Ultrasonic flowmeter

Abstract

To provide a clamp-on type ultrasonic flowmeter with which it is possible to measure a flow rate by a parallel multi-measurement line scheme.SOLUTION: An ultrasonic flowmeter conforming to an embodiment of the present invention measures the flow rate of a fluid in piping by a parallel multi-measurement line scheme. The ultrasonic flowmeter comprises: a plurality of ultrasonic sensors, each of which is provided with a pair of transmission and reception units capable of mutually transmitting and receiving an ultrasonic wave; a sensor case for arranging the transmission and reception units on the outer circumference of the piping while maintaining these at an inclined attitude in such a way that the measurement lines of the plurality of ultrasonic sensors are aligned in the radial direction of the piping; a wedge interposed between the outer circumferential surface of the piping and the transmission and reception units for causing the ultrasonic wave to enter the fluid, the wedge being formed from a material close to the sound velocity of the fluid; a clamp for removably attaching the sensor case to the outer circumferential surface of the piping; and a processing unit for outputting the flow rate of the fluid on the basis of information from the ultrasonic sensors.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a clamp-on type ultrasonic flow meter. [Background technology]

[0002] For example, ultrasonic flowmeters are known that measure the flow rate of fluids flowing through circular pipes. To achieve high accuracy in flow rate measurements using ultrasonic flowmeters, a multi-path method is used, which utilizes multiple ultrasonic propagation paths (paths). Typical methods are the parallel multi-path method and the diametric multi-path method. Wetted ultrasonic flowmeters, in which ultrasonic sensors are installed by drilling holes in the pipe, can use the parallel multi-path method to position the ultrasonic sensors. However, wetted types require the installation of ultrasonic sensors by cutting or replacing existing pipes, which makes installation difficult.

[0003] On the other hand, clamp-on ultrasonic flowmeters can be easily attached to existing pipes, but they use a multi-diameter measurement line system in which the measurement line passes through the center of the pipe. This multi-diameter measurement line system may not be able to provide sufficient measurement accuracy for fluids with turbulent flow velocity distribution within the pipe. Therefore, as long as clamp-on ultrasonic flowmeters use a multi-diameter measurement line system, there is a limit to how much measurement accuracy can be improved, even if the number of ultrasonic sensors is increased.

[0004] Clamp-on ultrasonic flowmeters using multiple parallel measurement lines have been considered in the past, but they have been difficult to put into practical use because the ultrasonic sensor is positioned radially off-center from the center of the pipe, making it difficult to direct ultrasonic waves into the fluid inside the pipe. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 5,228,347 [Patent Document 2] Japanese Patent Application Publication No. 5-223608 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a clamp-on type ultrasonic flowmeter that can measure flow rate using a multiple parallel measurement line method. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, an ultrasonic flowmeter according to an embodiment of the present invention is an ultrasonic flowmeter that measures the flow rate of a fluid in a pipe using a parallel multiple measurement line method, and is characterized by comprising: a plurality of ultrasonic sensors, each having a pair of transmitter / receivers that can transmit and receive ultrasonic waves to and from each other; a sensor case that supports the transmitter / receivers in an inclined position and is arranged on the outer periphery of the pipe so that the measurement lines of the plurality of ultrasonic sensors are aligned in the radial direction of the pipe; a wedge formed of a material whose sound speed is close to that of the fluid and that is interposed between the outer surface of the pipe and the transmitter / receivers to allow the ultrasonic waves to be incident on the fluid; a clamp that detachably attaches the sensor case to the outer periphery of the pipe; and a processing unit that outputs the flow rate of the fluid based on information from the ultrasonic sensors. [Effects of the Invention]

[0008] According to an embodiment of the present invention, a clamp-on type ultrasonic flowmeter using multiple parallel measurement lines can be realized by including a sensor case that supports a transmitter / receiver unit in an inclined position and is arranged around the outer periphery of a pipe so that the measurement lines of multiple ultrasonic sensors are aligned in the radial direction of the pipe, and a wedge that is interposed between the outer periphery of the pipe and the transmitter / receiver unit and that transmits ultrasonic waves into the fluid and is made of a material whose sonic speed is close to that of the fluid.As a result, the arrangement of measurement lines using the multiple parallel measurement lines enables highly accurate flow rate measurement even for fluids with a disturbed flow velocity distribution. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a pipe showing a state in which an ultrasonic flowmeter according to an embodiment is attached to a pipe. [Figure 2] 1 is a side view of a pipe showing a state in which an ultrasonic flowmeter according to an embodiment is attached to a pipe. [Figure 3] FIG. 2 is a perspective view of a sensor case of the ultrasonic flowmeter. [Figure 4] 2A to 2C are a plan view, a front view, and a side view of a sensor case of the ultrasonic flowmeter. [Figure 5] 3 is an explanatory diagram of the sensor incident angle of the ultrasonic flowmeter. FIG. [Figure 6] 3 is an explanatory diagram of the sensor incident angle of the ultrasonic flowmeter. FIG. [Figure 7] FIG. 2 is a block diagram of a control system of the ultrasonic flowmeter. [Figure 8] 4A and 4B are diagrams showing the results of flow rate measurement by the ultrasonic flowmeter. DETAILED DESCRIPTION OF THE INVENTION

[0010] An ultrasonic flowmeter according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings, in which the same components are designated by the same reference numerals.

[0011] An ultrasonic flowmeter 1 according to an embodiment is a clamp-on type ultrasonic flowmeter using a parallel multiple measurement line method. FIG. 1 shows the ultrasonic flowmeter 1 attached to the outer surface of a pipe 2, as viewed from the cross-sectional direction of the pipe. FIG. 2 shows the ultrasonic flowmeter 1 as viewed from the side of the pipe. The pipe 2 is a flow path, such as a circular pipe, through which the fluid to be measured flows. The fluid is pressure-fed by a liquid delivery device such as a pump. The liquid may also be delivered by using gravity, for example, without using a liquid delivery device, and the method of delivery is not particularly limited. Of course, there are no limitations on the flow of the fluid within the pipe 2. There may be disturbances in the flow velocity distribution within the pipe, or the flow may be fully developed.

[0012] The ultrasonic flowmeter 1 includes, for example, two ultrasonic sensors 3A and 3B. As shown in FIG. 1, the two ultrasonic sensors 3A and 3B are arranged so that the ultrasonic propagation paths (trajectory lines) U are parallel to the radial direction of the pipe 2. In other words, they are two parallel trajectory lines. "Parallel" refers to a typical example of an arrangement, and the parallel relationship is not necessary. It is sufficient that the trajectory lines U do not pass through the center of the pipe. As a preferred example, the two trajectory lines U are arranged symmetrically with respect to the center of the pipe 2. The distance r from the center of the pipe 2 is preferably within a range of 0.5R to 0.6R (R: inner radius of the pipe). On the other hand, when viewed from the side of the pipe, the trajectory lines U are arranged so that they intersect the longitudinal direction of the pipe 2, as shown in FIG. 2. As an example, the trajectory lines U are arranged so that the inclination of the trajectory lines U within the pipe is 15° to 25°.

[0013] The ultrasonic sensors 3A and 3B each include a pair of transceivers 31A, 32A, 31B, and 32B, each capable of transmitting and receiving ultrasonic waves. Specifically, the upstream transceivers 31A and 31B can transmit ultrasonic waves toward their downstream counterparts 32A and 32B, and can receive ultrasonic waves from the downstream transceivers 32A and 32B. The downstream transceivers 32A and 32B operate in a similar manner. The transceivers 31A, 32A, 31B, and 32B may be, for example, ultrasonic transducers. For example, in the case of a transit time difference measurement method, the paired transceivers 31A-32A and 31B-32B alternately transmit and receive ultrasonic waves. Based on the difference between the transit time from the upstream side to the downstream side and the transit time from the downstream side to the upstream side, the mean linear flow velocity v of the fluid in the pipe 2 is calculated, for example, by calculation. The flow rate is then calculated based on the calculated mean linear flow velocity v. An example of this calculation method will be described later.

[0014] In this embodiment, the transmitters and receivers 31A-32A and 31B-32B are arranged diagonally opposite each other using the Z method (transmission method) when viewed from the side of the pipe. However, the V method (reflection method) or X method (transmission method) may also be used. Furthermore, although the ultrasonic sensors 3A and 3B are arranged so that the measurement line U extends vertically (from 0° to 180°) when viewed from the cross section of the pipe, this arrangement is not limiting. For example, the direction of the measurement line U can be changed by arranging the ultrasonic sensors 3A and 3B so that the measurement line U extends horizontally (from 90° to 270°). Furthermore, the number of ultrasonic sensors 3A and 3B may be increased to provide three or more parallel measurement lines. Furthermore, for example, by adding another ultrasonic sensor between two pairs of ultrasonic sensors 3A and 3B, the multiple measurement lines U may include one that passes through the center of the pipe 2.

[0015] Each sensor case 33A, 34A, 33B, and 34B faces a pair of transceivers 31A-31B, 32A-32B so that a measurement line U is formed. To achieve this, each sensor case 33A, 34A, 33B, and 34B supports the corresponding transceiver 31A, 32A, 31B, and 32B in an inclined position. The multiple sensor cases 33A, 34A, 33B, and 34B may have the same shape. The configuration of the sensor cases 33A, 34A, 33B, and 34B will be described with reference to FIGS. 3 and 4. FIG. 3 is a perspective view of the sensor case 33A with the transceiver 31A attached. FIG. 4 is a plan view, a front view, and a side view of the sensor case 33A. The other sensor cases 34A, 33B, and 34B have the same configuration as the sensor case 33A, and therefore detailed description and illustrations will be omitted.

[0016] 3 and 4, the sensor case 33A has a sensor case main body 4 that has, for example, a rectangular appearance. The sensor case main body 4 has an inclined surface 41 on its top surface that supports the transmitter / receiver 31A in an inclined position, and legs 42 formed on the bottom surface, for example, at the four corners. The legs 42 come into contact with the outer peripheral surface of the pipe 2, causing the sensor case main body 4 to seat on the outer peripheral surface of the pipe 2. The sensor case main body 4 is made of a metal such as stainless steel.

[0017] The transmitter / receiver 31A is attached to the inclined surface 41 of the sensor case body 4 by a fastening means 43, such as a screw. The sensor case body 4 has an opening extending from its top surface to its bottom surface, in which a wedge 44 is disposed. The wedge 44 is also referred to as a sensor shoe material. The wedge 44 is formed of a material whose sonic velocity is closer to that of the fluid than engineering plastics, such as polymethyl methacrylate (PMMA) or polyetherimide (PEI). For example, the wedge 44 is formed of a material whose sonic velocity is within a range of 0.6 to 1.4 times the sonic velocity of the fluid. Specific examples of such a material include silicone rubber (sound velocity of approximately 1000 m / s) and medical water-based / oil-based gel (sound velocity of approximately 1389 m / s). Forming the wedge 44 from a material with such a sonic velocity is, in other words, forming the wedge 44 from a material that makes the incident angle θi of the ultrasound waves, described below, smaller than 45°. Of course, the material of the wedge 44 may be changed depending on the target fluid. The wedge 44 may be formed by filling the opening of the sensor case body 4 with a fluid material, or may be formed in advance and fitted in place.

[0018] To realize the parallel multiple measurement line method in a clamp-on type ultrasonic flowmeter 1, it is important how to make ultrasonic waves incident on the fluid inside the pipe 2. Therefore, in this embodiment, the transmitter / receiver units 31A, 32A, 31B, 32B are tilted at positions radially shifted from the center of the pipe 2 by sensor cases 33A, 34A, 33B, 34B, and further a wedge 44 formed of a material whose sound speed is close to that of the fluid is interposed, thereby making it possible to make ultrasonic waves incident on parallel multiple measurement lines inside the pipe 2.

[0019] For a more detailed explanation, we will explain the selection of the sensor incident angle and the material of wedge 44 to achieve multiple parallel measurement lines with a clamp-on type. The following explains the case where the fluid is water as an example. First, as shown in Figure 5, consider measurement line U, which is spaced r from the center on the pipe cross section and has an inclination angle α in the flow direction. Then, sin β = (r / R), and measurement line U within pipe 2 can be determined by angles α and β (0° < α, β < 90°). To position transmitter / receiver units 31A and 32A at the point of incidence of measurement line U, we newly adopted wedge 44 and sensor cases 33A, 34A, 33B, and 34B, which have an inclined surface 41 as shown in Figures 3 and 4 and transmit ultrasonic waves from inclined surface 41 to the bottom surface that contacts pipe 2. As shown in Figure 6, if the incident angle with respect to the normal to the installation surface is θi, the refraction angle in the fluid is θt, and the inclination of the incident line with respect to the longitudinal direction of the pipe when viewing the transmitter / receiver units 31A, 32A, 31B, and 32B from above is φ (see the plan view in Figure 4), the following holds true from the respective angular relationships and Snell's law.

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[0020] For example, if the measurement line U is α = 20°, β = 30° (r = 0.5R) and the target is water at room temperature (sound speed: approximately 1500 m / s), polyetherimide (PEI, sound speed: approximately 2400 m / s) or acrylic (sound speed: approximately 2700 m / s) are typically selected as the material for the wedge 44. However, if PEI is used in a clamp-on parallel multiple measurement line system, the incident angle θi will be approximately 70° according to the above equation. With such a large incident angle θi, the ultrasonic sensors 3A and 3B must be large to ensure the ultrasonic propagation path (measurement line) U, making their design difficult. This also reduces the reproducibility of the installation of the ultrasonic sensors 3A and 3B on the pipe 2. To address this issue, the sonic speed of the wedge 44 can be reduced to reduce the incident angle θi to 45° or less. As a result of the investigation, it was confirmed that when silicone rubber (sound speed: about 1000 m / s) is used, the incident angle can be reduced to about 23° and the attenuation of the ultrasonic waves is not so large.

[0021] In reality, ultrasonic waves cannot propagate from wedge 44 to the fluid inside the pipe without the presence of the pipe wall of pipe 2. For example, in a stainless steel pipe, the shear wave speed is approximately 3100 m / s, and according to Snell's law, the incidence angle θi described above results in total reflection when the ultrasonic waves enter the pipe wall from wedge 44. However, in this embodiment, it is believed that evanescent waves are generated within the pipe wall, and if the pipe thickness is approximately the wavelength, it is possible for ultrasonic waves to propagate to the fluid inside the pipe. In fact, ultrasonic simulations and tests using a prototype sensor, described below, have confirmed that ultrasonic waves can pass through the pipe wall of pipe 2 and propagate into the fluid.

[0022] Returning to FIGS. 1 and 2, the clamp 5 detachably attaches the ultrasonic sensors 3A and 3B to the outer peripheral surface of the pipe 2. The clamp 5 includes a pair of plate-like annular members 51A and 51B formed in a roughly semicircular shape, and is attached so as to surround the entire circumference of the pipe 2. The pair of annular members 51A and 51B may have the same shape. The annular members 51A and 51B are made of a metal such as stainless steel. The pair of annular members 51A and 51B are attached to the pipe 2, and their flanges are fixed together with fixing means 52 such as screws. At this time, as shown in FIG. 2 in particular, the upstream transceivers 31A and 31B and the downstream transceivers 32A and 32B are positioned by shifting the annular member 51B in the downstream direction of the pipe 2, for example. Openings corresponding to the sizes of sensor cases 33A, 34A, 33B, and 34B are formed in annular members 51A and 51B, and sensor cases 33A, 34A, 33B, and 34B are placed in the exposed portions of the outer periphery of pipe 2. Sensor cases 33A, 34A, 33B, and 34B are then fixed in place by pressing members 53. This fixing method makes it possible to prevent variations in the installation pressure of sensor cases 33A, 34A, 33B, and 34B against pipe 2 each time they are installed, and to keep the pressure constant.

[0023] 7, the transceivers 31A, 32A, 31B, and 32B are connected to a control unit 6. The control unit 6 includes a control unit 61 and a processing unit 62. The control unit 61 includes, for example, an integrated circuit (IC) and a memory. The processing unit 62, which calculates the flow rate based on signals from the transceivers 31A, 32A, 31B, and 32B, is constructed, for example, by the control unit 61 executing a program stored in the memory. The control unit 6 also includes a transmission circuit 63, a reception circuit 64, and a switch unit 65 that switches the transmission and reception paths. The transmission circuit 63 outputs, for example, a drive signal that vibrates an ultrasonic vibrator based on a control signal from the control unit 61. The switch unit 65 switches the transmission path based on the control signal from the control unit 61 so that the drive signal is input to the transmitting transceiver 31A (32A) or 31B (32B) of the transceivers 31A-32A and 31B-32B. The receiving circuit 64 converts the received signal from the receiving side transceiver 32A (31A), 32B (31B) of the pair of transceivers 31A-32A, 31B-32B into digital data and outputs it to the processing unit 62.

[0024] In the above-described configuration, the ultrasonic flowmeters 3A and 3B are attached to the pipe 2 by, for example, a worker. As they are clamp-on types, installation is easier than wetted types. The installation location is, for example, in a straight pipe section of the pipe 2 extending horizontally. It may also be in a straight pipe section extending vertically or diagonally. If there is a joint such as an elbow where turbulence is likely to occur, the ultrasonic flowmeters 3A and 3B are installed in a position where a certain amount of straight pipe length can be secured before and after the joint.

[0025] The material of the pipe 2 is metal such as stainless steel or steel, or resin such as polyvinyl chloride or polypropylene, but there is no particular limitation on the material of the pipe. The nominal diameter of the pipe 2 is, for example, 100 A to 3000 A. However, it is preferable to prepare a clamp 5 according to the nominal diameter of the pipe 2. There is also no particular limitation on the type of fluid flowing through the pipe 2. The fluid to be measured may be either a liquid or a gas.

[0026] With the ultrasonic sensors 3A and 3B attached to the pipe 2, the control unit 61 of the control unit 6 controls the upstream and downstream transmitting / receiving units 31A-32A and 31B-32B of each ultrasonic sensor 3A and 3B to transmit and receive ultrasonic waves alternately, for example. The processing unit 62 calculates the flow rate based on the difference in propagation time between the upstream and downstream ultrasonic waves. The flow rate measurement result is output as, for example, the average value of the flow rates measured by the two ultrasonic sensors 3A and 3B. Alternatively, the flow rates measured by the two ultrasonic sensors 3A and 3B may be displayed individually, or either one may be displayed.

[0027] As a preferred example of calculating the flow rate, the linear mean flow velocity v is calculated using the following formula, and the flow rate can be determined based on the cross-sectional area of ​​the pipe 2. Of course, the calculation method is not limited to this, and other calculation methods may be adopted.

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[0028] Figure 8 shows an example of the results of a measurement test using a prototype sensor of the ultrasonic flowmeter 1 shown in Figures 1 and 2. Specifically, two sets of ultrasonic sensors 3A and 3B and sensor cases 33A, 34A, 33B, and 34B were prototyped, with the distance r of the measurement line U from the center of the pipe 2 set to ±0.5R, to create a clamp-on type ultrasonic flowmeter 1 with two parallel measurement lines. Accuracy was then verified through actual flow tests using flow calibration equipment. 300A10S-standard stainless steel pipe was used for pipe 2. To create harsh conditions, performance was evaluated at a location 5.5D straight from the header pipe branch where the flow velocity distribution was disrupted. For comparison, a similar test was also conducted on a clamp-on type ultrasonic flowmeter with a two-diameter measurement line system.

[0029] When installing ultrasonic sensors 3A and 3B, there is still the freedom to rotate measurement line U by angle ψ relative to pipe 2, as shown in Figure 8, and when the flow velocity distribution is disturbed, the measured value will also change depending on this installation angle. Therefore, for the prototype sensor, the installation angle ψ was changed in fixed increments from 0° to 270°, and measurement tests were carried out for each angle. The table in Figure 8 summarizes the errors in the measured flow rate values ​​of the prototype sensors using the two parallel measurement lines and two diameter measurement lines method, relative to the flow rate values ​​of the master meter of the flow calibration equipment.

[0030] The flow velocity in the reference pipe was changed to approximately 4 m / s, 2 m / s, and 1 m / s, and the measurement error was confirmed for each flow velocity and installation angle. Note that the installation angle ψ was only changed for the two parallel lines, while the two diameter lines were fixed as two diameter lines equivalent to ψ = 45° and 135°. Furthermore, for both the two parallel lines and the two diameter lines, the errors are reported after averaging the measured values ​​of the two lines U.

[0031] As is clear from the results in Figure 8, the parallel two-line method has smaller errors than the diametric two-line method at any installation angle ψ, and achieves higher accuracy in locations where the flow velocity distribution is disturbed. In other words, it was confirmed that the clamp-on ultrasonic flowmeter 1 can achieve the parallel multiple line method and improve measurement accuracy.

[0032] According to the above-described embodiment, a clamp-on type ultrasonic flowmeter employing a multi-parallel measurement line system can be realized by providing a sensor case that supports the transmitter / receiver unit in an inclined position and is arranged around the outer periphery of the pipe so that the measurement lines of multiple ultrasonic sensors are aligned in the radial direction of the pipe, and a wedge that is interposed between the outer periphery of the pipe and the transmitter / receiver unit and that transmits ultrasonic waves into the fluid and is made of a material with a sound speed close to that of the fluid. As a result, the arrangement of measurement lines using the multi-parallel measurement line system enables highly accurate flow rate measurement even for fluids with a disturbed flow velocity distribution.

[0033] The pipe 2 is usually a circular pipe according to a standard, but it does not have to be a circular pipe as long as the outer circumferential surface in the direction intersecting the fluid flow direction is curved.

[0034] The embodiments of the present invention are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be embodied in various other forms, and various omissions, substitutions, and modifications may be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the inventions and their equivalents as defined in the claims. [Explanation of symbols]

[0035] 1 Ultrasonic flowmeter 2 Piping 3A, 3B ultrasonic sensors 31A, 31B Transmitter / receiver (upstream side) 32A, 32B Transmitter / receiver (downstream side) 33A, 33B, 34A, 34B sensor case 41 Slope 44 Wedge

Claims

1. An ultrasonic flowmeter that measures the flow rate of a fluid in a pipe using a parallel multiple measurement line method, a plurality of ultrasonic sensors each including a pair of transmitting and receiving units capable of transmitting and receiving ultrasonic waves to and from each other; a sensor case that supports the transmitting and receiving units in an inclined position and is disposed on an outer peripheral surface of the pipe so that the measurement lines of the plurality of ultrasonic sensors are aligned parallel to a radial direction of the pipe; a wedge formed of a material having a sound velocity close to that of the fluid, the wedge being interposed between the outer peripheral surface of the pipe and the transmitting / receiving unit to allow the ultrasonic waves to be incident on the fluid; a clamp that detachably attaches the sensor case to the outer peripheral surface of the pipe; a processing unit that outputs the flow rate of the fluid based on information from the ultrasonic sensor, The ultrasonic flowmeter is characterized in that the sensor case has an inclined surface on the top surface that supports the transmitter / receiver unit, and a leg on the bottom surface that abuts against the outer peripheral surface of the pipe, and the wedge is positioned within an opening that penetrates from the top surface to the bottom surface.

2. The ultrasonic flowmeter according to claim 1, characterized in that the clamp comprises a plate-shaped annular member that surrounds the outer peripheral surface of the piping, an opening formed in the annular member through which the outer peripheral surface of the piping is exposed, and a fixing member that fixes the sensor case placed in the opening.

3. 3. The ultrasonic flowmeter according to claim 1, wherein the plurality of ultrasonic sensors form measurement lines at positions radially shifted from the center of the pipe.

4. 4. The ultrasonic flowmeter according to claim 1, wherein the material forming the wedge is a material having a sonic speed such that the incident angle θi of the ultrasonic wave of the ultrasonic sensor is smaller than 45°.

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