JP2002250644A - Ultrasound transmitter/receiver for clamp-on type ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the performance of an ultrasound transmitter/receiver for a clamp-on type ultrasonic flowmeter by enhancing its directivity in ultrasound transmission/reception and its sensitivity with respect to ultrasound, by conrolling the acoustic vibration of an ultrasound propagating object of the transmitter/receiver, and by sharpening the directivity and reducing the ultrasound loss in propagation paths. SOLUTION: The ultrasound propagating object of the ultrasound transmitter/ receiver is made of a carbon-fiber composite material, and the carbon fibers thereof are oriented in a direction perpendicular to the propagation path of ultrasound. On the surface of the propagating object in contact with a flow tube, two or more projections are provided along the axial direction of the flow tube. The difference between neighboring two projections in the lengths of ultrasound propagation paths within the propagating object including the projections is set equal to one wavelength of the ultrasonic vibration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring the flow velocity or flow rate of a fluid from the propagation time difference of an ultrasonic wave flowing through the fluid, and more particularly, to an ultrasonic transducer which is in close contact with an existing flow tube. The present invention relates to a clamp-on type ultrasonic transducer for measuring the flow velocity of a fluid in an attached flow tube.

[0002]

2. Description of the Related Art FIG. 14 is a sectional view showing the principle of a clamp-on type ultrasonic flowmeter. The oblique wedge-shaped ultrasonic wave propagating objects 3a and 3b made of an isotropic object such as PTFE (polytetrafluoroethylene) for propagating ultrasonic waves are adhered to the outside of the flow tube 4 through which the fluid 5 flows. And ultrasonic waves into the fluid through the flow tube wall. The two ultrasonic transducers 2a and 2b are both transmitters and receivers of ultrasonic waves. At this time, the time for the ultrasonic wave to reach the receiver from the transmitter differs depending on the direction of the flow. Ultrasonic waves emitted in the same direction as the flow travel on the flow, so to speak, the time is shortened. Ultrasounds launched against the flow travel slowly and take longer. Thus, in FIG. _T 2 -T ₁
You can see the flow velocity more.

In the detecting section of the clamp-on type ultrasonic flow meter shown in FIG. 14, reference numerals 2a and 2b denote ultrasonic vibrators and 3a and 3b.
b denotes an oblique wedge-shaped ultrasonic wave propagating object for acoustically coupling the fluid 5 in the flow tube 4 and the ultrasonic vibrator, and the ultrasonic vibrators 2a and 2b and the oblique wedge-shaped ultrasonic wave propagation Objects 3a, 3b
Are acoustically coupled to form the ultrasonic transducers 1a and 1b.

When an excitation pulse is applied to the ultrasonic transducer 2a of the ultrasonic transducer 1a on the upstream side of the ultrasonic flow meter detecting section to excite it, an ultrasonic wave is emitted, and the emitted ultrasonic wave has an oblique wedge shape. The light propagates from the flow tube 4 to the fluid 5 in the flow tube via the ultrasonic wave propagating object 3a. Then, the sound wave propagated to the fluid 5 in the flow tube arrives at the opposing surface of the flow tube 4, and is guided by the oblique wedge-shaped ultrasonic wave propagating object 3b to be in the wave receiving mode. Guided by the ultrasonic transducer 2b and received by the ultrasonic transducer 2b. Such a configuration in which the two ultrasonic transducers 1a and 1b are located opposite to the central axis of the flow tube 4 expresses a propagation path of the ultrasonic wave and is called a Z-shape.

[0005] Such a clamp-on type ultrasonic flowmeter is attached in close contact with an existing flow pipe through which water, a chemical solution or the like flows in semiconductor equipment and chemical plant equipment, and measures the flow rate.

The ultrasonic wave radiated from the ultrasonic transducer 2 is
Although it is a wave packet of elastic waves with a certain spread and directivity, it is assumed that the source of the ultrasonic wave and the receiver are regarded as points located at the center, and the propagation path of the wavefront is treated as a sound ray passing through these two points General. At that time, in a place where the speed of sound changes discontinuously in the propagation medium, the law of reflection and refraction related to wave propagation is established, and such a model is generally called a point sound source model. The ultrasonic propagation path between the ultrasonic transducers is shown based on this point sound source model.

[0007]

However, since the oblique wedge-shaped ultrasonic wave propagating object constituting the above-described ultrasonic transducer is an isotropic material, the oblique angle is generated by the ultrasonic wave excited by the ultrasonic vibrator. Many vibration modes due to the shape of the wedge-shaped ultrasonic wave propagating object are excited. For this reason, there is a problem that the ultrasonic wave to be propagated becomes small because the ultrasonic wave is not converted into only the vibration mode that propagates the desired ultrasonic wave.
In addition, there is a problem that an unnecessary vibration mode propagates to the flow tube through which the fluid flows, and further enters the ultrasonic transducer on the receiving side and is confused with a signal component, which causes a measurement error. Furthermore, in transmission and reception of ultrasonic waves, there is a problem that a phase difference occurs due to the ultrasonic wave propagation path and the detected waveforms are synthesized, so that it becomes unclear or unclear which signal is the target signal. In addition, when there is a vibration component in which the phase of the ultrasonic signal is opposite in the ultrasonic transmitter / receiver on the receiving side, there is a problem that the detection level is lowered.

An object of the present invention is to solve the above-mentioned problems and to provide a highly accurate clamp-on type ultrasonic flowmeter.

[0009]

Means for Solving the Problems One or a pair of ultrasonic transducers constituted by an ultrasonic transducer and an ultrasonic wave propagating object are positioned on the outer periphery of a flow tube through which a fluid flows, and the flow direction of the fluid is changed. In an ultrasonic flowmeter that measures the flow rate of a fluid by transmitting ultrasonic waves in the opposite direction, two or more projections are provided in the axial direction of the flow tube on the surface of the ultrasonic wave propagating object that is in contact with the flow tube. thing. The distance between the two or more projections along the axial direction of the flow tube is the same for one or more pairs of ultrasonic transducers. The difference between the ultrasonic transmission distances in the ultrasonic wave propagating object including the protrusions between two or more protrusions is an integral multiple of one wavelength of the ultrasonic vibration. A fiber composite material in which the ultrasonic transmission object is oriented so that the fibers have regularity. The fiber composite material is to be a carbon fiber composite material.

[0010]

Embodiments of the present invention will be described in detail. FIG. 1 is a perspective view of an example showing the first embodiment. Reference numeral 1 denotes an ultrasonic transducer, which comprises an ultrasonic transducer 2 and an oblique wedge-shaped ultrasonic wave propagating object 3. The material of the ultrasonic wave propagating object 3 having the oblique wedge shape is CFRP (carbon fiber composite material). The ultrasonic vibrator 2 is a piezoelectric ceramic mainly composed of lead zirconate titanate, and is polarized in the thickness direction.

Next, the orientation and shape of the carbon fiber of CFRP will be described. The carbon fibers 6 in the CFRP are oriented parallel to the plane of the ultrasonic transducer 2. That is, they are oriented perpendicular to the ultrasonic wave propagation path. The oblique wedge-shaped ultrasonic wave propagating object 3 has one surface parallel to the ultrasonic vibrator 2 and is bonded to the ultrasonic vibrator 2 with epoxy resin on this surface. The surface in contact with the flow tube 4 has six protrusions, and the line connecting the tips of the protrusions is parallel to the central axis of the flow tube 4 made of PFA (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer). It is. And it is strongly pressed down by a fastening belt (not shown) in parallel with the flow tube.

Next, the shape of the projection will be described. In the projection 7 shown in FIG. 2, the center line of the projection 7 has an angle of 90 degrees with respect to the central axis of the flow tube 4, but other angles may of course be used. Further, as shown in FIG. 3, the projections 7 provided on the ultrasonic wave propagating object 3 can be divided at equal intervals in a direction orthogonal to the flow direction.

In the ultrasonic transducer 1 constructed as described above, the vibration of the ultrasonic transducer 2 is propagated in the CFRP, but as described in detail in JP-A-7-284198.
Since the vibration in the direction of the carbon fiber 6 in the RP is suppressed, the direction of the carbon fiber 6 is oriented in parallel with the surface of the ultrasonic vibrator 2 so that a vibration mode in which almost desired ultrasonic wave propagates can be obtained. Can be. Further, since the ultrasonic wave propagates in a direction orthogonal to the direction of the carbon fiber, the phase of the ultrasonic wave propagating from the direction orthogonal to the direction of the carbon fiber reaching the same carbon fiber becomes the same.

Further, a projection 7 is provided on the surface of the ultrasonic wave propagating object 3 having an oblique wedge shape which is in contact with the flow tube 4, and is strongly pressed against the flow tube 4. Is perpendicular to the contact surface. This state is shown in FIG. Also,
Even if the center line of the projection 7 is not orthogonal to the center axis of the flow tube 4 made of PFA, as shown in FIG.
The contact surface of the flow tube 4 made of A is vertical. Therefore, since the angle of incidence from the projection 7 to the flow tube 4 made of PFA is zero, there is no reflection based on the law of reflection and refraction. However, although the reflection due to the impedance difference of the substance exists, the ultrasonic wave can be efficiently propagated without being reflected by the effect of the projection 7.

Further, since the light is not obliquely incident, there is no possibility that the light is converted into unnecessary lateral vibration in the flow tube 4 made of PFA. As a result, unnecessary lateral vibrations are transmitted to the ultrasonic transducer 1 on the receiving side in the flow tube 4 made of PFA, and are detected together with the ultrasonic waves passing through the necessary fluid 5, so that the S / N ratio is poor. Some problems can be solved.

Further, as shown in FIG. 6, the pair of ultrasonic transmitters / receivers 1a and 1b are the same, and the projections 7 of the ultrasonic wave propagating object 3 having the oblique angle wedge are of course the same. Since the intervals between the projections match, ultrasonic waves can be transmitted and received efficiently.

As shown in FIG. 7, the difference between the distances from the interface between the ultrasonic vibrator 2 and the ultrasonic wave propagating object 3 constituting the ultrasonic transceiver 1 in the ultrasonic wave propagation path to the tips of the adjacent projections 7a and 7b ( The length obtained by subtracting L1 from L2) is set to be the length of one wavelength of the ultrasonic vibration of the ultrasonic wave propagating object 3 so that the protrusion 7
Since the phases of the ultrasonic vibrations at the tip are the same, strong excitation can be achieved.

Therefore, unnecessary vibration modes are suppressed as much as possible, so that a single vibration mode can be finally obtained. In addition, adjacent projections 7a from the interface between the ultrasonic transducer 2 and the ultrasonic wave propagating object 3 which constitute the ultrasonic transmitter / receiver 1,
The same can be achieved by setting the difference in the distance to the tip 7b to be an integral multiple of one wavelength of the ultrasonic vibration in the ultrasonic wave propagating object 3.

FIG. 8 is a dimensional diagram of the ultrasonic transceiver 1 according to the first embodiment, and the unit used is millimeter.

FIG. 9 shows an ultrasonic transceiver 1a according to the present invention.
It is sectional drawing which comprised the V-type clamp-on type ultrasonic flowmeter using 1b. The V-shaped clamp-on type ultrasonic flowmeter is a popular configuration in the field because it can be positioned on only one side of the flow tube 4. Here, the ultrasonic transceiver 1a,
The ultrasonic transmission objects 3a and 3b of the oblique angle wedge shape 1b are made of CFRP 6a and 6b, and the material of the flow tube 4 is made of PFA. As described with reference to FIG. 4 and FIG.
Are perpendicular to each other, so that the ultrasonic vibrator 2
The characteristic that the ultrasonic wave goes straight without refraction from a, 2b to the flow tube 4 made of PFA appears.

FIG. 10 is a perspective view of an example showing the second embodiment. The ultrasonic wave propagating object 3 is CFRP as in the first embodiment, but the direction perpendicular to the surface of the ultrasonic transducer 2 and the direction of the carbon fibers 6 in the CFRP are not parallel.
With such a configuration, vibration orthogonal to the direction of the carbon fibers 6 in the CFRP can be strongly excited. There is a flat portion between the projections 7. This configuration has the advantage that the degree of freedom in designing an ultrasonic transceiver having a high S / N ratio as described in detail in the first embodiment is increased.
Since the ultrasonic vibration can be strongly excited in the direction perpendicular to the carbon fibers 6 in the protrusions 7, there is an advantage that the shape of the protrusions can be changed to the shape shown in FIG. Here, the projection 7 is made of the same material as the ultrasonic wave propagating object 3. However, it is needless to say that only the carbon fiber direction of the projection 7 may be changed or the material of the projection may be made different.

FIG. 11 shows a case where the ultrasonic transceivers 1a and 1b shown in the second embodiment are used in a Z-type clamp-on ultrasonic flowmeter. In the Z-type clamp-on type ultrasonic flowmeter, two ultrasonic transceivers 1a and 1b must be located opposite to the central axis of the flow tube 4, so that it may be difficult to install the ultrasonic transmitter / receiver depending on the location. is there. But,
Compared with the V type, the Z type clamp-on type ultrasonic flow meter has a large signal because the distance between the ultrasonic transceivers 1a and 1b is small. Therefore, the V-type clamp-on ultrasonic flowmeter is suitable for a small-diameter flow tube in which a signal becomes small.

FIG. 12 is a perspective view of an example showing the third embodiment. The ultrasonic transmitter / receiver 1 includes an ultrasonic transducer 2 and a CFRP which is an ultrasonic wave propagating object 3. The ultrasonic transducer 2 is a lead titanate-based piezoelectric ceramic, and is polarized in a direction perpendicular to the electrode surface. And C
The carbon fibers 6 in the FRP are arranged in a direction orthogonal to the central axis of the flow tube 4. Further, the CFRP is processed so as to contact the flow tube with a curvature having substantially the same radius as the outer radius of the flow tube 4. And CFR in contact with stainless steel flow tube 4
A projection 7 is provided on the surface of P, and the projection 7 is in contact with the flow tube 4. FIG. 13 is a sectional perspective view of a CFRP which is an ultrasonic wave propagating object. As described above, by processing the ultrasonic wave propagating object so as to be in contact with the flow tube with a curvature having substantially the same radius as the outer radius of the flow tube 4, the contact area with the flow tube 4 is increased, thereby increasing the sound wave propagation efficiency. Can be.

In the present invention, an ultrasonic transmitter and an ultrasonic receiver are used as a pair, but the principle of the present invention can be applied to an ultrasonic transmitter / receiver that performs transmission and reception by one. Applications include ultrasonic microscopes, ultrasonic flaw detectors,
There are an ultrasonic diagnostic apparatus, an ultrasonic thickness gauge, an ultrasonic densitometer, a fish finder and a sonar.

[0025]

When the projection 7 is provided on the surface of the ultrasonic wave propagating object 3 which is in contact with the flow tube 4 and strongly pressed against the flow tube, the center line of the projection and the contact surface of the flow tube are orthogonal to each other, so Since the incident angle of is zero, there is no reflection due to the law of reflection and refraction. Therefore, the ultrasonic waves can be transmitted efficiently without being reflected by the effect of the projections. In addition, since there is no oblique incidence, there is no danger of conversion into unnecessary lateral vibration in the flow tube 4. As a result, unnecessary lateral vibration in the flow tube is transmitted to the ultrasonic transmitter / receiver 1 on the receiving side, and is detected together with the ultrasonic wave passing through the necessary fluid 5, so that the S / N ratio deteriorates. Solvable. Since the pair of ultrasonic transceivers is the same and the projection 7 of the ultrasonic wave propagating object 3 is also the same, the ultrasonic path and the interval between the projections match, so that the ultrasonic wave can be transmitted and received efficiently. In the ultrasonic path, the difference between the distance from the interface between the ultrasonic transducer 2 and the ultrasonic wave propagating object 3 constituting the ultrasonic transmitter / receiver 1 to the tip of the adjacent projection is defined as one wavelength of the ultrasonic vibration of the ultrasonic wave propagating object 3. By doing so, the phase of the ultrasonic vibration at the tip of the projection becomes the same, so that strong excitation can be achieved. Therefore, unnecessary vibration modes are suppressed as much as possible, so that a single vibration mode can be eventually obtained. As described above, the directivity and efficiency of ultrasonic transmission / reception can be simultaneously improved, so that an ultrasonic transceiver having a high S / N ratio and high sensitivity can be configured.

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment.

FIG. 2 is a diagram showing a shape of a projection.

FIG. 3 is a diagram showing a shape of a projection having an angle. .

FIG. 4 is a diagram showing a contact state between a projection and a PFA flow tube.

FIG. 5 is a diagram showing a contact state between a projection having an angle and a PFA flow tube.

FIG. 6 is a diagram showing an ultrasonic wave propagation path between a pair of ultrasonic transceivers.

FIG. 7 is a diagram showing an ultrasonic wave propagation path in an ultrasonic wave propagation object.

FIG. 8 is a dimensional diagram of the ultrasonic transceiver according to the first embodiment.

FIG. 9 is a diagram showing a V-shaped clamp-on ultrasonic flow meter according to the first embodiment.

FIG. 10 is a perspective view of an example showing the first embodiment.

FIG. 11 is a diagram showing a Z-shaped clamp-on ultrasonic flow meter according to a second embodiment.

FIG. 12 is a perspective view of an example showing the third embodiment.

FIG. 13 is a sectional perspective view of a CFRP which is an ultrasonic wave propagating object.

FIG. 14 is a principle diagram of a conventional clamp-on type ultrasonic flow meter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultrasonic transducer 2 Ultrasonic transducer 3 Ultrasonic wave propagating object 4 Flow tube 5 Fluid 6 Carbon fiber 7 Projection

Claims (5)

[Claims] An ultrasonic transducer constituted by an ultrasonic transducer and an ultrasonic wave propagating object is positioned at one or one or more pairs on the outer periphery of a flow tube through which a fluid flows, and is arranged in the flow direction and the reverse direction of the fluid. An ultrasonic flowmeter that measures the flow rate of a fluid by transmitting ultrasonic waves, characterized in that the surface of an ultrasonic wave propagating object in contact with the flow tube has two or more protrusions in the axial direction of the flow tube. Ultrasonic transducer in a clamp-on type ultrasonic flowmeter that does not work. 2. The clamp-on type ultrasonic wave according to claim 1, wherein the distance between the two or more projections along the axial direction of the flow tube is the same for one or more ultrasonic transducers. Ultrasonic transducer for flow meter. 3. The method according to claim 2, wherein, in the protrusions adjacent to the two or more protrusions, a difference in distance of an ultrasonic wave propagation path in an ultrasonic wave propagating object including the protrusions is an integral multiple of one wavelength of ultrasonic vibration. An ultrasonic transducer in the clamp-on type ultrasonic flowmeter according to claim 1 or 2. 4. An ultrasonic wave in a clamp-on type ultrasonic flowmeter according to claim 1, wherein said ultrasonic wave propagating object is a fiber composite material in which fibers are oriented with regularity. Transducer 5. An ultrasonic transducer in a clamp-on type ultrasonic flow meter according to claim 1, wherein said fiber composite material is a carbon fiber composite material.