JP7510682B2 - Guided wave ultrasonic flowmeter - Google Patents

Description

The present invention relates to a guided wave ultrasonic flowmeter that measures the flow rate of a fluid by propagating ultrasonic guided waves along the longitudinal direction of a straight tube.

Ultrasonic flowmeters are well known as devices for measuring the flow rate of fluids. In the case of conventional ultrasonic flowmeters, the tube that serves as the flow path is bent in order to place a pair of ultrasonic transducers facing each other. This has disadvantages such as large pressure loss and the occurrence of liquid pools. Under these circumstances, there is a strong demand for straight-type ultrasonic flowmeters that use straight tubes with no bent flow paths. Among straight-type ultrasonic flowmeters, several guided wave ultrasonic flowmeters have been proposed in the past that use ultrasonic guided waves that propagate along the longitudinal direction of the tube to measure the flow rate (see, for example, Patent Documents 1 and 2).

To give a specific example, a typical guided wave type ultrasonic flowmeter has a straight tube through which a fluid flows, and a pair of ultrasonic transducers are arranged on the outer surface of the tube. These ultrasonic transducers are, for example, annular, and are arranged at a distance from each other in the longitudinal direction of the tube. The area between the pair of ultrasonic transducers in the tube serves as a measurement section. When the fluid flows through the tube, an ultrasonic guided wave is transmitted from one ultrasonic transducer and received by the other ultrasonic transducer. This transmission and reception operation is performed in both the forward and reverse directions along the flow, and the flow rate is calculated by calculating the difference in propagation time of the ultrasonic guided wave.

Japanese Patent Application Laid-Open No. 10-122923 Japanese Patent Application Laid-Open No. 11-264750 JP 2020-60490 A

When a circular ultrasonic transducer is driven, ultrasonic guided waves are not only emitted from the inner end face facing the measurement section, but also from the outer end face that does not face the measurement section. In other words, ultrasonic guided waves not only propagate toward the receiving ultrasonic transducer used for measurement, but also propagate an equal amount in the opposite direction that is unrelated to measurement. For convenience, the former ultrasonic guided waves used for measurement are called "desired echoes," and the latter ultrasonic guided waves not used for measurement are called "unwanted echoes."

It is generally known that in guided wave ultrasonic flowmeters, the attenuation of ultrasonic guided waves is small. Therefore, unwanted echoes are not attenuated and are reflected back from the tube ends or joints, etc., and are superimposed on the waveform of the desired echo. This causes a decrease in measurement accuracy. Therefore, it has been desired to take some kind of measure to attenuate only the unwanted echoes without attenuating the desired echoes.

One possible measure to reduce the effects of unwanted echoes is to install an anti-vibration sheet made of an elastic material on the outer surface of the tube, or to install anti-vibration parts made of an elastic material (see, for example, Patent Document 3). However, even if an anti-vibration sheet is used, it is too thin to be expected to have a sufficient effect. Furthermore, simply using anti-vibration parts does not sufficiently suppress the effects of unwanted echoes, as the ultrasonic guided wave is reflected by the anti-vibration parts and returned. Furthermore, simply increasing the installation area of the anti-vibration sheet or anti-vibration parts may attenuate necessary echoes as well.

The present invention has been made in consideration of the above problems, and its purpose is to provide a guided wave type ultrasonic flowmeter that can improve measurement accuracy by reducing the influence of unnecessary echoes that are not used in measurement.

In order to solve the above problem, the invention described in claim 1 is an ultrasonic flowmeter that has a structure in which a pair of ultrasonic transducers are arranged on the outer peripheral surface of a straight tube through which a fluid flows, with the ultrasonic guided wave transmitted by one of the ultrasonic transducers propagating along the longitudinal direction of the tube in a measuring section located between the pair of ultrasonic transducers and received by the other ultrasonic transducer, thereby measuring the flow rate of the fluid. The gist of the invention is a guided wave type ultrasonic flowmeter that has a tube insertion hole penetrating a first end face and a second end face located on the opposite side thereof, and is provided with an elastic vibration-proof block fitted to the tube in an outer region of the measuring section of the tube, and is formed so that the contact area between the inner peripheral surface of the tube insertion hole and the outer peripheral surface of the tube increases from the first end face side to the second end face side.

Therefore, according to the invention described in claim 1, a vibration-proof block is fitted to the outside area of the measurement section of the tube. In this vibration-proof block, the contact area between the inner circumferential surface of the tube insertion hole and the outer circumferential surface of the tube increases from the first end face side to the second end face side. Therefore, the ultrasonic guided wave emitted toward the outside area of the measurement section enters the inside of the vibration-proof block without being reflected much by the first end face. In addition, since this vibration-proof block is a member made of an elastic body with a certain thickness, the ultrasonic guided wave that enters its interior is effectively attenuated. Therefore, it is possible to attenuate only the unnecessary echo without attenuating the necessary echo, and the influence of the unnecessary echo can be reduced.

The invention described in claim 2 is based on claim 1, and is characterized in that the tube insertion hole penetrates the center of the vibration-proof block, and the first end face side of the vibration-proof block is formed to have a cross-sectional shape that is rotationally symmetrical with respect to the central axis of the tube insertion hole.

Therefore, according to the invention described in claim 2, the thickness of the wall around the tube insertion hole in the vibration-proof block is ensured to be uniform and sufficient. Therefore, for example, when a pressing force is applied to the outer surface of the vibration-proof block, the force is applied evenly in the circumferential direction of the outer circumferential surface of the tube, making it difficult for the tube to bend.

The invention described in claim 3 is based on claim 1 or 2, and is characterized in that the vibration-proof block has a groove at the opening on the first end face side of the tube insertion hole.

Therefore, according to the invention described in claim 3, by forming a groove in the opening on the first end face side, the contact area between the inner circumferential surface of the tube insertion hole and the outer circumferential surface of the tube can be increased from the first end face side to the second end face side.

The invention described in claim 4 is based on any one of claims 1 to 3, and the vibration-proof block has a groove at the opening on the first end face side of the tube insertion hole, and the groove is a groove with a substantially V-shaped cross section formed in a part of the first end face so as to cross the opening on the first end face side.

Therefore, according to the invention described in claim 4, not only can such a groove be formed relatively easily, but the contact area can be gradually increased from the first end face side to the second end face side.

The invention described in claim 5 is based on any one of claims 1 to 4, in which the inner diameter of the tube insertion hole is set smaller than the outer diameter of the tube, and the tube is press-fitted into the tube insertion hole.

Therefore, according to the invention described in claim 5, the adhesion of the vibration-proof block to the outer peripheral surface of the tube is improved, so that ultrasonic guided waves can be reliably incident on the vibration-proof block and efficiently attenuated. In addition, with this configuration, the vibration-proof block can be easily assembled to the tube.

The gist of the invention described in claim 6 is that in any one of claims 1 to 5, the invention further includes an outer surface pressing member made of a material harder than the vibration isolation block and contacting and pressing against the outer surface of the vibration isolation block to reduce deformation of the vibration isolation block.

Therefore, according to the invention described in claim 6, the outer surface pressing member reduces the deformation of the vibration isolation block, thereby maintaining the adhesion of the vibration isolation block to the outer peripheral surface of the tube. As a result, ultrasonic guided waves can be reliably incident on the vibration isolation block and efficiently attenuated.

As described above in detail, the inventions described in claims 1 to 6 can provide a guided wave type ultrasonic flowmeter that can improve measurement accuracy by reducing the influence of unnecessary echoes that are not used in measurement.

1 is a perspective view showing an ultrasonic flowmeter according to an embodiment of the present invention; FIG. 1 is a cross-sectional view showing an ultrasonic flowmeter according to an embodiment. 1A is a perspective view of an anti-vibration block in an ultrasonic flowmeter according to an embodiment of the present invention; FIG. 1B is a cross-sectional view along the axial direction of FIG. 1A; FIG. 1C is a cross-sectional view along line A-A of FIG. 1B; FIG. 1D is a cross-sectional view along line B-B of FIG. 1B; and FIG. 1E is a cross-sectional view along line C-C of FIG. FIG. 13 is a perspective view of another vibration isolation block in the ultrasonic flowmeter according to the embodiment. 5 is a schematic partial cross-sectional view showing a state in which an outer surface pressing member is provided on the vibration-isolating block of FIG. 4 . FIG. 13 is a perspective view of yet another vibration isolation block in the ultrasonic flowmeter according to the embodiment. 7 is a perspective view showing a state in which an outer surface pressing member is provided on the vibration isolation block of FIG. 6 . 7 is a perspective view showing a state in which another outer surface pressing member is provided on the vibration isolation block of FIG. 6 . FIG. 1 is a schematic diagram of a test device for performing an evaluation test. 13A is a view of a vibration-isolating block according to another embodiment, seen from the first end face side, and FIG. 13B is a cross-sectional view taken along line DD of FIG.

Below, a guided wave type ultrasonic flowmeter according to one embodiment of the present invention will be described in detail with reference to Figures 1 to 5.

As shown in Figures 1 and 2, the ultrasonic flowmeter 11 of this embodiment is a device for measuring the flow rate of liquid flowing through a straight tube 12 by using ultrasonic guided waves that travel along the longitudinal direction of the tube 12. This ultrasonic flowmeter 11 is sometimes called a straight type ultrasonic flowmeter because it has a straight tube 12 as a flow rate measurement tube. The liquid flowing through the tube 12 can be any liquid and is not particularly limited, but in this embodiment, a heated high-temperature liquid (such as a semiconductor cleaning liquid) is flowed through the tube 12.

The tube 12 is made of a flexible resin, and in this example, is formed using tetrafluoroethylene perfluoroalkoxyethylene (PFA), a type of fluororesin. Of course, the tube 12 may be formed using a resin material other than PFA, such as polyvinyl chloride resin, silicone rubber, polyethylene resin, polybutadiene resin, polyurethane resin, polyolefin resin, polytetrafluoroethylene resin, etc.

As shown in Figs. 1 and 2, the ultrasonic flowmeter 11 includes a pair of ultrasonic transducers 21A and 21B. These ultrasonic transducers 21A and 21B are disposed on the outer peripheral surface 13 of the tube 12. For convenience, the ultrasonic transducer located on the left side in Figs. 1 and 2 is referred to as the first ultrasonic transducer 21A, and the ultrasonic transducer located on the right side in Figs. 1 and 2 is referred to as the second ultrasonic transducer 21B. The first ultrasonic transducer 21A and the second ultrasonic transducer 21B are disposed apart from each other along the longitudinal direction of the tube. Both ultrasonic transducers 21A and 21B in this embodiment are annular and have the same dimensions. Specifically, these ultrasonic transducers 21A and 21B are piezoelectric elements formed using piezoelectric ceramics such as lead zirconate titanate (PZT). The annular ultrasonic transducers 21A and 21B have a central hole 24, and the inner peripheral surface of the central hole 24 is in close contact with the outer peripheral surface 13 of the tube 12. At this time, the inner peripheral surface of the central hole 24 and the outer peripheral surface 13 of the tube 12 may be in direct contact and in close contact, or may be in close contact via a coupling material layer that functions as an acoustic matching layer, or may be in close contact via an adhesive layer.

The area between the pair of ultrasonic transducers 21A, 21B in the tube 12 is the measurement section 31. Each of these ultrasonic transducers 21A, 21B has a first side end face 22 and a second side end face 23. The first side end face 22 of the first ultrasonic transducer 21A and the first side end face 22 of the second ultrasonic transducer 21B are arranged opposite each other while facing the measurement section 31. The second side end face 23 of the first ultrasonic transducer 21A and the second side end face 23 of the second ultrasonic transducer 21B do not face the measurement section 31, and are arranged so as to face the opposite direction to the direction in which the measurement section 31 is located (i.e., the outer area 32 of the measurement section 31).

Next, the electrical configuration of the ultrasonic flowmeter 11 will be described with reference to FIG. 1.

The ultrasonic flowmeter 11 is equipped with a measurement control device 41. The measurement control device 41 is a device for calculating the flow rate of the liquid flowing through the tube 12 by driving a pair of ultrasonic transducers 21A, 21B to transmit and receive signals within the measurement unit 31. The measurement control device 41 of this embodiment is equipped with a signal processing unit 42, a calculation processing unit 43, an input device 44, a display device 45, etc. The signal processing unit 42 includes a circuit that outputs a drive signal for driving the pair of ultrasonic transducers 21A, 21B, etc.

The frequency at which the pair of ultrasonic transducers 21A and 21B are driven is not particularly limited as long as it is a high frequency, but it is necessary that the frequency is capable of exciting ultrasonic guided waves. In this embodiment, the frequency is set to, for example, 200 kHz to 500 kHz, and preferably to 230 kHz to 300 kHz.

The calculation processing unit 43 is a processing circuit including a conventionally known CPU 46 and memory 47. The memory 47 stores control programs and data, and the CPU 46 performs calculation processing and display processing of the flow rate based on the control program stored in the memory 47.

The input device 44 also has various operation buttons for starting and ending the measurement, setting the display mode, etc. The display device 45 is, for example, a liquid crystal display, and displays the flow rate calculated by the calculation processing unit 43.

Next, we will explain the measurement operation of the ultrasonic flowmeter 11 configured in this way.

The flow rate is measured when the liquid flows in a predetermined direction in the tube 12. For example, the liquid flows from the left to the right in FIG. 1 and FIG. 2. In this case, the first ultrasonic transducer 21A is the ultrasonic transducer located on the upstream side, and the second ultrasonic transducer 21B is the ultrasonic transducer located on the downstream side. The CPU 46 drives the pair of ultrasonic transducers 21A and 21B via the signal processing unit 42 to alternately transmit and receive ultrasonic guided waves. Specifically, the CPU 46 first drives the first ultrasonic transducer 21A on the upstream side to transmit ultrasonic guided waves, and propagates the ultrasonic guided waves in the positive direction of the flow in the measuring unit 31 along the tube longitudinal direction. Then, the ultrasonic guided waves propagated in the positive direction of the flow are received by the second ultrasonic transducer 21B. The CPU 46 then measures the propagation time of the ultrasonic guided waves in the positive direction. Next, the CPU 46 drives the second ultrasonic transducer 21B on the downstream side to emit an ultrasonic guided wave, and the ultrasonic guided wave propagates in the measurement unit 31 along the tube longitudinal direction in the opposite direction to the flow. The ultrasonic guided wave propagating in the opposite direction to the flow is received by the first ultrasonic transducer 21A. The CPU 46 then measures the propagation time of the ultrasonic guided wave in the opposite direction. The measurement of the forward propagation time and the measurement of the reverse propagation time may be repeated multiple times. Next, the CPU 46 inputs the forward propagation time and the reverse propagation time from the signal processing unit 42 into the calculation processing unit 43, and calculates the flow velocity of the liquid based on the difference in the propagation times. The calculation processing unit 43 then further calculates the flow rate from this flow velocity. The display unit 45 then displays the calculated flow rate value.

When the annular ultrasonic transducers 21A and 21B are driven, the ultrasonic guided wave is not only emitted from the first side end face 22 facing the measurement unit 31, but also from the second side end face 23 not facing the measurement unit 31. In other words, the ultrasonic guided wave includes a desired echo emitted from the first side end face 22 and an unwanted echo emitted from the second side end face 23. In this embodiment, in order to attenuate only the unwanted echo without attenuating the desired echo, the ultrasonic flowmeter 11 has the following vibration-proof structure.

As shown in Figures 1 to 3, the ultrasonic flowmeter 11 includes a pair of vibration-proof blocks 51. The vibration-proof blocks 51 are members that are attached to prevent the ultrasonic vibration of the unnecessary echo from being superimposed on the ultrasonic vibration of the necessary echo (preventing unnecessary vibration). The vibration-proof block 51 of this embodiment is a rectangular block-shaped member (specifically, a substantially hexahedral shape) and has a first end face 51a and a second end face 51b located on the opposite side. Four side faces 51c are located between the first end face 51a and the second end face 51b. The vibration-proof block 51 has a tube insertion hole 52. The tube insertion hole 52 has a circular cross section and passes through the center of the vibration-proof block 51 to penetrate between the first end face 51a and the second end face 51b. The diameter of the tube insertion hole 52 is not particularly limited and can be set arbitrarily, but is set, for example, to about 20% to 50% of the length of one side of the rectangular first end face 51a and second end face 51b. In this embodiment, the diameter is set to about 30%, so that a wall thickness larger than the diameter is ensured over the entire periphery of the tube insertion hole 52. Incidentally, the volume of the vibration isolation block 51 (which depends on the axial dimension of the tube insertion hole 52 and the radial dimension of the tube insertion hole 52) is generally better if it is large, as long as it does not result in an increase in the size of the entire device.

The vibration-proof block 51 is formed from an elastic material, specifically, from a rubber material having suitable elasticity. Examples of rubber materials that can be used for the vibration-proof block 51 include natural rubber, synthetic natural rubber, styrene butadiene rubber, butadiene rubber, chloroprene rubber, butyl rubber, nitrile rubber, ethylene-propylene rubber, chlorosulfonated polyethylene rubber, acrylic rubber, urethane rubber, silicone rubber, fluororubber, and polysulfide rubber. In this embodiment, fluororubber, which has excellent heat resistance and chemical resistance, is selected as the rubber material. The hardness of the rubber material is not particularly limited, but for example, a rubber material having a hardness of 50 degrees or more and 80 degrees or less is used. If the hardness is too low, there is a risk that sufficient pressing force cannot be applied to the tube when the vibration-proof block 51 is brought into close contact with the tube. If the hardness is too high, there is a risk that the adhesion to the tube will be poor. In addition, the tolerance of the outer diameter of the tube 12 cannot be absorbed, and there is a risk that the vibration-proof effect will vary. In this embodiment, fluororubber is used, with an angle of 55 degrees or more and 65 degrees or less.

The vibration-proof block 51 is fitted to the outer region 32 of the measuring section 31 in the tube 12. In other words, the tube 12 is inserted into the tube insertion hole 52 of the vibration-proof block 51, and the vibration-proof block 51 is attached to the tube 12. The pair of vibration-proof blocks 51 are arranged slightly apart from the ultrasonic transducers 21A and 21B, respectively. This distance is not particularly limited, but is set to, for example, 1 mm or more, and preferably set to 1 mm or more and 10 mm or less. If the distance is within this range, a structure that is easy to assemble and easy to miniaturize the entire device can be obtained. If the distance is too large, for example, it becomes necessary to enlarge the housing, and there is a risk that the entire device will become large. The inner diameter dimension of the tube insertion hole 52 is set to be slightly smaller than the outer diameter dimension of the tube 12. Therefore, the tube 12 is pressed into the tube insertion hole 52. This press-fitting brings the inner circumferential surface 53 of the tube insertion hole 52 into close contact with the outer circumferential surface 13 of the tube 12.

3(a) and the like, the shape of the first end face 51a side and the shape of the second end face 51b side of this vibration-proof block 51 are different. That is, the second end face 51b side has a flat simple shape. Therefore, the second end face 51b is in a positional relationship perpendicular to the axis of the tube 12 and the central axis C1 of the tube insertion hole 52. In contrast, the first end face 51a side is intended to reduce reflected waves, and therefore a shape that is not flat is adopted. In the case of this vibration-proof block 51, one groove portion 55 is formed in the opening 54 on the first end face 51a side of the tube insertion hole 52. The groove portion 55 is a groove with a substantially V-shaped cross section and a linear shape, and the opening width of the groove is approximately equal to the inner diameter of the tube insertion hole 52. The depth of the groove 55 is not particularly limited, but here it is set to about 1/3 to 1/6 of the length dimension of the vibration isolation block 51 (the distance between the first end face 51a and the second end face 51b). The groove 55 is formed in a part of the first end face 51a so as to cross the opening 54 on the first end face 51a side. The first end face 51a side of the vibration isolation block 51 has a cross-sectional shape that is rotationally symmetric with respect to the central axis C1 of the tube insertion hole 52.

3(b) to (e), the vibration-proof block 51 of this embodiment is formed so that the contact area between the inner peripheral surface 53 of the tube insertion hole 52 and the outer peripheral surface 13 of the tube 12 gradually increases from the first end face 51a side to the second end face 51b side. To explain this in detail, FIG. 3(b) is a cross-sectional view of the vibration-proof block 51 cut along the central axis C1, and FIGS. 3(b) to (e) are cross-sectional views of the first end face 51a side of the vibration-proof block 51 cut perpendicularly to the central axis C1 at different positions. In FIG. 3(c), which is cut at a relatively shallow position, about 50% of the inner peripheral surface 53 of the tube insertion hole 52 is in contact with the outer peripheral surface 13 of the tube 12. In FIG. 3(d), which is cut at a deeper position, about 70% to 80% of the inner peripheral surface 53 of the tube insertion hole 52 is in contact with the outer peripheral surface 13 of the tube 12. In FIG. 3(e), which is a cut taken at a deeper position, the entire inner circumferential surface 53 of the tube insertion hole 52 is in contact with the outer circumferential surface 13 of the tube 12. When an ultrasonic guided wave is emitted toward the vibration-proof block 51 configured in this manner, the ultrasonic guided wave enters the interior of the vibration-proof block 51 without being largely reflected by the first end surface 51a.

Here, we will explain some vibration-proof structures that are different from the one in FIG. 3. The vibration-proof structure shown in FIG. 4 is a vibration-proof block 51 provided with an outer surface pressing member 61. The vibration-proof block 51 made of rubber is easily deformed in the direction in which the V-shaped groove portion 55 opens, and this tendency becomes more pronounced when the block 51 is softened during the flow of high-temperature liquid. As a result, the adhesion of the vibration-proof block 51 to the tube 12 decreases, which may lead to a decrease in the vibration-proof effect. The outer surface pressing member 61 is a member used to prevent such deformation and prevent a decrease in the vibration-proof effect. The outer surface pressing member 61 is arranged so as to contact and press the outer surface of the vibration-proof block 51, specifically at least two of the four side surfaces 51c. In FIG. 4, the flat outer surface pressing member 61 is arranged in contact with the side surface 51c located on the upper side and the side surface 51c located on the opposite side, the lower side. The shape of the outer surface pressing member 61 is not particularly limited and can be arbitrary, but here it has approximately the same shape and size as the side surface 51c. These outer surface pressing members 61 are actually attached to a casing 62 that entirely covers the pair of ultrasonic transducers 21A, 21B and the pair of vibration isolation blocks 51 attached to the tube 12 (see FIG. 5). The casing 62 shown in FIG. 5 is made up of an upper member 63A and a lower member 63B that can be opened and closed, and the outer surface pressing members 61 are integrally attached to the inner surfaces of the upper member 63A and the lower member 63B.

The outer pressing member 61 is formed using a material harder than the vibration isolation block 51 in order to prevent deformation of the vibration isolation block 51. Suitable examples of such materials include resin materials such as PFA, PTFE, and PPS, as well as metal materials such as aluminum, stainless steel, iron, and copper. For example, if it is made of a metal material, it can provide a shielding effect in addition to the above-mentioned deformation prevention effect.

The vibration-proof block 51A shown in FIG. 6 is a cylindrical block-shaped member, not a rectangular block-shaped member. The one shown in FIG. 7 is a cylindrical block-shaped vibration-proof block 51A with a cylindrical outer surface pressing member 71 attached to its outer circumferential surface 51d. The outer surface pressing member 71 is in contact with the entire outer circumferential surface 51d of the vibration-proof block 51A. The vibration-proof block 51A is pressed into the outer surface pressing member 71, so that a pressing force acts on the entire circumference of the vibration-proof block 51A, preventing the vibration-proof block 51A from deforming. The one shown in FIG. 8 is also a cylindrical block-shaped vibration-proof block 51A with a cylindrical outer surface pressing member 72 attached to its outer circumferential surface 51d. However, in the case of this outer surface pressing member 72, a number of through holes 73 extending along the central axis C1 of the vibration-proof block 51A are formed. The outer surface pressing members 71 and 72 are also made of the same material as the outer surface pressing member 61.

Next, we will explain the tests we conducted to compare the vibration isolation effects of the above vibration isolation structures and their results.

In this test, a test device 81 as shown in FIG. 9 was used. This test device 81 is a model simulating an ultrasonic flowmeter 11, and is configured to have one annular ultrasonic transducer 21A provided in the middle of a straight tube 12 of a predetermined length. A vibration-proof structure B1 was placed in the tube 12 at a position 150 mm away from the ultrasonic transducer 21A. A liquid (here, water) was contained in the tube 12, and both ends were sealed. In FIG. 9, the length from the left end face of the ultrasonic transducer 21A to the left sealed end E1 was set to 220 mm, and the length from the right end face of the ultrasonic transducer 21A to the right sealed end E2 was set to 280 mm. A PFA tube with an outer diameter of 6 mm and an inner diameter of 4 mm was used as the tube 12. In addition, a vibration-proof block 51A was basically made of fluororubber (hardness 60 degrees).

Then, when the ultrasonic transducer 21A was driven to transmit ultrasonic guided waves, the signal strength (mV) was measured by a conventionally known method for the reflected wave from the first end face 51a of the vibration isolation structure B1 and the reflected wave from the left sealed end E1 of the tube 12. Note that in this test, multiple examples and multiple comparative examples were set and the test was performed.

For example, the vibration isolation block 51 in FIG. 3(a) having a V-shaped groove 55 (rectangular block shape with end faces measuring 15 mm square and axial dimension of 10 mm) was used as "Example 1."

In addition, "Example 2" used an anti-vibration block 51 (rectangular block shape with end faces measuring 15 mm square and axial dimension of 10 mm) whose outer surface was covered with a pair of outer surface pressing members 61 made of hard resin (see Figures 4 and 5).

In addition, a vibration-isolating block 51A (cylindrical block shape with an outer diameter of 12.5 mmφ and an axial dimension of 10 mm) was used, and the outer surface was covered with a cylindrical outer surface pressing member 72 (inner diameter 12.5 mmφ, outer diameter 19 mmφ) made of perforated PTFE (see Figure 8), which was designated "Example 3."

In addition, a vibration-isolating block 51A (cylindrical block shape with an outer diameter of 16 mmφ and an axial dimension of 10 mm) was used, and the outer surface was covered with a cylindrical outer surface pressing member 71 (inner diameter 16 mmφ, outer diameter 19 mmφ) made of PFA (see Figure 7), which was designated "Example 4."

In contrast, a comparison example in which the vibration-isolating structure B1 was not placed was designated "Comparative Example 1." In addition, a comparison example in which the vibration-isolating block 51 in FIG. 3(a) (rectangular block shape with end faces measuring 19 mm square and axial dimension of 5 mm) was used and the V-shaped groove portion 55 was omitted was designated "Comparative Example 2."

The test results are shown in Table 1. As can be seen from Table 1, in Comparative Example 1, the reflection from the left sealed end E1 of the tube 12 was very large (240.0 mV), and the unwanted echo returned with almost no attenuation. In Comparative Example 2, the reflection from the left sealed end E1 was somewhat smaller (52.0 mV) due to the placement of the vibration-proof structure B1. However, the reflection from the first end surface 51a of the vibration-proof structure B1 was quite large (93.2 mV), and the reflected wave returned as an unwanted echo. Therefore, the evaluation results for the vibration-proofing effect in Comparative Examples 1 and 2 were low.

On the other hand, in Examples 1 to 4, by disposing a suitable anti-vibration structure B1, it was found that the reflection from the first end surface 51a of the anti-vibration structure B1 was significantly reduced and could be suppressed to about a fraction of the measured value in Comparative Example 2. It was also found that the reflection from the left sealing end E1 could be suppressed to about a fraction of the measured value in Comparative Example 2. Therefore, the evaluation results for the anti-vibration effect were also high in Examples 1 to 4. It was found that the anti-vibration effect of Example 2 was particularly excellent. Incidentally, the evaluation results for the anti-vibration effect were marked as "◎" when the sum of the reflected signal strength from the left sealing end E1 and the reflected signal strength from the first end surface 51a of the anti-vibration structure B1 was less than 30 mV, "◯" when it was 30 mV or more and less than 50 mV, and "×" when it was 50 mV or more.

As described above in detail, this embodiment provides the following advantages:

(1) According to the guided wave type ultrasonic flowmeter 11 of this embodiment, the vibration isolation block 51, 51A is fitted to the outer region 32 of the measuring section 31 in the tube 12. In this vibration isolation block 51, 51A, the contact area between the inner peripheral surface 53 of the tube insertion hole 52 and the outer peripheral surface 13 of the tube 12 increases from the first end face 51a side to the second end face 51b side. Therefore, the ultrasonic guided wave emitted toward the outer region 32 of the measuring section 31 is not reflected much by the first end face 51a and enters the inside of the vibration isolation block 51, 51A. In addition, since the vibration isolation block 51, 51A is a member made of an elastic body having a certain thickness, the ultrasonic guided wave that enters the inside is effectively attenuated. Therefore, it is possible to attenuate only the unnecessary echo without attenuating the necessary echo, and the influence of the unnecessary echo can be reduced, so that the measurement accuracy can be improved.

(2) The vibration-proof blocks 51, 51A of this embodiment have a groove 55 in the opening 54 on the first end face 51a side of the tube insertion hole 52. This groove 55 is a groove with a generally V-shaped cross section formed in part of the first end face 51a so as to cross the opening 54. Such grooves 55 can be formed relatively easily, which is advantageous in manufacturing the vibration-proof blocks 51, 51A. It is also advantageous in that it is relatively easy to realize a structure in which the contact area gradually increases from the first end face 51a side to the second end face 51b side.

(3) In this embodiment, the inner diameter of the tube insertion hole 52 is set smaller than the outer diameter of the tube 12, and the tube 12 is press-fitted into the tube insertion hole 52. This improves the adhesion of the vibration isolation blocks 51, 51A to the outer peripheral surface 13 of the tube 12. As a result, ultrasonic guided waves can be reliably incident on the vibration isolation blocks 51, 51A and efficiently attenuated. Furthermore, with this configuration, the vibration isolation blocks 51, 51A can be easily assembled to the tube 12.

(4) The vibration isolation structure B1 of this embodiment includes vibration isolation blocks 51, 51A and outer surface pressing members 61, 71, 72 made of a harder material that contact and press the outer surfaces of the vibration isolation blocks 51, 51A. With this structure, the outer surface pressing members 61, 71, 72 reduce the deformation of the vibration isolation blocks 51, 51A, thereby maintaining the adhesion of the vibration isolation blocks 51, 51A to the outer peripheral surface 13 of the tube 12. As a result, ultrasonic guided waves can be reliably incident on the vibration isolation blocks 51, 51A and efficiently attenuated. Therefore, the effects of unwanted echoes can be more reliably reduced, and measurement accuracy can be further improved.

The embodiment of the present invention may be modified as follows:

- In the above embodiment, the ultrasonic transducers 21A and 21B are circular, but for example, the ultrasonic transducers may be semicircular, and two of them may be arranged in combination to form a ring as a whole. Alternatively, the ultrasonic transducers may be quarter-circular, and four of them may be arranged in combination to form a ring as a whole. Also, multiple ultrasonic transducers that are not semicircular or quarter-circular (e.g., disk-shaped or cylindrical) may be used and arranged to form a ring as a whole. Specifically, multiple ultrasonic transducers may be used and arranged at equal angles along the circumferential direction at the same position on the tube 12 so as to be rotationally symmetrical about the central axis of the tube 12.

- In the above embodiment, the vibration isolation blocks 51, 51A are rectangular or cylindrical, but they may be other shapes.

- In the above embodiment, the vibration-isolating blocks 51, 51A are made of rubber material, but the vibration-isolating blocks 51, 51A may be formed using an elastic body made of a material other than rubber (e.g., elastomer, etc.).

In the above embodiment, one V-shaped groove 55 is formed at a predetermined position so that the contact area between the inner circumferential surface 53 of the tube insertion hole 52 and the outer circumferential surface 13 of the tube 12 increases from the first end face 51a side to the second end face 51b side, but this is not limited to this. That is, the groove may be formed at a position different from that of the above embodiment, or multiple grooves may be formed. For example, in the vibration-proof block 91 of another embodiment shown in FIG. 10, four grooves 92 are formed at equal angular intervals in the opening 54 on the first end face 51a side of the tube insertion hole 52. These grooves 92 have an arc-shaped cross section and extend in the direction of the central axis C1 of the tube insertion hole 52. In addition, the depth of the groove 92 gradually becomes shallower as it moves from the first end face 51a side to the second end face 51b side. The width of the groove 92 gradually becomes narrower as it moves from the first end face 51a side to the second end face 51b side. Even with this configuration, it is possible to realize a configuration in which the contact area gradually increases from the first end surface 51a to the second end surface 51b.

In the above embodiment, a groove 55 is formed in the opening 54 on the first end surface 51a side of the tube insertion hole 52, but instead of a groove, for example, multiple small recesses may be formed.

- In the above embodiment, ultrasonic transducers 21A and 21B made of lead zirconate titanate (PZT) are used, but the material from which ultrasonic transducers 21A and 21B are made is not particularly limited. For example, ultrasonic transducers made of potassium sodium niobate (alkali niobate) piezoelectric ceramics may of course be used.

11... Guided wave type ultrasonic flowmeter 12... Tube 13... (Tube) outer surface 21A... (First) ultrasonic transducer 21B... (Second) ultrasonic transducer 31... Measurement section 32... Outer region 51, 51A of measurement section... Vibration isolation block 51a... First end face 51b... Second end face 52... Tube insertion hole 53... (Tube insertion hole) inner surface 54... Openings 55, 92... Groove portions 61, 71, 72... Outer surface pressing member C1... Central axis

Claims (6)

An ultrasonic flowmeter having a structure in which a pair of ultrasonic transducers are arranged on the outer peripheral surface of a straight tube through which a fluid flows, the pair of ultrasonic transducers being spaced apart in the longitudinal direction of the tube, and measuring a flow rate of the fluid by transmitting an ultrasonic guide wave from one of the pair of ultrasonic transducers in a measuring section located between the pair of ultrasonic transducers along the longitudinal direction of the tube and receiving the ultrasonic guide wave by the other ultrasonic transducer,
a vibration-isolating block made of an elastic material having a tube insertion hole penetrating a first end surface and a second end surface located on the opposite side thereof, the vibration-isolating block being fitted onto the tube in an outer region of the measurement portion of the tube;
a contact area between an inner surface of the tube insertion hole and an outer surface of the tube is formed so as to increase from the first end face side to the second end face side. The guided wave ultrasonic flowmeter according to claim 1, characterized in that the tube insertion hole passes through the center of the vibration isolation block, and the first end face side of the vibration isolation block is formed to have a cross-sectional shape that is rotationally symmetric with respect to the central axis of the tube insertion hole. The guided wave ultrasonic flowmeter according to claim 1 or 2, characterized in that the vibration isolation block has a groove at the opening on the first end face side of the tube insertion hole. The guided wave type ultrasonic flowmeter according to any one of claims 1 to 3, characterized in that the vibration isolation block has a groove at the opening on the first end face side of the tube insertion hole, and the groove is a groove with a substantially V-shaped cross section formed in a part of the first end face so as to cross the opening on the first end face side. A guided wave type ultrasonic flowmeter according to any one of claims 1 to 4, characterized in that the inner diameter of the tube insertion hole is set smaller than the outer diameter of the tube, and the tube is press-fitted into the tube insertion hole. The guided wave type ultrasonic flowmeter according to any one of claims 1 to 5, further comprising an outer surface pressing member made of a material harder than the vibration isolation block, which contacts and presses against the outer surface of the vibration isolation block to reduce deformation of the vibration isolation block.

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