GB2362010A - Utility metering communications system - Google Patents

Abstract

Described herein is a utility metering communications system which comprises a master unit (200) having an antenna (202) for transmitting signals to and receiving signals from a slave unit (220) having an antenna (222). The master unit (200) is connected to a radio time standard receiver (210). The slave unit (220) is connected to a radio real time clock/calendar unit (224) which receives timing signals from a radio time standard receiver (230). The master unit (200) provides a control signal for the slave unit (220) which effectively sets the time at which the slave unit (220) switches from a 'sleep' mode to an 'active' mode so that it can be interrogated by the master unit (200) and transmit data relating to utility usage. By using radio time standard receivers (210, 230), there is no requirement for a battery to be provided for powering the radio real time clock/calendar unit (224). Another embodiment omits the radio time standard receivers (210, 230) and has a battery for the slave end.

Description

2362010 IMPROVEMENTS IN OR RELATING TO METERING SYSTEMS The present

invention relates to improvements in or relating to metering systems, and is more particularly concerned with utility metering 5 communications systems.

A common problem with utility metering communication systems where the system may be of a one-to-one system in two parts, or of a one-tomany "master/slave" cellular nature, is that of power economy. Often one or both parts such systems are battery powered. As an example, where the system may be a two-part smart card prepayment system for a gas utility customer, both the separate gas meter and its associated smart card prepayment unit may be battery powered. In another example of, say, a twopart electricity meter system, only the smart card prepayment unit may be battery powered as the meter itself has access to the mains supply. Yet another example may be an automatic meter reading system where a cellular central data collector (the "master") may be mains powered, but the meters ("slaves") with which it communicates, for example, electricity, water or gas meters, or any combination thereof, may be battery powered.

In such systems as mentioned above, it will readily be appreciated that battery economy is of great importance if the utility owning the meters requires to make only infrequent visits to meters to change the batteries. Battery life is commonly maximised by the use of high energy- density primary cells but economy is still a major consideration.

In the systems as noted above, it is common practice to cause the system to adopt a low power "sleep" mode for as much of the time as possible. This is relatively simple to implement in a system where the parts are connected together by wire, when a simple "wake-up" signal may be sent whenever necessary.

However, some such systems may have other communication methods, such as, radio or impressed-signal mains power-line communication. From a communication point of view, because of the "sleep" mode, in these systems the parts are not permanently connected together. In such a situation, an approach must be adopted which provides secure communication at specific controlled times.

GB-A-2 302 198 discloses a system in which a "master" tells a "slave" to go to sleep for a period of time specified by the "master" as part of its last communication with the "slave". The sleep time in such systems is usually defined in numbers of blocks of, say, 5 minutes each.

Other systems are known where the "slave" of a two-part system wakes up on a regular basis say, every 10 seconds, to listen for a transmission addressed to it. If no transmission is detected, the "slave" goes back to sleep until its next regular wake-up time. On the other hand, if a transmission is detected, the "slave" 'locks-on' and a message exchange takes place between the "master" and the "slave". Such systems are commonly controlled by a "real-time" clock and a crystal controlled oscillator, one being located in each system part. However, crystal controlled oscillators will have errors and drifts so such a system must also have a provision for a regular wake-up to allow clock corrections to be made. This wake-up is set at a frequency related to the maximum expected clock error and drift but will commonly be much less often than the normal "message" wake-up frequency.

It is therefore an object of the present invention to provide a metering system in which there is no requirement for the correction of errors and drift.

It is a further object of the present invention to provide a metering system in which battery economy is maximised.

In accordance with one aspect of the present invention, there is provided a utility metering communications system comprising:

a master unit; and at least one slave unit which is controlled by signals transmitted by the master unit to operate in either a 'sleep' mode or an 'active' mode; characterised in that each slave unit includes a real time clock/calendar unit for providing a signal which switches the slave unit from the 'sleep' mode to the 'active' mode in accordance with data transmitted by the master unit.

Advantageously, the real time clock/calendar unit includes a radio time standard receiver for receiving timing signals from a radio time standard transmitter.

The master unit may also include a radio time standard receiver/clock/calendar unit.

In accordance with a second aspect of the present invention, there is provided a method of operating a utility metering communications system as described above, the method comprising the steps ofi providing each slave unit with an alarm setting; generating a signal in accordance with the occurrence of the alarm setting; switching each slave unit from a 'sleep' mode to an 'active' mode in accordance with the signal; receiving transmission signals from the master unit which interrogate each slave unit; and transmitting data from each slave unit to the master unit in accordance with data stored therein.

The system of the present invention avoids the inflexibility in the prior art systems where large fixed periods or increments for sleep time are 5 employed and, additionally, has an almost infinitely adjustable setting. Moreover, the refined sleep time setting capability of the "alarm clock" approach allows better optimisation of battery economy.

For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which:Figure 1 illustrates a conventional metering communications system; Figure 2 illustrates a first embodiment of a metering communications system in accordance with the present invention; and Figure 3 illustrates a second embodiment of a metering communications system in accordance with the present invention.

The present invention will be described with reference to a "slave" unit which may a utility meter, for example, a gas, electricity or water meter. The utility meter could also be operable for metering one or more of these utilities. The "master" unit is a central collection point which collects readings relating to usage of the utility from one or more "slave" units within a particular area for subsequent processing and billing.

Figure 1 illustrates a conventional metering communications system which comprises a "master" unit 10 which has an antenna 12. Signals are transmitted to a "slave" unit 20 via radio link 14. "Slave" unit 20 has an antenna 22 which receives signal transmissions over link 14 and also transmits signals to the "master" unit 10. The "slave" unit 20 is connected to an elapsed time clock 24 via link 26 and to a battery unit 30 via link 32. The elapsed time clock 24 is also connected to the battery unit via link 34.

In operation, the "master unit" 10 transmits a signal over link 14 to the "slave" unit 20 which provides information as to how long the "slave" unit is to enter the 'sleep' mode. This information is transferred via link 26 to the elapsed time clock 24. The elapsed time clock 24 tracks the time, counting down or up, until the end of the 'sleep' mode period. At this point, the elapsed time clock 24 sends a signal via link 26 to the "slave" unit 20 which switches it into an 'active' mode where it is capable of receiving signals from the "master" unit 10 and of transmitting signals to the "master" unit 10 when interrogated by an interrogation signal therefrom.

In Figure 2, a first embodiment of a metering communications system in accordance with the present invention is illustrated. The system comprises a "master unit" 100 having an antenna 102 for providing signals over a communications link 104 to at least one "slave" unit 120. Only one "slave" unit 120 is shown for simplicity, but it will readily be appreciated that any number of "slave" units can be present in the system.

"Slave" unit 120 has an antenna 122 for receiving and transmitting signals over the communications link 104, and is connected to a real time clock/calendar -unit 124 via link 126. The "slave" unit 120 and the real time clock/calendar unit 124 are both connected to a battery unit 130 via links 132 and 134.

In operation, the "master unit" 100 transmits a signal over link 104 to the "slave" unit 120 which provides information via link 126 for the real time clock/calendar unit 124 so that it is set with a 'wake-up' time in similar fashion to a conventional alarm clock. The real time clock/calendar unit 124 keeps track of the time and sends a 'wake-up' signal via link 126 to the "slave" unit 120 at the designated 'wake-up' time. The 'wake-up' signal switches the "slave" unit 120 into an 'active' mode where it is capable of receiving signals from the "master" unit 100 and of transmitting signals to the "master" unit 100 when interrogated by an interrogation signal therefrom.

In accordance with the present invention, the "slave" unit 120 is effectively told, as part of a transmission from the "master" unit 100 to the ccslave" unit 120, to go to sleep until a certain time and date, thereby implementing an "alarm clock" function. The time and date message passed to the "slave" unit 120 may contain information on the precise time, to the second, the day of the week, the date, the month and the year at which it should next wake up and switch into the 'active' mode. This provides a totally flexible system in that any sleep period may be set from 1 s to as many years as required.

Additionally and autonomously, another separate time and date may be included in the time and date message for effecting clock drift correction but this would be totally separate and transparent to the message exchange function.

In accordance with a second embodiment of the present invention, the system described in Figure 2 can be beneficially improved if a radio time standard receiver, such as one for the MSF Rugby national time standard, is incorporated into each of the system parts. MSF radio transmissions contain full time and date information and are thus compatible with the day/date and 6calarm, clocW' type operation of the system in Figure 2.

The system illustrated in Figure 3 is similar to that described with reference to Figure 2, but in this case there is no requirement for a battery unit to be associated with the "slave" unit. The system comprises a "master" unit 200 having an antenna 202 for transmitting and receiving signals over a communications link 204 as before. The "slave" -unit 220 has an antenna 222 for receiving signals from and for transmitting signals to the "master" unit 200 over communications link 204. The "slave" -unit 220 is connected to a radio real time clock/calendar unit 224 via link 226. The radio real time clock/calendar unit 224 is connected to receive signals from a radio time standard receiver 230 via link 232. The "master" unit 200 is also connected to a radio time standard receiver 2 10 via link 212.

It is preferred that the radio time standard receiver 2 10 also includes a clock/calendar unit (not shown) operated by signals received from the radio time standard receiver. Ideally, these signals provide the basis for the signals sent to the "slave" unit 220 by the "master" -unit 200 relating to the 'wake-up' time for switching between the 'sleep' mode and the 'active' mode.

It will readily be appreciated that, in this embodiment of the invention, there is no requirement for a battery unit as the radio time standard receiver 2 10 receives the timing signals directly from a radio time standard transmitter (not shown).

In operation, the "master" unit 200 and the "slave" unit 220 are effectively controlled by their associated radio time standard receivers 2 10 and 230. This removes all real-time clock errors and drifts and hence any requirement for clock correction. This is because all system parts would be controlled by a common time standard of exceedingly high accuracy and stability. Such a radio time standard would additionally serve in the utility meter as its real time clock controlling its metering functions.

The benefit of using the radio time standard in each system part is further enhanced if one considers the situation in an electricity meter on restoration of power after a loss of mains power. Commonly utility meters employ batteries to support their real time clocks in the event of loss of power. Such batteries will eventually run down and may have little capability to support the meter real time clock, particularly if the meter has been in storage for a significant period of time. In the system described with reference to Figure 3 which uses the radio time standard, the length of time for which the power is lost has no relevance to the events on power restoration. On power restoration, each radio receiver will re-acquire the time and date, and, provided the alarm clock setting was preserved in memory at the loss of power, the system will not be unaffected and will operate as if there were no power loss.

As mentioned above, the system of Figure 3 does not require the use of a battery to overcome the effects of power loss.

The system of the present invention has the following advantages:

w Flexibility in setting the wake-up "alarm clock" time and date.

E Use of a radio time standard removes all considerations over the length of the sleep period.

N Meter recovery after power down is independent of any battery.

0 The use of a radio time standard receiver in an electricity meter two part system removes the need for an internal battery.

0 For the specific electricity meter case, the removed requirement for a battery allows an extension of the product life by removing a primary constraint.

Claims (6)

CLAIMS:

1. A utility metering communications system comprising:a master unit; and at least one slave unit which is controlled by signals transmitted by the master unit to operate in either a 'sleep' mode or an 'active' mode; characterised in that each slave unit includes a real time clock/calendar unit for providing a signal which switches the slave unit from the 'sleep' mode to the 'active' mode in accordance with data transmitted by the master unit.

2. A system according to claim 1, wherein the real time clock/calendar unit includes a radio time standard receiver for receiving timing signals from a radio time standard transmitter.

3. A system according to claim 2, wherein the master unit includes a radio time standard receiver/clock/calendar unit.

4. A method of operating a utility metering communications system according to any one of the preceding claims, the method comprising the steps of.providing each slave unit with an alarm setting; generating a signal in accordance with the occurrence of the alarm setting; switching each slave unit ftom a 'sleep' mode to an 'active' mode in accordance with the signal; t receiving transmission signals from the master unit which interrogate each slave unit; and transmitting data from each slave unit to the master unit in accordance with data stored therein.

5. A utility metering communications system substantially as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings.

6. A method of operating a utility metering conimunications system substantially as hereinbefore described with reference to figures 2 and 3 of the accompanying drawings.