AU2008100551A4 - Wireless Sensor for Secondary Metering of Water Usage - Google Patents

Description

00 00 0 17 wiiprnliq 0 8 AUG 2008

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION INNOVATION PATENT WIRELESS SENSOR FOR SECONDARY METERING OF WATER USAGE The following statement is a full description of this invention, including the best method of performing it known to me 00

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1 WIRELESS SENSOR FOR SECONDARY METERING OF WATER USAGE 00

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Most households and business premises are connected to a water supply network via a mechanical water meter with a display of total volumetric flow of water. This display is Vroutinely read by local authorities for purposes of customer billing and for water supply management. A typical mechanical water meter includes moving parts and a _mechanical display and has no means of electrical connection to a device for the 0purpose of remote monitoring, whether by a wired connection or by some form of Owireless connection.

As water is flows through the water meter the internal components move and cause vibrations which can often be heard as an audible sound. A wireless sensor in accordance with this invention includes a transducer that converts such mechanical vibrations into electrical signals that can be used to digitally determine the volume of water that has passed through the meter. The digital information is used to indicate flow rate and can be accumulated over specified time periods to determine water consumption, peak flow rate, water demand and other quantities and statistics. This information can be transmitted over wires or preferably over a wireless connection to a monitoring device capable of displaying, recording and possibly re-transmitting the flow information to other locations, such as a central office. The monitoring device may be in the form of a dedicated display unit, or may be a personal computer, personal digital assistant (PDA), mobile phone or similar computer device.

In a wireless embodiment, batteries are used to power the wireless sensor which includes an amplifier, signal processing and discrimination circuitry and a low power radio transmitter or transceiver. Preferably the device would contain a microcontroller operating from interrupt signals generated by the discrimination circuitry to determine the rate or occurrence of water flow. Optionally the sensor may use a low cost microcontroller with a fast analog to digital converter to capture the real-time audio signal and process the digitised signal to detect water flow.

The invention is non-invasive and is intended to not require dismantling or modification of an existing water meter installation. A mechanical connection, in the form of a clamp 00 2 or bracket is provided to mechanically support the sensor and to provide a path for mechanical vibrations from the water meter to the transducer, located within or external 00 to the sensor enclosure.

The transmission of data from the sensor may take the form of simple transmission of detected flow units to a receiver, the receiver having the capability to interpret and totalise the flow information and to compute flow rate, peak flow, water demand and _histograms. Preferably the data is in the form of integer or floating-point channel values 00 representing flow rate, flow volumes and totals accumulated over specified time periods (eg daily total, quarterly total etc). This information is computed by, and stored within the sensor unit so that replacement of the display unit does not cause loss of the data for a given water meter. The transmitted data includes address and unique identification information to allow multiple sensors for one receiver. It also includes serial number, checksum information, communications status and other status information such as low battery indication.

The radio frequency transmit power may also be fixed or adjustable: the benefit of reducing power would be to prolong battery life at the expense of radio range. The sensor may be operated continuously, or in sampled mode to prolong battery life.

Sampled mode may involve transmitting data on occurrence or one or more detected pulses or at regular timed intervals, or, preferentially, a combination of both.

The receiver unit decodes the information from the wireless sensor and provides one or more outputs and displays visual information based on the data received from the sensor. The visual information may comprise graphical displays, numerical data and text. Light emitting diodes and/or output circuits may also be used for status indication (for example low battery or communications error) at the display unit. Outputs may take the form of serial communications including USB, or wireless, such as Bluetooth, to allow information transfer from the receiver to another system, such as a computer or communications networking device.

Optionally the receiver unit could be in the form of a personal computer, personal digital assistant (PDA) or mobile phone with appropriate wireless interface (eg Bluetooth) and with application software to perform the functions of receiving, accumulating and 00

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O3 performing computations on the information received from one or more wireless sensors.

The computer software includes the ability to provide visual displays of the information 00 and to store the data for historical reference and graphical historical display. It also has

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the ability to generate visual and audible alarms, retransmit the information and make the information available on a computer or mobile phone network.

A plastic or plastic/metallic enclosure is used to house the sensor with a required degree Sof environmental protection from dust and moisture ingress. A means is provided to 00 replace the battery in the sensor detector and where required to access potentiometers, Sbuttons, miniature switches and any other interfaces required to configure and to test the sensor.

A number of sensors may be installed within the same physical area by utilizing coded information unique to each sensor and/or by transmitting the information on separate radio frequencies. Antennas can be dipoles or preferentially loop antennas to provide a compact and integral unit.

The invention is illustrated in the attached figures which are explained as follows. Figure one shows the wireless sensor 1 attached to a water meter 2 separated by a distance and interconnected by radio frequency transmission 3 to a wireless receiver 4. Optional output from the receiver unit may be in the form of a wired connection, 5 or may be a wireless data interface (eg Bluetooth).

Figure two shows a possible embodiment of the wireless sensor circuitry. A transducer 6 may be in the form of a piezoelectric or capacitive sensor, such as a microphone or accelerometer, or in the form of a moving magnet and coil arrangement. It may also be in the form of an integrated circuit semiconductor acceleration sensor including MEMS types (Micro-Electro-Mechanical Systems technology) with analog or digital outputs.

The transducer may also be integrated with the wireless and/or microcontroller circuitry, in the form of a single integrated circuit.

In the case of transducers with analog outputs, signal amplification and filtering is performed by 7 to improve the signal amplitude at the frequency range of interest.

Filtering also has the function of rejecting unwanted signal components that may cause 00

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O4 false detection and may involve a combination of analog and digital circuitry acting on the signal frequency, timing and amplitude. A particular case for filtering is accounting 00 for the occurrence of water hammer caused by sudden changes in water pressure. To

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overcome this problem a secondary discriminator is used to detect water hammer and allow correction of the metered value. The amplified and filtered signal may be applied directly to a microcontroller 9. If the microcontroller includes a capability for high speed analog to digital converter it is possible to digitally process the real-time signal from 7 to determine the occurrence of a flow from the water meter. Alternately 7 may include 00 discriminator circuitry that converts the amplified and filtered analog signal into a digital Spulse whenever a specific mechanical vibration occurs. This digital pulse being suitable for use as an interrupt signal to the microcontroller. In the latter case, the microcontroller can enter a low power state to conserve battery life and wake only on the occurrence of a brief interrupt pulse from the discriminator circuitry within 7. The microcontroller has the capability to store information in non-volatile memory, such as serial number, configuration information (for example transmit power level) and unique identification codes. It has the capability to calculate and send checksums to ensure that the transmitted data is validated by the receiver/decoder. A low power RF Transmitter sends encoded data from the microcontroller and is only active when a signal transmission is required. Otherwise, and for the majority of time, the transmitter is in a low power inactive state to conserve battery power. The radio frequency transmission is in the range of 150 2400 Megahertz. A number of modulation schemes could be employed; the most likely would be Amplitude Shift Keying (ASK), preferably Frequency Shift Keying (FSK) and variations thereof, or On Off Keying (OOK). The sensor is powered from the battery supply 8 containing battery cells and circuitry for regulation, reverse polarity protection and battery voltage monitoring.

A key operation aspect of the invention would be to prolong battery life to minimise required maintenance. At least two timing schemes can be used to reduce power and are available for selection by the user. The first scheme accumulates a number of pulses from the discriminator and transmits the accumulated data at fixed intervals. In the absence of a pulse from the discriminator the circuitry can be put into a sleep mode to ensure power consumption is a minimum. This scheme would be most effective when the interval between pulses was significantly longer than the time to sample, encode and transmit the information. It also provides regular updating of information to the receiver 00

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D unit, even when there is no detected water flow. The mircocontroller requires low power ;timing circuitry to initiate the timed transmissions.

00 A second scheme is to accumulate pulses from the discriminator and to transmit the information after a fixed number of pulses has occurred. For example, the information could be sent for every 50 accumulated pulses. This would be very effective in prolonging battery life in the case where there was no water flow for long periods of time.

OIt may mean however that there are long periods of time where no signal is transmitted 00 to the receiver making it difficult to determine if the system is working properly. A combination of the above two methods is the preferred embodiment where a transmission occurs after an accumulated number of pulses from the discriminator and also after a period of time where no pulse activity has occurred.

Figure three shows a possible embodiment of the receiver unit. The radio frequency (RF) signals from the transmitter 10 are received by the antenna 12 and RF receiver 13 which uses a demodulation scheme corresponding to the RF transmitter modulation (ie ASK, FSK or OOK). The demodulated signals are fed into a microcontroller 14 which interprets the data and displays the information on the LCD display. This information may include the total flow, volumetric flow rate, daily totals, weekly totals, battery, checksums and communications status and other information transmitted from the wireless sensor.

The receiver has the ability to check the information from the sensor which contains a unique identification number matching a number stored within the receiver to ensure that the information transmitted from a specific wireless sensor is intended for reception by a specific receiver unit. This is required for situations where a number of wireless sensors are installed within the same vicinity. The sensor and receiver have the capability to store information in non-volatile memory for the purpose of unique identification, serial number and user settings. User settings may include the mode of operation, communications settings, latching, contact or pulsed output actions and actions to perform on low battery or loss of communications.

A voltage regulator 15 provides power to the circuitry and has a wired input connection 17 for connection to a suitable power supply, such as a plug-pack. The interface circuits 00

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6 16 may comprise a combination of communication circuits, such as USB, Bluetooth, Zigbee and emerging household protocols (CBus). The receiver unit may also provide 00 light emitting diode (LED) indication of the states of outputs, such as low battery and

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communications status OK.

In the presence of radio frequency interference the above embodiment may suffer some problems in that transmission of information may be corrupted. This is likely in _environments where spurious electromagnetic noise is significant. Two methods can be 00 used to alleviate this situation. In the first method the sensor/transmitter sends the same Sinformation a number of times at a regular intervals (this will be referred to as 'retries').

The number of retries may be adjusted depending on the severity of electromagnetic noise and on other factors, such as the negative effect on battery life. The receiver unit thus has more than one chance of faithfully receiving the information.

Alternately, both receiver and transmitter could be implemented as transceivers so that bi-directional communications were possible. Upon reception and decoding of information, the receiver unit sends appropriate messages back to the wireless sensor.

Such messages indicate that information was properly received or that a retry is required. And in the event that the wireless detector does not receive a reply then the encoder/transmitter automatically retransmits the information, up to a limited number of retries.

In preferred embodiment where the sensor and display unit incorporate transceivers then bi-directional radio communications are possible and there is another possible method of prolonging battery life. The RF transmit level can be automatically adjusted to achieve reliable error free communications using the minimum transmit power. The system adjusts the power level to the minimum where reliable communications are established.

Claims (2)

1. 3. A device as claimed in Claim 1 that has the capability to display flow and status information and/or to transmit information to a physically separate receiver unit or computer system.
2. 4. A wireless device as claimed in Claim 1 that is battery powered and employs one or more methods to prolong battery life, including: automatic adjustment of RF power to provide error free communications at the lowest possible power level; bi-directional radio communications so that information is retransmitted only when necessary; and transmission of information only on a change of water flow value. A wireless device substantially as described herein with reference to figures 1 to 3 of the accompanying drawings. Andrew James Stewart 13 June 2008