Patent Description:
As a conventional ultrasonic flowmeter of this type, for example, an ultrasonic flowmeter of PTL <NUM> is known. <FIG> are diagrams illustrating a conventional ultrasonic flowmeter disclosed in PTL <NUM>. <FIG> is a perspective view of the conventional ultrasonic flowmeter. <FIG> is a view taken in the direction of arrow S in <FIG> is a view taken in the direction of arrow T in <FIG>. <FIG> is a cross sectional view taken along line 13D-13D of <FIG>. <FIG> is a cross sectional view taken along line 13E-13E of <FIG>.

As illustrated in <FIG>, particularly <FIG>, the ultrasonic flowmeter is disposed in measurement flow path <NUM> having a rectangular cross-section in which a pair of ultrasonic transducers respectively including first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> are disposed. Entrainment flow suppression sheet <NUM> having opening portions <NUM>, <NUM> smaller than the openings of recessed portions <NUM>, <NUM> is disposed in a path extending from the ultrasonic transmission surfaces of first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> to measurement flow path <NUM>. Suppression sheet <NUM> can suppress attenuation of ultrasonic waves, suppress generation of vortex flows p and q in recessed portions <NUM>, <NUM>, which cause a measurement error, and secure the measurement accuracy.

<CIT> discloses: A method for setting a flow quantity measurement device provided with a main flow path having a rectangular cross-section, a plurality of flow paths formed by disposing a plurality of partition plates in layers in the main flow path, a pair of ultrasonic wave transceivers disposed in an upstream part and a downstream part of a measurement flow path that is a flow path among the plurality of flow paths, a propagation time measurement means for measuring the propagation time of ultrasonic waves between the pair of ultrasonic wave transceivers, and a flow quantity calculation means for calculating the actual flow quantity by multiplying a measured flow quantity by a correction factor is provided with: a step (A) of predicting the correction factor throughout a measured flow quantity range from the flow velocity distribution of an entrance part of the main flow path; and a step (B) of, on the basis of the correction factor predicted in step (A), setting the length of the flow path in the direction in which the partition plates are stacked in layers such that the correction factor is constant throughout the measured flow quantity range.

Recently, there is an increasing demand for a gas meter incorporating an ultrasonic flowmeter for measuring a gas flow rate for general household use and for business use for, for example, large and small stores and other facilities. In response to this increasing demand, there is a need for an ultrasonic flowmeter having a flow path having a size corresponding to a gas flow rate to be measured.

For example, in the conventional ultrasonic flowmeter disclosed in PTL <NUM>, the flow paths through which a measurement target fluid flows have substantially the same rectangular cross sectional shapes. That is, when the total number of flow paths including measurement flow path <NUM> is three, the three flow paths have cross sectional shapes with the same width and height. However, assume that in such a configuration, in order to measure a larger gas flow rate, the total number of flow paths is five by adding two flow paths. In this case, two flow paths having the same width and height as those of the existing flow paths are added. This poses a problem that an external size of the ultrasonic flowmeter is remarkably increased, and it is difficult to mount the ultrasonic flowmeter in a gas meter box housing the ultrasonic flowmeter. Note that the total number of measurement flow paths <NUM> shown in <FIG> is four.

An ultrasonic flowmeter according to the present disclosure includes a fluid flow path through which a measurement target fluid flows, a pair of ultrasonic transducers disposed upstream and downstream of an upper portion of the fluid flow path and configured to transmit and receive an ultrasonic signal, and a flow rate calculator configured to calculate a flow rate of the measurement target fluid based on a propagation time from when the ultrasonic signal transmitted from one of the pair of ultrasonic transducers propagates through the measurement target fluid to when the other of the pair of ultrasonic transducers receives the ultrasonic signal. The fluid flow path includes a main flow path including a plurality of divided flow paths obtained by dividing a flow path having a rectangular cross-section by the same width, and a sub flow path including an added flow path having a cross-section having the same width as that of the divided flow path and having a height lower than that of the divided flow path. Furthermore, flow rate calculator calculates the flow rate of the measurement target fluid flowing through the fluid flow path from the flow velocity or flow rate of the measurement target fluid obtained based on the propagation time.

According to this configuration, since each rectangular added flow path of the sub flow path has the same width as the rectangular shape of each flow path of the measurement flow path and has a low height, the external size of the ultrasonic flowmeter can be made relatively compact, and highly accurate measurement can be implemented even for measurement of a measurement target fluid with a large flow rate.

According to the present disclosure, it is possible to provide an ultrasonic flowmeter that can implement highly accurate measurement while having a compact outer shape when measuring a measurement target fluid of a larger flow rate.

Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.

<FIG> is a perspective view of an ultrasonic flowmeter according to a first exemplary embodiment of the present disclosure. <FIG> is a view taken in a direction of arrow A in <FIG> is a view taken in the direction of arrow B in <FIG>. <FIG> is a cross sectional view taken along line 1D-1D of <FIG>. <FIG> is a cross sectional view taken along line 1E-1E of <FIG>. <FIG> is an enlarged view of <FIG>.

As illustrated in <FIG> and <FIG>, ultrasonic flowmeter <NUM> includes flow path body <NUM> in which fluid flow path <NUM> through which a measurement target fluid flows is configured. A pair of ultrasonic transducers including first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> that can transmit and receive ultrasonic signals are disposed upstream and downstream of an upper portion of fluid flow path <NUM>. The ultrasonic flowmeter further includes flow rate calculator <NUM> that measures the flow velocity or flow rate of a fluid to be contacted based on the propagation time from when the ultrasonic signal transmitted from one of the pair of ultrasonic transducers including first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> propagates through a measurement target fluid to when the ultrasonic signal is received by the other ultrasonic transducer.

In fluid flow path <NUM>, measurement flow path <NUM>, which is a main flow path having a rectangular flow cross-section, is divided by partition plates 20a, 20b, and 20c and constitutes a plurality of divided flow paths 5a, 5b, 5c, and 5d having same width w and same height h. The fluid flow path <NUM> is provided with sub flow paths 22a, 22b constituted with added flow paths 24a, 24b, 24c, and 24d which have rectangular cross-sections having same width w as that of divided flow paths 5a, 5b, 5c, and 5d constituting measurement flow path <NUM> and having height lower than height h of divided flow paths 5a, 5b, 5c, and 5d. Measurement flow path <NUM> as a main flow path and sub flow path 22a are divided by sub partition plate 23a, and measurement flow path <NUM> as a main flow path and sub flow path 22b are divided by sub partition plate 23b. Sub flow path 22a is provided with added flow paths 24a, 24b which are divided by sub partition plate 23c and have rectangular cross-sections which have the same width w as that of divided flow paths 5a, 5b, 5c, and 5d and having a height lower than height h of divided flow paths 5a, 5b, 5c, and 5d. Sub flow path 22b is provided with added flow paths 24c, 24d which are divided by sub partition plate 23d and have rectangular cross-sections which have the same width w as that of divided flow paths 5a, 5b, 5c, and 5d and having a height lower than height h of divided flow paths 5a, 5b, 5c, and 5d.

Flow path body <NUM> includes trumpet-shaped inlet portion 19a into which the measurement target fluid flows and outlet portion 19b from which the measurement target fluid flows out, and may have, for example, a structure made by resin injection molding. Partition plates 20a, 20b, and 20c and sub partition plates 23a, 23b, 23c, and 23d are made of, for example, stainless metal plates and have same plate thickness t, which is about <NUM>, as illustrated in <FIG>. Partition plates 20a, 20b, and 20c and sub partition plates 23a, 23b, 23c, and 23d are attached to flow path body <NUM>.

<FIG> is an exploded perspective view of a flow path body and each partition plate according to the first exemplary embodiment of the present disclosure. <FIG> is a cross sectional view taken along line 3B-3B of <FIG>. <FIG> is a view taken in the direction of arrow C in <FIG>.

As illustrated in <FIG>, inflow-side fixing grooves 29a, 29b, 29c, 29d, 29e, 29f, and <NUM> and outflow-side fixing grooves 30a, 30b, 30c, 30d, 30e, 30f, and <NUM> are provided on the reflecting surface <NUM> side of a space through which the measurement target fluid flows. Reflecting surface <NUM> is a flat surface by which an ultrasonic signal transmitted from one of the pair of ultrasonic transducers including first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> is reflected to cause the ultrasonic signal to propagate through the measurement target fluid and reach the other ultrasonic transducer.

As shown in <FIG>, inflow-side slits 27a, 27b, 27c, 27d, 27e, 29f, and <NUM> and outflow-side slits 28a, 28b, 28c, 28d, 28e, 28f, and <NUM> are provided on entrainment flow suppression sheet installation surface <NUM> side of flow path body <NUM>.

In this case, inflow-side fixing grooves 29a to <NUM>, outflow-side fixing grooves 30a to <NUM>, inflow-side slits 27a to <NUM>, and outflow-side slits 28a to <NUM> all have the same width and a thickness of, for example, about <NUM>, which is slightly larger than plate thicknesses t of partition plates 20a to 20c and sub partition plates 23a to 23d. Further, as for the shapes of partition plates 20a to 20c and the sub partition plates 23a to 23d, as indicated by the shape of sub partition plate 23d in <FIG>, two protruding portions 23e are provided.

In the structure as described above, when partition plates 20a to 20c and sub partition plates 23a to 23d are attached to flow path body <NUM>, as illustrated in <FIG>, they are inserted from the entrainment flow suppression sheet installation surface <NUM> side. Protruding portions 23e of partition plates 20a to 20c and sub partition plates 23a to 23d are fitted into respective inflow-side fixing grooves 29a to <NUM> and respective outflow-side fixing grooves 30a to <NUM>, whereas the portions of the respective partition plates and the respective sub partition plates which are opposite to protruding portions 23e are sandwiched between inflow-side slits 27a to <NUM> and outflow-side slits 28a to <NUM> and fixed by clearance fit.

In this case, flow path body <NUM>, partition plates 20a to 20c, and sub partition plates 23a to 23d are configured as separate parts and are fixed and integrated by clearance fit. However, for example, partition plates 20a to 20c, sub partition plates 23a to 23d, and flow path body <NUM> may be configured to be integrally molded with resin.

<FIG> is a perspective view of ultrasonic flowmeter <NUM> according to the first exemplary embodiment of the present disclosure. As illustrated in <FIG>, first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> are set at predetermined positions of resin ultrasonic transducer fixing body <NUM> and fixed by resin ultrasonic transducer fixtures <NUM>. Projections 31a are provided on the ultrasonic transducer fixing body <NUM> side, and fitting holes 33a provided on the ultrasonic transducer fixture <NUM> side are fitted on the projections, thereby sandwiching and fixing first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> between ultrasonic transducer fixing body <NUM> and ultrasonic transducer fixtures <NUM>. Signal lines 6a, 7a of first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> are connected to flow rate calculator <NUM>.

Ultrasonic transducer unit <NUM> assembled in this manner is attached to an upper portion of flow path body <NUM> through entrainment flow suppression sheet <NUM>. Ultrasonic transducer fixing body <NUM> can be attached to flow path body <NUM> by, for example, thermal welding as long as both the components are made of a resin.

As illustrated in <FIG>, divided flow paths 5a, 5b, 5c, and 5d of measurement flow path <NUM> each have a rectangular cross sectional shape having width w and height h and are interposed between partition plates 20a, 20b, and 20c having same plate thickness t. Added flow path 24a of sub flow path 22a has a rectangular cross sectional shape with width w and height h2. Added flow path 24b has a rectangular cross sectional shape with width w and height h1. Added flow path 24a and added flow path 24b sandwich sub partition plate 23c having plate thickness t. Added flow path 24d of sub flow path 22b has a rectangular cross sectional shape with width w and height h2. Added flow path 24c has a rectangular cross sectional shape with width w and height h1.

In this case, with respect to the height, h2 < h1 < h is set so that the flow passage cross-section of fluid flow path <NUM> falls within circle F indicated by the dotted line. Added flow path 24d and added flow path 24c sandwich sub partition plate 23d having plate thickness t. Measurement flow path <NUM> and sub flow path 22a sandwich sub partition plate 23a having plate thickness t. Measurement flow path <NUM> and sub flow path 22b sandwich sub partition plate 23b having plate thickness t. Sub flow path 22a and sub flow path 22b are arranged so as to be symmetric with respect to widthwise center line X and heightwise center line Y of measurement flow path <NUM>.

The first function and effect of the ultrasonic flowmeter according to the first exemplary embodiment of the present disclosure will be described first.

<FIG> illustrates a flow path configuration diagram of ultrasonic flowmeter <NUM> using flow path body <NUM> to which a flow path is added to measure a larger gas flow rate in the conventional ultrasonic flowmeter according to PTL <NUM>. An example of a fluid flow path is illustrated in which sub flow path 52a having two flow paths and sub flow path 52b having two sub flow paths are added to measurement flow path <NUM> having four flow paths, thus having a total of eight flow paths. In this case, the rectangular cross sectional shapes of flow paths 54a, 54b of added sub flow path 52a and flow paths 54c, 54d of added sub flow path 52b are configured to have same width w and same height h as those of flow paths 45a, 45b, 45c, and 45d of measurement flow path <NUM>. That is, this corresponds to a case in which h = h1 = h2 is set in the first exemplary embodiment.

<FIG> is a comparison diagram between outlet portion 35b which is a view taken along arrow E of ultrasonic flowmeter <NUM> in which the outer diameter of outlet portion 35b is set to ΦD2 illustrated in <FIG> and outlet portion 19b, illustrated in <FIG> and <FIG>, which is a view taken along arrow B of ultrasonic flowmeter <NUM> in which the outer diameter of outlet portion 19b is set to ΦD1 according to the first exemplary embodiment illustrated in <FIG>. In ultrasonic flowmeter <NUM> according to the first exemplary embodiment, fluid flow path <NUM> falls within circle F indicated by the dotted line, whereas in ultrasonic flowmeter <NUM>, fluid flow path <NUM> falls within circle G larger than circle F. Circle F and circle G correspond to the minimum diameter of flow path body <NUM> necessary for internally forming a fluid flow path. That is, as can be seen from <FIG>, ΦD1 < ΦD2 is set, and according to ultrasonic flowmeter <NUM> according to the first exemplary embodiment of the present disclosure, a compact configuration can be implemented by arranging sub flow path 22a and sub flow path 22b in minimum circle F including measurement flow path <NUM>.

The second function and effect of ultrasonic flowmeter <NUM> according to this exemplary embodiment will be described next.

As illustrated in <FIG>, which is a view taken along arrow B in <FIG>, in ultrasonic flowmeter <NUM> according to the present exemplary embodiment, added sub flow path 22a and added sub flow path 22b are arranged so as to be vertically and horizontally symmetrical with respect to widthwise center line X and heightwise center line Y of measurement flow path <NUM>, including same plate thickness t of partition plates 20a, 20b, and 20c and sub partition plates 23a, 23b, 23c, and 23d.

In ultrasonic flowmeter <NUM>, the pair of ultrasonic transducers including first ultrasonic transducer <NUM> and second ultrasonic transducer <NUM> are disposed upstream and downstream of an upper portion of fluid flow path <NUM>. The ultrasonic flowmeter computes the flow velocity or flow rate of a measurement target fluid based on the propagation time from when the ultrasonic signal transmitted from one of the pair of ultrasonic transducers propagates through the measurement target fluid to when the ultrasonic signal is received by the other ultrasonic transducer. Accordingly, since an ultrasonic signal propagates only to the measurement flow path, the flow velocity or flow rate of a measurement target fluid passing through added sub flow path 22a and added sub flow path 22b is not directly measured.

Accordingly, as for the flow rate of a measurement target fluid passing through measurement flow path <NUM>, sub flow path 22a, and sub flow path 22b, the flow rate of the entire measurement target fluid including sub flow path 22a and sub flow path 22b is calculated from the measurement result obtained in measurement flow path <NUM> that directly measures the passing measurement target fluid.

For example, the flow rate can be calculated by multiplying the flow path cross-sectional area (the sum of the flow path cross-sectional areas of measurement flow path <NUM>, sub flow path 22a, and sub flow path 22b) of fluid flow path <NUM> by the flow velocity of the measurement target fluid obtained in measurement flow path <NUM>. The ratios between the flow rate of measurement flow path <NUM> and the flow rates of sub flow path 22a and sub flow path 22b may be obtained in advance. The flow rates of sub flow path 22a and sub flow path 22b may be calculated from the flow rate of measurement flow path <NUM> and added together. However, in any case, the flow velocities of measurement flow path <NUM>, sub flow path 22a, and sub flow path 22b are preferably the same even when the flow rate changes.

Therefore, the flow velocity distribution of a measurement target fluid passing through measurement flow path <NUM>, sub flow path 22a, and sub flow path 22b needs to be as uniform as possible. In the present exemplary embodiment, since sub flow path 22a and sub flow path 22b are vertically and horizontally symmetrical with respect to measurement flow path <NUM>, a more uniform flow of the passing measurement target fluid can be implemented, and highly accurate measurement can be implemented.

Even if added sub flow path 22a and added sub flow path 22b are arranged vertically and horizontally symmetrically with respect to measurement flow path <NUM> and are also arranged within circle F of outlet portion 19b in the first exemplary embodiment described as "in the case illustrated in <FIG>" in the lower part of <FIG>, the measurement result may not be preferable.

<FIG> illustrate ultrasonic flowmeter <NUM> as an example of the above case. <FIG> is a flow path configuration diagram in a case in which a large flow rate can be measured by the conventional ultrasonic flowmeter. <FIG> is a cross sectional view taken along line 6B-6B of <FIG>. <FIG> is a view taken in the direction of arrow J in <FIG>.

As illustrated in <FIG>, in ultrasonic flowmeter <NUM>, sub flow path 37a and sub flow path 37b are arranged on the left and right of measurement flow path <NUM> so as to be vertically and horizontally symmetrical with respect to widthwise center line X and heightwise center line Y. However, the flow path cross-sectional shapes of sub flow path 37a and sub flow path 37b are substantially semicircular unlike the rectangles of divided flow paths 65a, 65b, 65c, and 65d of measurement flow path <NUM>, and the flow path cross-sectional areas of sub flow path 37a and sub flow path 37b are about <NUM> times larger than those of divided flow paths 65a to 65d of measurement flow path <NUM>.

<FIG> is a graph illustrating the flow rate measurement result obtained by ultrasonic flowmeter <NUM> illustrated in <FIG> in the form of actual flow rates and flow rate coefficients. In this case, a flow rate coefficient (k) is a coefficient for computing an actual flow rate from a measured flow rate and is defined as k = Qt/Qm when the actual flow rate is Qt and the measured flow rate is Qm. Note that measurement flow rate Qm is calculated as the total flow rate by multiplying the sum of the flow path cross-sectional areas of measurement flow path <NUM>, sub flow path 37a, and sub flow path 37b by the flow velocity obtained in measurement flow path <NUM>.

Flow rate coefficient k is ideally <NUM> with respect to actual flow rate Qt on the horizontal axis. In this case, the flow rate coefficient indicates that actual flow rate Qt of the passing measurement target fluid coincides with the flow rate of the entire measurement target fluid, including sub flow path 37a and sub flow path 37b, which is calculated from the flow rate measured by measurement flow path <NUM>. Therefore, it is ideal that flow rate coefficient k on the vertical axis changes in the vicinity of the value <NUM> with respect to actual flow rate Qt on the horizontal axis. This indicates that the measurement accuracy is high.

On the other hand, the result illustrated in <FIG> shows a transition in which flow rate coefficient k shows a value larger than <NUM> at the time of a small flow rate, and flow rate coefficient k gradually approaches <NUM> at the time of a large flow rate. This indicates that, at the time of a small flow rate, the flow rate of the entire measurement target fluid, including sub flow path 37a and sub flow path 37b, which is calculated from the flow rate actually measured in measurement flow path <NUM> is smaller than actual flow rate Qt, and hence the flow rate does not match actual flow rate Qt unless flow rate coefficient k larger than <NUM> is multiplied. This indicates that the measurement accuracy is low.

The reason is that since the flow path cross-sectional area of sub flow path 37a or sub flow path 37b is larger than that of divided flow paths 65a to 65d of measurement flow path <NUM>, the fluid does not flow to the measurement flow path <NUM> side having a large flow path resistance at the time of a small flow rate but easily flows to the sub flow path 37a or sub flow path 37b side having a small flow path resistance, and the flow does not become uniform, resulting in the large velocity distribution of the measurement target fluid. In addition, at the time of a large flow rate, the measurement target fluid does not sufficiently flow only by the flow path cross-sectional area of sub flow path 37a or sub flow path 37b, and hence flows also to the measurement flow path <NUM> side and gradually changes to a uniform flow.

Even if sub flow path 37a and sub flow path 37b added in this way are arranged vertically and horizontally symmetrically with respect to measurement flow path <NUM>, the measurement accuracy may not be preferable. It is important to make the flow velocity distribution of the measurement target fluid uniform as much as possible from the small flow rate region to the large flow rate region.

In contrast to this, <FIG> illustrates the flow rate measurement result obtained by ultrasonic flowmeter <NUM> according to the first exemplary embodiment of the present disclosure illustrated in <FIG> and <FIG>. According to <FIG>, flow rate coefficient k changes in the vicinity of <NUM> in the flow rate region from the small flow rate region to the large flow rate region, there is almost no change in flow rate coefficient as illustrated in <FIG>, and the characteristic of the flow rate coefficient is flat and the measurement accuracy is high. This is because the flow path widths of added flow paths 24a, 24b of sub flow path 22a and added flow paths 24c, 24d of sub flow path 22b are set to same width w as the flow path widths of divided flow paths 5a, 5b, 5c, and 5d of measurement flow path <NUM>, which is the main flow path, so that the difference in flow path resistance can be reduced.

As described above, according to the present exemplary embodiment, it is possible to provide an ultrasonic flowmeter that can implement highly accurate measurement while having a compact outer shape when measuring a measurement target fluid of a large flow rate.

In ultrasonic flowmeter <NUM> according to the first exemplary embodiment of the present disclosure illustrated in <FIG> and <FIG>, as indicated by arrow B in <FIG> shown in a lower part of <FIG>, the flow path height of added flow path 24b of sub flow path 22a and added flow path 24c of sub flow path 22b is selected as h1 and the flow path height of added flow path 24a of sub flow path 22a and added flow path 24d of sub flow path 22b is selected as h2 so as to fall within circle F. However, when the flow path width is set to width w, even if the flow path height is changed, highly accurate measurement can be performed.

<FIG> are configuration diagrams of ultrasonic flowmeter <NUM> according to the first modification. <FIG> is a cross sectional view taken along line 9B-9B of <FIG>. <FIG> is a view taken in the direction of arrow N in <FIG>.

Measurement flow path <NUM> includes divided flow paths 85a, 85b, and 85c having a rectangular cross-sectional shape with width w and height h with partition plate 90a and partition plate 90b interposed between the divided flow paths. Sub flow path 92a and sub flow path 92b are added to measurement flow path <NUM> with sub partition plate 93a and sub partition plate 93b interposed, respectively, and are configured to have a rectangular cross-sectional shape with width w and height h1.

<FIG> shows the flow rate measurement results obtained when flow path height h1 of sub flow path 92a and sub flow path 92b is changed. <FIG> is a graph illustrating flow rate coefficients with respect to the actual flow rates when flow path height h1 is set to <NUM>, <NUM>, <NUM>, and <NUM>. As can be seen from this graph, if the flow path widths of divided flow paths 85a, 85b, and 85c, sub flow path 92a, and sub flow path 92b of measurement flow path <NUM> are set to width w, there is no large difference in the results even when the flow path heights are changed to four different heights, and the measurement can be stably performed with high accuracy. Accordingly, when there is a restriction on the external size of the ultrasonic flowmeter, since the flow path height can be arbitrarily changed while the flow path widths are aligned with width w, flexible design can be performed.

The graph shown in <FIG> illustrates flow rate coefficient k when actual flow rate Qt falls within the range of <NUM>/h to <NUM>,<NUM>/h in ultrasonic flowmeter <NUM> according to the first modification. The solid line of the graph shown in <FIG> indicates flow rate coefficient k when the range of actual flow rate Qt is from <NUM>/h to <NUM>,<NUM>/h (inclusive) on the smaller flow rate side and flow path height h1 is <NUM>.

As can be seen from <FIG>, when flow path height h1 is <NUM>, actual flow rate Qt has a characteristic that flow rate coefficient k decreases both on the small flow rate region side and the large flow rate region side with a peak around <NUM>,<NUM>/h. In particular, the flow rate tends to remarkably decrease on the small flow rate region side. This indicates that the flow in measurement flow path <NUM> and sub flow paths 92a, 92b is nonuniform at the time of the small flow rate, and the measurement target fluid flows more on the measurement flow path <NUM> side. Accordingly, in consideration of further suppressing the fluctuation range of flow rate coefficient k to improve the measurement accuracy, studies have been made to increase the flow path cross-sectional areas of sub flow paths 92a, 92b in order to make the flow more uniform at the time of a small flow rate.

<FIG> are configuration diagrams of ultrasonic flowmeter <NUM> according to the second modification.

Referring to <FIG>, a difference from the shape of ultrasonic flowmeter <NUM> illustrated in <FIG> is that the shapes of sub flow paths 94a, 94b of ultrasonic flowmeter <NUM> are not rectangular but trapezoidal. That is, the flow path widths (the interval between parallel sides of the trapezoid) of sub flow paths 94a, 94b is set to same width w as the flow path widths of divided flow paths 86a, 86b, and 86c of measurement flow path <NUM>, the flow path heights are set such that the long side is set to same height h as the flow path heights of divided flow paths 86a, 86b, and 86c and the short side is set to height h1 shorter than height h, and the sides corresponding to the legs of the trapezoid are formed obliquely along the circle including divided flow paths 86a, 86b, and 86c. Therefore, the flow path cross-sectional areas of sub flow paths 94a, 94b according to the present modification can be made larger than those of the rectangular sub flow paths shown in <FIG>. As compared with the total flow path cross-sectional area in ultrasonic flowmeter <NUM> illustrated in <FIG>, the total flow path cross-sectional area in ultrasonic flowmeter <NUM> is increased by the areas of the four portions having the substantially triangular shapes, each indicated by the hatched lines in the enlarged view of <FIG>, each corresponding to one of the upper and lower end portions of sub flow paths 94a, 94b.

In addition, a difference from the structure shown in <FIG> is that flow path body <NUM>, partition plates 20a, 20b, and sub partition plates 23a, 23b shown in <FIG> are integrally molded using the same material (for example, a resin) in ultrasonic flowmeter <NUM> shown in <FIG>. Ultrasonic flowmeter <NUM> may be integrally molded using the same material including ultrasonic transducer fixing body <NUM> illustrated in <FIG>.

Referring to the enlarged view shown in <FIG>, which is the view taken in the direction of arrow Q in <FIG>, the added corners having the substantially triangular shape indicated by the hatching each have an appropriate substantially R shape. For example, in the case of integrally molding flow path body <NUM>, partition plates 91a, 91b, and sub partition plates 95a, 95b with a resin, it can be expected that the mold release resistance can be reduced.

The broken line in <FIG> indicates the flow rate measurement result obtained by ultrasonic flowmeter <NUM> configured as described above when, in particular, h1 = <NUM> is set. As can be seen from the graph of <FIG>, as compared with the solid line indicating the result obtained by ultrasonic flowmeter <NUM> illustrated in <FIG>, the fluctuation range of flow rate coefficient k is suppressed (approximately <NUM>% to approximately <NUM>%) particularly on the small flow rate side where actual flow rate Qt is <NUM>/h to <NUM>,<NUM>/h (inclusive). That is, the measurement accuracy is improved. This may be because a more uniform flow was able to be implemented in measurement flow path <NUM> and sub flow paths 94a, 94b at the time of a small flow rate due to an increase in the flow path cross-sectional areas of sub flow paths 94a, 94b.

Assume that ultrasonic flowmeter <NUM> shown in <FIG> is integrally formed, including ultrasonic transducer fixing body 31a, by resin molding using the same material. In this case, in the configuration as shown in <FIG>, the thickness of the resin becomes thick at the portion where flow path body 19a and ultrasonic transducer fixing body 31a are joined to each other. However, since the substantially triangular flow path cross-section increasing portion is provided on the upper side of each of sub flow paths 94a, 94b, the thickness of the resin becomes more uniform, so that it can be expected to implement resin molding with higher dimensional accuracy.

Accordingly, when there is a restriction on the external size of the ultrasonic flowmeter, it is basically considered that the cross-sectional shape of each sub flow path is formed into a rectangular cross-section by arbitrarily changing the flow path height upon aligning the flow path widths to width w. However, in order to implement more uniform flow and highly accurate measurement, sub flow paths 94a, 94b are arranged symmetrically with respect to measurement flow path <NUM>, which is a main flow path, while the cross-sectional shapes of sub flow paths 94a, 94b each are formed into a trapezoidal cross-section upon aligning the flow path widths of sub flow paths 94a, 94b to width w of divided flow paths 86a to 86c of measurement flow path <NUM> and the flow path height directions are made parallel within the range of predetermined values of the heights of divided flow paths 86a to 86c of measurement flow path <NUM>. This allows flexible design for implementing a uniform flow.

Claim 1:
An ultrasonic flowmeter (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a fluid flow path (<NUM>, <NUM>, <NUM>) through which a measurement target fluid flows;
a pair of ultrasonic transducers (<NUM>, <NUM>) disposed upstream and downstream of an upper portion of the fluid flow path and configured to transmit and receive an ultrasonic signal; and
a flow rate calculator (<NUM>) configured to calculate a flow velocity or flow rate of the measurement target fluid based on a propagation time from when the ultrasonic signal transmitted from one of the pair of ultrasonic transducers propagates through the measurement target fluid to when the ultrasonic signal is received by the other of the pair of ultrasonic transducers,
wherein
the fluid flow path includes:
a main flow path including a plurality of divided flow paths (5a, 5b, 5c, 5d, 85a, 85b, 85c, 86a, 86b, 86c) obtained by dividing a flow path having a rectangular cross-section by a same width; and
sub flow paths (22a, 22b, 92a, 92b, 94a, 94b) including an added flow path (24a, 24b, 24c, 24d) having a rectangular cross-section having the same width as the width of the divided flow path and a height lower than the height of the divided flow path, and
the flow rate calculator calculates a flow rate of the measurement target fluid flowing through the fluid flow path from the flow velocity or flow rate of the measurement target fluid obtained based on the propagation time,
wherein the sub flow paths are disposed within a smallest circle (F) including a flow path cross-section of the main flow path