Ultrasonic flow meter

Abstract

An ultrasonic flow meter comprises: a meter body comprising a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of the fluid flow; and two sets of ultrasonic transducers attached to the meter body by respective manifolds and comprising a first set of transducers arranged to emit ultrasound into the through channel and a second set of transducers arranged to receive ultrasound emitted by the first set of transducers.

Description

[0001] Ultrasonic Flow Meter

[0002] Technical field

[0003] The invention concerns an ultrasonic flow meter.

[0004] Background

[0005] A transit time ultrasonic flow meters can be used to measure the flow velocity of fluids (either gas or fluid) in pipes / conduits. An ultrasonic transducer emits ultrasound that travels through the fluid at an angle to the flow and is then received by a second transducer. The differences in transit time between upstream and downstream directions is used to calculate the velocity of the fluid flow.

[0006] There are two main types of transit-time ultrasonic flow meters:

[0007] • “Clamp-on” meters, where the transducers and the electronics are external to the pipe that carries the fluid. Ultrasonic shear or lamb waves are directed from the transducer through the pipe, which are then refracted and converted to longitudinal waves that travel through the fluid in the pipe and are received by the second transducer as shear waves. Clamp-on meters can be installed onto existing pipes and the transducer location depends on the pipe parameters.

[0008] • Inline meters, which have a fixed assembly where the transducers are mounted within the meter housing and the emitted ultrasound is typically perpendicular to the transducer face and goes directly into the fluid. In large meter sizes (e.g. > DN100) direct paths are usually used, whereby sound travels directly from transducer to transducer without reflections. In smaller inline meters, reflectors (or “mirrors”) can be placed in the flow channel to direct the ultrasound between transducers while increasing the path length.

[0009] Both types of meters have their relative advantages and disadvantages, which also depend on the specific application. The clamp-on approach can suffer from a low signal to noise ratio (SNR) and may only allow a limited portion of the pipe cross section to be sampled. Inline meters can often provide greater SNR and allow for greater freedom in choosing ultrasound paths through the fluid, but they can have significant assembly complexity, e.g. in regards to the transducer mounting location which has to provide a hermetic seal throughout the whole term of operation of the meter.

[0010] A multi-path ultrasonic flow meter arranges pairs of transducers at different locations around the circumference of the flow channel to sample the flow velocity along different lines through the flow. An approximate average flow velocity can then be calculated from the signals of the different paths.

[0011] Both types of meters measure velocities along one or a few paths across the flow meter’s cross-section and require assumptions about the portions of the cross-section not being measured.

[0012] Summary of invention

[0013] According to a first aspect there is provided an ultrasonic flow meter comprising: a meter body comprising a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of the fluid flow; and two sets of ultrasonic transducers attached to the meter body by respective manifolds and comprising a first set of transducers arranged to emit ultrasound into the through channel and a second set of transducers arranged to receive ultrasound emitted by the first set of transducers.

[0014] Typically, the flow meter is configured to then electronically switch the emitting and receiving transducers in order measure the velocity both upstream and downstream.

[0015] The respective manifolds can be arranged with respect to the through channel to sample substantially a whole of the fluid flow across the cross section. The manifold may be a separate structure attached to the meter body or may be formed directly in the meter body. For example, the manifold may comprise an array of recesses in the meter body for inserting ultrasonic transducers into. The manifold can be arranged so that the plurality of transducers overlap each other, to cover the space between transducers in one row with a second row of transducers and may be further configured so that transducers along the outer edge of the array overlap the side walls of the through channel. The two sets of ultrasonic transducers are preferably arranged outside the through channel. For example, the respective manifolds can be arranged with respect to the meter body so that the two sets of ultrasonic transducers are separated from the through channel by parts of the meter body, whereby ultrasound emitted by the first set of transducers travels through a part of the meter body before entering the through channel. In the preferred embodiment, the transducers are not wetted and are separated from the flow by a part (wall) of the meter body. The wall thickness can be determined for optimal signal for a given frequency or frequency range while maintaining sufficient structural integrity for the pressures of the intended application of the flow meter.

[0016] The two sets of ultrasonic transducers may comprise a plurality of pairs of transducers, wherein each pair comprises a first transducer comprised by the first set of transducers and a second transducer comprised by the second set of transducers, wherein for each pair there is a respective ultrasound path between the first transducer and the second transducer via the through channel. The ultrasound path between transducers in a pair can be referred to as the straight path (though the path may comprise one or more bounces). A straight path in this sense lies within a plane that is parallel to the direction of flow and intersects the top and bottom of the cross-sectional shape of the through channel at right angles (wherein the ultrasound is emitted and / or received through the top).

[0017] The transmit time of the respective ultrasound paths of the plurality of pairs may be substantially equal. The first and second set of transducers may be arranged in respective straight lines at equal distance from each other. This arrangement is facilitated by the rectangular (or cross-shaped) cross-section of the through channel, which can provide a substantially flat plane for arranging the manifold on.

[0018] Further (diagonal) ultrasound paths between a first transducer in a pair and a second transducer in an adjacent or nearby pair can be used to sample the flow field between adjacent pairs of transducers.

[0019] The ultrasound path is one of a direct path through the through channel, a V-path through the through channel, or a W-path through the through channel. Any number of bounces may be used depending on the application. Each manifold of the respective manifolds is configured to hold an array of ultrasonic transducers in preferably a flat plane. The array of ultrasonic transducers may comprise a row of transducers spaced in a direction perpendicular to the direction of fluid flow.

[0020] The meter body may comprise connecting structures for attaching the respective manifolds to the meter body, wherein the connecting structures are arranged to align the two sets of ultrasonic transducers. Alternatively, the connecting structures may form the manifolds for holding the transducers directly in the meter body.

[0021] The first set of transducers can be arranged to provide ultrasound into the through channel at an angle within the range of 10° to 80° with respect to the direction of fluid flow (where 90 degrees is perpendicular to the flow direction). For example, when the ultrasonic flow meter is configured to measure a fluid flow, the first set of ultrasound transducers can be arranged to provide ultrasound into the through channel at an angle within the range of 10° and 80° with respect to the direction of fluid flow. For example, the angle may be 45°. When the ultrasonic flow meter is configured to measure a gas flow, the first set of transducers can be are arranged to provide ultrasound into the through channel at an angle within the range of 45° and 80° with respect to the direction of fluid flow. For example, the angle may be 60°.

[0022] The ultrasonic flow meter can be configured to simultaneously fire a plurality of transducers of the first set of transducers and to receive on a plurality of transducers of the second set of transducers. The transducers may be grouped or “ganged”. For example, all transducers of the emitting set may be fired simultaneously. The ultrasonic flow meter can be configured to provide an output signal based on a combination of signals from the respective plurality of transducers.

[0023] The ultrasonic flow meter is configured to fire a first transducer of the first set of transducers and of a first pair of transducers and receive on a second transducer of the second set of transducers and of a second pair of transducers, wherein the second pair of transducers is adjacent (e.g. nearest neighbour) to the first pair of transducers. This can provide additional diagonal paths for sampling the flow between adjacent transducers. Alternatively or in addition, the ultrasonic flow meter can be configured to sequentially fire individual transducers of the first set of transducers and to sequentially receive ultrasound on individual respective transducers of the second set of transducers. The signal(s) from the simultaneous firing of transducers can be combined with the signals from the sequential firing to provide improved measurement results.

[0024] The meter body and / or the manifold(s) may comprise one or more internal baffles between the first set of transducers and the second set of transducers. This can reduce the amount of noise and thereby improve SNR.

[0025] According to a second aspect there is provided a method of measuring flow velocity, the method comprising: providing an ultrasonic flow meter comprising a meter body comprising a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of the fluid flow, and two sets of ultrasonic transducers attached to the meter body by respective manifolds and comprising a first set of transducers arranged to emit ultrasound into the through channel and a second set of transducers arranged to receive ultrasound emitted by the first set of transducers; firing the first set of transducers; receiving on the second set of transducers, wherein the second set of transducers provides one or more output signals in response to receiving; and determining the flow velocity from the one or more output signals.

[0026] The provided ultrasonic flow meter may an ultrasonic flow meter according to the first aspect.

[0027] The method may comprise: simultaneously firing a plurality of transducers of the first set of transducers; and receiving on a respective plurality of transducers of the second set of transducers.

[0028] The determining may comprise combining a plurality of output signals from the second set of transducers. According to a third aspect there is provided a method of making an ultrasonic flow meter. The method comprises: forming a meter body, wherein the forming comprises: forming a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of fluid flow; and forming connecting structures for attaching two sets of ultrasonic transducers to the meter body by respective manifolds, wherein the respective manifolds may be formed in the meter body as part of the connecting structures.

[0029] The method of the third aspect may be used to form an ultrasonic flow meter according to the first aspect.

[0030] Brief description of the drawings

[0031] Figures 1A to 1 E show different views of an example of an ultrasonic flow meter;

[0032] Figure 2 shows a schematic cross section of a part of the meter body;

[0033] Figure 3 shows a schematic cross section of a flow meter;

[0034] Figure 4 shows a schematic diagram of a cross section of a through channel;

[0035] Figures 5 and 6 show different cross sections of a through channel with acoustic energy shown;

[0036] Figure 7 shows a set of transducers in an array;

[0037] Figure 8 shows a graph of the acoustic energy weighted by the area measured from the transducers in Figure 7;

[0038] Figure 9 shows another set of transducers in an array;

[0039] Figure 10 shows a graph of the acoustic energy weighted by the area measured from the two rows of transducers in Figure 9;

[0040] Figure 11 shows a schematic diagram of two opposing sets of transducers;

[0041] Figure 12 shows a chart of the emitting and receiving transducers for the arrangement in Figure 11 ; Figure 13 shows a schematic cross section of a flow meter;

[0042] Figure 14 shows comparative graphs of results from the flow meter of Figure 13 and traditional ultrasonic flow meters;

[0043] Figure 15 and 16 show graphs with results from using a DN25 meter;

[0044] Figure 17 shows a waveform from a single transducer in a flow meter as described herein;

[0045] Figure 18 shows a schematic diagram of ganging paths between transducers;

[0046] Figures 19A and 19B show the waveform from the ganging paths;

[0047] Figure 20 shows a transducer signal from driving the transducer over a range of frequencies;

[0048] Figure 21 shows an example of combining seven paths into a broadcast;

[0049] Figure 22 shows a schematic cross section on a flow meter; and

[0050] Figure 23 shows a flow diagram illustrating some steps of a method of measuring the flow of a fluid.

[0051] Detailed description

[0052] A problem with existing ultrasonic flow meters (USMs) is that they sample a relatively small area of the total cross section of the flow field in the meter, which can lead to errors when estimating the overall average flow velocity. Examples of the ultrasonic flow meter described herein can at least partly overcome this problem by providing a through channel with a rectangular (or cross-shaped) cross section and two sets of transducers attached to the meter body by respective manifolds so as to cover at least a significant part, and preferably the whole, of the width of the through channel.

[0053] Figures 1 A to 1 E show different views of an example of an ultrasonic flow meter 2. The flow meter 2 comprises a meter body 4 comprising a through channel 6 (also referred to as a “flow channel” herein) for a liquid or gas to flow through. An electronics / control unit 8 is connected to the meter body 4 and comprises transducer electronics and a readout display. Figure 1 D shows a cross-sectional view of the flow meter 2. A pair of transducers comprising a first transducer 10A and a second transducer 10B are arranged so that there is an ultrasound path (also referred to as “acoustic path” herein) between the two. In the illustrated embodiment, the ultrasound path is a V-path (one bounce). Ultrasound is emitted by the first transducer 10A through a part of the meter body 4 and into the through channel 6. The ultrasound travels through the through channel 6 and is reflected off an inner wall of the through channel 6. The reflect ultrasound travels to the second transducer 10B via another part of the meter body 4. The transducers 10A, 10B are arranged outside the through channel (not wetted), which can provide improved safety.

[0054] The transducers 10A, 10B can be configured to both emit and receive ultrasound to provide both upstream and downstream measurements. The flow meter 2 can be configured to perform sequential measurements upstream and downstream and to combine the outputs to determine the flow velocity and / or the flow profile. The flow meter 2 comprises further pairs of transducers (not shown) arranged to sample different parts of the cross-section of the through channel 6.

[0055] The transducers are arranged in a manifold 12, which is a structure providing a plurality of openings for holding the transducers, and which is formed in or attached to the meter body 4. The meter body 4 is shaped to provide connecting structures 11 (e.g. recesses) for attaching the manifolds 12 to the meter body 4 and thereby correctly aligning the two sets of transducers with respect to the through channel 6 and with each other.

[0056] The sets of transducers provide a plurality of ultrasound paths between respective pairs of transducers. Preferably, all ultrasound paths between the transducers of the pairs are substantially equal in length and transit time. The flow meter 2 may typically comprise one or more rows of transducers in the same plane arranged in a row perpendicular to the direction of flow. The or each row of transducers may together cover the whole width of the through channel 6, in order to sample the whole flow field (i.e. the whole cross section perpendicular to the flow). The or each respective manifold 12 may be configured to hold a second row of transducers. The second row of transducers may be laterally offset with respect to the first row. For example, a manifold 12 may be configured to hold a set of transducers in a closely packed array. The through channel 6 comprises a rectangular cross-section (perpendicular to the flow direction) between the two sets of transducers. As seen in Figure 1 D, three sides of the cross-section of the through channel remain constant throughout the meter body and in particular throughout the section of the meter body where the flow velocity is sampled. The “top” side, being the side on which the transducers are located may vary, for example to accommodate the ultrasound path between the transducers 10A, 10B. The corners of the rectangular cross section may be slightly rounded and may for example have a radius of less than 3 mm.

[0057] The transducers 10A, 10B are typically piezoelectric ultrasonic transducers, comprising a piezoelectric active element for generating ultrasound in response to an electric input signal. Transducers with other active elements may be viable for some applications. The active element may have circular or rectangular footprint. For example, the active element may be cylindrical (e.g. disk shaped) or cuboid.

[0058] Figure 1 E shows the two manifolds 12 wherein one is inserted into the flow meter 2 and the other has been removed to show how it fits into a connecting structure 11 in the meter body. The connecting structure is a recess for inserting the manifold 12 into. Each manifold comprises two rows of openings / recesses for inserting ultrasonic transducers into. When inserted, the transducers in a manifold and their emitting / receiving faces lie in the same plane.

[0059] While Figure 1 A to 1 E provide example dimensions, other examples with a similar setup with a manifold 12 of transducers 10A, 10B and a rectangular through channel 6 may have different dimensions as required for the specific application. In an example, the flow meter 2 comprises two sets of seven transducers, wherein each set is arranged in a row along the width of the channel (perpendicular to the flow). For a small diameter pipe, each manifold may hold as few as two transducers.

[0060] Figure 2 shows a schematic cross section of a part of the meter body 4 of a flow meter, which may be the flow meter illustrated in Figure 1 . The same reference numerals have been used in different figures for equivalent or similar features to aid understanding and are not intended to limit the illustrated embodiments. The path 14 through the meter body 4 between the two sets of transducers (i.e. between the upstream and downstream manifolds) is illustrated. The introduction of baffles 13 in the meter body creates an “arduous” path 14. This “arduous” path 14 can reduce noise and improve SNR. The meter body 14 may also comprise cast metal, which attenuates higher frequencies. Other geometries are also possible.

[0061] Figure 3 shows a schematic cross section of a flow meter 2 comprising a through channel 6 with a rectangular cross section. The rectangular shape allows the full flow field to be sampled by an array of transducers with substantially equal acoustic path lengths. The dimensions in the figure are provided as an example only. Transducers (not shown) may be arranged in / on a manifold to cover the whole width of the through channel in order to sample the whole flow field in the through channel 6.

[0062] The shape of the cross section comprises relatively sharp corners to facilitate making a complete velocity profile measurement right up to the wall of the through channel. A plurality of sensors can be packed into the manifold as necessary.

[0063] Figure 4 is a schematic diagram of a cross section 15 of a through channel 6, which may the through channel 6 of the flow meter 2 described in relation to Figure 1 A to Figure 1 D. The arrows 16 illustrate the ultrasound / acoustic path from the top side to the bottom side. Each arrow 16 corresponds to a pair of transducers (not shown). All ultrasound paths are the same length and together cover substantially the whole cross section 15.

[0064] Figures 5 and 6 illustrate different cross sections 15 of a through channel. Figure 5 illustrates a rectangular cross section 15. The rectangle may have any aspect ratio. Figure 6 illustrates a cross-shaped cross section 15. The cross shape may be formed by two overlapping rectangles or “ganged” rectangles. The shape of the cross-section together with the manifolds described herein allow the flow field to be measured right out to the walls of the through channel.

[0065] The flow meter manifolds can use three different arrangements to make the flow field measurement:

[0066] 1. using arrays of circular / rectangular sensors - arranged in 1 , 2 or more rows of sensors (preferred design is 2 rows). The sensors are preferably overlapping (though not a requirement) 2. Using arrays of square / rectangular sensors arranged in 1 , 2 or more rows (preferred design is 1 row) where the array uses overlapping electrode connections to create overlapping sensors.

[0067] 3. Using arrays of rectangular / circular sensors that use adjacent sensor pairs to also measure the space between sensors. This approach may provide the lowest cost approach.

[0068] Figure 7 illustrates a set of transducers 10 being circular sensors in an array 18 comprising two rows. The outermost sensors (P1 and P16) overlap the edges of the flow field 20 (shaded area). This arrangement allows the full flow field 20 to be sampled. The transducer array 18 may comprise a PZT crystal arrangement comprising sixteen sensors.

[0069] Figure 8 shows a graph of the acoustic energy weighted by the area measured from the two rows of transducers described in relation to Figure 7 above individually as well as the combination of both rows.

[0070] Figure 9 illustrates a set of transducers 10 being rectangular sensors in an array 18. The outermost sensors (P1 and P16) overlap the edges of the flow field 20 (shaded area). This arrangement allows the full flow field 20 to be sampled. The transducer array 18 may comprise a piezocomposite sectioned into sixteen sections with eight overlapping arrangements of electrodes.

[0071] Figure 10 shows a graph of the acoustic energy weighted by the area measured from the two rows of transducers described in relation to Figure 9 above, individually as well as the combination of both rows.

[0072] Figure 11 shows a schematic diagram of two sets of transducers 10 for measuring the flow field 20. The straight lines 16 illustrate the path within a pair of transducers and the diagonal lines 17 illustrate paths using adjacent pairs. Hence, this sensor arrangement can allow measurement of the space between sensor pairs.

[0073] Figure 12 shows a chart of the emitting and receiving transducers for the arrangement described in relation to Figure 11 above. For N transducers, there are 3N - 1 combinations / paths. Hence, examples described herein can provide the following features:

[0074] • The flow meter comprises sensors arranged right out to the pressure vessel wall (and beyond)

[0075] • The flow meter can provide 100% flow field measurement

[0076] • The flow meter can provide close to uniform acoustic energy (in aggregate). The graphs assume uniform energy from the sensors (which is a simplification from the effects of focusing)

[0077] Meter performance

[0078] There are an infinite number of potential upstream disturbances. To illustrate that the meter is insensitive to disturbances a DN50 meter was tested in a straight pipe and then with a 25% area blockage inserted. One test with the blockage 3 diameters upstream and the other test with the blockage on the flange of the test meter. The change in error averaged to less than 0.1 % at 3D and 0.2% at 0D (a 10:1 turndown was used). From tests using 50% blockage at 3 diameters upstream of the meter, the data showed a + / - 0.2% sensitivity, which is a significant improvement over conventional USMs.

[0079] Figure 13 shows a schematic cross section of a flow meter 2 having a through channel 6 with a rectangular cross section. The flow meter comprises a manifold 12 for holding an array of transducers that covers the width of the through channel 6. The manifold 12 is configured to hold eight transducers with a 9.5 mm diameter arranged side by side with approximately 10 mm spacing. Whilst the corners of the cross section of the through channel 6 of this example have the dimensions 4XR.12[R3.0] (3 mm radius corners) improved results have been achieved with sharper corners such as 4XR.04[R1.0] ( 1 mm radius corners). In fact, the radius can be made as small / sharp as desired.

[0080] Figure 14 shows comparative graphs of results from the flow meter described in relation to Figure 13 above and a conventional eight path UFM which measures velocities along four chords in the flow meter. The velocity profile can change from “Laminar” to “Transition” to “Turbulent”. For USMs, insensitivity to Reynolds Number has been highly sought after, and conventional USMs are not able to deliver in this regard and require software correction curves. For the performance test the test meter illustrated in Figure 13 (4 inch 150#) was tested at the National Engineering Laboratory (NEL) in Scotland.

[0081] Figures 15 and 16 show graphs with results from using a DN25 meter prototype and testing against a piston prover. Figure 15 shows the error plotted against Reynolds number and Figure 16 shows the error plotted against flow rate.

[0082] Figure 17 shows a waveform from a single transducer in a flow meter as described herein. The window thickness is 12.7 mm (0.5 inches) with fluid of SAE 30 motor oil.

[0083] The ultrasonic flow meter described herein is unlike conventional multi-path USMs in several ways. The flow meter can measure the complete flow field, which is comparable to an Electromagnetic meter or a Coriolis meter. An Electromagnetic meter measures an electric field induced by the complete flow field, while the Coriolis meter measures vibrating tube phase change caused by the full mass flow.

[0084] Potential benefits of the ultrasonic flow meter described herein:

[0085] • Inherent accuracy without requiring flow conditioners to “fix” the flow. Further, flow conditioners can cause clogging.

[0086] • Improved installation freedom to install the meter in tight piping installations, which can eliminate the need for expensive upstream piping.

[0087] • Insensitivity to changes in Reynolds number (due to viscosity or flow rate) that changes the shape of the flow field - particularly near to the wall of the through channel.

[0088] • The ultrasonic flow meter can be used for a wide range of flow velocities, while providing only a low pressure drop.

[0089] • Possibility to calibrate with one fluid / gas and use the single calibration to be used everywhere (similar to calibration of a Coriolis or a Mag Meter). This can make the calibration transferrable from the lab to the field.

[0090] Conventional / traditional USMs, on the other hand, rely upon approximations and software post-processing and thus require flow conditioners and long inlet runs. A conventional USMs bases its flow measurement upon measurements along 1 to 4 “elevations” or “chords” across the flow cross-section (even 8 and 12 “path” meters typically only have 4 elevations). Due to the relatively small number of elevations / chords, conventional USMs must rely upon assumptions and approximations to determine an average flow (velocity times area).

[0091] The ultrasonic flow meter described herein can be configured to completely see the flow field and thereby provide a 100% measurement of the flow field. The shape of the through channel together with the arrangement of ultrasonic transducers with respect to that shape allows the flow across a whole cross section of the through channel to be sampled.

[0092] Measuring the whole flow field can eliminate errors caused when Reynolds Numbers change. Validation tests of the described ultrasonic flow meter show that Reynolds Number changes are not a problem. T raditional USMs will have their flow indication error change dramatically in the Reynolds number range between 1000 and 20,000. Using software to correct these errors is exceptionally vulnerable to the subtle differences between the Reynolds Numbers that exist during a meter’s calibration and when installed in the field. Calibration laboratories rarely create Reynolds Numbers that match those in the field. The difference in Reynolds Numbers introduces errors into past USM calibration constants.

[0093] Measuring the whole flow field can also address difficult hydraulics, short run inlets and unexpected flow conditioner fouling. Conventional USMs produced substantial measurement errors when installed with short inlet runs (adjacent to elbows, tees, valves, etc.) - up to 10% of their flow indications.

[0094] Manifold and Meter Body Construction

[0095] Examples of the ultrasonic flow meter described herein provide ultrasonic sensors / transducers installed on an exterior manifold / surface of the pressure vessel (also referred to as “meter body” herein) comprising the flow channel. The manifolds are arranged in pairs where one is an upstream manifold, and one is a downstream manifold.

[0096] Since a set of sensors / transducers are arranged on or within a common manifold outside of the pressure containment they can provide a number of benefits:

[0097] 1 . There is no leak path through the pressure vessel’s wall. 2. Since the manifold manages the pressure vessel concerns, many sensors can be added to the manifold, creating many acoustic paths through the flow field. Individual sensors can have a simple construction and use less expensive materials than sensors arranged at multiple locations around the pressure vessel.

[0098] 3. While arranged in pairs the sensors can cross-communicate with other sensors on the opposing manifolds, allowing measurements between pairs.

[0099] The flow channel is constructed such that the sensor manifolds produce acoustic signal paths that are specifically directed through the flow field. Each acoustic path can be illustrated with a “line” but are beams that have a 3-dimensional path (or swath) through the fluid / gas. Each acoustic path measures an average velocity along the path of its acoustic beam, using transit time ultrasonic velocity measurement (i.e. , the difference in transit times of upstream and downstream combined with transit times compute path average velocity). The pressure vessel shape can include a connecting structure such as recesses or other spaces for the manifolds. In a preferred design, the manifolds are attached with either welds or O-rings. The pressure vessel / meter body together with the acoustic manifolds create and direct acoustic paths through the flow field in predetermined target locations.

[0100] The pressure vessel’s shape can be configured such that the acoustic manifold directs the acoustic energy from the transducers at a predetermined angle relative to the direction of flow. Any angle can be used (other than 90 degrees). In a preferred design the angle of approximately 60 degrees is used for measuring for gas flow or liquid flow. In another example, the angle is 45 degrees for measuring liquid flow.

[0101] The flow channel’s shape is configured to allow a plurality (i.e., a multitude or an “ensemble”) of independent acoustic signal paths to be combined. For example, the shape can be configured with respect to the manifolds such that the ultrasound paths between pairs of transducers have the same transmit time, allowing for the signals from different pairs of transducers to be directly combined. The ensemble can integrate the flow field across a cross section, comprising also the boundaries of the flow field. A complete (100%) velocity measurement can be derived from the composite of transducer sensors (“Velocity Composite”). The ensemble of acoustic paths can be made such that the ensemble completely acoustically samples the flow cross-sectional area. As a result, the flow field’s average velocity can be integrated using the ensemble of acoustic velocity measurements. This is achieved using a plurality of acoustic paths or by using paths that cover larger areas of the cross-section.

[0102] The ensemble’s ability to integrate the flow field results from the flow channel’s shape. For example, the shape can have a symmetric cross-section such as rectangular. The acoustic paths can go directly across the flow field with or without bouncing on the interior walls / sides of the flow channel. The number of bounces (from 0 to n) depends on the desired length of the flow channel and the locations of the manifolds.

[0103] The pressure vessel can be designed for uniform and well mixed fluids. The pressure vessel can be designed to create the transit times of each acoustic path so that they are substantially equal. Examples of such flow channel geometries are rectangular. An advantage of equal transit times is that the acoustic path signals can be summed without destructive interference. Summing acoustic path signals can allow paths to be fired either independently or fired in gangs (a group of ultrasound paths or transducer pairs). A gang may be just a pair of paths, but it may comprise further paths including up to all acoustic paths being ganged and fired simultaneously.

[0104] With ganged firing, a ganged average velocity over the fired paths can be measured. A correction factor may be required with ganged firings to account for individual path signal amplitudes and durations. These ganged paths effectively create larger acoustic beams that sample larger areas of the cross sections of the flow field.

[0105] Figure 18 shows a schematic diagram of ganging paths between transducers 10. The Up-Down waveform of the A+B gang test is a combination of the four paths 16.

[0106] Figure 19A and 19B show the waveform from the ganging paths as an assemblage of individual components.

[0107] Waveforms from ganged transducers can face additional challenges. These include, additional noise from sound “reverberating” within the metal, and smaller transducers will have broader beam angles, resulting in more signal cross talk later in the waveform. To address these concerns, higher frequencies may be used to provide more focused beams (smaller beam angles). Further, highly damped transducer technology is preferred, which can reduce the impact of cross talk and the magnitude. Piezocomposite 1-3 (PZT 5A material) and porous PZT 5A (in this case, APC 860) are the preferred materials, but PZT5A (and similar) materials can be used as well.

[0108] The design can be improved by using transducers with higher damping. Additionally, by controlling the thickness of the pressure vessel wall between the transducer and the fluid an optimal frequency can be selected.

[0109] These design choices can create distinct reverberations within the waveform such that the reverberations create better waveforms for the ganged transducer case, separation between the waveform reverberations, such that multiple reverberations can be used within the signal processing, and such that the broadband nature of the transducer lets the electronics drive the transducers at a range of frequencies. The noise-signal phase relationship varies over frequency such that noise effects can be removed or reduced.

[0110] Figure 20 illustrates the transducer signal from driving the transducer over a range of frequencies. The signal is driven with four cycles at each frequency.

[0111] Figure 21 illustrates an example of combining seven paths into a broadcast. The illustrated waveforms in this particular example are from a three-inch flow meter. The signals / waveforms from the individual transducers (P1 to P7) are broadcast simultaneously to create one path.

[0112] The geometry of the pressure vessel’s cross section can be designed to make a 100% flow field measurement possible. The geometry of pressure vessel allows for attaching acoustic manifolds that comprise an array of transducers. An ensemble of paths can integrate complex and distorted velocity profiles more accurately than what is possible using velocity integration approximations. Ganged firing can allow sampling of the flow profile more frequently, as fewer firings may be needed to fully sample the flow profile. One example of ganged firing is when adjacent sensor pairs are interconnected to measure the space between matched pairs. The sensor size, frequency and location can be chosen to minimize or reduce destructive interference when ganged firing is used, while achieving maximum or greater sampling of the cross-section.

[0113] An ensemble of paths can be used in both independent and ganged firing modes to capture the benefits of both approaches. This can provide better integration and sampling speed, while also allowing granular measurement of the velocity profile.

[0114] The ultrasonic flow meter described herein can provide 100% spatial integration and may provide errors of less than 0.25% for even extremely difficult applications (e.g. partially opened valves upstream or other extreme conditions).

[0115] Conventional USMs, on the other hand, depended on approximations to compute average flow. Conventional USMs depend on a necessary correction for both single (diametral paths) and multichord / multipath meters (2, 3, or 5 paths through the flow fields) to correctly compute the average flow. Even USMs that have “12 or 36” paths, typically produce only 4 chords / elevations across the cross-section of the flow field and still have to rely on an approximations and assumption about the parts of the velocity field not measured.

[0116] Single chord meters can have errors beyond 20% (with typical errors for good installations of about 5%). Multichord meters have errors up to 2% to 3% for installations close to flow field disturbance and may have an error of less than 1% for good installations.

[0117] Further, multi-chord meters with circular cross sections have a vulnerability to changes in Reynolds Numbers below 100,000. This vulnerability is most notable between Reynolds Numbers between 1 ,000 and 10,000. This vulnerability is due to the thick and unmeasured boundary layer and creates errors up to 10%. Conventional USM technology use software corrections to attempt to address these errors.

[0118] Ganged firings can allow for immediate spatial integration. This fast integration may be critical to calibration / proving against small volume proving standards (i.e., piston or ballistic provers). Fast spatial integration can also reduce the magnitude of observed random turbulent variations, because the projection of the turbulence is averaged over a larger space. When all paths are ganged the effect of high frequency turbulence may be cancelled. Conventional USMs, on the other hand, require more time to get to an average computed velocity. Since there are large unmeasured portions of the flow field, only time can be used to achieve an average computed velocity that has a small statistical error bound.

[0119] Noise reduction

[0120] Examples of the ultrasonic flow meter described herein may further comprise a baffle or similar structure to isolate noise form the transducers and provide arduous paths for the acoustic energy to travel between a transmitting transducer to a receiving transducer through the meter body. The baffling can improve the signal to noise ratio, SNR (signal is the acoustic energy that goes through the flow fields and noise is the acoustic energy that stays within the pressure vessel walls). As an additional method to improved SNR, multiple signal echoes (reverberations of the signal through the wall of the pressure vessel) can be used to average the signal and achieve a reduction of noise.

[0121] As an additional method to improve SNR, the driving signal to the transducer can be optimized to achieve randomness in noise phase (for example, the configuration of the driving signal may vary the frequency, number of cycles, duty cycles and other things like frequency chirps.

[0122] A design issue for ultrasonic flow meters is the acoustic “short circuit” or acoustic multipaths. The short circuit is an acoustic path from the transmitting transducer to the receiving transducer that travels not on the desired path through the fluid but through another path that goes through the metal walls of the pressure vessel. The short circuit adds signal (or noise) to the desired waveform, as the noise may persist as long as the transit time of the desired acoustic signal (the signal that travels through the fluid along the intended path).

[0123] The short circuit can be managed effectively in flow meters that use “housings” to hold the transducers, as these housings can use isolators and arduous geometries to reduce the noise that goes through the vessel walls between transducers. However, the flow meter described herein provides an alternative solution to this problem. The housing design option is not part of this design, this design uses the following tools to address / eliminate this noise: • Use of high frequency transducers, such that the sound energy dissipates faster and is also more attenuated by the time desired acoustic signal arrives.

[0124] • Use of highly damped transducers, reducing the quantity of acoustic energy that can travel through the short circuits.

[0125] • Use of a range of transmitted frequencies, such the phase relationship of the noise and the signal can be “averaged” out.

[0126] • Use of cross-correlated signal that uses a “swath of time” for better noise rejection.

[0127] The described flow meter has two further methods to address / reduce acoustic short circuits by designing the pressure vessel itself:

[0128] 1. The pressure vessel may comprise an appropriate material. For example, the meter body may be cast stainless steel (CF8M or CF8 are examples). Cast metal has the property of attenuating high ultrasound frequencies. The target ultrasound signal takes a shorter path than the arduous path, hence SNR is improved. Other methods include 3D printed metal, which can have natural porosity or porosity can be intentionally added to the material (e.g., voids / since the pressure vessel is cast, structures / cavities).

[0129] 2. The pressure vessel can be designed to have “silencer” walls, by adding geometries / baffles that are arduous for sound transmission and thus discouraging acoustic short circuits, which is not possible with round pipe meter bodies.

[0130] Figure 22 shows a schematic cross section on a flow meter 2 comprising a baffle structure 22 in the meter body 4 between the locations of the two sets of transducers (not shown). The meter body 4 comprises connecting structures 24 for attaching the manifolds to the meter body 4. The connecting structure are recesses in the meter body 4 that provide a contact surface for the transducers that is parallel to an internal surface in contact with the fluid flow. The connecting structures 24 are arranged to direct the ultrasound into the through channel 6 at a target angle with respect to the flow. In this example, the ultrasound path is a V-path (one bounce). In other examples, the ultrasound path may be a direct path or W-path for example. Adding just one baffle improved the observed SNR (using a single frequency of 1.5 MHz) from 60:1 to 180:1 (A 9 dB improvement). This baffle test was done on a forged stainless steel prototype.

[0131] Figure 23 is a flow diagram illustrating some steps of a method of measuring the flow of a fluid. The method may be carried out using a flow meter as described herein. The method comprises providing an ultrasonic flow meter comprising a meter body comprising a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of the fluid flow, and two sets of ultrasonic transducers attached to the meter body by respective manifolds and comprising a first set of transducers arranged to emit ultrasound into the through channel and a second set of transducers arranged to receive ultrasound emitted by the first set of transducers (step S1), firing the first set of transducers (step S2), receiving on the second set of transducers (step S3), wherein the second set of transducers provides one or more output signals in response to receiving. The method further comprises determining the flow velocity from the one or more output signals (step S4).

[0132] Figure 24 is a flow diagram illustrating some steps of a method of forming an ultrasonic flow meter. The method comprises forming a meter body (S5), wherein the forming comprises: forming a through channel for fluid flow (S5A), wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of fluid flow; and forming connecting structures for attaching two sets of ultrasonic transducers to the meter body by respective manifolds (S5B), wherein the respective manifolds may be formed in the meter body as part of the connecting structures.

[0133] Whilst specific embodiments have been described above, it will be appreciated that other embodiments can be made that fall within the scope of the claims. Any one or more features of one embodiment may be suitably combined with the features of any of the other embodiments.

Claims

CLAIMS:

1. An ultrasonic flow meter comprising: a meter body comprising a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of the fluid flow; and two sets of ultrasonic transducers attached to the meter body by respective manifolds and comprising a first set of transducers arranged to emit ultrasound into the through channel and a second set of transducers arranged to receive ultrasound emitted by the first set of transducers.

2. An ultrasonic flow meter according to claim 1 , wherein the respective manifolds are arranged with respect to the through channel to sample substantially a whole of the fluid flow across the cross section.

3. An ultrasonic flow meter according to claim 1 or 2, wherein the two sets of ultrasonic transducers are arranged outside the through channel.

4. An ultrasonic flow meter according to any one of the preceding claims, wherein the respective manifolds are arranged with respect to the meter body so that the two sets of ultrasonic transducers are separated from the through channel by parts of the meter body, whereby ultrasound emitted by the first set of transducers travels through a part of the meter body before entering the through channel.

5. An ultrasonic flow meter according to any one of the preceding claims, wherein the two sets of ultrasonic transducers comprise a plurality of pairs of transducers, wherein each pair comprises a first transducer comprised by the first set of transducers and a second transducer comprised by the second set of transducers, wherein for each pair there is a respective ultrasound path between the first transducer and the second transducer via the through channel.

6. An ultrasonic flow meter according to claim 5, wherein a transmit time of the respective ultrasound paths of the plurality of pairs is substantially equal.

7. An ultrasonic flow meter according to claim 5 or 6, wherein the ultrasound path is one of a direct path through the through channel, a V-path through the through channel, or a W-path through the through channel.

8. An ultrasonic flow meter according to any one of the preceding claims, wherein each manifold of the respective manifolds is configured to hold an array of ultrasonic transducers in a substantially flat plane.

9. An ultrasonic flow meter according to claim 8, wherein the array of ultrasonic transducers comprises a row of transducers spaced in a direction perpendicular to the direction of fluid flow.

10. An ultrasonic flow meter according to any one of the preceding claims, wherein the meter body comprises connecting structures for attaching the respective manifolds to the meter body, wherein the connecting structures are arranged to align the two sets of ultrasonic transducers.

11. An ultrasonic flow meter according to any one of the preceding claims, wherein the first set of transducers is arranged to provide ultrasound into the through channel at an angle within the range of 10° to 80° with respect to the direction of fluid flow.

12. An ultrasonic flow meter according to any one of claims 1 to 10, wherein the ultrasonic flow meter is configured to measure a fluid flow and the first set of ultrasound transducers are arranged to provide ultrasound into the through channel at an angle within the range of 10° and 80° with respect to the direction of fluid flow.

13. An ultrasonic flow meter according to any one of claim 1 to 10, wherein the ultrasonic flow meter is configured to measure a gas flow and the first set of transducers are arranged to provide ultrasound into the through channel at an angle within the range of 45° and 80° with respect to the direction of fluid flow.

14. An ultrasonic flow meter according to any one of the preceding claims, wherein the ultrasonic flow meter is configured to simultaneously fire a plurality of transducers of the first set of transducers and to receive on a plurality of transducers of the second set of transducers.

15. An ultrasonic flow meter according to claim 14, wherein the ultrasonic flow meter is configured to provide an output signal based on a combination of signals from the respective plurality of transducers.

16. An ultrasonic flow meter according to any one of the preceding claims, wherein the ultrasonic flow meter is configured to fire a first transducer of the first set of transducers and of a first pair of transducers and receive on a second transducer of the second set of transducers and of a second pair of transducers, wherein the second pair of transducers is adjacent to the first pair of transducers.

17. An ultrasonic flow meter according to any one of the preceding claims, wherein the ultrasonic flow meter is configured to sequentially fire individual transducers of the first set of transducers and to sequentially receive ultrasound on individual respective transducers of the second set of transducers.

18. An ultrasonic flow meter according to any one of the preceding claims, wherein the meter body or manifold comprises one or more internal baffles between the first set of transducers and the second set of transducers.

19. A method of measuring flow velocity, the method comprising: providing an ultrasonic flow meter comprising a meter body comprising a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of the fluid flow, and two sets of ultrasonic transducers attached to the meter body by respective manifolds and comprising a first set of transducers arranged to emit ultrasound into the through channel and a second set of transducers arranged to receive ultrasound emitted by the first set of transducers; firing the first set of transducers; receiving on the second set of transducers, wherein the second set of transducers provides one or more output signals in response to receiving; and determining the flow velocity from the one or more output signals.

20. A method according to claim 19, and comprising: simultaneously firing a plurality of transducers of the first set of transducers; and receiving on a respective plurality of transducers of the second set of transducers.

21. An ultrasonic flow meter according to claim 18 or 19, wherein the determining comprises combining a plurality of output signals from the second set of transducers.

22. A method of making an ultrasonic flow meter, the method comprising: forming a meter body, wherein the forming comprises: forming a through channel for fluid flow, wherein the through channel has a substantially rectangular or cross-shaped cross section perpendicular to a direction of fluid flow; and forming connecting structures for attaching two sets of ultrasonic transducers to the meter body by respective manifolds, wherein the respective manifolds may be formed in the meter body as part of the connecting structures.

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