Patent Description:
Flow meters are commonly used to measure the flow rate of fluids within buried pipes and open channels or culverts. Transit time acoustic flow meters are an established measurement technology. When flow meters are installed in pipes which are below ground, servicing requirements mean that these flow meters are traditionally installed within a buried meter pit, typically a concrete box construction. The pit is typically accessible so that technicians may access the components of the flow meter. The construction and installation of these service pits is generally a high proportion of the total flow meter installation cost.

When ultrasonic (transit time) flow meters are installed in open channels and pipes they are typically installed as a collection of sub-components which must be assembled and then calibrated to their installation. The commissioning of these metering systems requires the precise measurement of the path length between each transducer, the angle of the measurement path relative to the mean direction of flow, and of water level transducer datum's and other meter configuration parameters. Other acoustic flow meter products available in the marketplace are assembled on site by strapping the acoustic transducers around the external or internal diameter of the pipe which passes the flow. In open conduit applications the transducers are bolted to the opposing walls of the conduit. The transducers are connected by signal cables to processor electronics. The assembly must be precision installed and calibrated in the field. For installations in which the transducers are installed on the internal diameter of the pipe, the pipe must be of sufficient diameter that a person may safely access it for the purpose of installation. For installations in which the transducers are installed on the outer diameter of the pipe, the pipe must be above ground or a large concrete pit must be constructed around the pipe to permit a person to safely access the external diameter for the purpose of fitting and maintaining the sensors.

In open channel flow meter applications, the accuracy of the flow meter is affected by the flow meter surroundings. The geometry of the channel upstream and downstream of the flow meter can influence the velocity distribution of the fluid passing through the flow meter. This velocity distribution is measurable at all points within the flow meter except for the surface. The velocity of the fluid on the floor/walls of the flow meter is zero. The velocity at set elevations within the flow meter can be measured, and the velocity at elevations between these measurements can be interpolated from the measured elevation velocities. However generally the surface velocity of the flow is not measured and so the velocity distribution in the upper levels of the flow must be extrapolated with potentially high uncertainty. To minimise the uncertainty in the surface velocity of the flow, the variation in surface velocity behaviour needs to be minimised.

Some examples of assemblies of the state of the art can be found on the following documents:
<CIT> provides a control gate adapted to be installed across a channel for liquids, wherein the control gate has a barrier member that is pivotally mounted at or adjacent the base of flow channel and at least one side member attached to barrier member. A drive means co-operates with the at least one side member or central member to allow raising and lowering of barrier member to regulate flow of liquid through control gate.

<CIT> aims to control the opening of a flow rate adjusting gate by detecting the position of the gate with a potentiometer provided to a drive motor and calculating a flow rate from the pressure signal detected from a pressure gauge and the gate position signal supplied from the potentiometer.

<CIT>enable measurement of flow-rate of fluid even if the specimen contains floating substances, by dividing a cross-section of flowing path in a plurality of sections in the depth direction and when the floating substances mixed in the fluid stops transmission of ultrasonic-wave pulses, obtaining the required flow-rate per unit of time by multiplication by the sectional area of the section concerned.

Finally, <CIT> discloses a device that utilises the propagation of an acoustic wave through the canalisation between emitting and receiving transducers. The device comprises means for determining the propagation time of the acoustic wave between the transducers and means for computing the differences between the propagation times of the acoustic wave in one direction and in the other. Means permit the processing of the differences between the propagation times in order to deduce therefrom the parameter measured. The device comprises at least two pairs of transducers which are disposed on a measurement channel passing through the axis of the canalisation, the position of each one of the measurement channels being deduced from the position of another measurement channel by a rotation of 2n pi about the axis of the canalisation. Use is made of the mean value of the differential measurements obtained for each one of the measurement channels in order to compute the parameter which is being measured. The invention is applied, in particular, to power measurements on the primary circuit of a pressurised water reactor.

It is an object of the present invention to reduce the infrastructure costs of a flow meter installation to allow installation of more flow meters which provide more data to be gathered to locate distribution system losses.

A further object of the invention is to provide a flow meter which completely defines its own geometry and does not require calibration to its installation or surroundings.

In another object of the invention there is provided an undershot flow gate which influences the flow profile to create non-turbulent, streamlined and repeatable flow behaviour.

Yet another object of the invention is to provide a flow meter, for use in a closed conduit, which includes a gate valve or the equivalent, but without what is referred to as a "bonnet" of the type which constitute an integral component of a traditional gate valve.

The invention is defined by claim <NUM> of the present application. Further related examples disclosed in this application not covered by claim <NUM> are provided for disclosure purposes only.

With these objects in view an example provides an acoustic flow meter assembly for pipes or open channels, said assembly including a frame with a predetermined geometry, said frame including at least one user accessible port, said at least one user accessible port adapted to receive an interchangeable cartridge which contains at least one acoustic transducer to measure fluid velocity through said frame.

Preferably the acoustic flow meter assembly further includes a plurality of user accessible ports with an associated cartridge. The user accessible ports may be located in corners of a rectangular or square orientation formed by said frame. Preferably a pair of cartridges are diagonally directed towards each other.

In a further example each cartridge includes a plurality of acoustic transducers for measuring flow at predetermined depths. The acoustic flow meter assembly may further include a hollow tube for coupling at either end to a pipeline to determine the velocity through said pipeline. In a practical example each transducer is located at one end of a respective sound transmission tube and the other end opens into said hollow tube. Each sound transmission tube can be associated with a respective cartridge and angled towards an associated facing sound transmission tube. Each sound transmission tube may contain fluid from said hollow tube. Each sound transmission tube may contain still fluid which is not in the path of the fluid flow.

In a further example each sound transmission tube is filled with an acoustic transmissive material. The acoustic flow meter assembly may further include a boundary interface between the fluid in said sound transmission tube and the flowing fluid, said boundary interface formed of a material of suitable acoustic properties to enable ready transmission of the acoustic signals. The fluid in the sound transmission tubes may also be contained in a sealed well such that the fluid couples the transducers to the inner face of the sound transmission tubes.

The invention may provide a tilt lift gate assembly including a gate member which can be raised and lowered from a vertically closed position through to a substantially horizontal disposition, said gate member being pivotally mounted at the top end thereof to a mechanism for pulling said gate member inwardly from the vertically closed position to the substantially horizontal disposition and at least one extension projecting from said gate member with a pivot point at the end of said at least one extension, said pivot point co-operating with a downwardly angled guide means whereby movement of said gate member does not cross said downwardly angled guide means.

It is preferred that a pair of extensions are located on each side of said gate member which co-operate with respective downwardly angled guide means. The tilt lift gate assembly may be located in an open fluid channel, said at least one extension being positioned substantially two thirds of the depth of the fluid.

A further example provides an open channel fluid velocity system for measuring the fluid velocity of the fluid flowing through said system, said system including an open channel containing said flowing fluid, an acoustic flow meter assembly as previously described and a tilt lift gate assembly as previously described downstream of said acoustic flow meter assembly,
wherein said gate member predictably influences the surface velocity of said flowing fluid.

A further example provides an open channel fluid velocity system for measuring the fluid velocity of the fluid flowing through said system, said system including an open channel containing said flowing fluid, an acoustic flow meter assembly as previously described and an undershot gate downstream of said acoustic flow meter assembly, wherein said gate allows the fluid level in front of said gate to back to provide a uniform depth of fluid through said acoustic flow meter assembly.

A further example provides a method of measuring fluid velocity in a pipe or open channel, said method including the steps of: providing a timing circuit which includes a first circuit having at least one upstream acoustic transducer and a second circuit having at least one downstream acoustic transducer, measuring the time delay in detecting the acoustic signal from said at least one upstream acoustic transducer to said at least one downstream acoustic transducer from said first circuit, measuring the time delay in detecting the acoustic signal from said at least one downstream acoustic transducer to said at least one upstream acoustic transducer from said second circuit, measuring the time delay in said first circuit when said at least one upstream acoustic transducer is bypassed in said first circuit, measuring the time delay in said second circuit when said at least one downstream acoustic transducer is bypassed in said second circuit, and calculating the fluid velocity using said measurements.

In yet a further example there may be provided an acoustic flow meter for a pipe, said assembly including at least three pairs of acoustic transducers, each pair of said acoustic transducers located on opposing sides of said pipe and offset longitudinally along said pipe to provide upstream and downstream transducers, each pair of acoustic transducers, in use, having their acoustic paths intersecting at a point along the axis of said pipe to provide redundancy in measuring flow through said pipe if one of said acoustic transducers should fail.

A further example provides a lift gate assembly including a gate member associated with a frame and which can be raised and/or lowered from between respective closed and open configurations, said frame having associated therewith and upstream thereof an apparatus for measuring transit turn of fluid, said apparatus being in the form of a conduit having one or more opposed pairs of acoustic transducers or the like associated therewith.

In another aspect there is provided a method of measuring acoustic transit times in an open channel or river, said method including the steps of:
providing a first circuit having at least one upstream acoustic transducer on one side of said open channel or river and a second circuit having at least one downstream acoustic transducer on the opposite side of said open channel or river, said first and second circuits including respective timing circuitry which are not synchronised with one another, each of said timing circuits measuring their respective signal transmit and receive events, at least one of said first or second circuits including an RF or laser to provide synchronising signals between said first and second circuits, an RF or laser synchronising signal is transmitted between said first and second circuits prior to an acoustic signal transmitted from one of said acoustic transducers between said first and second circuits whereby said RF or laser synchronising signal allows synchronisation between the respective timing circuitry of said first and second circuits of said acoustic signal.

In order that the invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings, in which:-.

Throughout this specification the same reference numerals will be utilised, where applicable, to avoid repetition and duplication of description across all embodiments. The description of constructions and operation will be equally applicable.

The only embodiments for which protection is sought in the present application are those covered by claim <NUM>, the rest of the related examples are provided for disclosure purposes only.

In <FIG> of the drawings there is shown an acoustic flow meter assembly <NUM> which is adapted to be fitted between a pipeline (not shown) through which fluid flows, preferably a liquid. In this example the fluid is water but the invention is not limited to such an environment. The examples are particularly useful for the metering of irrigation water consumption in irrigation channels in international irrigated agriculture regions and the metering of urban water supplies in international urban water networks. The acoustic flow meter <NUM> is buried in the ground <NUM> (<FIG>) and includes a frame <NUM> which supports a pipe section <NUM>. Pipe section <NUM> is adapted to be coupled to either end of the pipeline through which the flow rate is to be determined. Frame <NUM> in this example is basically of a square shape and has two end members <NUM>, <NUM> and two side members <NUM>, <NUM>. The shape and construction of the frame <NUM> can vary to suit the requirements of the particular flow meter assembly. Four hollow legs <NUM>, <NUM>, <NUM> and <NUM> form part of the frame <NUM> and slidably receive cartridges <NUM> which can be inserted therein. The number and positioning of the cartridges <NUM> can vary depending on the environment in which flow rate is to be determined. In this example each cartridge includes four acoustic transducers <NUM>. The number and positioning of the acoustic transducers <NUM> can also be varied. The acoustic transducers <NUM> are integrated into electronic circuitry (not shown) which can be included in the cartridges <NUM> and frame <NUM>. The serviceable components including the acoustic transducers <NUM> and processing electronics are all contained within sealed cartridges <NUM> which can be interchanged. Typically, the cartridges <NUM> can provide their measurements by wired or wireless means to an external computing device.

Pipe section <NUM> has number of sound transmission tubes <NUM> which are mounted in a horizontal disposition as clearly shown in <FIG> and <FIG>. The sound transmission tubes <NUM> are typically cylindrical in shape and are made of an acoustically transmissive material which couples the aligned acoustic transducers <NUM> to the internal bore of the pipe section <NUM>. The sound transmission tubes <NUM> are arranged to intersect the pipe section <NUM> at an angle Θ (<FIG>) to the direction of fluid flow <NUM>. The preferred intersection angle Θ is <NUM> degrees, however other implementations could be manufactured with an intersection angle Θ between <NUM> and <NUM> degrees to suit geometry requirements of various applications. The sound transmission tubes <NUM> provide an acoustic path for the acoustic transducers <NUM> located within the flow meter cartridges <NUM>. In <FIG> the sound transmission tubes <NUM> are hollow so that they contain the fluid within the pipe section <NUM> and the sound propagates through this fluid only. The sound transmission tubes <NUM> will contain still water and will not be in the path of the water flow.

Alternatively, as shown in <FIG>, the sound transmission tubes <NUM> may be filled or plugged with a solid material of appropriate acoustic behaviour so that the pipe section <NUM> is completely sealed and the cartridges <NUM> may be retrieved while the pipe is operating under a positive or negative pressure without the requirement to seal access ports <NUM> against this pressure. The sound transmission tubes <NUM> could also be filled with water with a boundary interface (not shown) between the still water in the sound transmission tubes <NUM> and the flowing water. This interface would be made of a material of appropriate acoustic properties that enables the ready transmission of the acoustic signals. An advantage of this example with the closed sound transmission tubes <NUM> is that the internal bore of the pipe section <NUM> will be smooth and there will be no potential for clogging or trapping of debris in the pipe section <NUM> or the sound transmission tubes <NUM>. In this arrangement a good acoustic coupling would be achieved between the acoustic transducers <NUM> contained within the cartridges <NUM> and the end faces of the sound transmission tubes <NUM> by employing a camming mechanism within the access ports <NUM> which would positively engage the acoustic transducers <NUM> against the faces of the sound transmission tubes <NUM>.

Alternatively, a simpler coupling mechanism can be achieved by filling access ports <NUM> with water or similar fluid which acoustically couples the transducers <NUM> contained within cartridges <NUM> to the end faces of the sound transmission tubes <NUM>. In this implementation, the access ports <NUM> are a sealed well containing a fluid which couples the transducers <NUM> to the inner face of the sound transmission tubes <NUM>. The access ports <NUM> are typically aligned vertically and accessed through sealed lids <NUM> at ground level. In some applications the access ports <NUM> might be aligned horizontally and accessed through wall mounted lids. The access ports may be installed at any other angle as the installation requires.

Within a horizontal plane of the acoustic flow meter assembly <NUM> there are four acoustic transducers <NUM>, which are arranged to provide two acoustic paths <NUM>, <NUM> within each horizontal plane (<FIG>). As there are four acoustic transducers in each cartridge <NUM> there will be four horizontal planes <NUM>, <NUM>, <NUM> and <NUM> (<FIG>). These acoustic paths are at right angles to each other, and this arrangement eliminates cross flow errors as discussed in Section <NUM>. <NUM> of ASTM D5389-<NUM>(<NUM>) Standard Test Method for Open-Channel Flow Measurement by Acoustic Velocity Meter Systems.

The acoustic transducers <NUM> transmit a high frequency (in the kilohertz to megahertz range) sound pulse across the pipe section <NUM>. The travel time of the acoustic signal is measured in a direction upstream to the direction of flow <NUM>, and also in a direction downstream to the direction of flow <NUM> as seen in <FIG>. The flow velocity creates a difference in the sound wave travel times in the upstream and downstream direction. This travel time difference is recorded and used to determine the average velocity of the fluid along the line of the acoustic path. The four measurement paths provide an average velocity of the fluid at four different planes <NUM>-<NUM> as shown in <FIG>. The velocity distribution within the pipe section <NUM> is then calculated from the velocities at each of the four planes <NUM>-<NUM> using a calibrated mathematical relationship.

A water level sensor, preferably an acoustic water level sensor <NUM>, will be associated with each cartridge <NUM>. In the examples of <FIG>, for example, each cartridge <NUM> includes a port, generally designated <NUM>, for receiving and releasably retaining an acoustic water level sensor <NUM>. It should be understood, however, that it is not essential for the water level sensor to be physically integrated into or with the associated cartridge <NUM>, so long as a water level sensor is located at or in the vicinity of each cartridge <NUM>.

The water level sensors <NUM> function to provide an accurate measurement of the profile of the water surface at or in the vicinity of the overall flow meter assembly. Since a measurement is being made of the average velocity of flow of the water, then in order to be able to accurately compute the volumetric flow rate an accurate measurement of the cross-sectional area of flow at the location of the flow meter assembly is also required.

The preferred arrangements as illustrated and described, with an acoustic water level sensor <NUM> associated with each of the four cartridges <NUM>, ensures an accurate determination of volumetric flow of water, even in situation/circumstance wherein the surface of the water is disturbed or uneven, as for example with there being turbulent flow or, in the alternative, a sloping surface gradient.

Other examples may include any number and combination of acoustic transducers <NUM>, as required, to realise other signal path configurations. The use of signal reflectors to replace some of the transducers in each measurement plane could also be used. It is not necessary to have four planes <NUM>-<NUM> across the acoustic flow meter assembly <NUM>. Any number of planes may be used, for example, one or a plurality of planes. The planes need not be horizontal as shown in this example.

<FIG> show the use of the acoustic flow meter assembly <NUM> in an open channel environment, typically used for water irrigation. A U-shaped channel <NUM> having a base <NUM> and sidewalls <NUM>, <NUM> is used to control flow of irrigation water. The acoustic flow meter assembly <NUM> shown in <FIG> can be used but does not require the access ports <NUM> as the installation is not buried in the ground. Pipe section <NUM> is not required. This example is similar in construction to the previous example in that four retrievable cartridges <NUM> are provided. However the system can also be designed with one, two, three, or more retrievable cartridges <NUM>, similar to the previous example. The acoustic flow meter assembly <NUM> is manufactured under high tolerance and completely defines the geometry that the metered fluid passes through. This assembly <NUM> ensures that the fluid always passes through the same geometry through the body of the acoustic flow meter assembly <NUM> regardless of the geometry of the channel <NUM> into which it is installed. The cartridges <NUM> can be slidably removed and replaced without changing the geometry of the acoustic flow meter assembly <NUM>. The cartridges <NUM> are each individually calibrated with a calibration referenced to their mounting points within the four hollow legs <NUM>, <NUM>, <NUM> and <NUM>. This allows the cartridges <NUM> to be interchanged without effecting the calibration of the acoustic flow meter assembly <NUM>. The acoustic transducer behaviour and geometry requirements are the same as described for the previous example.

In <FIG> the acoustic flow meter assembly <NUM> of <FIG> includes a downstream control gate <NUM>. In this example the control gate <NUM> is a simple guillotine gate which is raised and lowered vertically and closes on a seal <NUM>. The control gate <NUM> can be separate from the acoustic flow meter assembly <NUM>, as shown, or could be integrated into a combined assembly. The control gate <NUM> forms an undershot gate which influences the surface velocity of the fluid <NUM> flowing through the acoustic flow meter assembly <NUM> and reduces the influence of the surrounding world on the flow profile passing through the acoustic flow meter assembly <NUM>. As previously described the velocity is measured at a number of vertical elevations by acoustic transducers <NUM>, and the velocity at each of these elevations is then fitted to a relationship which is used to interpolate the velocity at heights between the sampled elevations.

The surface velocity of the fluid <NUM> is typically not measured because the elevation of the surface thereof varies during operation and so it is generally not possible to locate an acoustic transducer plane at the surface <NUM> of the fluid. The floor velocity is always zero, and the velocity at all elevations below the top transducer plane <NUM> can be interpolated from the measured values obtained in the planes above and below the elevation of interest. The unknown surface velocity means that the velocity at elevations above the top transducer plane <NUM> must be extrapolated based on assumptions of the shape of the velocity profile. This top section of the flow is typically where the greatest uncertainties in the velocity profile occur, as there is no information about the velocity at the surface. In worst case scenarios this velocity could be extremely high or even in a reverse direction to the flow due to surface influences such as wind. By locating control gate <NUM> downstream of acoustic flow meter assembly <NUM> and ensuring that the lower tip <NUM> of control gate <NUM> is always submerged, the control gate <NUM> maintains a laminar and streamlined flow profile which is free of turbulence. The velocity of the fluid will be zero in front of control gate <NUM>. This flow profile is repeatable and may be characterised by a flow model which computes the flow rate using measurements of gate position and the fluid velocities measured by the acoustic transducer system. The repeatability of the flow profile passing under the control gate <NUM> is combined with the measured flow velocities at each of the sensor plane elevations <NUM>, <NUM>, <NUM> and <NUM> and is used to reduce the uncertainty in the estimation of the fluid's surface velocity through the body of the acoustic flow meter assembly <NUM>.

The influence of the undershot control gate <NUM> reduces the potential variation in the flow pattern through the acoustic flow meter assembly <NUM>.

In <FIG> the guillotine control gate <NUM> of <FIG> is replaced with a tilt-lift type gate <NUM>. The control gate <NUM> can be separate from the acoustic flow meter assembly <NUM>, as shown, or could be integrated into a combined assembly. Gate <NUM> allows the gate to be in vertical disposition when closed on seal <NUM> and an angular or horizontal disposition when in the open position. Gate <NUM> is held between a frame <NUM> which includes a horizontal track <NUM> and a vertical track <NUM>. Pins or rollers <NUM>, <NUM> are located on the corners of gate <NUM> and are held captive in tracks <NUM>, <NUM>. The pins or rollers <NUM>, <NUM> will move along their respective tracks to allow opening and closing of gate <NUM>. Movement of gate <NUM> is controlled by a motor driven or hydraulic arm (not shown) coupled to the top <NUM> of gate <NUM>. By pulling or pushing the top <NUM> of gate <NUM> the gate will be raised or lowered to act as an undershot gate.

The tilt lift gate <NUM> allows for both a repeatable flow streamline for a given gate position as well as keeping the velocity of the fluid at the surface to a minimum. Both the above ensure minimal error in computing the flow for the segment between the sensors <NUM> in the top sensor plane elevation <NUM> and the water surface <NUM>. The undershot gate <NUM> being located downstream creates a surface velocity distribution through the body of the acoustic flow meter assembly <NUM> meter that is more repeatable and predictable than would be the case if the undershot gate <NUM> were not present. The gate <NUM> forces the flow to be non-turbulent and laminar. The gate <NUM> allows creation of a flow computation algorithm which is a function of the gate position and the velocities measured by the acoustic transducers <NUM>.

The open channel and closed conduit implementations of the acoustic flow meter assembly <NUM> are supplied as a single assembly which completely defines its own geometry such that in-field commissioning of meter geometry parameters is not required.

<FIG> show a further variation of the tilt-lift gate <NUM> shown in <FIG>. In this embodiment gate <NUM> does not have the pins or rollers <NUM>, <NUM> at both ends of gate <NUM> in <FIG>. The control gate <NUM> can be separate from the acoustic flow meter assembly <NUM> or could be integrated into a combined assembly, as shown. The integration of the control gate <NUM> and the acoustic flow meter assembly <NUM> will allow a drop in solution which has already been calibrated. Top <NUM> of gate <NUM> is pivotally mounted by brackets <NUM> and axle <NUM>. The axle <NUM> runs in guiding tracks <NUM>. Horizontally mounted arm members <NUM> are pivotally mounted to axle <NUM> and will allow gate <NUM> to be moved from a closed to an open position and vice versa. The arm members <NUM> can be moved by an electric motor or hydraulic means depending on requirements. In this embodiment the arm members <NUM> are cable driven by spools <NUM> which are coupled to an electric motor <NUM>. A gear box <NUM> will drive the spools <NUM>. The cables from spools <NUM> will be attached to the arm members <NUM> or axle <NUM>.

The positioning of the gate <NUM> is controlled by an extension arm <NUM> attached to the underside <NUM> of gate <NUM>. Extension arm <NUM> has a pivot point <NUM> at its free end. The pivot point <NUM> is at a position that will result in a minimal force (actuation force) to open gate <NUM>. This will result in a low cost actuation and drive train system <NUM>-<NUM>. The preferred pivot point location is that of the line of the net resultant force when the gate is in the closed position, typically <MAT> the depth of water below the water surface level. This point represents the neutral axis about which the net forces above the axis equal the net forces below the axis. The force on the gate <NUM> is due to water pressure and which equals:
ρ * g * h, at a given depth h below the water surface Where.

The pivot point is offset perpendicular from the underside <NUM> of gate <NUM>. Pivot point <NUM> is constrained to move along a rail or slot <NUM> which is at a downward angle towards gate <NUM>. The offset assists in providing a downward force when closing the gate from its fully open substantially horizontal position. The offset also ensures the gate side seals (not shown) do not cross the rail or slot <NUM> in order to avoid leakage around the side seals. The angle of the rail or slot <NUM> also assists with the downward force when closing gate <NUM> from its fully open substantially horizontal position.

In order to minimise leakage a seal <NUM> is provided on the free end edge and sides of the gate <NUM>. The seal is in the form of a bulb seal which engages on a slightly raised face <NUM> on the base <NUM> and sides <NUM>, <NUM> and of the U-shaped channel <NUM> when gate <NUM> is in the vertical i.e. closed position. Seal <NUM> will undergo minimal compression when in contact with the U-shaped channel <NUM>.

<FIG> shows the situation of the downstream gate <NUM> backing up the water level <NUM> through the body of the acoustic flow meter under the same flow and water depth conditions as <FIG> which has no downstream obstruction. It can be seen that the gate <NUM> acts to maintain a deeper flow through the body of the meter, such that all transducers are submerged below the water surface. In <FIG> the water surface drops as the flow velocity increases through the body of the acoustic flow meter such that several of the transducers <NUM> are not submerged below the water surface. This key advantage, discovered through fluid dynamic simulations causes the water to back-up in front of it in situations where there is no downstream tail water. This depth profile is problematic as many of the sensor paths will be above water and so not able to be used in the measurement. A partially open gate located downstream of the meter backs the water up so that it flows through the body of the meter at approximately constant depth such that more measurement paths can be used. This allows the flow meter to be used in hydraulic conditions which would otherwise not be compatible with metering using this approach.

Variations can be made to the embodiments to suit various environmental or design requirements. The angular position of sensor pairs <NUM> is not restricted to horizontal planes and preferred <NUM> degrees to the centreline. The sensor pairs <NUM> can be at angular orientation.

The sensor <NUM> is not limited to a send and receive device with a matching pair. Many sensors could receive signals from the one transmit sensor.

In <FIG> the examples could be incorporated in-situ into an existing pipeline. Sound transmission tubes <NUM> could be tapped and welded onto an existing pipeline rather than providing a separate acoustic flow meter assembly <NUM> which is inserted into the pipeline. The assembly would include the cartridges <NUM> in a modified frame <NUM>.

In <FIG> the acoustic transducers <NUM> have been described together with their operation. The acoustic transducers <NUM> preferably work in opposing pairs. The acoustic flow meter assembly <NUM> measures the travel time of the acoustic signal in a direction upstream 58B, 60B to the direction of flow <NUM>, and also in a direction downstream 58A, 60A to the direction of flow <NUM> as seen in <FIG>. The flow velocity creates a difference in the sound wave travel times in the upstream and downstream direction. This travel time difference is recorded and used to determine the average velocity of the water along the line of the acoustic path.

The time difference is recorded using transducers and circuitry which together have intrinsic time delays which add to the actual travel time of the acoustic signal. These transducer <NUM> and circuitry time delays must be subtracted from the recorded acoustic signal travel time so that the actual travel time of the acoustic signal may be determined.

The transducer <NUM> and circuit time delays are typically measured in a calibration of the acoustic flow meter assembly <NUM>, and characterized as a numerical constant which is subtracted from the measured acoustic signal travel time to calculate a best estimate of the actual acoustic signal travel time.

Two constants could be determined by calibrating the acoustic signal travel time measurements in both the upstream and downstream directions. This is not necessary however, as the acoustic signal travel time in the upstream direction is subtracted from the acoustic signal travel time in the downstream direction, a single calibrated time delay constant is sufficient to calibrate the required system measurement. Under zero flow conditions the upstream signal travel time is precisely equal to the downstream signal travel time. However, due to different circuit and transducer time delay characteristics in the circuitry used to measure the travel times in the upstream and downstream directions, the measured travel times will not be identical. The difference in the measured travel times will reflect the different time delay characteristics in the circuitry used to measure the upstream and downstream travel times, and can be determined as a single numerical value at an instant in time by calibrating the measurement system under still water zero flow conditions.

Unfortunately however, the time delays contributed by the transducers <NUM> and the upstream and downstream measurement circuitry are not constant, but are a function of environmental influences such as temperature and pressure, and of electronic circuit conditions such as operating voltage and temperature. Changes in these time delays result from changes in temperature, pressure, operating voltages and other environmental disturbances. These changes result in a change to the calibration of the flow metering system <NUM> which results in errors in measuring the precise difference in acoustic signal travel times. This results in errors in the measurement of flow velocity, which are particularly significant to the measurement of low flow velocities.

To compensate for changes in the time delays within the upstream and downstream measurement circuitry, a self-calibrating measurement system is proposed which is capable of calibrating itself against a reference standard on every flow velocity measurement, thereby preventing errors in the measurement of the acoustic signal travel times. Although the embodiment will be described with reference to its operation with irrigation systems the use of this invention is not limited to that purpose.

Referring to <FIG> a measurement system <NUM> is represented as a timer <NUM> which has a start input <NUM> and a stop input <NUM>, together with several signal paths through which electrical information is transmitted. The drawings show only two transducers being represented in this measurement system <NUM> namely transducer 46A and transducer 46B from <FIG> for simplicity. All paired transducers <NUM> from <FIG> will be connected in the same manner.

As indicated in <FIG>, there are electronic system time delays present in the measurement system <NUM>. These are shown as:.

The acoustic signal travel time from transducer 46A to transducer 46B along path 58A is represented as TFLOW_A→B and the acoustic signal travel time from transducer 46B to transducer 46A along path 58B is represented as TFLOW_B→A.

<FIG> shows only the signal path when measuring the acoustic signal travel time from transducer 46A to transducer 46B. This signal travel time is determined by sending a transmit signal <NUM> to transducer 46A. This transmit signal <NUM> has an initial signal characteristic which defines the start of the transmit signal. This signal characteristic is input to the timer <NUM> and defines the start of the time measurement. The transmit signal <NUM> is transmitted to transducer 46A which responds by transmitting an acoustic signal to transducer 46B. Transducer 46B converts this acoustic signal to an electrical signal which is input into the timer <NUM> and defines the end of the time measurement. The time measured when transmitting the acoustic signal from transducer 46A to transducer 46B is <MAT>.

This procedure is then repeated in the opposite signal direction as illustrated in <FIG>. The acoustic signal travel time from transducer 46B to transducer 46A is determined by sending a transmit signal <NUM> to transducer 46B. This transmit signal <NUM> has an initial signal characteristic which defines the start of the transmit signal. This signal characteristic is input to the timer <NUM> and defines the start of the time measurement. The transmit signal <NUM> is transmitted to transducer 46B which responds by transmitting an acoustic signal to transducer 46A. Transducer 46A converts this acoustic signal to an electrical signal which is input into the timer <NUM> and defines the end of the time measurement. The time measured when transmitting an acoustic signal from transducer 46B to transducer 46A is <MAT>.

The difference in the sound wave travel times in the upstream and downstream direction is then measured as <MAT>.

In order to calculate the calibration constant the example provides additional measurements without using the transducers 46A, 46B. This aspect is shown in <FIG>. This example switches in an alternative signal path which bypasses the ultrasonic transducers 46A, 46B to allow the circuitry time delays to be measured. If the transducers 46A, 46B are switched out of the circuit and a delay path ∂C is switched in, then when transducer 46A is configured as the transmitting transducer then the following equation is applicable: <MAT>.

This system configuration is shown in <FIG>.

Similarly, if transducers 46a, 46B are switched out of the circuit and the delay path ∂C is switched in then when transducer 46B is configured as the transmitting transducer then the following equation is also applicable: <MAT>.

These calibration measurements can then be used in conjunction with the acoustic signal travel time measurements to eliminate the circuit delays ∂TA, ∂TB, ∂RA, ∂RB from the estimation of the acoustic signal travel times such that these travel times can be determined precisely.

The measurement process will be as follows:.

The four system measurements are then combined to determine the result <MAT>.

If the calibration times are subtracted from the flow measurement times, then the results are <MAT> <MAT>.

The difference in transmit time can then be determined as <MAT>.

It can be seen in the above formula that the electronic circuit delay times have been removed from the acoustic signal transit time measurements, and the difference in signal transit time measurements is determined precisely. With high speed computer technology the calibrations can occur in real time or the calibrations may be monitored at predetermined intervals.

Another aspect provides a further method of measurement of velocity of fluid flowing in a pipe. In the conventional application of acoustic transit time technology to measure the rate of flow in pipes it is common to use either a single path or cross path technique. These applications rely on the pipe being full or pressurized. The single path technique assumes a symmetrical velocity distribution around the centre line of the pipe with oppositely facing and offset top and bottom acoustic transducers. The cross path technique is used where the velocity distribution is non-symmetrical around the pipe centre line. In this cross path technique two pairs of oppositely facing and offset top and bottom acoustic transducers are used and their acoustic paths cross the pipe centre line. Many flow meter applications not only require the ability to detect the real time failure of a flow meter but also the ability to record flow measurement without any loss of continuity of data. This is especially a requirement of meters that are used for revenue billing applications with strong quality compliance requirements. It also applies to meters that are remotely located and can take some time to service. Accordingly, the failure of an acoustic transducer in the non-symmetrical velocity distribution will result in inaccurate readings as the resulting single path technique will only provide accurate readings in a symmetrical velocity distribution.

In <FIG> there is shown a pipe <NUM> with a fluid flowing therethrough in direction <NUM>. Four pairs of acoustic transducers <NUM>,<NUM>; <NUM>,<NUM>; <NUM>,<NUM>; and <NUM>,<NUM> are equi-spaced around pipe <NUM>. The positioning of the acoustic transducers is not restricted to being equi-spaced but can be placed in positions to suit requirements. The number of pairs of acoustic transducers can vary but at least three pairs must be provided. The upstream and downstream acoustic paths <NUM>-<NUM> all cross at a central point <NUM> along the central axis <NUM> of pipe <NUM>. Accordingly, measurements along the four paths <NUM>-<NUM> can be made to increase accuracy. If one of the acoustic transducers <NUM>-<NUM> fails, then measurements can still be made with the remaining acoustic transducers. The failure can be detected and the faulty acoustic transducer replaced at a convenient time.

This aspect of the invention provides at least three single or cross paths located around the centre line <NUM> of pipe <NUM>. This approach will provide at least three independent flow meters formed by the co-operating pairs of acoustic transducers on pipe <NUM>. The result is to allow the real-time detection of the failure of any one of the independent flow meters, but also to be able to maintain flow measurement until the fault is corrected. To achieve this effect using other metering technologies, for example, magnetic flow meters, would require three meters to be installed in series along a section of pipe.

It is evident to the man skilled in the art that the example shown in <FIG> can be readily incorporated into the example shown in <FIG>.

In accordance with a further preferred aspect of the present invention, and in this regard reference is made to <FIG> inclusive of the drawings, what is referred to hereinafter as a time of flight or transit time measuring apparatus is located immediately upstream of a slide or control gate <NUM>. The control gate <NUM> may be of the type referred to in the present applicant's <CIT>, as referred to and described earlier in this specification.

As shown in <FIG> and <FIG>, preferably the measurement apparatus will take the form of a conduit <NUM>, of any cross-section but more particularly of either a circular, as in <FIG>, or a parallelepipedal as in <FIG>, cross-section, which conduit <NUM> will be associated with - either fixedly or removably - the frame of a flow or control gate <NUM>.

In <FIG> there is shown a control gate <NUM> to be located within a conduit, as for example an irrigation channel (not shown), the function of the control gate being to allow a controlled flow of water through the channel. The control gate <NUM> includes a gate leaf <NUM> which slides within a frame <NUM>. Frame <NUM> has an outer frame member, which may be permanently secured to floor and sides of an irrigation channel or conduit and an internal frame member which slides within that outer frame member. The internal frame member may be connected to and separated from the external frame member with no requirement to undertake civil works on the floor and sides of the irrigation channel. This type of internal/external frame mechanism is further detailed in the specification of the present applicant's International (PCT) Patent Application No. <CIT>. Gate leaf <NUM> may be raised or lowered by a lifting mechanism <NUM> of any known type, as for example that illustrated and described in the present applicant's International Patent Application No. <CIT>. It should be understood, however, that the invention is not limited to usage only with such a flow or control gate.

A typical installation would involve a control or flow gate (of any given type) with the associated measuring apparatus <NUM> attached, in any known manner and using any known means, to the upstream inlet of a conduit or pipe, located for example in a canal, reservoir or the like watercourse. In an alternative installation there may be provided conduit connection means at both upstream and downstream ends or sides of the overall flow meter assembly as referred to earlier in this specification.

The conduit <NUM> has associated therewith acoustic transducers <NUM> for the generation of acoustic beams which traverse the flow through that conduit <NUM>.

It should be understood that conventional or traditional transit time flow measurement apparatus have, for their operation, prescribed conditions both upstream and downstream of the measuring device in order to ensure that there is minimal disturbance to flow. These prescribed conditions are set out in detail in, for example, Australian Standard AS747.

The arrangement in accordance with the present invention relies for its operation on a derived relationship between the flow through the conduit and the transit time measurements of acoustic beams which traverse the fluid. The relationship further relies on the measurement inputs of water level (as determined by the level sensors) and gate position. In that regard reference is also made to the present applicant's International Patent Application No. <CIT>.

In practice the number of acoustic beams which traverse the flow can be singular or many, and can exhibit a variety of different orientations. However, preferred arrangements as shown in the drawings will include three (<NUM>) pairs of acoustic transducers <NUM> for the parallelepipedal conduit <NUM> of <FIG> and one (<NUM>) pair for the circular conduit <NUM> of <FIG>.

The relationship between the flow and transit time, gate opening and water level may be derived using data flow experiments as explained in detail in the present applicant's International (PCT) Application No. <CIT> entitled "Fluid Regulation".

The arrangement is such that the conduit <NUM> is substantially fixed within the channel, whilst the control gate leaf <NUM> is movable substantially vertically within that channel, whereby to allow for variation of flow through the conduit <NUM>. The arrangement utilises a double seal <NUM>, see in particular <FIG>, which runs the entire circumference of the gate <NUM>. That double seal <NUM> ensures complete sealing of the conduit <NUM> from both upstream and downstream thereof, as well as external thereto. The gate <NUM> employs a flat face or surface on both the upstream and downstream sides of the leaf <NUM> to ensure position sealing through the full travel of the gate <NUM>.

With conventional/traditional gate valve designs a bonnet is included in the overall assembly for purposes of enclosing the gate within a conduit, protecting against leakage. With the arrangement in accordance with the present invention, utilising a double seal of the type referred to earlier, there is no need for a bonnet or the equivalent.

In the embodiments of <FIG> there is shown a variation of the embodiment of <FIG> with dividers <NUM>. <FIG> has a single divider <NUM> whilst <FIG> has a pair of dividers <NUM>. The dividers <NUM> have a plurality of acoustic transducers <NUM> attached on either side which cooperate with the acoustic transducers <NUM> on the inner opposing walls of conduit <NUM>. As is evident from <FIG> the acoustic path lengths f the embodiment shown in <FIG> will be reduced as the acoustic transducers of the embodiment shown in <FIG> will be between the divider <NUM> and the inner walls of conduit <NUM> on either side. Similarly, for the embodiment of <FIG> the acoustic path lengths will be further reduced because the acoustic path lengths are between the divider <NUM> and the inner walls of conduit <NUM> on either side and between the dividers <NUM> in the middle of conduit <NUM>. This reduced acoustic path length will allow a reduction in the length of conduit <NUM>. It is possible to have further dividers <NUM> but the cost of the additional acoustic transducers <NUM> would be expensive and not justifiable.

The embodiments shown in <FIG> there is shown a variation of the embodiment of <FIG> with dividers <NUM>. The dividers <NUM> operate in the same manner as that described with respect to <FIG>. Again the resulting reduction in acoustic path length will allow a reduction in the length of conduit <NUM>.

The embodiment shown in <FIG> is similar to the embodiment of <FIG>.

The difference between the embodiments is the slanting of the slide or control gate <NUM>. The angling rearwardly of the slide or control gate <NUM> reduces the headroom required when installing the system. <FIG> relate to the use of dividers <NUM> for the embodiment of <FIG> and operate identically to the embodiments of <FIG> previously discussed.

<FIG> show a schematic drawing of a further measurement system in the form of an acoustic transit time flow meter designed to measure fluid flows <NUM> which does not require linked cabling to connect all acoustic transducers <NUM> to a central location. The measurement system <NUM> described in <FIG> requires cabling which traverses opposite sides of the open channel. The system shows a left river or channel bank <NUM> and an opposite right river or channel bank <NUM>. Conventionally, cabling would be required to cross the river or channel bed <NUM> between banks <NUM>, <NUM>. It may not be feasible to dig up or cut into the river or channel bed <NUM> to lay the required cables. This example allows no cabling to be used or limit the cabling to be disposed along each of the banks <NUM> and <NUM> where it can be readily installed. Acoustic transducers <NUM> are schematically shown attached to the banks <NUM>, <NUM> for ease of description but it is understood that they could also be contained in cartridges 44A as previously described and inserted into a flow meter assembly <NUM> installed in the river or channel.

In order to be self contained the cartridges 44A may contain the acoustic transducers <NUM> as previously described. The cartridge 44A contains the required electronics and processing circuitry and is powered by a solar panel <NUM>. A telemetry radio <NUM> allows generation of RF signals which can be sent and received using data radio antenna <NUM>. Data can also be sent to a central location for storage and further processing.

<FIG> shows use of the transit time flow meter where the transit time flow meter measures flows by the standard transit time method. The flow meter consists of two or more cartridges 44A which provide their own power supply <NUM>, a shared radio communications link, the acoustic transducers <NUM>, and a synchronising radio signal which is used to synchronise the signal sampling system clock in each cartridge 44A.

As a minimum, two cartridges 44A are installed - one on either side of each bank <NUM>, <NUM>. Four cartridges 44A may also be installed as shown in <FIG>, two per side to provide the standard crossed-path metering arrangement. Further cartridge pairs may be used to provide additional velocity information within the flow channel.

The cartridge pairs 44A act alternately as an acoustic transmitter and an acoustic receiver. For example, cartridge <NUM> in the pair acts as a transmitter, and cartridge <NUM> acts as a receiver and receives the acoustic signal <NUM> transmitted by cartridge <NUM>. Cartridge <NUM> records the time of the firing event in its high resolution timing circuitry, and cartridge <NUM> records the time of the receive event in its high resolution timing circuitry. The timing circuitry in each cartridge is a high speed binary counter, which is initialised to a zero value and then proceeds to count upwards. Each count in these counters is updated in a <NUM> pico-second period, and so a single counter increment represents a <NUM> pico-second duration. The transmit event is captured by circuitry in cartridge <NUM>, and the timing count value at this instant is stored in a register in cartridge <NUM>. The receive event is captured by circuitry in cartridge <NUM> and the timing count value at this instant is stored in a register in cartridge <NUM>. However, the counter in cartridge <NUM> is not synchronised with the counter in cartridge <NUM>, and so the time difference between the register value stored in cartridge <NUM> and cartridge <NUM> is indeterminate. In order to synchronise the time register value in each cartridge, an RF synchronisation pulse is transmitted from cartridge <NUM> to cartridge <NUM> prior to the firing pulse. This RF pulse travels between the two cartridges <NUM>, <NUM> at the speed of light (3x10<NUM> m/s), meaning that the time elapsed for a cartridge spacing of <NUM> is <NUM> ns. This RF pulse is captured by both timing systems in cartridges <NUM>, <NUM> and provides a common time tag with which to refer the firing event and receive event within the two cartridge timing circuits. The acoustic transit time is then calculated by subtracting the firing event time from the receive event time. The cartridges <NUM>, <NUM> then swap roles and the transmitter cartridge <NUM> becomes the receiver cartridge and vice-versa. The acoustic transit time in the reverse direction is then calculated, allowing the differential transit time to be recorded and used to deduce flow rate through the channel.

Claim 1:
A lift gate assembly (<NUM>) comprising a gate member (<NUM>) and a frame (<NUM>), wherein said gate member (<NUM>) is slidably within the frame (<NUM>) and said gate member (<NUM>) can be raised and/or lowered from between respective closed and open configurations, the lift gate assembly (<NUM>) may be located in an open fluid channel and further comprises an acoustic flow meter apparatus (<NUM>) for measuring transit times of acoustic signal through a fluid flowing through the acoustic flow meter apparatus, wherein the frame (<NUM>) is attached to and upstream of the acoustic flow meter apparatus (<NUM>) for measuring transit times of acoustic signals through the fluid, said acoustic flow meter apparatus (<NUM>) being in the form of a conduit (<NUM>) having one or more opposed pairs of acoustic transducers (<NUM>), wherein the frame (<NUM>) includes a double seal (<NUM>) disposed around the entire periphery thereof, characterised in that the lift gate assembly (<NUM>) further comprises at least three pairs of acoustic transducers (<NUM>-<NUM>), each pair of said acoustic transducers (<NUM>,<NUM>) located on opposing sides of said conduit (<NUM>) and offset longitudinally along said conduit (<NUM>) to provide upstream and downstream transducers(<NUM>,<NUM>), each pair of acoustic transducers (<NUM>-<NUM>), in use, having their acoustic paths intersecting at a point (<NUM>) along the axis of said conduit <NUM>) to provide redundancy in measuring flow through said conduit (<NUM>) if one of said acoustic transducers (<NUM>-<NUM>) should fail.