GB2496420A - Magnetic sensor subsystem for the automatic reading of water, gas and electricity utility meters - Google Patents

Abstract

The present invention relates to a utility meter data recording system. The system comprises a sensor unit 2 which is arranged to attach to a utility meter 1 in a retrofit and non-­invasive fashion. The sensor unit comprises a magnetic sensor unit (12, Fig 3), a first processing unit (10, Fig 3), a data storage means (16, Fig 3), a communication circuit (20, 21, Fig 3) and a signal conditioning circuit (14, Fig 3). A receiver unit is further provided which comprises a second processing unit for processing data from the sensing unit. The receiver unit also comprises a transmitting unit for transmitting data to a remote location across a public or private communication network. This provides the benefit that a reduced volume of data may be transferred whilst data is processed locally at the sensing unit allowing significant data processing savings.

Description

Magnetic Sensor Subsystem for the Automatic Reading of Water, Gas and Electricity Utility Meters

1. Background

In the quest efficiency and a better use of resources, there is currently a trend towards automatic meter reading (AMR) in the utility industry. The problem the utility companies are faced with, is not only the investment requited to replace the existing mechanical meters with AMR devices, but the investment in training required to install the new devices and the disruption caused by having to cut off the supply to do so. Not only is the extra investment a concern, but also the fact that the existing mechanical meters aie based on technologies that have been improved and perfected during many years and proven to work in the most extreme conditions. Furthermore, mechanical meters. in particular for the case of water or gas meters, do not require a power source to providing accurate and continuous readings, which is potentially a problem with most AMR devices. Additionally there is the problem of disposal of the old meters, many of which contain mercury, which is an environmental hazard.

The utility industry has currently installed millions of analogue mechanical metering devices for metering water and gas consumption.

The invention is based on taking advantage of the existing stock of mechanical metering devices and using a retrofit universal non-invasive magnetic sensor subsystem to convert the mechanical meters into highly versatile AMR devices.

Some water and gas utility meters have built in magnets as part of their mechanisms or they have been equipped with a rotating magnet to enable an external magnetic detector to be used to extract puhes colTesponding to the meter movement and implement an AMR solution. The AMR solution provided by most water meter manufacturers utilises a magnetic proximity switch (Reed switch) which opens and closes depending the position of the moving magnet in the meter. The proximity switch output is connected to a data logger or data communications device to store and transmit the resulting pulses as an indication of water and gas consumption.

2. The problem The proximity switch solution suffers from the foflowing limitations: I. Each proximity switch product is dedicated to one type of water and gas meter and model. Considering the large number of meter manufacturers and the wide range of water and gas meter types and sizes, the dedicated proximity solution requires utility companies and other AMR providers to carry a large inventoly of different types of proximity switches. Therefore, there is a total lack of a standardised and universal solution.

2. Some mechanical utility meters are not designed for interfacing to proximity switch products and therefore, cannot be monitored remotely using this technique.

3. Many of the proximity switch products, especially for water meters, are bulky and can be difficult to fit in meters located in confined spaces. In addition, they can cover part of the meter face making it difficuh to read the meter register. This may result in the utility companies removing the proximity switch as a result of complaints from their meter reading staff.

4. Proximity switch products do not have any local intelligence or capability to accumulate the meter reading at the sensor unit. Therefore, a proximity switch has to communicate with an associated data logger continuously and cannot operate independently.

5. The lack of local intelligence prevents the data logger from getting any infoimation relating to tampering with the proximity switch.

6. Only one proximity sensor can be used per meter. Therefore, if two data loggers are required to monitor the meter reading, special wiling to the proximity switch is required whilst it is installed in the field to comply with the regulations of the utility companies.

7. Proximity switches suffer from serious limitations at high flow rates due to mechanical switch bouncing which may result in incolTect number of pulses being reported.

8. As a mechanical switch, a proximity switch has a limited life beyond which it has to be replaced due to mechanical failure, thus adding to the cost of the AMR system.

9. The magnetic field detection sensitivity of utility meter proximity switches is fixed and therefore, if there is a change in the strength of the rotating magnet or internally generated magnetic field due to aging of the meter, the proximity switch is likely to fail in detecting the true figures for water or gas usage.

10. In many cases the proximity switch for a utility meter is already installed on the meter. Tn such cases, the installation of an AMR system requires the installer to wire the wire the proximity switch cable to the AMR system. This manual can be time consuming and error prone. In addition, water meters in particulars are located in deep pits or boundary boxes further complication the wiring operation during installation of the AMR system.

Features and advantages of the invention The magnetic sensor subsystem operates in conjunction with the data logger and the remote server to foirn a complete AMR system.

The main features and advantages of the magnetic sensor subsystem are: 1. Universal retrofit sensing solution for monitoring of water and gas utility meters with detectable rotational magnetic field with rotations corresponding to the usage of water and gas. The magnetic sensor subsystem is not restricted to a specific utility meter manufacturer or type.

2. Small size enabling easy attachment to water and gas meters without obscuring any part of the meter register to comply with the regulations of the utility companies.

3. Low power consumption enabling the batteries of the external data logger to last for several years.

4. Local intelligence within the magnetic sensor subsystem enabling adaptive control of the gain and filtering of the signal from the ferromagnetic sensor. This enables the magnetic sensor subsystem to operate with different meters regardless of the specific characteristics of their rotating magnets. In addition, it enables the subsystem to recover from strong external magnetic fields which may impact on the accuracy of other magnetic detectors such as the proximity switches provided by utility meter manufacturers.

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5. Local storage of accumulated and time stamped data enabling the magnetic sensor subsystem to minimise its interaction with the external data logger and thus, reducing power consumption further.

6. Data storage in non-volatile memory enables the date and time stamped data to be preserved in the event of power loss to the sensor for any reason including tampering with the device.

7. Automatic programming and configuration of the sensor by the external data thgger for optimisation of operation. power consumption and programming of events. These events may include frequency of communications with the data logger, alarms for specific water and gas usage levels, data quality and tampering conditions.

8. Simple and remotely controlled installation process from a remote server to avoid incorrect installation.

9. LED indicators to provide visual feedback to installers and users about the status of the magnetic sensor and the associated data logger.

10. ATEX Zone 0 approved with all electronic components potted.

3. Statement of invention

What is hereby provided is a utility meter sensing device according to claims Ito 14.

What is further provided is an automatic meter reading according to claims 15 to 17.

What is yet further provided is a sensor unit according to claims 18 to 24.

Additionally what is provided is a method according to claim 25.

4. Brief description of the drawings

Figure 1 -The full AMR system including the magnetic sensor system data logger and remote server.

Figure 2 -Example of attachment of the magnetic sensor subsystem to a water meter.

Figure 3 -Block diagram of the magnetic sensor subsystem.

Figure 4-Block diagram of the signal conditioning block in the magnetic sensor subsystem.

Figure 5 -Block diagram of an alternative implementation of the signal conditioning block.

Figure 6 -Block diagram of the wired version of communication block.

Figure 7 and 8 -Illustration of the multiple magnetic sensor subsystems connected via wire, or wireless, respectively, to a single data logger using a junction box.

Figure 9 -Block diagram of the wireless version of the communications block.

Figure 10 -Flow chart of magnetic sensor subsystem microcontroller software/system operation.

Figure II -Diagram of a typical Wheatstone bridge used in the preferred embodiment of the magnetic sensor.

Figure 12 -Illustration of the preferred embodiment of the modular AMR system of the invention

5. Detailed description

The magnetic sensor subsystem forms part of the AMR system which also consists of the data logger and the remote server as shown in figure 1.

5.1 AMR system Figure 1 shows the full AMR system of the invention comprises the magnetic sensor subsystem 2 (which is attached non-invasivdy to the gas or water meter 1), the data logger 4 and the remote server 7 The magnetic sensor subsystem 2 communicates with the data logger 4 via the local communication link 3. The ocal communication link 3 may be impkrnented in a number ways including: * Using a direct cable from the magnetic sensor subsystem.

* Using a wired network configuration such as Ethernet or RS485 serial network.

* Wireless network using proprietary protocols or standard wireless network configuration such as Bluetooth and IEEE 802. 1 5.4 networks.

A combination of the above implementation of the local communication link 3 may be used.

This means that multiple magnetic sensor systems 2 may be connected to the data logger 4.

Some of these subsystems 2 may be connected to the data logger 4 using a wired network, whilst other subsystems 2 may be connected simultaneously to the same data logger using a The data logger 4 preferably communicates with the remote server via the public tdephone network, mobile or wired. and the internet via the remote communication link 5. The remote communication link 5 may be implemented in a number of different ways including: * The data logger 4 may include a mobile phone modem (OSM, GPRS or 3G) which communicates uses the mobile phone network (6) as a gateway to access the Internet 6 The remote server 7 is connected to the internet 6 and can then communicate with the data logger 4 * The data logger 4 may include a wireless network transceiver that connects to a standard wireless LAN router which will enable it to access the internet 6 via a broadband telephone connection 5 * The data logger 4 may have an Ethernet interface which will enable it to communicate with a standard wired router or broadband model to access the broadband wired telephone link and connect to the sever 7 via the internet.

* The data logger 4 may include a standard tdephone line wired modem and can be connected to the telephone network 5 to access the internet 6. Accessing the internet will require dialling to an internet service provider aSP).

* The skilled person could also implement the communications link S via radio. wi-fl or other common forms of wired, optical or radio communication means The data logger 4 consists of the following building blocks: * Microcontroller.

* Non-volatile memory NVM).

* Communication circuit to implement the local communication link 3 described above.

* Communication circuit to implement the remote communication link 5 described above.

* Power supply circuit for the mains powered version of the data logger 5 or a battery pack.

The functions of the data logger 4 include: * Control of communications with server 7 and the magnetic sensor subsystem 2 * Contr& of the operation of magnetic sensor subsystem 2 * Provision of memoty space for the storage of metei 1 usage data received from the magnetic sensor subsystem 2 * Provision of power to the magnetic sensor subsystem 2 for the wired version of the subsystem.

Magnetic sensor subsystem (2) Figure 2 shows how the magnetic sensor subsystem 2 is attached to the meter non-invasively using a strap 23, andlor an adhesive resin or adhesive pad 21. It illustrates an example of the preferred attachment method to a typical water meter.

Figure 3 shows the magnetic sensor subsystem 2, which is fully integrated and housed in a single small enclosure, preferably made of plastic. The enclosure is preferably transparent or semi-transparent in all or part, allowing a green and a red light emitting diodes (LED5) 18 inside the sensor enclosure to be clearly seen.

The building blocks of the magnetic sensor subsystem 2 are shown in figure 3 and include: Magnetic sensor (12) The magnetic sensor 12 shown in figure 3 is preferably a solid state magneto-resistive device. A magnet-resistive material changes its resistance when exposed to a magnetic field.

Sensors based on different types of niagneto-resistive technology are available commercially.

There are usually four magneto-resistive elements in a magnetic sensor connected in a Wheatstone bridge configuration as shown in figure II. The Wheatstone bridge is powered by DC voltage (Yb) and devdops a voltage across its outputs (Yo+ and Vo-) when exposed to an external magnetic field. The developed voltage is proportional to the strength or direction of the applied magnetic field depending on the type of magnetic sensor used.

Signal conditioning block (14) The signal conditioning block] 4 in figures 3 to 6 consists of the following circuits: Amplification circuit (26) The amplification circuit 26 of figure 4 amplifies the differential voltage of the magnetic sensor bridge that appears between termina's Vo+ and Vo-(figure 11), as a result of a change in the magnetic field strength or direction. This differential voltage is usually small and amplification is required to enable its reliable by other pails of the sensor subsystem.

This analogue circuit may be implemented as a difference amplifier using one or more operational amplifiers. The prefened implementation is to use an instrumentation amplifier due to its superior performance.

The gain of the amplification circuit is determined by the values of the gain resistors. In this, implementation the gain of the circuit is variable and may be altered under the control of the microcontroller. This is implemented by using analogue switched or digital potentiometers.

The reason for the including a variable gain capability is to enable the sensor subsystem of this invention to be optimised for use with different types of water and gas meter. as the strengths of the magnetic fields generated by the meter types vary considerably. This allows the same unit to cater for a wide range of meters with the consequential advantages in costs due to scale of manufacturing, spare parts and training costs.

The variable gain capability is used in two ways in this invention: i. The first is to receive the optimum gain setting for a specific type of meter from the remote data logging device and store it in the non-volatile memory 16. The microcontroller will then set the gain of the amplification circuit for the sensor subsystem at the time of installation. The gain value will not be changed unless a new value is downloaded and stored in the non-volatile memory.

2. The second approach is to alter the gain adaptively during the operation of the sensor subsystem. This achieved by increasing or decreasing the gain value to achieve optimum operation.

Filtering circuit (30) The filtering circuit 30 in figure 4 perfons analogue filtenng of the amplified sensor signal that appears at the output of the amplification circuit. The purpose of the filtering is to remove unwanted noise resulting from external electrical or magnetic interference. An example of such interference is mains noise from adjacent equipment. Such unwanted noise may affect the operation of the threshold circuit and result in false detections.

The filtering circuit is implemented with operational amplifiers and passive components. The filter configuration and parameters may be fixed or variable. lii this implementation variable filter configuration and parameters are proposed to ensure optimum operation. Changing the filter configuration and parameters are achieved by utilising analogue switches and digital potentiometers under the control of the microcontroller. As an examp'e, the filtering circuit can be configured to implement a high pass filter if there are large static magnetic fields, a notch filter to remove 50Hz mains noise or a low pass filter to remove all signal frequency above the maximum rotation speed of the water or gas meter. As with amplification circuit, the filter parameters may be sent by the remote data logger 4 and stored in the non-volatile memory 16 by the microcontroller 10 Threshold detection circuit (34) The threshold detection circuit 34 of figure 4 converts the analogue sensor signal representing the strength or direction of the magnetic field to digital pulses. Each pulse may represent a full rotation of part of a rotation for the internal magnet of the water or gas meter.

These pulses are fed into a counter circuit or the microcontroller 10 to be counted as representing rotations of the meter and thus, the movement of its least significant register digit.

The threshold detection circuit receives its input from the output of the filtering circuit. The circuit is a comparator circuit that may be implemented with commercially available analogue comparators or an operational amplifier configured as a comparator. Hysteresis is included in the configuration of the comparator to ensure reliable operation by avoiding false triggering from noise and interference. As with amplification circuit, the threshold detection and hysteresis parameters may be sent by the data logger 4 and stored in the non-volatile memory 16 by the microcontroller tO.

Microcontroller (10) The microcontroller performs a wide rage of functions in the magnetic sensor subsystem 2.

Its main functions are: i. Counting the pulses representing the rotations of meter (1) magnet. These pulses are counted for a specific time interval based on a parameter received from the remote data logger. At the end of this time interval, the reading is stored in the non-volatile memory 16 with an associated time stamp. A new pulse counting time interval is started on completion of the previous interval. This time interval represents the meter usage profile resolution. For example, pulses may be counted for 15 minutes before storing accumulated count value. In his case, the meter usage profile resolution is 15 minutes.

The time interval parameter may be varied depending on the requirements of the application. It may be received from the data logger 4 and stored in the non-volatile memory 16 of the magnetic sensor subsystem 2 2. Sending the stored pulse count values with their associated time stamps to the data logger 4 via the communication block 3 of figure 3. The pu'se count data is sent to the data logger 4 at fixed time intervals based on the communication interval parameter that is downloaded to the magnetic sensor subsystem 2 and stored in non-volatile memory 16.

This parameter may be changed and a new parameter sent to the microcontroller 10 by the data logger 4 3. Receiving the parameters for the gain, filtenng and threshold detection circuits from the data logger 4 and storing them in the non-volatile memory 16. Figure 4 shows the microcontroller 10 which then applies these parameters to the gain 26 filtenng 30 and threshold detection 34 circuits. The parameters will be applied again if a new set of parameters is received from the data logger 4 4. Generate alarm conditions and communicate them to the data logger 4. These alarm conditions are based on alert parameters received from the data logger 4and stored in non-volatile memory 16. These alarm parameters may include maximum and minimum water or gas usage level over a specific period of time, device tampering conditions, and malfunction of other parts of the magnetic sensor subsystem 2.

5. Control of the LED indicators 18 to provide diagnostic information during the installation of the sensor subsystem.

5.1.1 Non-volatile memory (16) The non-volatile memory (NVM) 16 may be implemented as a separate integrated circuit (IC) or as part of the microcontroller. Many commercially available microcontroflers have bufit-in non-volatile memory.

The technology of the NVM should enable its contents to be written to and erased for large number of cycles. Such technologies may include EEPROM, flash or other types of multi-time time erasable memories.

As stated above, the NYM 16 is used to store the collected meter data with the associated time stamps and the operating parameters for the magnetic sensor subsystem 2 including: 1. Operating parameters for the gain 26, filtering 30 and threshold detection 34 circuits.

2. The meter usage profile resolution parameter and the communication period parameter.

3. Alert parameters for the alarm conditions relating to the meter usage profile and the function of the magnetic sensor subsystem 2.

LED indicators (18) In this implementation two LED indicators 18 with different colours (for example: red and green) are used to provide diagnostic information during the installation of the magnetic sensor subsystem 2. This information may include: I. Success of failure of communications between the magnetic sensor subsystem 2 and the data logger 4.

2. Detection of the rotating magnetic field of the water or gas meter I to which the magnetic sensor subsystem 2 is attached.

3. Power status of the magnetic sensor subsystem 2.

Communication block (20) The communication block 20 of figure 3 enables the magnetic sensor subsystem 2 to communicate with the data logger 4. The magnetic sensor subsystem 2 communicates with the data logger for the following purposes: I. Send the accumulated meter usage data from the NVM 16 to the data logger 4.

2. Send a'arm conditions and diagnostic information about the operation of the magnetic sensor subsystem 2 to the data loggcr 4.

3. Receive operating parameters for the magnetic sensor subsystem 2 circuits from the data logger 4.

4. Receive timing parameters and alarm conditions from the data logger 4.

In this invention the communication block 20 is implemented using a number of methods.

These methods can be classified into two categories: 1. Wired communications: The wired communications methods include a range of direct link methods using metal cables or fibre optic cables. These methods may include a number of different implementations including: a. Direct cable link enabling the connection of a single magnetic sensor subsystem 2 to the data logger 4 as shown in figure 6.

b. Network cable connection using proprietary or standard network protocols such as Ethernet and RS485. This approach enables more than one magnetic sensor subsystem 2 to be connected to a single data logger 4 as shown in figure 7.

2. Wireless communications: The wireless communication approach (figures 8 & 9) includes a range of radio frequency communication methods. These methods may include a number of different implementations including: a. Proprietary wireless communications circuits using standard frequencies which normally do not require a licence of used at a specified power level such as 2.40Hz.

In this implementation a wireless transceiver IC, with associated external passive components and antenna, is included in the communication block 20 of the magnetic sensor subsystem 2. A similar IC will also be included in the data logger 4 circuit to enable the magnetic sensor subsystem 2 to communicate with the data logger 4. The software for the communication protocol may be executed by a processor included in the transceiver IC, a separate processor or the microcontroller 10 of the sensor subsystem.

b. Wireless communications based on standard protocols such as Bluetooth, Wireless LAN (WiFi) and sensor networks using the standard IEEE8O2. 15.4 protocol including the Zigbee implementation. With this implementation also a communication IC, with the associated external passive components and antenna, is included in the communication block 20 of the magnetic sensor subsystem 2. A similar IC will also be included in the data logger 4 circuit to enable the magnetic sensor subsystem 2 to communicate with the data logger 4. The software for the standard communication protocol may be executed by a processor included in the communication IC, a separate processor or the microcontroller 10 of the magnetic sensor subsystem 2.

The choice of the communication type (wired or wireless) is not exclusive and the skilled would realise that the invention could be implemented with both types working in parallel (i.e. the sensor sub system 2 and/or the datalogger itself could be equipped with both wired and wireless communication circuits.

Figures 7 and 8 shows that in both of the above implementations one or more magnetic sensor subsystems may communicate with a single data logger depending on the communication protocol used. This offers an imp'ementation with a network of sensors communicating with a single data logger.

Power supply (22) In this invention, the power supply 22 of the magnetic sensor subsystem 2 shown in figure 3 is implemented in one of two possible methods: 1. Remote power supply.

In this method the power supply for the magnetic sensor subsystem 2 is provided by the data logger 4 using a separate cable or the communication cable with separate wires for power supply. It is also possible to use alternative approaches to derive power for the sensor subsystem from the signal lines if the communication standard permits this.

2. Local power supply (figures 3, 6 & 9).

In this method the power block of the sensor subsystem includes a power source. The power source may be implemented using a number of approaches including: a. A primary battery. In this case the battery has to replaced after its energy is exhausted.

b, A mains derive power source. In this case the sensor subsystem will include a power supply circuit to convert the AC power to the required DC power.

c. A secondary battery (rechargeable) that requires charging by an addition circuit such as a mains power supply or an energy harvesting circuit. Energy harvesting may utilise a number of schemes, such as photovoltaic cells or thermo-generators.

Figure 10 shows a flowchart that describes the interaction between the datalogger 4 and the magnetic sub sensor 2 in order to configure the sub sensor with the adequate settings for sensing a specific utility meter.

The process starts at 70 when an operator fitting the device on site powers up the device.

Communication is then initiated between the data logger 4 and the magnetic sub sensor 2. If unsuccessful, at 74, an LED light alerts the operator of a problem.

V/hen communication is set up, the operator can select or identify the specific meter I to which the ARM system is to be connected to. Once the meter model is selected or identified, which can be done by using a serial number or a model descriptor, or aiding an operator with a picture or image driven selection menu (which can be stored in electronic form on a device, on the sensor 2, on the datalogger 4, on the server 7. or altematively in physical fomi, as for example in a book or catalogue), the configuration data can be downloaded at 76 from the datalogger or the server. The configuration data is then used at 78 to set up the signal conditioning parameters and the magnetic sensor 12 starts detecting the rotating magnetic field of the meter I. Once the field is detected at 82, if the device is colTectly set up, at 86 the LED lights start pulsing with a predetermined ratio to each revolution upon the rotation of the disk on the meter 1 (however, if the field is not detected correcfly, an alert is triggered, preferably via the LED lights at 102).

The microprocessor 10 will then count the magnetic field rotations and determine the pulse counting interval at 86. The count value will be stored at time stamped at 88, and once the communication interval is reached at 96, sent to the datalogger 4 at 98. The data may still be kept and the memory flushed after a predetermined period of time after the data is sent to the datalogger. The count continues/resumes again at 86 and under normal conditions the process continues a cycle through 86, 88, 96 and 98.

If the microprocessor detects a Zero pulse counting value at 92 or detects abnormal conditions that would merit triggering an alert, it triggers an exception alert at 94 and instructs the communication block 20 to transmit the alert to the datalogger at 100.

In turn the data stored at the Datalogger 4 can be sent to the server 7 also at predefined intervals (generally and preferably, the latter intervals being less frequent than the intervals at which data is sent between the subsystem 2 and the datalogger 4). Having data storage means at different stages in the communication chain that spans between the sub sensor 2, the datalogger 4 and the server 7, enables high definition readings (i.e. higher frequency readiiigs), with higher resiliency and lower energy consumption.

The high definition data can be accumulated at the data storage means on the subsystem 2 itself. The fact that the subsystem 2 is also provided with a microprocessor 10. enables data processing locally at the sensor, which allows savings in the amount of data that needs to be transmitted (for example if readings taken every 15 seconds remain constant for 8 hours, then a single reading coupled with a time range can be sent instead of 1.920 single readings, resulting from 4 readings per minute during 8 hours). Accumulated pre-processed data can then be sent in bursts to the datalogger 4. Such bursts can be at predetermined intervals, or alternatively they can be sent on an opportunistic basis (e.g. as soon as communications signal strength reaches a threshold, or as soon as a certain file size is reached) The other advantage of having a local microprocessor is that any uTegular situation can be detected in real time by the local sub sensor 2, and alarms transmitted to the server when that happens, without the need of constant communication with the datalogger 4 or the server 7.

To provide equivalent near real time awareness, absence of the local microprocessor would instead require constant communication between the magnetic sensor 12 with the datalogger 4 (and/or the server 7) so that the remote processing of the data could alert of any irregular situation. That requirement of constant communication is a constant drain on the energy required to operate the AMR system. The constant drain reduces battery life and that in turn affects reliability and resilience, as a device with an exhausted battery is less likely to be able to successfully send data or an alarm signal, perhaps when it is most needed.

In turn the datalogger 4 can also be used to further process the data and store it, so that it can be sent in predetermined or opportunistic bursts to the Server 7. In order to reduce even more the energy consumption of the AMR system, these bursts between the datalogger and the server are preferably less frequent than the bursts between the subsystem 2 and the datalogger 4. Therefore the datalogger would be consolidating log data from the sensor and transmitting less frequently, which is more efficient because it reduces the communication overhead required for each event in which a transmission needs to be established.

Figure 12 shows the modular construction adopted for the magnetic sensor of the invention.

The magnetic subsystem 2 is housed in a small separate container from that of the main datalogging unit 4 housed in a second container 110. They are preferably linked by a cable 118, but the skilled person could also implement the connection via a wireless link (in which case a local power source would be required at subsystem 2. The datalogging unit comprises a receiver unit for receiving and transmitting data to the sub-system 2 and an antenna 120 for wireless communication with (or transmission to) a server 7 at a remote location via a public or private communication network 5, 6. The communication with the server could, of course.

also be a cable connection. The datalogger also comprises a second processing unit.

In the preferred embodiment, the main power source for the datalogging unit is housed in a third separate container i12 and connected thereto via cable 116. This has the advantage of allowing change of batteries without any need of opening the housing that contains the delicate electronics, which is a consideration in harsh environments as those encountered particularly by gas and water meters. Additionally such modular construction with a separate housing for the power source makes "hot swapping" the power source a much easier proposition.

Claims (1)

1. <claim-text>Claims 1. A utility meter sensing device for attaching in a non-invasive fashion to an existing meter in retrofit fashion, the device comprising: a sensor unit (2) comprising a magnetic sensor unit (12) and a first processing unit (10), said sensor unit for attachment to an existing meter (1), a receiver unit capable of collecting readings and status information from the sensor unit, said receiver unit also comprising a second processing unit, said receiver unit also comprising a transmitting unit for transmitting data to a remote location across a public or private network.Whereby, the arrangement allows for a reduced need for continuous data transmission between the sensor unit and the receiver unit in order to maintain a predetermined level of data logging frequency.</claim-text> <claim-text>2. The sensing device of claim 1, wherein said first processing unit (10) is configured to automatically adapt the gain of the magnetic sensor unit (12) according to the existing meter it is attached to.</claim-text> <claim-text>3. The sensing device of any preceding claim, wherein said sensor unit (2) comprises memory means (16).</claim-text> <claim-text>4. The sensing device of any preceding claim, wherein said first processing unit (10) is capable of automatically storing a predetermined quantity of logging data, before it sent to the receiver unit.</claim-text> <claim-text>5. The sensing device of any preceding claim, wherein said sensor unit (2) comprises a signal conditioning circuit (14).</claim-text> <claim-text>6. The sensing device of claimS, wherein said signal conditioning circuit (14) comprises an amplification circuit (26).</claim-text> <claim-text>7. The sensing device of claims 5 or 6, wherein said signal conditioning circuit (14) comprises a filtering circuit (30).</claim-text> <claim-text>8. The sensing device of claims 5 to 7, wherein said signal conditioning circuit (14) comprises a threshold detection circuit 30).</claim-text> <claim-text>9. The sensing device of claim 5 or 6, wherein said signal conditioning circuit (14) comprises an analogue to digital converter (35).</claim-text> <claim-text>10. The sensing device of any preceding claim, wherein said sensor unit (2) comprises illumination means (1 8).</claim-text> <claim-text>11. The sensing device of any preceding claim, comprising power supply (22) within the housing of the sensor unit (2).</claim-text> <claim-text>12. The sensing device of any preceding claim, wherein said sensor unit (2) comprises a wired communication inteiface circuit (21') 13. The sensing device of any preceding claim, wherein said sensor unit (2) comprises a wireless 21 communication interface circuit (21') and an internal power supply (22).14. The sensing device of any preceding claim, wherein said sensor unit (2) comprises a magnetic sensor unit (12) with magneto-resistive elements in a magnetic sensor connected in a Wheatstone bridge configuration (65).15. An automatic meter reading system comprising a utility meter sensing device as claimed in any preceding claim.16. An automatic meter reading system according to claim 15, wherein the said receiver unit is housed in a second container that is separate from a first container housing the sensor unit (2).17. An automatic meter reading system according to claim 16, wherein the said second container that is neither contained within, nor is containing the first container.18. A sensor unit (2) for autility meter sensing device comprising: a magnetic sensor unit (12), a processing unit (10).a data storage means (16), a communication circuit (20, 21) and a signal conditioning circuit (14).19. A sensor unit as defined in claim 18, wherein the signal conditioning circuit comprises an amplification circuit (26).20. A sensor unit as defined in claims 18 or 19, wherein the signal conditioning circuit further comprises a filtering circuit (30).21. A sensor unit as defined in claims 18 to 20, wherein the signal conditioning circuit further comprises a threshold detection circuit (34).22. A sensor unit as defined in claims 18 or 19, wherein the signal conditioning circuit further comprises an analogue to digital converter (35) 23. A sensor unit as defined in claims 18 to 22 further comprising an internal power source.24. A sensor unit as defined in claims 18 to 22, wherein the communication circuit is configured as a wireless communication circuit.25. A method of configuring a sensor unit (2) as defined in claims 18 to 24 comprising the steps of: providing a data connection to a second processing unit comprising data storage means holding configuration files for different models of meters, downloading the configuration data to the sensor unit, setting up signal conditional parameters on the sensor unit.detecting rotating magnetic field on the meter.26. A utility meter sensing device as herein descnbed with respect to the drawings.27. An automatic meter reading as herein described with respect to the drawings.28. A sensor unit as herein descnbed with respect to the drawings.29. A method of configuring a sensor unit as herein described with respect to the drawings.</claim-text>