WO2009007690A2

WO2009007690A2 - Device for remotely monitoring a meter

Info

Publication number: WO2009007690A2
Application number: PCT/GB2008/002298
Authority: WO
Inventors: Matthew Middleton; Anthony Hughes; Lee Francis
Original assignee: C & G Management Limited
Priority date: 2007-07-09
Filing date: 2008-07-02
Publication date: 2009-01-15
Also published as: GB2450880A; GB0713303D0; WO2009007690A3

Abstract

A device (10) for remotely monitoring a moving magnetic field produced by a meter comprising a magnetic sensor (12), a processor (16) for processing an output signal of the magnetic sensor, and transmission means (14) for wireless transmission of a processed output signal to a remote device.

Description

Device for Remotely Monitoring a Meter

The present invention relates to a device for remotely monitoring a meter and particularly but not exclusively to a device for remotely monitoring a utility meter, for example, a water or a gas meter.

Although it is known to provide a system for the remote reading of a utility meter, for example as disclosed in GB 2336272, there is a need for an improved non-invasive device capable of monitoring a meter from a short distance. Typically, existing meter monitors, known as loggers, are expensive, inaccurate, dependent on hard wiring and have bulky battery packs or require frequent changes of the battery pack. Furthermore, the typical device often needs to be in such close proximity to the meter being monitored, that the device has to be removed to read the meter conventionally by the metering authority.

Most water and gas meters have a built-in magnet attached to a rotating shaft that is normally used for testing and calibration purposes during manufacturing of the meter. This magnet rotates once per revolution of the meter shaft and produces a moving magnetic field, which is an indicator that there is a flow through the meter. Furthermore, the number of revolutions of the shaft and magnet is proportional to the flow through the meter. In other words, if the number of rotations of the shaft of the meter is accurately determined, then the flow through the meter can also be accurately determined.

A problem associated with using a magnetic effect to determine the number of rotations of the shaft remotely is that it is susceptible to errors caused by external anomalies.

It is an object of the invention to provide an improved device for remotely monitoring a meter, the output of which is substantially unaffected by external magnetic anomalies.

According to the first aspect of the present invention there is provided a device for remotely monitoring a moving magnetic field produced by a meter comprising a magnetic sensor, a processor for processing an output signal of the magnetic sensor, and transmission means for wireless transmission of a processed signal to a remote device.

The device of the invention is advantageous because it provides for a non-invasive, non contact, fully approved meter monitoring device that can be positioned side-by- side with an existing gas or water meter to record minute by minute energy usage, with on board electronic data storage and on-demand data recall.

Preferably a second magnetic sensor is provided, the axis of which is disposed at 90° to the axis of the first magnetic sensor.

By providing two sensors disposed at right angles to one-another, the device can be positioned in any orientation relative to a meter to be monitored.

Preferably the transmission means is a wireless radio system. It will be appreciated that any suitable wireless radio system or device could be used including, but not limited to, GSM, GPRS, SMS and ZigBee.

Preferably the device is contained in a water-tight enclosure. The enclosure may comprise any suitable shape known to the skilled person. However, preferably, the enclosure is tubular, with end caps at its respective ends. This allows the device to be operated in submerged conditions, for example, in a flooded water meter pit.

An LED indicator is visibly mounted in the enclosure. Preferably the LED is a dual colour LED and illuminates when the device is detecting pulsed outputs from the or each sensor.

Preferably at least one battery is provided for powering the device. Two, three or more batteries may be provided as desired.

Preferably an amplifier is provided for the or each sensor.

The device preferably includes an analogue-to-digital converter. Preferably a digital gain and offset control circuit is provided for the or each sensor.

According to a second aspect of the invention there is provided a method of remotely monitoring a moving magnetic field produced by a meter using a device in accordance with the first aspect of the invention, comprising sensing the magnetic field, processing a sensed output signal to remove anomalies and background noise, and transmitting the processed signal wirelessly to a remote device.

Preferably the processing includes amplification of the sensed signal.

Preferably the processing includes adjusting the amplified signal for gain and offset.

Preferably the processing includes digitising the adjusted signal.

Preferably the processing includes converting the digitised signal to a pulsed signal.

Preferably the processing includes transmitting the pulsed signal to the remote device.

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1 shows a schematic cross-sectional view and a schematic side view of a device for remotely monitoring a meter in accordance with the invention of the invention;

Figure 2 is a diagram illustrating magnetic fields cutting through a dual sensor;

Figure 3 is a graph showing the signal output voltage of two sensors (A and B) against the angular position of a magnet attached to a spinning disk; Figure 4 is a graph showing the signal output voltage of a single sensor against the angular position of a magnet attached to a spinning disk showing a small signal offset;

Figure 5 is a circuit diagram for the meter of Figure 1; Figure 6 is a graph indicating detected signals which are out of the voltage range of an analogue-to-digital converter;

Figure 7 is a graph showing the detected signals of Figure 6 after the amplifiers Gain and Offset has been adjusted into the correct operational range for the analogue-to-digital converter;

Figure 8 is a graph indicating the process of calculating signal amplitude and offset;

Figure 9 is a graph indicating the process of detecting the maximum positive voltage of the signal waveform; and Figure 10 is a graph showing a pulsed signal.

Referring firstly to Figure 1, a device for remotely monitoring a moving magnetic field produced by a meter is indicated generally at 10. The device 10 includes a magnetic sensing head 12 including a pair of magnetoresistive sensors disposed at right angles to one another, a GSM-GRPS antenna 14, a printed circuit board (PCB) and GSM module (including a modem) 16, and a plurality of batteries 18 for powering the device. Three batteries 18 are illustrated, but any suitable battery pack can be utilised. The parts of the device are contained within a tubular enclosure 20.

The tubular enclosure 20 comprises a tubular body 22 with a circular cross-section and is closed at its lower end (as viewed) by an end cap 24 and a watertight seal 26. The end cap 24 has a circumferential groove, into which the wall of the tubular body 22 locates. The upper end of the tubular body 22 is sealed by a substantially dome shaped cap 28, which may be screw threaded onto the body 22. A seal 30 is provided to ensure that the upper cap 28 is also watertight. An LED indicator 32 is disposed in the cap and is visible from the upper end of the enclosure 20. The LED is a dual colour LED and indicates that both sensors of the device 10 are picking up a moving magnetic field. The outer profile of the enclosure 20 can be seen clearly in the right hand drawing of Figure 1.

Magnetoresistive sensors are made of a nickel-iron (Permalloy) thin film deposited on a silicon wafer and patterned as a resistive strip. In the presence of an applied magnetic field, ie caused by a moving magnet, a change in the sensor's Wheatstone bridge resistance causes a corresponding change in voltage output. An external magnetic field applied normally to the side of the film causes the magnetization vector to rotate and change angle. This in turn causes the resistance value to vary (ΔR/ R) and produce a voltage output change in the Wheatstone bridge of the sensor as described below with reference to Figure 5.

This change in the Permalloy resistance is termed the Magnetoresistive Effect and is directly related to the angle of the current flow and the magnetization vector. The relative direction of the resulting moving magnetic field can be quantified electronically from this information.

Two magnetoresistive sensors are required as described above, with the sensors mounted at right angles to each other, to allow omni-directional operation of the device 10, ie the device can operate in any position with respect to a meter which has already been installed. In other words, the need for correct orientation of a sensor with a magnetic field becomes unnecessary with the use of two sensors. Figure 2 shows flux lines 36 of a magnetic field produced by a moving magnet 34 cutting through a dual sensor, indicated at 38. Use of the two sensors (or a dual sensor) 38 allows for the device 10 to be fitted into very cramped conditions where ideal positioning is not possible.

The use of two sensors also provides improved detection of the moving magnetic field irrespective of the sensor position. The second sensor output obtained can be compared to the primary sensor output in order to confirm detection of the moving magnetic field. Figure 3 shows an example voltage output signal obtained from two sensors (A and B) against the angular position of a magnet attached to a spinning disk, or meter rotor. Figure 4 shows the signal output voltage of a single sensor plotted against the angular position of a magnet attached to a spinning disk for a full 360° revolution of the magnet.

Referring now to Figure 5, an example of circuitry associated with a two sensor system is indicated at 40. This sensor includes two Wheatstone bridge networks indicated at 42 and 44. Each resistance element in the bridges has a nominal resistance (in ohms) with a very high average magnetic field sensitivity of 1 milli-volt per gauss per volt applied on the bridge.

With the two bridge elements of orthogonal orientation, each bridge has an axis of sufficient sensitivity to break the earth's magnetic field, or any other magnetic disturbance, into X and Y vector components that can be measured, quantified and manipulated.

The bridge elements provide a balanced signal output biased on half the supply voltage. Any imbalance across the outputs (OUTA-, 0UTA+, OUTB-, and OUTB+) will be due to earth's magnetic field plus other magnetic disturbances plus the manufacturing tolerance error on the bridges, known as bridge offset.

The output voltages of each sensor bridge are next fed into an instrumentation amplifier stage. Two independent instrumentation amplifiers are represented by AMPl and AMP2. The amplifiers AMPl and AMP2 perform the difference measurement and amplify the result by several thousand times for conversion into a digital number for both sensor outputs.

The amplified signals are then fed to two independent dual digital control variable resistors, indicated as CONTROLl and CONTROL2. The dual digitally controlled variable resistor devices CONTROLl and C0NTR0L2 are used to adjust the gain and offset in each instrumentation amplifier, thus providing a means to adjust the input signals gain and offset.

A SET/RESET module 46 provides a means of providing high current pulses into a dual magnetic sensor Set/Reset strap resistance RSR. A microcontroller provides the digital portion of the circuit by providing a digital output SET/RESET.

When the SET/RESET switches from a low to high logic state, the SET/REST module creates a current pulse of over a half an ampere flowing into RSR to create the "set" magnetic field for bridge element re-alignment. The dual colour LED Light emitting indicator 32 is used as an indicator to show pulses are being detected on each of the sensor bridges 42,44.

In operation, with the circuit fully powered up, sensor bridge 42, composed of the RlA, R2A, R3A, and R4A permalloy resistive elements, creates a voltage difference across OUTA- and 0UTA+ that is then amplified by the instrumentation amplifier and presented to microcontroller analogue input, indicated ANO.

Similarly, bridge B permalloy resistive elements RlB, R2B, R3B, and R4B create a voltage difference across OUTB- and OUTB+ that is amplified by the instrumentation amplifier and presented to microcontroller analogue input, indicated ANl.

These analogue voltages at ANO and ANl can be thought of as "X" and "Y" vector representations of the magnetic field.

In order to extract these X and Y values, the voltages at ANO and ANl are digitized by an Analogue-to-Digital Converter (ADC), which is onboard the microcontroller.

In order for the microcontroller to operate and detect the correct meter pulses, a series of software algorithms are performed in order to ascertain the environmental parametric values and calculate the correct operational parameters, detect the signal peaks, clear any new magnetic disturbances caused by ferrous content, count and accumulate the detected pulses and send the data out.

When the device 10 is powered up, the functions below are performed by algorithms in the following order:

(a) Monitor and store the surrounding magnetic fields and magnetic anomalies that are caused by metal parts in the meter, the enclosure, the earth's magnetic field and any other disturbances.

(b) Adjust the amplifier's Gain and Offsets in order to get these signals into the correct operational range for the ADC. (c) Search for the faint meter signal (Two changing signals sinusoidal in pattern and out of phase, caused by the changing magnetic fields of the rotating disk / vane of the meter).

(d) If no signal is observed, adjust the increment in the amplifier's Gain until the signal is found.

(e) Upon detection of two moving sinusoidal waveforms (shown in Figure 6), digitise the complete waveforms; calculate the signal amplitudes and signal offsets (shown in Figures 7 and 8).

(f) Subtract all interference and background anomalies from the digitised signals and adjust the amplifier's Gain and Offsets so the detected signals are optimised for the ADC.

After the calibrations algorithm is completed, the incoming pulse sinusoidal waveforms are tracked and digitised and their maximum positive voltages are found, as indicated at 48 in Figure 9, in order to detect a full revolution of the meter rotor, which equates to a unit of measure indicated by that particular meter.

Referring to Figure 10, once the peak voltages 48 of the waveforms have been detected these are changed into pulses 50, so that the software algorithm can then count them and measure the distance between them, in order to calculate the time intervals and thus the frequency of the pulses.

Once the meter pulses 50 have been identified, they are stored at regular intervals in an internal non volatile memory. Then, at a preset time and date interval, the data is packetised and sent via the internal wireless radio system to a remote site where further data processing can take place.

The following advantages are provided by the device 10: (a) The device 10 is able to operate in any position with respect to a meter already installed. This allows for the device to be fitted into very cramped conditions where positioning of other devices may not be possible.

(b) The device 10 is able to operate up to 6" (154.2mm) away from the meter being monitored. This provides for instances where the device cannot be fitted immediately adjacent the meter being monitored.

(c) The device 10 is able to be retrofitted to all standard types of monitoring devices currently installed.

(d) The device 10 is non-invasive, has no attachments and the can operate without any physical connection to the metering device being monitored.

(e) The device 10 can be fitted and operated inside existing meter pits without requiring any modifications or changes to the meter pit.

(f) The device 10 is able to differentiate between meter pulses and external anomalies.

(g) The device 10 has low power consumption, and can operate over 12 months, before requiring battery replacement.

(h) The device 10 is water-proof and is able to operate in submerged conditions, for example in a flooded meter pit.

(i) The device 10 can operate at very low temperatures.

(h) The device 10 is able to collect data automatically and send to it out to another device via its on board radio system, without human intervention.

(i) The device 10 is low cost, thus making it very attractive to service providers. The device 10 also meets all of the standard requirements and necessary UK regulatory conditions. (j) The device 10 is capable of determining real pulses from those of ghost signals, false signals and magnetic disturbances. This can be referred to as intelligent sensing.

The device 10 is intended to be used with an external data management system for the monitoring and cost analysis of water and gas consumption in a premises, giving the user an almost minute by minute analysis of running costs and providing detailed indications of energy usage. Wastage and inappropriate usage of energy resources can be easily and efficiently identified, thus enabling the user to make great financial and environmental savings.

Claims

1. A device for remotely monitoring a moving magnetic field produced by a meter comprising a magnetic sensor, a processor for processing an output signal of the magnetic sensor, and transmission means for wireless transmission of a processed signal to a remote device.

2. A device as claimed in claim 1, in which a second magnetic sensor is disposed at a position at 90° to the first magnetic sensor.

3. A device as claimed in claim 1 or claim 2, in which the or each magnetic sensor is a magnetoresistive sensor.

4. A device as claimed in any preceding claim, in which the transmission means is a wireless radio.

5. A device as claimed in any preceding claim, in which the device is contained in a water-tight enclosure.

6. A device as claimed in claim 5, in which an LED indicator is visibly mounted on the enclosure.

7. A device as claimed in any preceding claim, in which at least one battery is provided for powering the device.

8. A device as claimed in any preceding claim, in which an amplifier is provided for the or each sensor.

9. A device as claimed in any preceding claim, in which an analogue-to- digital converter is provided.

10. A device as claimed in any preceding claim, in which a digital gain and offset control circuit is provided for the or each sensor.

11. A method of remotely monitoring a moving magnetic field produced by a meter using a device as claimed in any preceding claim, comprising sensing the magnetic field, processing a sensed output signal to remove anomalies and background noise, and transmitting the processed signal wirelessly to a remote device.

12. A method as claimed in claim 11, in which the sensed output signal is amplified.

13. A method as claimed in claim 12, in which the amplified signal is adjusted for gain and offset.

14. A method as claimed in claim 13, in which the adjusted signal is digitised.

15. A method as claimed in claim 14, in which the digitised signal is converted to a pulsed signal.

16. A method as claimed in claim 15, in which the pulsed signal is transmitted to the remote device.

17. A device and method for remotely monitoring a moving magnetic field produced by a meter substantially as described herein with reference to and as illustrated in Figures 1 to 10 of the accompanying drawings.