JP7462271B2 - Ultrasonic Flow Meter - Google Patents

Description

The present invention relates to reducing measurement errors in ultrasonic flowmeters.

Conventionally, in ultrasonic flowmeters, there has been a known technique for reducing measurement errors caused by vortexes that occur in a cavity formed in front of an ultrasonic transmitter/receiver in a mounting hole for mounting the ultrasonic transmitter/receiver (see, for example, Patent Document 1).

Figure 8 shows the configuration of the mounting holes for the ultrasonic transmitter/receiver of the ultrasonic flowmeter described in Patent Document 1.

As shown in FIG. 8(a), in this flowmeter 100, ultrasonic transmitters and receivers 102 and 103 arranged in a measurement flow path 101 are obliquely attached to mounting holes 114 and 115, so that cavities 104 and 105 are formed in front of the ultrasonic transmitters and receivers 102 and 103 between the flow path and the ultrasonic transmitters and receivers 102 and 103. The insides of the cavities 104 and 105 are divided by dividing members 106 and 107.

That is, cavity 104 is divided into divided passages 104a, 104b, and 104c, and cavity 105 is divided into divided passages 105a, 105b, and 105c. In this case, dividing members 106 and 107 are formed in a direction that blocks the flow inside cavities 104 and 105.

In this configuration, the flow velocity of the flow F passing through the measurement flow path 101 tends to generate large vortices throughout the entire cavity inside the cavities 104 and 105, but the dividing members 106 and 107 divide the insides of the cavities 104 and 105 into smaller portions, making it difficult for vortices to occur, and the dividing passages 104a, 104b, 104c, 105a, 105b, and 105c act as inflow inhibitors to reduce the inflow of fluid, resulting in a configuration that reduces the occurrence of errors.

Also, as another example of a configuration using a divided member, the configuration shown in Figure 8(b) is presented.

Figure 8(b) shows the opening hole of the measurement flow path surface 111 (corresponding to the measurement flow path surface 108 in Figure 8(a)) viewed from the vertical direction inside the flow path, and in this case, the cavity 109 is divided into three divided flow paths, divided passages 109a, 109b, and 109c, by a dividing member 110. In this case, the dividing member 110 is formed inside the cavity 109 in the same direction as the flow. Here, only one of the cavities 109 with an ultrasonic transmitter/receiver attached is shown, but the other is similar.

Even in this configuration, the inside of the cavity is divided into small parts, and the divided flow paths act as inflow inhibitors to reduce the flow of fluid, thereby reducing the occurrence of measurement errors due to the effects of vortices generated in the cavity.

JP 2004-101542 A

However, in the conventional configuration, the measures to reduce measurement errors caused by the effects of vortices generated in the cavity were limited to the inside of the cavity, and there was an issue in that they did not take into account the flow near the cavity, which has a significant effect on the flow inside the cavity.

The present invention takes into account the flow near the cavity and aims to keep the flow conditions inside the cavity constant regardless of the flow velocity, making corrections easier and reducing errors.

In order to solve the above-mentioned problems, the ultrasonic flowmeter of the present invention comprises a measurement flow path with a rectangular cross section, a pair of ultrasonic transmitters and receivers arranged on the short sides of the rectangular cross section so that ultrasonic waves cross the measurement flow path diagonally, a propagation time measurement unit that measures the propagation time of ultrasonic waves between the pair of ultrasonic transmitters and receivers, a calculation unit that calculates the flow rate from the propagation time measured by the propagation time measurement unit, and a dividing plate arranged parallel to the long side of the measurement flow path so as to divide the cavity formed between the pair of ultrasonic transmitters and the measurement flow path and the vicinity of the cavity in the measurement flow path. This makes it possible to keep the flow conditions in the cavity constant regardless of the flow velocity, making corrections easier and improving measurement accuracy.

The flow rate measuring device of the present invention extends a part of a dividing plate arranged parallel to the long side of the measurement flow path in the measurement flow path section in front of the cavity formed between a pair of ultrasonic transmitter/receivers and the measurement flow path so as to divide the inside of the cavity, and keeps the flow conditions in the cavity constant regardless of the flow velocity, making correction easier and reducing the amount of correction, thereby reducing errors in the cavity.

FIG. 1 is a schematic configuration diagram of a measurement unit of an ultrasonic flowmeter according to a first embodiment of the present invention. (a) is a block diagram of an ultrasonic flowmeter according to a first embodiment of the present invention; (b) is a cross-sectional view taken along the line CC' of (a); (a) is a partial perspective view of the vicinity of the cavity 8, and (b) is a view taken along the arrow B in (a). FIG. 1 is an explanatory diagram of an error that occurs when there is no dividing plate in the AA′ cross-sectional view in the first embodiment of the present invention. In the first embodiment of the present invention, the flow state diagram near the cavity when there is no dividing plate is shown. FIG. 1 shows another embodiment of the present invention. FIG. 1 shows another embodiment of the present invention. FIG. 1 is a cross-sectional view showing the configuration of a conventional ultrasonic flowmeter.

The first invention comprises a measurement flow path with a rectangular cross section, a pair of ultrasonic transmitters and receivers arranged on the short sides of the rectangular cross section so that ultrasonic waves cross the measurement flow path diagonally, a propagation time measurement unit that measures the propagation time of ultrasonic waves between the pair of ultrasonic transmitters and receivers, a calculation unit that calculates the flow rate from the propagation time measured by the propagation time measurement unit, and a dividing plate arranged parallel to the long side of the measurement flow path so as to divide a cavity formed between the pair of ultrasonic transmitters and the measurement flow path and the vicinity of the cavity in the measurement flow path, thereby making it possible to keep the flow conditions in the cavity constant regardless of the flow velocity, making corrections easier and improving measurement accuracy.

The second invention, particularly in the invention of claim 1, sets the interval between the divided flow paths divided by the dividing plate as a representative length, and sets the interval so that the Reynolds number determined by the representative length and the maximum flow velocity to be measured results in laminar flow, thereby reducing the amount of correction and improving measurement accuracy.

Below, the embodiments will be described in detail with reference to the drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of already well-known matters or duplicate explanation of substantially the same configuration may be omitted.

The accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

(Embodiment 1)
The first embodiment will be described with reference to FIGS. 1 to 3. FIG.

Figure 1 is a perspective view showing the schematic configuration of the measurement unit of an ultrasonic flowmeter in embodiment 1 of the present invention.

In Figure 1, the measurement section 1 of the ultrasonic flowmeter is composed of a measurement flow path 2 with a rectangular cross section and an ultrasonic transmitter/receiver holding section 3. The measurement flow path 2 is formed by an upper surface 2a and a lower surface 2b on the short side of the rectangular cross section, and a side surface 2c and a side surface 2d on the long side of the rectangular cross section.

Figure 2(a) is a block diagram of the ultrasonic flowmeter 14, the measuring unit 1 shows the AA' cross section of Figure 1, and Figure 2(b) is a CC' cross section of Figure 2(a).

The ultrasonic transmitter-receiver holder 3 attached to the top of the measurement flow path 2 has ultrasonic transmitter-receiver mounting holes 4 and 5, and ultrasonic transmitter-receivers 6 and 7 are attached to the respective mounting holes 4 and 5. The ultrasonic transmitter-receivers 6 and 7 are attached at an angle to the flow direction of the measurement flow path 2 so that they transmit ultrasonic waves at a predetermined angle, so that cavities 8 and 9 are formed between the ultrasonic transmitter-receivers 6 and 7 and the measurement flow path 2 in the transmission direction of the ultrasonic signals from the ultrasonic transmitter-receivers 6 and 7. Dividing plates 10 and 11 that divide the measurement flow path 2 are provided on the measurement flow path 2 near the cavities 8 and 9, i.e., on the upper surface 2a side. The dividing plate 10 has dividing plate extensions 10a and 10b, and the dividing plate 11 has dividing plate extensions 11a (not shown) and 11b, and are formed to divide the insides of the cavities 8 and 9, respectively. The height m of the dividing plates 10 and 11 is approximately the same size as the opening width w of the cavity 8. In addition, the length of the dividing plates 10 and 11 in the flow direction is from near the upstream end of cavity 8 to near the downstream end of cavity 9.

One of the ultrasonic transmitters 6 and 7 is set on the transmitting side, and the other on the receiving side. The ultrasonic transmitter set on the transmitting side is driven by a drive signal to transmit an ultrasonic signal, and the ultrasonic transmitter set on the receiving side receives the ultrasonic signal. Then, by alternately switching the ultrasonic transmitters 6 and 7 between the transmitting side and the receiving side, ultrasonic waves are transmitted and received from the ultrasonic transmitters and receivers 6 to the ultrasonic transmitters and receivers 7, or in the opposite direction, via the ultrasonic propagation paths UP1 to UP2 (shown by dashed lines). At this time, the lower surface 2b of the measurement flow path 2 acts as a reflecting surface for the ultrasonic waves.

The ultrasonic reception signals generated by the ultrasonic transmitters and receivers 6 and 7 set on the receiving side are processed by the processing means 12 to obtain the ultrasonic propagation time, and then the calculation means 13 performs calculation processing to obtain the flow velocity or flow rate.

The measurement unit 1, the processing means 12, and the calculation means 13 constitute the ultrasonic flowmeter 14.

The processing means 12 performs the processes required for measuring the propagation time of ultrasonic waves, such as switching between transmitting and receiving the ultrasonic transmitters 6 and 7, outputting the drive signal, and amplifying the received signal.

Figure 3(a) is a partial perspective view of the vicinity of cavity 8 in Figure 2, and Figure 3(b) is a view from the direction of arrow B.

Dividing plates 10 and 11 are arranged in the measurement flow path 2 near the cavity 8.

In FIG. 3(a), in order to avoid cluttering the drawing, the thickness of the dividing plates 10 and 11 is omitted and shown by dotted lines, but in reality, they have a thickness t, as shown in FIG. 3(b).

As shown in FIG. 3(b), the measurement flow path 2 is divided by dividing plates 10 and 11 to form divided flow paths 15, 16, and 17. In this example, the intervals h1, h2, and h3 between these divided flow paths 15, 16, and 17 are uniform. If these values are h, the dimension of h is set so that, when h is the representative length and the maximum flow velocity in this ultrasonic flowmeter is Vmax, the Reynolds number at the maximum flow velocity is approximately 2300 or less, i.e., laminar flow.

Although not shown here, the area near cavity 9 in Figure 2 has a similar configuration.

In this embodiment, the intervals h1, h2, and h3 of the divided flow paths 15, 16, and 17 are configured to be equal, but even if they are unequal, the largest dimension among them is taken as the representative length, and when the maximum flow velocity in this flowmeter is taken as Vmax, the Reynolds number at the maximum flow velocity may be set to be approximately 2300 or less, i.e., laminar flow.

To explain the operation of this configuration, we will first use Figures 4 and 5 to explain the flow conditions in the cavities and the errors that occur in the cavities when there are no dividing plates 10, 11 near the cavities 8, 9.

Figure 4 shows a measurement flow path similar to that shown in Figure 2, but without dividing plates 10, 11 in cavities 8, 9. The symbols in this figure are the same as those in Figure 2, and their explanations are omitted.

First, we will use Figure 4 to explain the flow measurement method and the causes of errors in the cavity.

Let V be the flow velocity of the fluid flowing through the measurement flow path 2, C be the speed of sound in the fluid, and θ be the angle between the direction of the fluid flow and the direction of ultrasonic propagation until the ultrasonic wave is reflected by the lower surface 2b.

The ultrasonic propagation paths of the ultrasonic waves propagating between the ultrasonic transmitter/receiver 6 and the ultrasonic transmitter/receiver 7 are UP1 and UP2 shown by the dashed lines in Figure 3. If each point on the ultrasonic propagation paths UP1 and UP2 of the ultrasonic waves is defined as the transmission plane P1 of the ultrasonic transmitter/receiver 6, the boundary between the cavity 8 and the measurement flow path 2 as P2, the reflection point as P3, the boundary between the cavity 9 and the measurement flow path 2 as P4, and the transmission plane P5 of the ultrasonic transmitter/receiver 7, then the ultrasonic propagation paths UP1 and UP2 can be broken down into P1-P2-P3-P4-P5.

Here, P1 to P2 is the ultrasonic propagation path inside the cavity 8, and its length is L1. Next, P2 to P3 is the ultrasonic propagation path from leaving the cavity 8 to being reflected by the lower surface 2b of the measurement flow path 2, and its length is L2.

Next, P3 to P4 are the ultrasonic propagation paths that the ultrasonic waves take after being reflected by the lower surface 2b until they reach the cavity 9, and their length is L3. After that, P4 to P5 are the ultrasonic propagation paths within the cavity 9, and their length is L4. After passing through these ultrasonic propagation paths, the ultrasonic waves reach the ultrasonic transmitter/receiver 7.

Now, if we assume that the total length of the path from P1 to P5, from when the ultrasonic wave leaves ultrasonic transmitter/receiver 6 until it reaches ultrasonic transmitter/receiver 7, is L, then L is given by the following formula.

L = L1 + L2 + L3 + L4 (1)
At this time, the propagation time t1 required for the ultrasonic wave emitted from the ultrasonic transmitter/receiver 6 to reach the other ultrasonic transmitter/receiver 7 is expressed by the following formula.

t1=L/(C+Vcosθ) (2)
Next, the propagation time t2 required for the ultrasonic wave emitted from the ultrasonic transmitter/receiver 7 to reach the other ultrasonic transmitter/receiver 6 is expressed by the following formula.

t2=L/(C-Vcosθ) (3)
By eliminating the sound speed C of the fluid from equations (2) and (3), the following equation is obtained.

V = (L / 2 cos θ) (1 / t1 - 1 / t2) (4)
As can be seen from equation (4), if L and θ are known, the flow velocity V can be found using the propagation times t1 and t2 measured by the processing means 12.

Next, the flow rate q through the measurement flow path 2 is calculated by multiplying this flow velocity V by the cross-sectional area S of the measurement flow path 2 as shown in the formula below.

q = k x V x S (5)
Here, k is a correction coefficient for converting the flow velocity V obtained as above into a correct flow velocity, taking into consideration that the flow velocity V obtained as above contains various errors.

For example, the propagation times t1 and t2 calculated using the above equations (2) and (3) contain errors because they include the propagation times in cavities 8 and 9, respectively.

Substituting equation (1) into equations (2) and (3) and rearranging, we get the following equation.

t1=((L2+L3)/(C+Vcosθ))+(L1/(C+V1cosθ))
+(L2/(C+V2cosθ)) (6)
t2=((L2+L3)/(C-Vcosθ))+(L1/(C-V1cosθ))
+(L2/(C-V2cosθ)) (7)
Here, V1 and V2 represent the flow velocities in cavities 8 and 9, respectively.

In equations (6) and (7), the second term represents the propagation time within cavity 8, and the third term represents the propagation time within cavity 9.

As can be seen from these equations, if no flow occurs in cavities 8 and 9, then V1 = V2 = 0, so the accurate propagation time can be obtained by simply subtracting the elapsed time for the ultrasonic wave to pass through cavities 8 and 9 from t1 and t2.

However, if a flow occurs within cavities 8 and 9, a propagation time will occur according to the flow conditions, and if the propagation time within cavities 8 and 9 cannot be determined, an error will occur.

Next, using Figure 5, we will explain the flow conditions near cavities 8 and 9 when cavities 8 and 9 do not have dividing plates 10 and 11.

Figure 5 shows the flow conditions near cavities 8 and 9 in Figure 4.

Figure 5 (a) shows the state when the flow velocity is small, and then Figure 5 (b) and Figure 5 (c) show the state when the flow velocity increases in that order.

As shown in FIG. 5(a), when the flow velocity is low, the viscous force of the fluid is greater than the inertial force, so the flows near cavities 8 and 9 become flows Sa1 and Sa2 that flow into cavities 8 and 9 and then exit.

When the flow velocity in FIG. 5(c) is high, the inertial force is greater than the viscous force of the fluid, so the flow does not flow into cavities 8 and 9, but becomes flows Sc1 and Sc2, and closed vortices Vc1 and Vc2 are formed within cavities 8 and 9.

Figure 5(b) shows a flow velocity intermediate between that of Figure 5(a) and Figure 5(c), where a flow Sb1 flows into cavity 8 on the upstream side, but a vortex Vb2 is generated by flow Sb2 on the downstream side.

In the explanation above using Figure 4, it was explained that errors occur in the propagation time due to the influence of the flow inside cavities 8 and 9. In light of Figure 5, when the flow velocity is small, i.e., in the state of Figure 5(a), the error is caused by the flow into cavities 8 and 9. On the other hand, when the flow velocity is large, i.e., in the state of Figure 5(c), the error is caused by vortexes inside cavities 8 and 9. As can be seen by comparing these two cases, the flow conditions inside the cavities are completely different depending on the flow velocity, and the methods for correcting the errors are different. In other words, it is necessary to use different correction methods depending on the flow velocity.

Furthermore, in the case of intermediate flow velocity (b), the flow conditions in the upstream cavity 8 and the downstream cavity 9 are different, making the handling of error correction even more complicated.

Next, the operation of this embodiment will be explained using Figures 3 and 5.

In FIG. 3(b), when the flow velocity in the measurement flow path 2 is small, if the flow velocities passing through the divided flow paths 15, 16, and 17 divided by the dividing plates 10 and 11 are F1, F2, and F3, these flow in the same manner as in FIG. 5(a), and all of them flow into the cavity 8.

Next, when the flow velocity increases, if the dividing plates 10 and 11 were not present, the flow would be as shown in (b) and (c) in Figure 5, and the flow in the cavity 8 would transition from an inflow state to a vortex formation. However, in the case of this embodiment, because the dividing plates 10 and 11 are present, this does not happen.

In other words, the flow in the divided flow passages 15, 16, and 17 separated by the dividing plates 10 and 11 has a Reynolds number set so that the flow is laminar at the maximum flow velocity, so the flow does not generate vortices and remains in an inflow state as shown in Figure 5 (a) until the maximum flow velocity is reached.

This makes it easier to correct errors caused by the flow that occurs within cavity 8, since the flow conditions do not change depending on the flow velocity.

In addition, by making the flow inside the cavity 8 laminar, the resistance to the inflow itself increases, so the amount of inflow is reduced, and even if an error does occur, the amount of error can be reduced.

The above describes cavity 8, but the same can be said about the downstream cavity 9, which is not shown in Figure 3.

As described above, according to this embodiment, by keeping the flow conditions in cavities 8 and 9 constant regardless of the flow velocity, correction is made easier and the amount of correction can be reduced, thereby reducing errors in cavities 8 and 9.

In this embodiment, the height m of the dividing plate 10 is approximately the same as the opening width w of the cavity 8, but m may be any value greater than that, and may extend to the height M of the measurement flow path 2 shown in FIG. 2.

The length of the dividing plates 10 and 11 in the flow direction is from near the upstream end of cavity 8 to near the downstream end of cavity 9, but it can be longer than that and can extend to the length from the inlet to the outlet of the measurement flow path 2 shown in Figure 2.

Other Embodiments
As described above, the first embodiment has been described as an example of the technology disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made.

Therefore, other embodiments are given below as examples.

Figure 6(a) shows a cross-sectional view of the measurement section when a dividing plate is provided in the multilayer flow path, and Figure 6(b) shows a DD' cross-sectional view. Note that the same reference numerals as in embodiment 1 have the same structure, and the description will be omitted.

In FIG. 6, the configuration of the measurement unit 21 is the same as in embodiment 1, but the measurement flow path 22 is divided into three multi-layered flow paths 25a, 25b, and 25c by two partition plates 23 and 24. Furthermore, flow path 25b is divided by dividing plates 10 and 11 near the cavity 9.

In this embodiment 1, the measurement flow path 2 is a single layer, but even in a multi-layer flow path as shown in Figure 6, the same effect can be achieved by providing a dividing plate in each layer under the same conditions as described in embodiment 1.

Although the number of dividing plates is two in the above example, the present invention is not limited to this. The same effect can be achieved even if there is one dividing plate or three or more dividing plates, as long as the spacing between the divided flow paths is the same as described above.

Figure 7 is a cross-sectional view showing a measurement section in which an ultrasonic transmitter/receiver is arranged corresponding to the measurement flow path. Note that the same reference numerals as in embodiment 1 have the same structure, and the description will be omitted.

In FIG. 7, the measurement unit 31 is arranged so that the ultrasonic transmitter/receiver 6 held by the ultrasonic transmitter/receiver holder 33 and the ultrasonic transmitter/receiver 7 held by the ultrasonic transmitter/receiver holder 37 face each other on the opposing sides of the measurement flow path 32 with a rectangular cross section.

In the first embodiment, a pair of ultrasonic transmitters and receivers are arranged on the same surface of the measurement flow path, and ultrasonic waves transmitted from one ultrasonic transmitter and receiver are reflected on the opposing surface and received by the other ultrasonic transmitter and receiver, which is the so-called V-path method. In the present embodiment, however, a pair of ultrasonic transmitters and receivers are arranged on opposing surfaces of the measurement flow path, and ultrasonic waves are transmitted and received directly, which is the so-called Z-path method.

The measurement flow path 32 is divided by two dividing plates 35 near the cavity 8 and inside the cavity 8, and by two dividing plates 36 near the cavity 9 and inside the cavity 9.

Therefore, if the dividing plate is provided under the same conditions as described in embodiment 1, the same effect can be achieved.

As described above, the ultrasonic flowmeter of the present invention has a dividing plate disposed in the measurement flow path in front of the cavity that divides the inside of the cavity as well, which keeps the flow conditions within the cavity constant regardless of the flow velocity, facilitating correction and reducing errors in the cavity. This makes it possible to use the ultrasonic flowmeter as a flowmeter that requires high measurement accuracy, such as domestic and commercial gas meters and industrial flowmeters.

2, 22, 32 Measurement flow path 2a Top surface (short side)
2c Side (long side)
6, 7 Ultrasonic transmitter/receiver 8, 9 Cavity 10, 11, 35, 36 Dividing plate 10a, 10b, 11a, 11b Dividing plate extension portion 12 Processing means (propagation time measuring portion)
13 Calculation means 14 Ultrasonic flow meter 15, 16, 17 Divided flow path

Claims (2)

A measurement flow path having a rectangular cross section;
a pair of ultrasonic transducers disposed on the short sides of the rectangular cross section so that ultrasonic waves obliquely cross the measurement flow path;
a propagation time measuring unit that measures a propagation time of an ultrasonic wave between the pair of ultrasonic transmitters and receivers;
A calculation unit that calculates a flow rate from the propagation time measured by the propagation time measurement unit;
a dividing plate disposed parallel to a long side of the measurement flow path so as to divide a cavity formed between the pair of ultrasonic transmitter/receivers and the measurement flow path and a vicinity of the cavity of the measurement flow path;
An ultrasonic flow meter equipped with An ultrasonic flowmeter as described in claim 1, in which the interval between the divided flow paths divided by the dividing plate is set as a representative length, and the interval is set so that the Reynolds number determined by the representative length and the maximum flow velocity measured is a laminar flow.