Ultrasonic flowmeter

Abstract

To provide an ultrasonic flowmeter capable of easily detecting a drift current in a measurement tube.SOLUTION: An ultrasonic flowmeter 1 comprises: a measurement tube 2; at least two pairs of sensor units 7, 8 having an ultrasonic sensor 5; and an arithmetic processing unit 6 for computing the flow rate of a fluid on the basis of a flow velocity value measured using the difference in propagation time between ultrasonic sensors arranged in pairs. The sensor units include: a pair of first sensor units 7 in which an ultrasonic sensor is disposed in such a way that at least a part of a transmitting / receiving wave front 41 of the ultrasonic sensor is located on an outer wall of the measurement tube; and a pair of second sensor units 8 in which an ultrasonic sensor is disposed in such a way that all of the transmitting / receiving wave fronts of the ultrasonic sensor are located protruding to the inside of a flow path rather than to the outer wall of the measurement tube.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic flow meter. [Background technology]

[0002] Conventionally, ultrasonic flowmeters that measure the flow rate of a fluid passing through a measuring pipe are known. For example, the ultrasonic flowmeter described in Patent Document 1 transmits and receives ultrasonic waves between a pair of ultrasonic sensors attached to the upstream and downstream sides of a measuring pipe through which a fluid flows. The ultrasonic flowmeter measures the flow velocity based on the difference between the propagation time from the upstream side to the downstream side and the propagation time from the downstream side to the upstream side, and is able to measure the flow rate of the fluid passing through the measuring pipe using the cross-sectional area of ​​the flow path.

[0003] In addition, some ultrasonic flowmeters have been designed with sensors in mind to increase coverage of the flow velocity distribution within the cross section of the flow path by using multiple measurement lines or reflections from the wall surfaces inside the measurement pipe, thereby enabling accurate measurements even when the flow velocity distribution is not uniform.For example, with such ultrasonic flowmeters, it was believed that by averaging the measurement results of multiple measurement lines or selecting an appropriate measurement line, it was possible to measure with a certain degree of accuracy even when the flow velocity distribution in the measurement pipe is not uniform and there is a drift flow. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-217780 Summary of the Invention [Problem to be solved by the invention]

[0005] However, ultrasonic flowmeters with enough measurement lines to ignore the effects of drift in the pipe are extremely expensive, and even if they have multiple measurement lines, if the number of measurement lines is insufficient, they will still be affected by drift to a certain extent. In other words, they are unable to sufficiently average out the flow measurement bias caused by drift. For this reason, most practical flowmeters require a steady flow in the pipe for accurate measurement, but it is difficult for users to know the flow conditions in the pipe themselves, and most users rely on the piping conditions provided by the manufacturer, such as the front and rear straight pipe lengths. Furthermore, even when trying to detect drift, there is a problem in that the measurement values ​​for each measurement line are difficult to discern depending on the state of drift, making it impossible to detect drift at all.

[0006] SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an ultrasonic flowmeter that can easily detect drift in a measuring pipe. [Means for solving the problem]

[0007] (1) To achieve the above-mentioned object, according to one aspect of the present disclosure, there is provided an ultrasonic flowmeter comprising: a measuring pipe having a flow path through which a fluid flows; at least two pairs of sensor units having ultrasonic sensors, the sensor units being located on the upstream and downstream sides of the flow path and being provided in the measuring pipe so as to be able to transmit and receive ultrasonic signals; and a processing unit that calculates the flow rate of the fluid based on a flow velocity value measured using a difference in propagation time between the pair of ultrasonic sensors, wherein the sensor units include a pair of first sensor units that arrange the ultrasonic sensors so that at least a part of the transmitting and receiving surface of each ultrasonic sensor is located on an outer wall of the measuring pipe, and a pair of second sensor units that arrange the ultrasonic sensors so that the entire transmitting and receiving surface of each ultrasonic sensor protrudes into the flow path beyond the outer wall of the measuring pipe.

[0008] According to this ultrasonic flowmeter, the ultrasonic sensor of the first sensor unit is positioned so that at least a portion of its transmitting and receiving surface is located on the outer wall of the measuring pipe. On the other hand, the ultrasonic sensor of the second sensor unit is positioned so that its entire transmitting and receiving surface protrudes into the flow path beyond the outer wall of the measuring pipe. That is, the first sensor unit measures the entire flow path, while the second sensor unit measures a region closer to the center of the flow path that is narrower than the entire flow path. Therefore, the measurement line taken by the second sensor unit is more significantly affected by drift in the measurement pipe than the measurement line taken by the first sensor unit. Therefore, differences are likely to occur between the flow velocity values ​​obtained based on the measurement lines of the first sensor unit and the second sensor unit. That is, drift in the measurement pipe can be easily detected. Furthermore, when measuring fluids such as gases that easily attenuate ultrasonic waves, using the second sensor unit, which measures a region narrower than the entire flow path, makes it possible to perform measurement.

[0009] (2) In the ultrasonic flowmeter of the above form, a drift detection unit may be further provided that detects the presence or absence of drift in the measuring pipe, and the drift detection unit may detect the presence or absence of drift in the measuring pipe using a measurement difference value that is a value related to the difference between the flow velocity value measured by the first sensor unit and the flow velocity value measured by the second sensor unit.

[0010] According to this type of ultrasonic flowmeter, a drift in the measurement pipe can be easily detected by using a measurement difference value, which is a value relating to the difference between the flow velocity value measured by the first sensor unit and the flow velocity value measured by the second sensor unit, for drift detection. Note that the "flow velocity value measured by the first sensor unit" refers to a flow velocity value calculated based on a measurement line propagating between a pair of first sensor units. Similarly, the "flow velocity value measured by the second sensor unit" refers to a flow velocity value calculated based on a measurement line propagating between a pair of second sensor units.

[0011] (3) The ultrasonic flowmeter of the above configuration may further include a drift detection notification unit that notifies an external device that a drift has been detected when the drift detection unit detects a drift in the measuring pipe.

[0012] According to this type of ultrasonic flowmeter, the drift detection notification unit can notify an external party that a drift has been detected, so that, for example, the user can be informed of whether the ultrasonic flowmeter is installed properly. This notification allows the user to take appropriate measures, such as re-installing the ultrasonic flowmeter in a location where there is no drift.

[0013] (4) In the ultrasonic flowmeter of the above form, the drift detection unit may compare the measured differential value with a reference differential value that is preset as a reference value for the difference between the flow velocity value measured by the first sensor unit and the flow velocity value measured by the second sensor unit in a flow without drift, and detect the presence of drift in the measuring pipe if there is a difference between the reference differential value and the measured differential value that is equal to or greater than a predetermined value that is preset.

[0014] According to this type of ultrasonic flowmeter, if the difference between the reference differential value and the measured differential value is equal to or greater than a predetermined value, the presence of drift is detected. Drift can be easily detected by comparing the reference differential value with the measured differential value.

[0015] (5) In the ultrasonic flowmeter of the above form, a natural gas measurement unit may be further provided that measures the flow rate of the natural gas in the measurement pipe, and the natural gas measurement unit may measure the flow rate of the natural gas in the measurement pipe using the flow velocity value obtained by the second sensor unit.

[0016] According to the ultrasonic flowmeter of this type, even if the ultrasonic signal can no longer be measured by the first sensor unit, the flow rate of natural gas can be continuously measured using the ultrasonic signal measured by the second sensor unit.

[0017] (6) In the ultrasonic flowmeter of the above aspect, the ultrasonic sensor of the first sensor unit and the ultrasonic sensor of the second sensor unit may be the same type of sensor having the same characteristics.

[0018] According to the ultrasonic flowmeter of this type, the ultrasonic sensors of the first sensor section and the second sensor section are configured from the same type of sensor, thereby improving versatility. [Effects of the Invention]

[0019] The ultrasonic flowmeter according to the present invention can provide an ultrasonic flowmeter that can easily detect drift in a measuring pipe. Furthermore, the ultrasonic flowmeter according to the present invention can provide the user with information to determine the reliability of the measurement results by detecting and displaying the drift in the measuring pipe by itself. The user can obtain more reliable measurement results by reviewing the piping conditions as necessary. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a perspective view of an ultrasonic flowmeter according to a first embodiment of the present invention. [Figure 2] FIG. 1 is a front view of an ultrasonic flow meter. [Figure 3] FIG. 1 is a side view of an ultrasonic flow meter. [Figure 4] FIG. 2 is a cross-sectional view of the ultrasonic flowmeter, illustrating the configuration of a sensor unit. [Figure 5] FIG. 10 is a diagram illustrating an example of a flow velocity distribution in a flow channel in a flow without drift. [Figure 6] 10A and 10B are diagrams illustrating an example of a flow velocity distribution in a flow channel in a flow with drift. [Figure 7] This is a table showing the flow velocities obtained from two measurement lines and their ratios. [Figure 8] FIG. 10 is a schematic diagram illustrating an installation form of a sensor unit in another embodiment. [Figure 9] FIG. 10 is a front view of an ultrasonic flowmeter according to another embodiment. [Figure 10] FIG. 10 is a side view of an ultrasonic flow meter according to another embodiment. [Figure 11] FIG. 10 is a front view of an ultrasonic flowmeter according to another embodiment. [Figure 12] FIG. 10 is a side view of an ultrasonic flow meter according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First Embodiment An ultrasonic flowmeter 1 according to a first embodiment of the present invention will be described with reference to FIGS. [Overall configuration of ultrasonic flowmeter 1] As shown in FIGS. 1 and 2, the ultrasonic flowmeter 1 of the first embodiment has a measurement pipe 2, a calculation and display unit 6, a first sensor unit 7, a second sensor unit 8, and a pipe 20.

[0022] The measuring tube 2 is a cylindrical member, and is made of metal such as stainless steel. The measuring tube 2 is open at both ends in the direction in which the central axis C (see FIGS. 3 and 4) extends (hereinafter simply referred to as the "direction of the central axis C"). A cylindrical flow path 9 is formed inside the measuring tube 2, connecting both ends in the direction of the central axis C. A fluid to be measured flows through the flow path 9. The inner diameter of the flow path 9 is formed to be approximately the same over the entire length in the direction of the central axis C.

[0023] Flanges 10 are provided at both ends of the measuring pipe 2, protruding radially outward from the measuring pipe 2. A plurality of through holes 10a are formed in each flange 10 at appropriate intervals in the circumferential direction around the central axis C of the flow path 9. A feed pipe (not shown) for passing a fluid is connected to the outside of each flange 10 in the direction of the central axis C. Then, bolts are inserted through the through holes 10a of the flanges 10 and through holes provided in the feed pipe, and the bolts and By screwing the nut, the measuring pipe 2 and the feeding pipe are connected.

[0024] Depending on the arrangement of the connected feed pipe, the direction of the central axis C of the flow path 9 can be positioned in any direction, such as vertically or horizontally. Also, by changing the mutual connection position between the through hole 10a of the flange 10 and the through hole of the feed pipe, the mounting angle of the ultrasonic flowmeter 1 in the circumferential direction relative to the feed pipe can be changed.

[0025] As shown in Figures 1 to 4, a pair of a first sensor unit 7 and a second sensor unit 8 are provided on the upstream and downstream sides of the measuring pipe 2, respectively. Figure 4 is a cross-sectional view of the ultrasonic flowmeter 1 taken along a plane perpendicular to the central axis C, and is a diagram for explaining the internal configuration of each of the sensor units 7, 8. In Figure 4, for the sake of clarity, the internal components of each of the sensor units 7, 8 are shown hatched. In Figure 4, the calculation and display unit 6 is omitted.

[0026] The pair of sensor units 7, 8 are provided such that imaginary lines V1, V2 (see FIG. 4) connecting the axes of the ultrasonic sensors 5 of the sensor units 7, 8 are positioned on a straight line inclined with respect to the direction of the central axis C. In other words, ultrasonic waves can be transmitted and received between the pair of ultrasonic sensors 5 of the pair of sensor units 7, 8 in a direction diagonally intersecting the central axis C of the flow path 9. The flow rate of the fluid passing through the flow path 9 can be measured based on the propagation time of the ultrasonic signal between the ultrasonic sensors 5 from the upstream side to the downstream side and the propagation time of the ultrasonic wave between the ultrasonic sensors 5 from the downstream side to the upstream side.

[0027] Mounting holes 11 (see FIG. 2) for mounting the display base 6a of the calculation and display unit 6 are formed in the peripheral wall of the measuring pipe 2. Furthermore, as shown in FIGS. 1 and 4, two mounting portions 12 for mounting the first sensor unit 7 are provided in the peripheral wall of the measuring pipe 2. One mounting portion 12 is provided at the upstream side and one at the downstream side in the direction of the central axis C of the measuring pipe 2, and the mounting portions 12 are provided at positions 180 degrees apart in the circumferential direction of the measuring pipe 2. In other words, when the sensor unit 7 is mounted to each mounting portion 12, one ultrasonic sensor 5 is located upstream of the flow path 9, and the other ultrasonic sensor 5 is located downstream of the flow path 9. The two ultrasonic sensors 5 are capable of transmitting and receiving waves to and from each other.

[0028] Furthermore, two mounting portions 13 for mounting the second sensor unit 8 are provided on the peripheral wall of the measurement pipe 2. One mounting portion 13 is provided at the upstream side and one at the downstream side in the direction of the central axis C of the measurement pipe 2, and the mounting portions 13 are provided at positions 180 degrees apart in the circumferential direction of the measurement pipe 2. In other words, when the second sensor unit 8 is mounted on each mounting portion 13, one ultrasonic sensor 5 is located at the upstream side of the flow path 9, and the other ultrasonic sensor 5 is located at the downstream side of the flow path 9. Both ultrasonic sensors 5 are capable of transmitting and receiving waves to and from each other.

[0029] A cylindrical mounting hole 12a penetrating the inside and outside of the measuring pipe 2 is formed in the mounting part 12 of the measuring pipe 2, with the central axis L of this mounting hole 12a perpendicular to the central axis C of the measuring pipe 2. A mounting surface 12c is formed on the outer surface of the mounting part 12. The mounting surface 12c is perpendicular to the central axis L of the mounting hole 12a and forms a flat surface that is annular in plan view. Four female threads 12d are formed on this mounting surface 12c at appropriate intervals in the circumferential direction centered on the central axis L of the mounting hole 12a.

[0030] A positioning portion 14 is provided on the mounting surface 12c at a position closer to the center in the direction of the central axis C of the measuring pipe 2, protruding from the mounting surface 12c outward in the radial direction of the measuring pipe 2. The outer peripheral surface of the positioning portion 14 is arc-shaped with its center on the central axis L of the mounting hole 12a, and the inner surface is flat.

[0031] A cylindrical mounting hole 13a penetrating the inside and outside of the measuring pipe 2 is formed in the mounting portion 13 of the measuring pipe 2 so that the central axis M of this mounting hole 13a intersects with the central axis C of the measuring pipe 2. A mounting surface 13c is formed on the outer surface of the mounting portion 13. The mounting surface 13c is perpendicular to the central axis M of the mounting hole 13a and forms a flat surface that is annular in plan view. Four female threads (not shown) are formed at appropriate intervals in the circumferential direction centered on the central axis M of the mounting hole 13a.

[0032] A positioning portion 24 is provided on the mounting surface 13c at a position closer to the center in the direction of the central axis C of the measuring pipe 2, protruding from the mounting surface 13c to the outside in the radial direction of the measuring pipe 2. The positioning portion 24 has an outer peripheral surface that is arc-shaped with its center on the central axis M of the mounting hole 13a, and an inner surface that is flat.

[0033] Referring again to FIGS. 1 to 3, the calculation and display unit 6 is equipped with a known microcomputer or the like and functions as a control unit that controls the ultrasonic flowmeter 1. The calculation and display unit 6 calculates the flow rate based on the received signal from the receiving ultrasonic sensor 5 and is capable of displaying the result on the monitor 6b. The calculation and display unit 6 is also capable of detecting the presence or absence of drift in the flow path 9 based on the received signal from the receiving ultrasonic sensor 5 and is capable of displaying the detection of drift on the monitor 6b. For example, if drift is detected, the monitor 6b of the calculation and display unit 6 displays "drift present" or "improper installation", etc. The calculation and display unit 6 corresponds to an example of a "calculation processing unit", a "drift detection unit", a "drift detection notification unit", and a "natural gas measurement unit".

[0034] In this embodiment, the calculated flow rate and drift detection results are displayed by the calculation display unit 6, but the results of various measurements may be output as numerical data to a data logger, etc. Alternatively, a wireless or wired data transfer function may be installed so that the data can be output to a location separate from where the ultrasonic flowmeter 1 is installed.

[0035] 1 to 3, this embodiment shows an example in which the direction of the central axis C of the flow path 9 coincides with the horizontal direction, and the axial direction of the display base 6a of the arithmetic and display unit 6 is positioned in the vertical direction. In other words, the arithmetic and display unit 6 is positioned above the measuring pipe 2. In addition, the angle θ of the line connecting the axes of the ultrasonic sensors 5 with the horizontal direction is 22.5 degrees (see FIG. 3).

[0036] [Configuration of first sensor unit 7] Next, the configuration of the first sensor unit 7 will be described with reference to Fig. 4. As shown in Fig. 4, the first sensor unit 7 has a sensor case 3, a sensor bracket 4, and an ultrasonic sensor 5. The ultrasonic sensor 5 has a transmitting and receiving surface 41 at one end for transmitting and receiving ultrasonic waves, and is provided so that this transmitting and receiving surface 41 is positioned substantially in line with the outer wall of the measuring pipe 2.

[0037] The sensor bracket 4 is integrally molded from resin and holds the ultrasonic sensor 5 therein. A lead wire 46 connected to the ultrasonic sensor 5 protrudes from the rear surface of the ultrasonic sensor 5. The tip of this lead wire 46 is connected to a terminal 32 of the sensor bracket 4. The terminal 32 and the calculation display unit 6 are connected by a connection wire 47 arranged inside the piping 20.

[0038] The sensor case 3 can accommodate the sensor bracket 4 inside. The sensor bracket 4 has an attachment part 16 that corresponds to the attachment part 12 provided on the measuring pipe 2. The attachment part 16 has four through holes (not shown) formed at positions that correspond to the female threads 12d on the attachment surface 12c of the measuring pipe 2. When assembling the sensor part 7 to the measuring pipe 2, bolts are inserted into these through holes. 1 and 2) is inserted through the sensor case 3, and the bolt 51 is threaded into the female thread 12d on the mounting surface 12c of the measuring pipe 2. This fixes the sensor case 3 to the measuring pipe 2 in a direction perpendicular to the direction of the central axis C of the flow path 9.

[0039] [Configuration of second sensor unit 8] Next, the configuration of the second sensor unit 8 will be described with reference to Fig. 4. As shown in Fig. 4, the second sensor unit 8 has a sensor case 30, a sensor bracket 40, and an ultrasonic sensor 5. The ultrasonic sensor 5 has a wave transmitting and receiving surface 41 at one end for transmitting and receiving ultrasonic waves, and is provided so that the entire wave transmitting and receiving surface 41 protrudes into the flow path 9 beyond the outer wall of the measuring pipe 2. The pair of ultrasonic sensors 5 that make up the second sensor unit 8 have the same protrusion amount. In this embodiment, the entire ultrasonic sensor 5 protrudes into the flow path 9 beyond the outer wall of the measuring pipe 2.

[0040] This protrusion amount is appropriately set so that the measurement area of ​​the ultrasonic sensor 5 is approximately 50% to 80% of the diameter. Hereinafter, the radial length corresponding to this measurement area will also be simply referred to as the "sensor-to-sensor distance." The sensor-to-sensor distance D2 of the second sensor unit 8 (see FIG. 5) is shorter than the sensor-to-sensor distance D1 of the first sensor unit 7 (see FIG. 5). The ultrasonic sensors 5 of the first sensor unit 7 and the ultrasonic sensors 5 of the second sensor unit 8 are the same type of sensors with the same characteristics.

[0041] The configurations of the sensor case 30 and the sensor bracket 40 are functionally similar to those of the sensor case 3 and the sensor bracket 4 of the first sensor unit 7, but their shapes are different. In the second sensor unit 8, the ultrasonic sensor 5 is disposed inside the flow path 9 as described above, that is, at a position away from the outer wall and closer to the central axis C, so the axial length of the sensor case 30 is longer than that of the sensor case 3 of the first sensor unit 7. The mounting unit 13 of the measuring pipe 2 is configured to have a length and shape that allows the sensor case 30 to be held in a state where it is attached in a direction intersecting the central axis C.

[0042] 4, the lead wires connected to the ultrasonic sensor 5, the terminals of the sensor bracket 40, and the connecting wires are not shown because they have the same connection structure as those in the first sensor unit 7. As with the first sensor unit 7, the ultrasonic sensor 5 of the second sensor unit 8 and the calculation and display unit 6 are connected by connecting wires (not shown) arranged inside the piping 20. Furthermore, the sensor case 30 has an attachment part 26 that corresponds to the attachment part 13 provided in the measuring pipe 2, and, as with the sensor case 3 of the first sensor unit 7, is fixed to the measuring pipe 2 via the attachment part 13 with four bolts 52 (see FIGS. 1 and 2).

[0043] [How to assemble the ultrasonic flowmeter 1] Next, we will explain how to assemble the ultrasonic flowmeter 1 described above in detail. As an example, we will explain in detail the first sensor unit 7 as to how the sensor units 7 and 8 are attached to the measuring pipe 2. The second sensor unit 8 can also be attached in substantially the same way as the first sensor unit 7.

[0044] First, the ultrasonic sensor 5 is housed in the sensor bracket 4. Next, the lead wires 46 of the ultrasonic sensor 5 are soldered to the terminals 32 to establish electrical continuity. Next, with the sensor case 3 not attached to the measuring pipe 2, the sensor bracket 4 is housed and fixed in the sensor case 3 from the terminal 32 side. In other words, the ultrasonic sensor 5 is fixed to the sensor case 3. As a result of the above, the ultrasonic sensor 5, sensor bracket 4, and sensor case 3 are unitized.

[0045] Next, the unitized sensor case 3 is attached to the measuring pipe 2. Specifically, first, from the outside of the measuring pipe 2, the sensor case 3 is attached in a direction perpendicular to the central axis C of the measuring pipe 2. The sensor case 3 is fitted into the mounting hole 12a of the mounting portion 12 of the measuring pipe 2. Then, the mounting portion 16 of the sensor case 3 is brought into contact with the inner surface of the positioning portion 14, and the mounting surface 16c of the mounting portion 16 is brought into contact with the mounting surface 12c of the mounting portion 12.

[0046] Next, bolts 51 are inserted into the through holes (not shown) of the mounting portions 16 of the sensor cases 3, and the bolts 51 are screwed into the female threads 12d on the mounting surface 12c of the measurement pipe 2, thereby fixing the pair of sensor cases 3 to the measurement pipe 2 in a direction perpendicular to the central axis C. In a similar manner, the second sensor unit 8 is fixed to the measurement pipe 2. That is, the sensor case 30 is fixed to the measurement pipe 2 in a state in which the ultrasonic sensor 5, sensor bracket 40, and sensor case 30 are unitized. In this way, the pair of first sensor units 7 and the pair of second sensor units 8 are fixed to the outer wall of the measurement pipe 2.

[0047] Next, the display base 6a of the calculation and display unit 6 is attached to the mounting hole 11 of the measuring pipe 2. One end of the pipe 20 is connected to the sensor units 7 and 8. The other end of the pipe 20 is connected to the calculation and display unit 6, as shown in FIG. 1, and the other end of the connection wire 47 inside the pipe 20 is also connected to the calculation and display unit 6. This electrically connects the ultrasonic sensors 5 of each sensor unit 7 and 8 to the calculation and display unit 6, forming the ultrasonic flowmeter 1. The pipe 20 is pulled out from the sensor units 7 and 8 in a direction approximately parallel to the central axis C of the measuring pipe 2 and is provided to the calculation and display unit 6 so as to follow the outer circumferential surface of the measuring pipe 2.

[0048] [About drift detection] Next, the principle of detecting drift in the flow path 9 using the ultrasonic flowmeter 1 described above will be described. FIG. 5 is a diagram illustrating an example of the flow velocity distribution in the flow path 9 in a flow without drift, and FIG. 6 is a diagram illustrating an example of the flow velocity distribution in the flow path 9 in a flow with drift. FIG. 6 shows the flow velocity distribution immediately downstream of an L-shaped bent pipe as an example of a flow in which drift occurs. In each diagram, the magnitude of the flow velocity is indicated by the density of dots. That is, areas with higher flow velocity are illustrated as areas with higher dot density. In each diagram, the flow velocity at R1 is the largest, followed by R2, R3, R4, and R5 in that order. In each diagram, the horizontal direction is the X-axis, and the vertical direction perpendicular to the X-axis is the Y-axis.

[0049] As shown in Figure 5, the flow velocity in a flow without drift is greatest in the region close to the central axis C and gradually decreases as it moves from the central axis C toward the outer wall, that is, radially outward from the central axis C. On the other hand, as shown in Figure 6, the flow velocity distribution in a flow with drift is not constant, with the flow velocity being greatest in the region lower in the flow path and closer to the outer wall, and the flow velocity being lowest in some regions near the central axis C.

[0050] Here, we will explain an example of a comparative ultrasonic flowmeter having multiple measurement lines, in which two pairs of sensor units are both located on the wall surface. In the comparative ultrasonic flowmeter, all four ultrasonic sensors have part of their transmitting and receiving surfaces located on the wall surface and do not protrude into the flow path.

[0051] In a comparative ultrasonic flowmeter, when measuring a flow path with the flow velocity distribution shown in Figure 6, if the configuration is such that measurements are taken along two measurement lines shown as solid line S1 (12-6 o'clock direction) and solid line S2 (3-9 o'clock direction), a difference in flow rate occurs between the two measurement lines, making it possible to detect the occurrence of drift in the pipe. However, if the configuration is such that measurements are taken along two measurement lines shown as dashed two-dot line S3 (2-8 o'clock direction) and dashed two-dot line S4 (4-10 o'clock direction), no difference in flow rate occurs between the two measurement lines, making it impossible to determine whether a small value is measured compared to the true flow rate due to the influence of drift, or whether the small value is actually measured because the flow rate is low. In other words, even if there are multiple pairs of ultrasonic sensors, if all of the ultrasonic sensors are placed on the wall surface and the configuration is such that measurements are taken over the entire diameter of the flow path, it is not possible to determine whether a small value is measured due to the influence of drift. However, there are cases where the drift current cannot be detected correctly even if the above comparison is made.

[0052] While the above-described comparison examples are extreme, it is generally difficult for users to accurately determine the flow conditions in a pipe by comparing values ​​using multiple ultrasonic flowmeters or by using analytical or flow visualization methods. Therefore, when installing and using an ultrasonic flowmeter, users have no choice but to rely on the standard piping conditions recommended by the manufacturer and use the flowmeter with the assumption that no drift occurs, trusting that the flowmeter values ​​are correct. However, even under the standard piping conditions recommended by the manufacturer, it is not necessarily true that drift does not occur.

[0053] In this regard, in the ultrasonic flowmeter 1 of the first embodiment, the second sensor unit 8 measures an area that is narrower than the entire diameter of the flow path 9 and is closer to the central axis C of the flow path 9, as shown as area A2 in Figures 5 and 6, for example. For this reason, the measurement line acquired by the second sensor unit 8 is more significantly affected by drift in the flow path 9 than the measurement line acquired by the first sensor unit 7 that covers the entire diameter, as shown as area A1. Therefore, differences are likely to occur between the measurement values ​​of the measurement lines between the first sensor unit 7 and the second sensor unit 8, making it easy to detect drift in the measuring pipe 2.

[0054] Furthermore, the operation and effect of the ultrasonic flowmeter 1 of the first embodiment will be described in detail, citing the results of analysis by the inventors. FIG. 7 shows flow velocities obtained from two measurement lines and their ratios. In Table T shown in FIG. 7, the data shown in columns T1 and T2 are from an ultrasonic flowmeter of a comparative embodiment. T1 is data measured for a flow without drift, and T2 is data measured for a flow with drift. In Table T, the data shown in columns T3, T4, and T5 are from an ultrasonic flowmeter having a configuration corresponding to that of the ultrasonic flowmeter 1 of the first embodiment. "Corresponding to the configuration of the ultrasonic flowmeter 1 of the first embodiment" means a configuration in which, of the two pairs of sensor units, the ultrasonic sensors 5 of one pair of sensor units 7 are fixed to the outer wall of the measuring pipe 2, and the ultrasonic sensors 5 of the other pair of sensor units 8 are fixed to a position protruding into the flow path 9 of the measuring pipe 2.

[0055] T3 is data obtained by measuring a flow with no drift, with the measurement line taken by the second sensor unit 8 corresponding to the X direction. T4 is data obtained by measuring a flow with drift, with the measurement line taken by the second sensor unit 8 corresponding to the X direction. T5 is data obtained by measuring a flow with drift, with the measurement line taken by the second sensor unit 8 corresponding to the Y direction. In addition, "whole" in the "measurement area" column of Table T means that the entire diameter is the measurement area (see area A1 in Figures 5 and 6), and "protruding" means that only the center of the diameter, or approximately 50% of the diameter, is the measurement area (see area A2 in Figures 5 and 6).

[0056] The "ratio" in Table T indicates the ratio of the flow velocity measured from one of the X- and Y-direction measurement lines to the flow velocity measured from the other of the X- and Y-direction measurement lines. For example, the ratio "1.14" shown in the data for T3 indicates that the flow velocity value based on the X-direction measurement line (hereinafter simply referred to as the "X-direction flow velocity value") is 1.14 times the flow velocity value based on the Y-direction measurement line (hereinafter simply referred to as the "Y-direction flow velocity value"). The larger this ratio value, the greater the difference between the measured values ​​on the two measurement lines. The ratio value "1.14" shown in the data for T3 corresponds to an example of a "reference difference value" that is preset as a reference value for the difference between the flow velocity value measured by the first sensor unit 7 and the flow velocity value measured by the second sensor unit 8 in a flow without drift.

[0057] First, as shown in T1 and T2, we will explain the case where both measurement lines are configured to measure the entire diameter. As shown in T1, when there is no drift, the measured values ​​of the two measurement lines match and the ratio is "1". When there is drift, as shown in T2, the ratio in the X direction is "0.96" and the ratio in the Y direction is "1.04". When there is no drift, the ratio in either direction is "0.96". There is a 4% difference from the combined ratio of 1.00.

[0058] Next, we will explain the case where the X-direction measurement line measures a partial area, as shown in T3 and T4. As shown in T3, when there is no drift, the X-direction ratio is 1.14. As shown in T4, when there is drift, the X-direction ratio is 0.92. As shown in T5, when the Y-direction measurement line measures a partial area and there is drift, the Y-direction ratio is 0.92. That is, the ratio of the direction corresponding to the measurement line by the second sensor unit 8 protruding into the flow path 9 is 0.92, which is approximately 20% different from the ratio of 1.14 when there is no drift. As such, it can be seen that the configuration in which one measurement line protrudes into the flow path 9 is more susceptible to drift than a configuration in which no drift is present. The value indicating the ratio of 0.92 in the data of T4 and T5 corresponds to an example of a "measurement difference value."

[0059] As described above, the presence or absence of drift in the flow path 9 can be detected by comparing the reference difference value, which is the ratio of two measurement lines that serve as a reference when no drift occurs, with the measurement difference value, which is the ratio of two measurement lines. As a specific example, if there is a difference between the reference difference value and the measurement difference value that is equal to or greater than a predetermined value, it can be determined that drift exists in the measurement pipe. For example, the predetermined value can be set to "0.14" in the above example, and if the measurement difference value is below "1.0," it can be determined that "drift exists." Note that while the "predetermined value" is "0.14" in the above example, it can be appropriately set to a value that is predicted to be highly likely to have drift through experiments or the like, depending on the usage environment, such as the type of fluid being measured.

[0060] When calculating the flow rate after installing the ultrasonic flowmeter 1 in a location with an appropriate flow and no drift, correction is performed by multiplying the measured value by a weighting factor that is predetermined according to the areas A1 and A2 (distances D1 and D2 between the sensors) to be measured by the ultrasonic sensor 5. Then, the flow rate is calculated by taking the average of the measured values ​​from the sensor units 7 and 8, or by selecting the measured values ​​from an appropriate measurement line.

[0061] The ultrasonic flowmeter 1 of the first embodiment has the above-described structure and thereby provides the following functions and effects.

[0062] In the ultrasonic flowmeter 1 of the first embodiment, the ultrasonic sensor 5 of the first sensor unit 7 is disposed so that at least a part of its wave transmitting and receiving surface 41 is located on the outer wall of the measuring pipe 2. On the other hand, the ultrasonic sensor 5 of the second sensor unit 8 is disposed so that the entire wave transmitting and receiving surface 41 protrudes into the flow path 9 beyond the outer wall of the measuring pipe 2. The inter-sensor distance D2 of the second sensor unit 8 is shorter than the inter-sensor distance D1 of the first sensor unit 7.

[0063] That is, the first sensor unit 7 measures the entire diameter of the flow path 9, whereas the second sensor unit 8 measures an area closer to the center of the flow path 9, which is narrower than the entire diameter of the flow path 9. For this reason, the measurement line acquired by the second sensor unit 8 is more significantly affected by drift in the measurement pipe 2 than the measurement line acquired by the first sensor unit 7. Therefore, differences are likely to occur between the measurement values ​​of the measurement lines between the first sensor unit 7 and the second sensor unit 8, making it easy to detect drift in the measurement pipe 2.

[0064] In the ultrasonic flowmeter 1 of the first embodiment, the calculation and display unit 6, which also functions as a drift detection and notification unit, can notify the user that a drift has been detected, and therefore can indicate to the user whether the installation state of the ultrasonic flowmeter 1 is appropriate. This allows the user to know whether the flow in the flow path 9 is appropriate for flow rate measurement without having to compare values ​​using multiple ultrasonic flowmeters or analyze or visualize the flow in the measuring pipe 2. This notification allows the user to take appropriate measures, such as re-installing the ultrasonic flowmeter 1 in another location where there is no drift.

[0065] For example, there may be a case where a valve is located upstream of the measuring pipe 2 to which the ultrasonic flowmeter 1 is attached, and the valve is only partially open, causing a drift in the measuring pipe 2. In such a case, the calculation display unit 6 of the ultrasonic flowmeter 1 once attached will display the detection of the drift, allowing the user to check the open / closed state of the valve and correct it. Then, once the drift has been eliminated, the ultrasonic flowmeter 1 can be attached to the same location again and used in a state where it can measure correctly.

[0066] The ultrasonic flowmeter 1 of the first embodiment can relatively easily measure fluids (e.g., natural gas) containing difficult-to-measure gases, such as carbon dioxide and hydrogen, through which ultrasonic signals propagate. For example, when measuring natural gas, which has an unstable composition, conventional ultrasonic flowmeters for gases may become unable to measure the gas if the concentration of the difficult-to-measure gas exceeds a certain level and the ratio of the components increases. "Natural gas" is primarily composed of methane and contains large amounts of carbon-hydrogen compounds, such as butane and propane, and may also contain carbon dioxide and hydrogen. Since natural gas is extracted and used as is, the ratio of the above components is not necessarily constant. In particular, large-diameter flowmeters, such as those with a diameter exceeding 100 mm, are prone to becoming unable to measure the gas due to the influence of the difficult-to-measure gases.

[0067] In this regard, in the first embodiment, the pair of ultrasonic sensors 5 that make up the second sensor unit 8 protrude into the flow path 9, and the measurement area A2 (distance D2 between the sensors) by the second sensor unit 8 is approximately 50% to 80% of the entire diameter. This makes it possible to improve the signal detection performance of the natural gas in the second sensor unit 8 without significantly changing the frequency or signal strength of the ultrasonic sensor 5. Note that when measurement is performed using only the second sensor unit 8 in this way, there is a risk of a decrease in accuracy, but it is possible to continue measuring the flow rate, albeit with lower accuracy.

[0068] Furthermore, if a signal can be acquired by the second sensor unit 8 but a signal cannot be acquired by the first sensor unit 7, this can be interpreted as a change in the composition of the measured gas. To detect a change in gas composition, it is common to calculate the speed of sound from an ultrasonic signal or use a dedicated sensor such as a composition meter. However, according to the first embodiment, changes in gas composition can be easily detected without relying on these methods. Furthermore, when calculating the speed of sound, if the ultrasonic signal is attenuated, it becomes impossible to detect, and providing a separate dedicated sensor increases costs. However, the first embodiment can solve these problems.

[0069] Furthermore, as described above, the first sensor unit 7 and the second sensor unit 8 can use the same ultrasonic sensor 5, eliminating the need to use multiple types of ultrasonic sensors with different characteristics. This means there is no need to select an ultrasonic sensor with a dedicated frequency for the type of gas being measured and then build circuits and software to match it. This makes the flowmeter highly versatile and enables measurement of difficult-to-measure gases at low cost. Furthermore, because the ultrasonic signal is not amplified to compensate for attenuation, it can be used with large-diameter ultrasonic flowmeters without being subject to limitations on power consumption or oscillator input voltage. While increasing the input voltage may not meet explosion-proof certification requirements, the first embodiment described above can be configured in a way that does not affect explosion-proof certification.

[0070] <Other embodiments> In the first embodiment, the protrusion amount of the ultrasonic sensor 5 of the second sensor unit 8 may be set to a distance that allows measurement of the anticipated difficult-to-measure gas composition. In other words, the inter-sensor distance of the second sensor unit 8 may be determined based on the distance at which the target gas can be measured. The measurable distance is constant for each type of gas, regardless of the diameter.

[0071] For example, the ease of propagation of an ultrasonic signal in a particular gas varies with the gas parameters. Typical gas parameters are, for example, temperature (negative correlation), pressure (positive correlation), and the distance between the transmitting and receiving ultrasonic sensors (negative correlation). Therefore, once the type of gas to be measured and the minimum pressure and maximum temperature specifications are determined, the maximum distance between sensors at which ultrasonic signals can be measured, i.e., flow rate can be measured, is uniquely determined.

[0072] A more specific example will be used. For example, in the environment in which the ultrasonic flowmeter 1 is used, if the natural gas to be measured is expected to contain 10% carbon dioxide as the worst possible condition, then it is assumed that measurement is possible for natural gas containing 10% carbon dioxide if the sensor-to-sensor distance is up to 90 mm. In this case, the first sensor unit 7, in which the ultrasonic sensor 5 is disposed on the wall surface, will be unable to measure a measurement pipe 2 with a diameter exceeding 90 mm.

[0073] However, the second sensor unit 8 can perform measurements even when 10% carbon dioxide is mixed in. In this way, the distance between the sensors may be determined according to the expected conditions of the usage environment, and then the protrusion amount of the ultrasonic sensor 5 of the second sensor unit 8 may be set.

[0074] In the ultrasonic flowmeter 1 of the first embodiment, the installation form of each of the sensor units 7, 8 can be changed in various ways. For example, as shown in Fig. 8, the sensor units 7, 8 may be disposed in the measuring pipe 2 so that the measurement lines of the sensor units 7, 8 are perpendicular to each other in a side view seen from the direction of the central axis C. Note that Fig. 8 shows a simplified schematic diagram of the configuration of each of the sensor units 7, 8.

[0075] The ultrasonic flowmeter 1 of the first embodiment has two pairs of sensor units 7 and 8, but may have three or more pairs of sensor units. The plurality of pairs of sensor units may have at least a pair of first sensor units 7 and a pair of second sensor units 8.

[0076] Furthermore, in a configuration having multiple second sensor units 8, the amount of protrusion of the ultrasonic sensor 5 into the flow path 9, i.e., the distance between the sensors, may be different for each second sensor unit 8. As described above, the type and state of gas that can be measured by each sensor unit differs depending on the distance between the sensors, so by varying the distance between the sensors, it is possible to detect changes in the composition of different types of desired measurement gases at the multiple second sensor units 8.

[0077] In the ultrasonic flowmeter 1 of the first embodiment, if there is a difference of a predetermined value or more between the flow velocity value measured by the first sensor unit 7 and the flow velocity value measured by the second sensor unit 8, it is determined that there is drift in the flow path 9. In other words, the "ratio of flow velocity values" is used as the "reference difference value" that is a value related to the difference between the flow velocity values ​​measured by the sensor units 7 and 8. Alternatively, drift may be detected using, for example, the difference in flow velocity values ​​without calculating the ratio.

[0078] In the ultrasonic flowmeter 1 of the first embodiment, when drift is detected, the fact is displayed on the monitor 6b of the calculation and display unit 6 so that it is visually recognizable. However, the fact that drift has been detected may also be notified to the outside by a buzzer, voice, or other sound.

[0079] In the ultrasonic flowmeter 1 of the first embodiment, the measuring pipe 2, the flange 10, the mounting portions 12 and 13 of the sensor portions 7 and 8, and the display base 6a may be individually manufactured and welded together, or may be integrally constructed by casting or the like.

[0080] In the ultrasonic flowmeter 1 of the first embodiment, the arrangement of the mounting portions 12, 13 of the sensor units 7, 8 can be changed as appropriate. For example, as shown in Figures 9 and 10, the mounting portions 12, 13 of the sensor units 7, 8 may be arranged on the same plane passing through the central axis C of the measuring pipe 2. Alternatively, as shown in Figures 11 and 12, the mounting portions 12, 13 of the sensor units 7, 8 may be arranged on a plane perpendicular to the central axis C of the measuring pipe 2.

[0081] Furthermore, for example, as shown in FIG. 12 in the above configuration, the measurement lines of the sensor units 7 and 8 do not have to pass through the central axis C in a side view seen from the direction of the central axis C.

[0082] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in each embodiment corresponding to the technical features in the form described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0083] 1:Ultrasonic flowmeter 2: Measuring tube 3,30: Sensor case 4,40: Sensor bracket 5: Ultrasonic sensor 6: Calculation display unit (calculation processing unit, drift detection unit, drift detection notification unit, natural gas measurement unit) 7: First sensor section 8: Second sensor section 9: Flow path 10: Flange 20: Piping

Claims

1. a measuring tube having a flow path through which a fluid flows; At least two pairs of sensor units each having an ultrasonic sensor are located on the upstream side and the downstream side of the flow path and are provided in the measuring pipe so as to be capable of transmitting and receiving ultrasonic signals; a calculation processing unit that calculates a flow rate of the fluid based on a flow velocity value measured using a difference in propagation time between the pair of ultrasonic sensors; Equipped with The sensor unit a pair of first sensor units each of which is arranged such that at least a part of a transmitting and receiving surface of the ultrasonic sensor is positioned on an outer wall of the measuring pipe; a pair of second sensor units each of which is disposed such that the entire transmitting and receiving surface of the ultrasonic sensor is positioned so as to protrude into the flow path beyond the outer wall of the measuring pipe; An ultrasonic flow meter comprising:

2. a drift detection unit for detecting whether or not a drift occurs in the measuring pipe, The drift detection unit 2. The ultrasonic flowmeter according to claim 1, wherein the presence or absence of drift in the measuring pipe is detected using a measurement difference value which is a value relating to the difference between the flow velocity value measured by the first sensor unit and the flow velocity value measured by the second sensor unit.

3. 3. The ultrasonic flowmeter according to claim 2, further comprising a drift detection notification unit that notifies an external device that a drift has been detected when the drift detection unit detects a drift in the measuring pipe.

4. The drift detection unit 4. The ultrasonic flowmeter according to claim 2, wherein the measured differential value is compared with a reference differential value that is set in advance as a reference value for the difference between the flow velocity value measured by the first sensor unit and the flow velocity value measured by the second sensor unit in a flow without drift, and when there is a difference between the reference differential value and the measured differential value that is equal to or greater than a predetermined value that is set in advance, it is detected that drift exists in the measuring pipe.

5. Further provided is a natural gas measurement unit that measures the flow rate of natural gas in the measurement pipe, The natural gas measurement unit 3. The ultrasonic flowmeter according to claim 1, wherein the flow rate of the natural gas in the measuring pipe is measured using the flow velocity value obtained by the second sensor unit.

6. 3. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic sensor of the first sensor unit and the ultrasonic sensor of the second sensor unit are the same type of sensor having the same characteristics.

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