior 51 weeks. As week old half-hour data is removed from the first section of storage, it is accumulated into the periods of the next section of storage and then written thereto. Of course, in some embodiments a week's worth of half-hourly values from the first section could also be accumulated on a weekly basis to provide a weekly value for storage in a location of the second section. In addition, the contents of any individual buffer, or section of a buffer or memory, could be further compressed, either partially or completely, in accordance with the system hereinbefore described where the capacity of that buffer/section is reached or where the capacity of a related or connected buffer/section is reached.

The system of compression described above is not limited to application in meters and can be applied to any system used to store periodic data. A particular example is a communications system used to transfer periodic metered data. Such a system may contain a number of devices which read data from meters and then use "store and forward" techniques to communicate the data to a point where it is required. Using store and forward means that a device will receive the data and internally store it in a temporary memory. Then, when the device is able to forward the data to the next device in the series (the series being the sequence of devices required to get the data from A-the meter-to B-the recipient), the data is removed from memory and transferred. Using any number of communications techniques, including store and forward, results in devices within the communication system having to store data. Potentially new data may be received by a device when the device does not have spare memory. It may be possible simply to discard the new (or possibly some of the old) data, or leave the new data unacknowledged. However, conditions may arise, particular under fault conditions for example, where this is not possible and the capacity of a device or section of the communication system is exceeded. In those systems, the device can employ the compression techniques described above to avoid loss or corruption of data. Compression as described above may also be beneficial where storage or bandwidth in a communication is limited or where it is desirable to limit either for a particular purpose or function. A basic circuit structure for such a device is illustrated schematically in Figure 10. The device comprises data input means 40 for receiving periodic data from the previous stage, a memory 41 and data output means 42 for transferring data which has been temporarily stored in the memory 41 to the next stage of the system. The device also includes control means in the form of an address logic/look-up unit 43 and overall system controller 44 connected as shown. When periodic data is received by the input means 40, periodic data items are stored in the memory 41 under control of the address logic 43 as previously described. Under normal circumstances, this data will be temporarily stored and then, under control of the controller 44, read out of the memory 41 and transmitted onward in the system via the output means 42. However, if for some reason, for example due to a fault condition in the system, the output means 42 is unable to output stored data, and the input means 40 receives new periodic data for which storage is unavailable in the memory 41, then the controller 44 controls the memory 41 and address logic 43 as previously described to effect compression of data to make storage available for the new data. The compression may be performed in any manner previously described, for example starting with the oldest stored data items to produce compress data items with lower time resolution (ie. corresponding to longer periods), and may utilise the time set system as described above. Thus, the compression system proposed herein can be used in any system which contains periodic data, including a communication system. If a capacity limit is reached, for whatever reason, data items can be compressed as they can be within an individual meter.

Embodiments of the present invention also provide a system for reading metered data and one which can exploit additional benefit from the compression system proposed above. Meters for electricity and other utilities are generally located in consumer locations remote from the place where the metered data is actually used, thus the metered data must of course be read from the meters. Currently, various transportable devices, including cards, keys and tokens (referred to here as "media") can be used for pre-payment purposes. A consumer can pay an amount at a local point (for example a shop) and have the credit added to a media. Subsequently connecting the media to the meter causes the credit to be transferred from the media and added to the meter's current credit value. As the user consumes electricity (or other services) the credit value is reduced accordingly.

In embodiments of the present invention, such media can be used to read metered data from the meter. Thus, when a media is inserted into a meter, any credit can be loaded into the meter and the consumption data can be loaded from the meter to the media. Thus, a media, preferably an electronic smart card, can be used both for credit purposes and to transfer periodic metered data. Of course, the media could also be used to transfer cumulative metered data. In operation, the supplier of electricity (for an electricity meter) may send a smart card to the consumer. The consumer then inserts the card into the meter whereupon periodic metered data is loaded onto the card. The consumer then returns the card to the supplier where the periodic data can be read from the card. Credit and other information could also be transferred to or from the meter using known techniques.

A problem may however exist when a meter transfers periodic data (or other data) onto the media and then deletes that data from its memory. If the card is subsequently lost or damaged, then the data is also lost. Embodiments of the present invention address this problem in that a command is loaded onto the media, and is subsequently transferred to the meter on conneαion thereto, which identifies the previously read data which can now be safely deleted. This process is illustrated in the flow diagram of Figure 11. As indicated by step 46, at time A a consumer inserts a card into the meter. This is detected by the meter control means whereupon periodic data (data A) for the period up to time A is read from the memory and loaded onto the card's data memory. Data A will not, however, be deleted from the meter's memory at this stage. The card is then returned to the supplier at step 47 (or used to purchase credits in known manner) whereupon at step 48 data A is read from the card into a data collection system. (This data collection system will be substantial and generally under the control of the supplier or a nominee. It will generally also be robust and reliable). Having read the card, a command D_A, identifying the data which can now be deleted from the meter's memory, is loaded onto the card at the reading ">->

point (step 49), and the card is then transferred back to the meter (step 50). When, at time B, the card is again inserted into the meter (step 51), command D_A is transferred to the meter control means whereupon data A can now be deleted from the memory. The next set of data, data B can then be loaded to the card and the process repeated for the new data. Thus, in step 51 periodic data up to time A is deleted from the meter's memory and periodic data up to time B is loaded onto the card. Of course, while deletion of the "safe" data may be performed immediately by clearing the associated memory locations, the control means may simply allow subsequent overwriting of the safe data, in which case the deletion may be performed gradually. To handle the functions described above for transfer of data and commands between the meter and a transportable device such as a smart card, the meter control means and smart card processor can be configured by appropriate software to perform the functions indicated above as will be apparent to those skilled in the art.

If the operation of the data collection system cannot be ensured, then when periodic data is extracted from a card it can be communicated to other systems at least one of which can be relied upon. Once data is loaded into that system, that data can be deleted from the meter. Either at that time or subsequently, the consumer's card can be loaded with a suitable command to delete the periodic data which has been safely transferred to a secure system. If, as a result of a delayed delete command or in situations where multiple systems can issue commands, then two commands for the same meter may meet. One command may be to delete data up to time A, and the other to delete data up to time B. The processor in the smart card can be configured to retain only the command which corresponds to the most recent point in time up to which data can be deleted. Particularly if the postal system is used to send a card between a consumer and supplier, there may be a long cycle time. The card may therefore only be inserted into the meter (thereby explicitly deleting periodic data) for example monthly or even quarterly. Because of the use of an explicit delete command, the meter must therefore keep data for twice that period. Some of the stored data will be data which has already been read and loaded onto a card but which has not been deleted. The rest will be new data which has not yet been read. The meter can of course implement the compression system described above as necessary in dependence on the data storage capacity of the meter. Compression can be performed on both read and unread periodic data as necessary to ensure the operation of the meter over any period. However, the meter control means may conveniently be configured to favour compression of read but undeleted data rather than unread data. If a system of time sets as described above is used by the meter, then initially all data could be formatted using tj. The meter may then compress periodic data to avoid corruption or loss as necessary. However, preferably compression is performed first on data which has been read, and the compression can be performed using a time set several time sets higher in the series than that being used for unread data. Qearly, the compression can be performed gradually on an as required basis. For example, data which has been read could be formatted using, say, t₄ before unread data is compressed to t_j. Then, read data could be compressed to t₅ or possibly t before unread data is compressed to t₃. The periods or time sets, order of compression and any other relevant aspects can all be programmed into the meter control means which can be configurable for these features.

Embodiments of the invention can also apply the compression system described above when data is transferred from one stage to the next stage in a metering system in dependence on the data handling capacity of the stage to which data is transferred. Media used to retrieve periodic data from a meter will generally have finite data storage capacity. Similarly, a communication system used to transfer periodic data may have finite bandwidth or it may otherwise be desirable to limit the use of the communication system (for example to limit the duration of telephone calls when using modems). Where a meter has recorded periodic data, then current data to be read from the meter may exceed either the media capacity, the communication system bandwidth limits (or the bandwidth limit when considering data to be transferred from all meters) or the desired data transfer capacity for the communications system. In such a situation, data can be compressed when transferred to a media or communications system in dependence on the available capacity. As a particular example, in a meter as shown in Figures 5 and 6, the control means may be configured to perform data compression in accordance with a system described above when transferring data to the next stage, eg. transportable media such as a smart card or a communications link in a communication system, in dependence on the capacity of that stage. In the case of transfer to a smart card for example, on insertion of the card in the meter, the processor of the card may transmit to the meter control means data indicating the available data storage capacity on the card. The meter control means can then retrieve and effect compression of the periodic data (using a working memory provided in the control means for this purpose if required) in dependence on the card's capacity, and supply the compressed data to the card for storage therein. For example, a number of periodic data items may be compressed to a single data value which is then written to the card.

Where periodic data is retrieved by a communication system, the available capacity of the system may be communicated to a meter via the system when a request to transfer stored data is transmitted. This capacity may vary, for example, where specific conditions or faults cause a reduction in the bandwidth or capabilities of the system. In alternative embodiments, the meter could send to the smart card or communication controller data values as stored in the meter's memory. The processor within the smart card or communication controller can then compress these data values in order to fit the capacity of the unit.

When a meter compresses data for transfer to the next stage in a metering system, it is not of course necessary for data recorded in the meter memory itself to be compressed, although this may be done if required.

The embodiment described above performs compression with respect to time of periodic data from a single measurement source. Further embodiments of the invention implement compression of data from a plurality of measurement sources. For example, a meter embodying the invention may be used to record consumption via multiple electrical supplies. Alternatively, a number of supplies may be monitored by separate meters, and a data logger, data recorder or similar unit could be used to aggregate periodic data from the meters. Similarly, one of the meters could equally perform the compression task. Where periodic data for a specific period is available from multiple sources forming a logical group, this data can be compressed to form a total for that period for all the sources. Potentially, the data from individual sources could be formatted into a number of discrete values representing sub-periods of the period which is common to all source data. In such circumstances data from each meter is compressed to form a data value for the common period for each meter and these data values can then be compressed to form a single data value. However, more usually, compression will be performed to provide data from all sources for a common period. A particular embodiment of this aspect of the invention is indicated schematically in Figure 12. Here, a hand-held meter reading unit 55 (indicated schematically by the broken lines) comprises input/output (I/O) means 56, a memory 57 and a control processor 58. The unit 55 is designed to be carried between various metering points (MP) for reading the meter at each point. At each metering point, the unit 55 can communicate with the meter by any suitable mechanism, conveniently by releasably connecting the unit to the meter whereby the I O means 56 can receive periodic data read therefrom. Periodic data read from a meter may be temporarily stored in the I/O means 56. The control processor 58 is programmed to effect compression of periodic data corresponding to a given time period collected from different meters according to one or more logical grouping schemes. Thus, for example, if a number of the metering points form a logical group by virtue of the customer's supplier ie. the company responsible for providing supply services to that customer, then as periodic data for a given period is collected from the first metering point in the group, the control processor 58 will store the data in an associated location of the memory 57. When corresponding periodic data is collected from the next metering point in the group, the control processor 58 accumulates that data with the data previously stored from the first metering point to form a new value for storage in the memory location. This continues for all metering points in the logical group as successive metering locations are visited.

In the above embodiment, meter supplies can be classified according to a variety of logical groupings, including the customer identifier, geographical location, customer's supplier, tariff arrangements being used by the customer, postcode, address or customer type (family size, age, type of residence etc.). Identification codes for these logical groups may be programmed in the meter control means and transferred with the periodic data to the I/O means 56 for analysis by the control processor 58. For example, if a variety of companies provide supply services (a single company being responsible for any individual metered supply) then a supplier identifier can be allocated to each metered supply either by loading such data to the hand-held unit 55 or the associated meter being programmed with an identifier which can be verified by the hand-held unit. For each supplier, the hand-held unit can aggregate data from associated meters. Thus, data from a meter will be added to the data in the hand-held unit in dependence on the meters supplier identifier. Thus, the data from multiple meters will be compressed to represent a single set of data values for a particular supplier.

The system can of course operate with a variety of predefined logical groupings. The control processor 58 can be programmed with the logical grouping system and effect the required accumulation of data according to the programmed system for storage in the memory 57. Thus, the unit 55 can accumulate periodic data for metered supplies associated with each logical group. It need not be necessary for the unit 55 to visit meters of a single grouping and data can be accumulated for multiple groups and meters can be read in any order or sequence.

Where a logical group is determined by customer type, this can advantageously be used to gain aggregated data useful for sampling purposes. Thus, if customers are classified according to a set of criteria, then total periodic data for a set of similarly classified customers provides valuable information about the average consumption behaviour and quantum for those customers. Alternatively for example, data for individual customers need only be sampled at periodic intervals. For example, half- hourly data for the most recent whole week may be read every three months to provide a useful sample of customer consumption.

Where the supplier has to account for periodic consumption by the customers they supply, then periodic consumption aggregated by supplier is sufficient and is significantly compressed in comparison to the periodic data from all individual customers. Thus, such a compression system can beneficially be employed by any communication system used to retrieve such data.

It will of course be appreciated that many variations and modifications may be made to the specific embodiments described above without departing from the scope of the invention.

Claims

1. A device for storing periodic data indicative of the consumption of a metered quantity, the device comprising: means for receiving periodic data; data storage means having a plurality of data storage locations; and control means for controlling storage of periodic data items indicative of consumption during respective first periods of time in respective data storage locations, the control means being arranged to determine when additional storage is required for new received periodic data and then to accumulate a plurality of periodic data items, including at least one stored data item, to produce a compressed data item for a second period, equal to the sum of the first periods to which the accumulated data items correspond, and to control storage of the compressed data item in a said data storage location.

2. A device as claimed in claim 1 wherein the control means is arranged to accumulate a plurality of stored data items for said first periods to produce a compressed data item for said second period, thereby to free at least one data storage location for storage of new received periodic data.

3. A device as claimed in claim 1 or claim 2, which device forms part of a communications system for transferring periodic data from one or more meters.

4. A meter comprising a device as claimed in any one of the preceding claims.

5. A meter for generating and storing data indicative of the consumption of a metered quantity, the meter comprising: timer means for monitoring the time while said data is being generated; data storage means having a plurality of data storage locations; and control means for controlling storage of data generated during a plurality of predefined, finite first periods of time in respective data storage locations; the control means being arranged to determine when additional storage is required for new generated data and then to accumulate the data stored for a plurality of said first periods to produce compressed data for a second period, equal to the sum of said first periods, and to control storage of said compressed data in a said data storage location, thereby to free at least one data storage location for storage of data generated during a further said first period.

6. Apparatus as claimed in any preceding claim wherein at least one of said first periods consists of non-continuous time intervals.

7. Apparatus as claimed in any preceding claim wherein at least some of said first periods are of different durations.

8. Apparatus as claimed in any preceding claim wherein the control means is arranged to select stored data for compression in dependence on the age and time resolution of the data.

9. Apparatus as claimed in claim 8 wherein the oldest stored data with the highest time resolution is selected for compression.

10. Apparatus as claimed in any preceding claim wherein, when all stored data for said first periods has been compressed, the control means repeats the compression process for said second periods to produce compressed data for third periods each equal to the sum of a plurality of said second periods.

11. Apparatus as claimed in claim 10 wherein the control means is arranged to repeat the compression process iteratively for the n^ft periods when all stored data for the (n-l)⁰¹ periods has been compressed.

12. Apparatus as claimed in any preceding claim wherein a series of time sets t_j to t_n are defined in said control means, each time set comprising a plurality of time set periods and each time set period corresponding to a predefined, finite period of time, wherein each time set period of each of time sets to t_B coπesponds to a period of time equal to the accumulated periods of a plurality of time set periods from other time sets, and wherein the control means is arranged for associating said first and subsequent periods of time for which data is stored with respective time set periods.

13. Apparatus as claimed in claim 12 wherein each time set period of time set t_B corresponds to the accumulated periods of a plurality of time set periods of time set t *._-.^•

14. Apparatus as claimed in claim 13 wherein the period of time to which any t_B__j time set period corresponds forms part of the accumulated period to which only one t_B time set period corresponds.

15. Apparatus as claimed in any preceding claim wherein the control means is programmable to define said first and subsequent periods, and the algorithm for compression of data therefor, in response to a command received by the apparatus.

16. A meter for generating and storing data indicative of the consumption of a metered quantity, the meter comprising: timer means for monitoring the time while said data is being generated; data storage means having a plurality of data storage locations; and control means for controlling storage of data generated during a plurality of predefined, finite first periods of time in respective data storage locations; the control means being arranged to determine when additional storage is required for new generated data and then to accumulate new generated data with data stored in a said data storage location and store the accumulated data in a said data storage location.

17. A meter for generating and storing data indicative of the consumption of a metered quantity, the meter comprising: timer means for monitoring the time while said data is being generated; data storage means having a plurality of data storage locations; and control means for controlling storage of data generated during a plurality of time periods in respective data storage locations, wherein the control means is programmable to define said time periods in response to receipt of a programming command by the meter.

18. Metering apparatus for recording and communicating data indicative of the consumption of a metered quantity, the apparatus comprising: a meter for generating said data, the meter having first data storage means for storing generated data, and control means for controlling storage of the generated data in the data storage means; and a transportable device, for releasable connection to the meter, having second data storage means; the control means being operable, when the transportable device is connected to the meter, to transfer stored data from the first storage means to the transportable device for storage in the second data storage means thereof.

19. Apparatus as claimed in claim 18 wherein the transportable device is a smart card.

20. Apparatus as claimed in claim 18 or claim 19 wherein the control means is arranged to delete or allow over-writing of data stored in said first storage means in response to a command from said transportable device identifying the data to be deleted or overwritten.

21. Apparatus as claimed in claim 20 comprising a meter as claimed in any one of claims 4 to 15, wherein the control means is arranged to select first for compression stored data which has been transferred to the transportable device.

22. A method for transferring data indicative of the consumption of a metered quantity from a meter in which the data is stored, the method comprising: transferring the data from data storage means of the meter to a transportable medium; reading the data from the transportable medium; and deleting from the data storage means of the meter data which has been read from the transportable medium in response to a command communicated by the transportable medium to the meter identifying the data which has been read.

23. Apparatus for storing and communicating periodic data indicative of the consumption of a metered quantity during a plurality of time periods, the apparatus comprising: a first device comprising data storage means having a plurality of data storage locations for storing periodic data items indicative of consumption during respective time periods; and control means for accessing said data storage locations to transfer stored data to a second device; wherein the control means is responsive to the data capacity of the second device to accumulate, in dependence on said capacity, the stored data items from a plurality of said locations to produce a compressed data item for transfer to the second device.

24. Apparatus as claimed in claim 23 wherein the control means forms part of the first device.

25. Apparatus as claimed in claim 23 or claim 24 wherein the first device comprises a meter.

26. Apparatus as claimed in any one of claims 23 to 25 wherein the second device comprises a transportable data transfer device.

27. Apparatus as claimed in claim 26 wherein the second device comprises a smart card.

28. Apparatus as claimed in any one of claims 23 to 25 wherein the second device comprises a communication link in a communications network.

29. A method for retrieving periodic data indicative of the consumption of a metered quantity from a plurality of metering points, the method comprising: accumulating data items indicative of consumption during a time period at different metering points, forming a predefined logical group of metering points, to produce a compressed data item indicative of the consumption for that logical group in that time period; and storing the compressed data item in data storage means.

30. A method as claimed in claim 29 including accumulating data items indicative of consumption at a plurality of different predefined logical groups of said metering points to produce respective compressed data items for said different groups, and storing the compressed data items in respective data storage locations.

31. A method as claimed in claim 29 or claim 30 wherein said data items are accumulated and stored by a portable meter-reading unit which communicates with the meter at each metering point to retrieve said periodic data.

32. Apparatus for processing periodic data indicative of the consumption of a metered quantity at a plurality of metering points, the apparatus comprising: means for receiving data items, indicative of consumption during a time period at a metering point, from said plurality of metering points; processing means for accumulating respective data items from different metering points, forming a predefined logical group of metering points, to produce a compressed data item for that group; and data storage means for storing the compressed data item in a data storage location.

33. Apparatus as claimed in claim 32 wherein the processing means is configured to accumulate data items indicative of consumption at a plurality of different predefined logical groups of said metering points to produce respective compressed data items for said different groups, and wherein the storage means is arranged to store the compressed data items in respective data storage locations thereof.

34. Apparatus as claimed in claim 32 or claim 33 comprising a portable unit for communicating with the meter at each metering point to retrieve the periodic data therefrom.

35. A meter for generating and recording data indicative of the consumption of a metered quantity, the meter comprising: timer means for monitoring the time while said data is being generated; data storage means having a plurality of data storage locations; and control means for generating first periodic data items indicative of consumption during respective first periods of time and for generating second periodic data items indicative of consumption during respective second periods of time, each said second period comprising a plurality of said first periods; wherein said control means is arranged to effect storage of said first data items in respective locations of a first section of the data storage means and to effect storage of said second data items in respective locations of a second section of the data storage means.

36. A meter as claimed in claim 35 wherein the control means is arranged to generate the first data items independently of the second data items.

37. A device for recording periodic data items indicative of the consumption of a metered quantity during respective first periods of time, the device comprising: means for receiving said periodic data items; data storage means having a plurality of data storage locations; and control means for effecting storage of the first data items in respective locations of a first section of the data storage means, and for accumulating successive groups of first data items to generate respective second data items, and for effecting storage of the second data items in respective locations of a second section of the data storage means.

38. Apparatus as claimed in claim 35 or claim 37, wherein the control means is arranged to accumulate first data items previously stored in said first section to produce said second data items for storage in the second section.

39. Apparatus as claimed in claim 38 wherein, as successive new first data items are generated or received, successive oldest data items stored in said first section are accumulated to generate a second data item for storage in a location of the second section.

40. Apparatus as claimed in any one of claims 35 to 39 wherein said first and second sections of the data storage means are configured to operate as respective FIFO buffers.

41. Apparatus as claimed in claim 40 and claim 39 wherein the FIFO buffers are connected in series.

42. Apparatus as claimed in claim 40 when dependent on claim 36 or claim 37 wherein the FIFO buffers are connected in parallel.

43. A method for storing data indicative of the consumption of a metered quantity, the method comprising: monitoring the time while said data is being generated; and storing the data generated during a plurality of predefined, finite periods of time in respective data storage locations; wherein at least one of said predefined, finite periods of time consists of non- continuous time intervals, such that the associated data storage location stores the total data generated during said non-continuous time intervals.

44. A method as claimed in claim 43 wherein said predefined finite periods of time collectively constitute a continuous period of time.

45. A method as claimed in claim 43 or claim 44 wherein at least some of said predefined finite periods of time comprise a common time interval.

46. A method as claimed in any one of claims 43 to 45 wherein at least some of said predefined finite periods are of different durations.

47. A meter for generating data indicative of the consumption of a metered quantity, the meter comprising: timer means for monitoring the time while said data is being generated; data storage means having a plurality of data storage locations; and control means for associating a plurality of predefined finite periods of time with respective data storage locations, at least one of said periods of time consisting of non-continuous time intervals, and for controlling storage of generated data such that data generated during each said period is stored in the associated data storage location.

48. A meter as claimed in claim 47 wherein the control means is arranged to clear a data storage location when that location is first, but not subsequently, accessed for a said period or to overwrite the contents of a data storage location when data is first stored therein, but not when data is subsequently stored therein, for a said period.

49. A meter as claimed in claim 47 or claim 48 wherein said data storage means comprises a memory having a plurality of addressable memory locations forming said data storage locations.

50. A meter as claimed in claim 49 wherein, during a said period, the data generated is accumulated in the associated memory location.

51. A meter as claimed in any one of claims 47 to 49 including a temporary store for accumulating data generated during a said period and loading the same to the associated memory location.

52. A meter as claimed in any one of claims 47 to 51 wherein the data storage means is arranged to allow simultaneous access to a plurality of said data storage locations, which data storage locations are associated with respective said periods comprising a common time interval.

53. A meter as claimed in claim 52 wherein at least some of the said data storage locations are provided by respective registers.

54. A meter as claimed in any one of claims 47 to 53 wherein the control means is operable to define the association of said periods and data storage locations in response to receipt of a command by the meter.

55. Apparatus substantially as hereinbefore described with reference to any of Figures 5 to 12 of the accompanying drawings.

56. A method for storing, retrieving or transferring data which method is substantially as hereinbefore described with reference to any of Figures 5 to 12 of the accompanying drawings.