JP2005241494A - Clamp-on type doppler type ultrasonic flow velocity distribution meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a flow velocity distribution or a flow rate accurately by removing an ultrasonic echo based on a longitudinal wave between ultrasonic echoes by two measuring lines of the longitudinal wave and a longitudinal wave propagating in a pipe. <P>SOLUTION: In this clamp-on type Doppler-type ultrasonic flow velocity distribution meter, an ultrasonic wave is allowed to enter fluid inside the pipe from an ultrasonic transducer outside the pipe, and the flow velocity distribution is measured by utilizing the change of an ultrasonic frequency reflected by a reflector in the fluid caused by a Doppler effect. A wedge 52 is constituted of a material whose acoustic impedance is similar to that of the pipe 53, and an ultrasonic vibrator 51 is tilted and fixed on the wedge 52 so that the incident angle of the ultrasonic echo entering the pipe 53 from the fluid 54 to be measured becomes larger than a critical angle of the longitudinal wave determined from the sound velocity of the fluid 54 to be measured and the flow velocity of the longitudinal wave in the pipe 53, and simultaneously smaller than a critical angle of the longitudinal wave determined from the sound velocity of the fluid 54 to be measured and the sound velocity of the longitudinal wave in the pipe 53. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  In the present invention, ultrasonic waves are incident on a fluid to be measured inside the tubular body from an ultrasonic transducer installed outside the tubular body, and the flow velocity distribution of the fluid to be measured is measured in a non-contact manner using the Doppler effect. The present invention relates to a clamp-on type Doppler ultrasonic flow velocity distribution meter.

  The clamp-on type ultrasonic flowmeter is a flowmeter in which an ultrasonic transducer is attached to a part of the outer peripheral surface of a pipe or the like and the flow rate of the fluid to be measured moving inside the pipe is measured from the outside of the pipe. It is. This clamp-on type ultrasonic flowmeter can be mainly classified into a propagation time difference type and a Doppler type.

The propagation time difference formula reciprocates the ultrasonic wave in a path that crosses the measured fluid moving inside the tube diagonally, and the difference in time required for the ultrasonic wave to propagate in each of the forward path and the return path This is a method for measuring the flow rate of a fluid.
On the other hand, the Doppler method is a method of measuring the flow rate of the fluid to be measured from the moving speed of the suspended particles and the like, assuming that the suspended particles and bubbles contained in the fluid to be measured move at the same speed as the fluid. That is, when an ultrasonic wave is transmitted into the fluid to be measured, the frequency of the ultrasonic wave reflected by the suspended particles changes according to the moving speed of the suspended particles due to the Doppler effect. The moving velocity of suspended particles, that is, the velocity of the fluid to be measured is detected, and the flow velocity distribution and flow rate are measured.

  As a prior art of such a Doppler type ultrasonic flow meter, for example, there is a “Doppler type ultrasonic flow meter” described in Patent Document 1 described later. FIG. 3 shows a schematic configuration of the flow meter.

The Doppler ultrasonic flow meter shown in FIG. 3 includes an ultrasonic velocity distribution measurement unit (hereinafter referred to as a UVP unit) 10 that measures the flow velocity of the fluid 22 to be measured flowing inside the pipe 21 in a non-contact manner. The UVP unit 10 transmits ultrasonic pulses having a required frequency (fundamental frequency F ₀ ) along the measurement line ML to the fluid 22 to be measured, and the ultrasonic pulses incident on the fluid 22 to be measured. The ultrasonic echo reflected from the measurement region is received, the flow velocity distribution measurement circuit 12 that measures the flow velocity distribution of the fluid to be measured 22 in the measurement region, and the arithmetic processing based on the flow velocity distribution of the fluid to be measured 22 and the radial direction of the pipe 21 , And a computer 31 such as a microcomputer, CPU, MPU or the like as a flow rate calculation means for obtaining the flow rate of the fluid 22 to be measured in a time-dependent manner, and a display device 32 for displaying the output from the computer 31 in time series. And.

The ultrasonic transmission unit 11 generates an electrical signal having a fundamental frequency F ₀ such as 1 [MHz], 2 [MHz], 4 [MHz], and the electrical signal from the oscillator 13 for a predetermined period (1). / F _rpf ) includes a signal generator 15 including an emitter 14 that outputs a pulse having a frequency F _rpf , and the pulse electric signal having the fundamental frequency F ₀ is input to the ultrasonic transducer 16 from the signal generator 15. .
From the ultrasonic transducer 16, an ultrasonic pulse having a fundamental frequency F ₀ is transmitted along the measurement line ML to the fluid 22 to be measured inside the pipe 21. This ultrasonic pulse is, for example, a straight beam having a pulse width of about 5 [mm] and hardly spreading.

  The ultrasonic transducer 16 also serves as a transmitter / receiver, and is configured to be able to receive an ultrasonic echo in which a transmitted ultrasonic pulse is reflected by a reflector in the fluid to be measured 22. The reflector is a bubble or suspended particle that is uniformly contained in the fluid to be measured 22, in other words, a foreign substance having an acoustic impedance different from that of the fluid to be measured 22.

  The ultrasonic echo received by the ultrasonic transducer 16 is converted into an echo electric signal by the transducer 16. The echo electric signal is amplified by an amplifier 17 in the UVP unit 10, digitized through an A / D converter 18, and the digital echo signal is input to the flow velocity distribution measuring circuit 12.

An electric signal having a fundamental frequency F ₀ from the oscillator 13 is digitized and inputted to the flow velocity distribution measuring circuit 12 by the A / D converter 18, and a change in the flow velocity based on the Doppler shift is calculated from the frequency difference between the two signals. The measurement is performed to calculate the flow velocity distribution of the fluid 22 to be measured in the measurement region along the measurement line ML. The flow velocity distribution of the fluid 22 in the cross section of the pipe 21 is measured by correcting the flow velocity distribution in the measurement region with the inclination angle α of the ultrasonic transducer 16 (the inclination angle with respect to the direction orthogonal to the longitudinal direction of the pipe 21). Can do.

Next, the operation principle of the Doppler type ultrasonic flowmeter will be described in more detail with reference to FIG.
As shown in FIG. 4A, in the state where the ultrasonic transducer 16 is inclined and installed in the flow direction of the fluid 22 to be measured, the ultrasonic pulse of the fundamental frequency F ₀ is sent from the ultrasonic transducer 16 into the pipe. 4, the ultrasonic pulse hits a reflector such as suspended particles uniformly distributed on the fluid to be measured 22 on the measurement line ML, and is reflected as an ultrasonic echo a as shown in FIG. It is received by the ultrasonic transducer 16.

In FIG. 4B, the symbol b is a multiple reflection echo reflected from the tube wall of the pipe 21 on the ultrasonic pulse incident side, and the symbol c is a multiple reflection echo reflected from the tube wall of the pipe 21 on the opposite side. is there. The transmission period of the ultrasonic pulse transmitted from the ultrasonic transducer 16 is (1 / F _rpf ) as illustrated.

  When the echo signal a received by the ultrasonic transducer 16 is subjected to filtering processing and the flow velocity distribution is measured along the measurement line ML using the Doppler shift method, it is displayed as shown in FIG. This flow velocity distribution is measured by the flow velocity distribution measurement circuit 12 of the UVP unit 10 and is displayed on the display device 32 via the computer 31.

As described above, in the Doppler shift method, when an ultrasonic pulse is radiated into the fluid 22 to be measured flowing inside the pipe 21, the ultrasonic pulse is reflected by a reflector that is mixed or uniformly distributed in the fluid 22. This is an ultrasonic echo, and applies the principle that the frequency of the ultrasonic echo is frequency shifted by a magnitude proportional to the flow velocity.
The flow velocity distribution signal of the fluid under measurement 22 measured by the flow velocity distribution measurement circuit 12 is sent to the computer 31, and the flow velocity distribution signal is integrated in the radial direction of the pipe 21 to make the flow rate of the fluid under measurement 22 time-dependent. Can be sought. The flow rate m (t) of the fluid 22 at time t can be expressed by Equation 1.

  The flow rate m (t) can be rewritten as Equation 2.

In the conventional Doppler type ultrasonic flowmeter described above, in order to measure the flow rate of the fluid 22 to be measured with high accuracy regardless of whether it is in a steady state or an unsteady state, the flow velocity distribution of the fluid 22 to be measured inside the pipe 21 is measured. Must be detected with high accuracy.
As can be seen from the above-described measurement principle, the flow velocity distribution of the fluid 22 to be measured is obtained by performing signal processing on the ultrasonic echo generated by the reflector in the fluid 22 to be measured. It is necessary to include only the acoustic signal to be transmitted, and it is necessary to eliminate acoustic and electrical noise.
Some acoustic noise that affects this ultrasonic echo is generated from reflection or scattering between media with different acoustic impedances. is there.

In general, in solids such as metals, there are two types: longitudinal waves that have displacement in the same direction as the propagation direction of waves called dense waves, and transverse waves that have displacement in the direction orthogonal to the propagation direction of waves called shear waves. There are sound waves.
Here, as described in Reference Document 1, “Introduction to Electroacoustic Engineering” (Shoyodo Publishing Co., Ltd. (p247-251)), when a sound wave is obliquely incident on a solid from a fluid, It is generally known that longitudinal waves and transverse waves are generated in both transmission and reflection when a sound wave propagates from a solid to a solid.

Below, the influence of the ultrasonic echo by the longitudinal wave and the transverse wave in the solid will be described.
As shown in FIG. 5, when a sound wave propagates from the medium 1 to the medium 2, the propagation angle θ _in of the sound wave in the medium 1 and the medium 2 (incident angle at the boundary surface between both media), θ _out (also the refraction angle or emission) The relationship of (corner) is as shown in Equation 3.

Further, when the sound waves from the medium 1 to the medium 2 is incident, if the sound velocity c ₂ in the medium 2 is greater than the acoustic velocity c ₁ at the medium 1 (c 1 _{<c 2),} sound waves at the boundary surfaces of the medium There is a critical angle that causes total reflection. This critical angle θ _c is expressed by Equation 4.

Here, the inclination angle of the ultrasonic transducer 16 (the incident angle of the ultrasonic wave to the pipe 21) in the conventional Doppler ultrasonic flow velocity distribution meter shown in FIG. 3 will be described based on the following references 2 and 3. To do.
Reference 2: “Development of Flow Measurement Method Using Ultrasonic Velocity Distribution Measurement (UVP) (6) Measurement with NIST (USA) Calibration Flow Measurement Loop-Test Results and Accuracy Verification” H13)
Reference 3: “Development of a novel flow metering system using ultrasonic velocity profile measurement”

Reference 2 is an example of a so-called clamp-on type in which a Doppler type ultrasonic flow velocity distribution meter is installed on the outer wall of a stainless steel pipe, and the inclination angle of the ultrasonic transducer is 10 degrees or 5 degrees.
In Reference 3, an ultrasonic transducer driven at a frequency of 1 [MHz] is installed at an inclination angle of 5 degrees with respect to a pipe, and an ultrasonic transducer driven at a frequency of 4 [MHz] Although it is installed at an inclination angle of 0 to 20 degrees with respect to the pipe, it is described that acrylic having a thickness of 2 [mm] is sandwiched between the ultrasonic transducer and the pipe as a wedge.

A configuration corresponding to the measurement conditions described in Reference 3 is illustrated in FIG.
In FIG. 6, an ultrasonic transducer 41 is fixed to a wedge 42 made of acrylic. However, the ultrasonic transducer 41 is installed to be inclined by an angle θ _in with respect to a direction orthogonal to the longitudinal direction of the pipe 43. That is, the incident angle of the ultrasonic wave from the wedge 42 to the pipe 43 is θ _in .

  According to References 2 and 3, the fluid to be measured 44 shown in FIG. 6 is water, and the pipe 43 is made of stainless steel. The sound speed in water is about 1500 [m / s], the sound speed of longitudinal waves in stainless steel is about 5750 [m / s], and the speed of sound of transverse waves is about 3206 [m / s]. Furthermore, the acoustic velocity of the longitudinal wave in the acrylic wedge 42 is 2730 [m / s].

When the critical angle θ _c between the longitudinal wave and the transverse wave is calculated from Equation 4 described above, the critical angle of the longitudinal wave at the interface between the wedge 42 and the pipe 43 is 28.3 degrees, and the critical angle of the transverse wave is 58.4. Degree.
For example, when a sound wave is emitted from the ultrasonic transducer 41 having an inclination angle (incident angle) θ _in of 20 degrees, a longitudinal wave and a transverse wave are generated at the boundary surface between the wedge 42 and the pipe 43, both of which are solid. Since the incident angle θ _{in at the} boundary surface is less than the critical angle of both the longitudinal wave and the transverse wave, both longitudinal and transverse acoustic waves propagate in the pipe 43.

Furthermore, since the longitudinal wave and transverse wave components propagating through the pipe 43 are refracted and enter the water, two measurement lines ML are generated.
In the pipe 43 shown in FIG. 6, the longitudinal wave refraction angle (exit angle) θ _pl is 46.1 degrees, and the transverse wave refraction angle θ _ps is 23.7 degrees.

When sound waves enter the water from the pipe 43, the sound waves are converted into longitudinal waves, and the refraction angle θ _{fl in} water is 10.84 degrees. Thus, the transmittance | permeability of the sound wave at the time of a sound wave entering into water from a metal is shown by the following reference documents 4.
Reference 4: “Ultrasonic Handbook” Ultrasonic Handbook Editorial Committee Maruzen Co., Ltd.

The example described in Reference 4 is the case where the medium 1 is aluminum and the medium 2 is water in FIG.
Further, FIG. 7 is a diagram described in Reference Document 4, and the incident angle and energy reflection when a transverse wave is incident on the boundary surface between the aluminum plate corresponding to the medium 1 and the water corresponding to the medium 2. The relationship between the coefficient (reflectance) and the energy transmission coefficient (transmittance) is shown. The SV wave is a transverse wave, and the L wave is a longitudinal wave. According to FIG. 7, it can be seen that even if the incident angle of the transverse wave exceeds 28 degrees, the total wave is not reflected and the longitudinal wave is transmitted.

  Further, FIG. 8 shows the relationship between the incident angle, the reflectance, and the transmittance when the longitudinal wave is incident on the boundary surface between the aluminum plate and the water. According to FIG. 8, only the longitudinal wave is transmitted. I understand that.

Next, FIG. 9 is a diagram for explaining the behavior of ultrasonic echoes in the configuration of FIG.
The ultrasonic echo from the underwater reflector returns to the ultrasonic transducer 41 from the water following the same path as when entering the water from the pipe 43 side. Since the incident angle θ _f of the ultrasonic echo when entering the aluminum pipe 43 from underwater is 10.84 degrees, both a longitudinal wave and a transverse wave are generated.

Also, as shown in FIG. 9, when ultrasonic echoes enter the pipe 43 from underwater, two measurement lines of longitudinal wave component and transverse wave component are generated, so there are four ultrasonic echoes in the pipe 43. To do. Further, when an ultrasonic echo is incident on the wedge 42 from the pipe 43, the sound wave is refracted according to Equation 3, but since the sound speed of the material of the wedge 42 is slower than the sound speed of the material of the pipe 43, there is no critical angle. Instead, total reflection does not occur, and four ultrasonic echoes travel in the direction of the ultrasonic transducer 41 through the inside of the wedge 42.
For this reason, the four ultrasonic echoes propagating inside the wedge 42 are incident on the ultrasonic transducer 41 with a time difference according to the sound velocity of the propagation path of the ultrasonic transducer 41.
In FIG. 9, θ _pl is the refraction angle of the longitudinal wave at the interface between the fluid (water) 44 to be measured and the pipe 43, θ _ps is the refraction angle of the transverse wave, and θ _wl is the interface between the pipe 43 and the wedge 42. Is the refraction angle of the longitudinal wave, θ _ws is the refraction angle of the transverse wave.

The time axis of the ultrasonic echo received by the ultrasonic transducer 41 corresponds to the radial position in the pipe 43. In the pipe 43, there is a difference in sound speed between the longitudinal wave and the transverse wave.
For this reason, the ultrasonic echo received at a certain time by the ultrasonic transducer 41 is the flow velocity at point A of the fluid 44 measured by the transverse wave in the pipe 43 in FIG. 10 and the fluid 44 measured by the longitudinal wave in the pipe 43. And the flow velocity of point A ′ (the point A is a position different along the radial direction of the pipe 43).
That is, as conceptually shown in FIG. 11, the flow velocity obtained from the ultrasonic echo received at a certain time by the ultrasonic transducer 41 is a combination of the flow velocities at points A and A ′ that are actually different positions. Thus, the accurate flow velocity distribution of the fluid 44 inside the pipe 43 and thus the flow rate cannot be measured.

  As described above, in the Doppler type ultrasonic flowmeter that determines the flow rate by measuring the flow velocity distribution inside the pipe, the sound wave transmitted from the ultrasonic transducer generates longitudinal and transverse waves in the pipe, and the two measurement lines are Since the ultrasonic echoes from the respective reflectors are received by being incident on the fluid to be measured, there is a problem that the flow velocity distribution becomes inaccurate and adversely affects the measurement accuracy.

  Therefore, the present invention more accurately eliminates the ultrasonic echo based on the longitudinal wave out of the ultrasonic echo caused by the two measurement lines of the longitudinal wave and the transverse wave propagating in the pipe body such as a pipe, and the flow velocity distribution and the flow rate. It is intended to provide a clamp-on type Doppler type ultrasonic flow velocity distribution meter that can measure the above.

JP 2000-97742 A (FIGS. 1 and 2)

In order to achieve the above object, the invention described in claim 1 is the ultrasonic wave incident on the fluid to be measured inside the tubular body from the ultrasonic transducer installed outside the tubular body, and exists in the fluid to be measured. A clamp-on type Doppler ultrasonic flow velocity distribution meter that measures the flow velocity distribution of the fluid under measurement by utilizing the fact that the frequency of the ultrasonic wave reflected by the reflector changes due to the Doppler effect. In a clamp-on type Doppler ultrasonic flow velocity distribution meter in which a sound wave propagation wedge is interposed between a sound wave generation source of a transducer and the tube body,
The wedge is made of a material having an acoustic impedance close to that of the tubular body,
The incident angle of the ultrasonic echo incident on the tube from the fluid to be measured is
A longitudinal wave that is equal to or greater than the critical angle of the longitudinal wave determined from the sound velocity in the fluid to be measured and the longitudinal wave in the tube, and the transverse wave determined from the sound velocity in the fluid to be measured and the sound velocity of the transverse wave in the tube. The sound wave generation source is tilted and fixed to the wedge so as to be equal to or less than the critical angle.

According to the second aspect of the present invention, an ultrasonic wave is incident on a fluid to be measured inside the tubular body from an ultrasonic transducer installed outside the tubular body, and the frequency of the ultrasonic wave reflected by a reflector existing in the fluid to be measured. Is a clamp-on type Doppler type ultrasonic flow velocity distribution meter that measures the flow velocity distribution of the fluid to be measured by utilizing the change due to the Doppler effect, the ultrasonic wave generation source of the ultrasonic transducer that generates ultrasonic waves and the tube body In a clamp-on type Doppler ultrasonic flow velocity distribution meter with a sound-propagating wedge interposed between
The wedge is made of a material having an acoustic impedance close to that of the tubular body,
The incident angle of the ultrasonic echo incident on the tube from the fluid to be measured is
The sound wave source is inclined and fixed to the wedge so as to be equal to or less than the critical angle of the longitudinal wave determined from the sound velocity in the fluid to be measured and the longitudinal wave velocity in the tube, and
The sound wave generation source is arranged at a position where only the transverse wave of the ultrasonic echo propagated through the tube body and the wedge can be received.

Further, as described in claims 3 to 8, a sound propagation resin or metal can be used for the wedge and the tube.
Examples of the sound propagation resin include polyvinyl chloride, acrylic, FRP (fiber reinforced plastic), polyethylene, Teflon (registered trademark), tar epoxy, mortar, and the like, and the sound propagation metal includes iron, steel, Tag tile cast iron, cast iron, stainless steel, copper, lead, aluminum, brass, etc.
In particular, the wedge and the tube are preferably formed of the same type of resin or metal having sound wave propagation properties.

According to the first aspect of the present invention, the longitudinal wave of the ultrasonic echo propagating in the tubular body is removed from the fluid to be measured, and the ultrasonic transducer has an ultrasonic echo along one measurement line due to the transverse wave. Since only the signal is received, the acoustic noise caused by the longitudinal wave is reduced.
Further, according to the invention described in claim 2, even if a longitudinal wave of an ultrasonic echo propagating in the tubular body is generated as a result of reducing the inclination angle of the ultrasonic transducer, the position where only the transverse wave can be received Since the ultrasonic transducer is disposed in the same manner as in the first aspect, the acoustic noise caused by the longitudinal wave is reduced.
Accordingly, in any of the inventions, the measurement accuracy of the flow velocity distribution is improved, and the flow rate can be calculated with high accuracy.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 is a block diagram of the main part of a first embodiment corresponding to claim 1. The constituent elements are substantially the same as those shown in FIGS. 6, 9, 10 and the like, but the reference numerals are changed for convenience.

In FIG. 1, reference numeral 51 denotes an ultrasonic transducer as a sound wave generation source of an ultrasonic transducer, which is made of a piezoelectric material such as PZT (zircon / lead titanate) and also serves as an ultrasonic transmitter / receiver.
Reference numeral 52 denotes a wedge, and an ultrasonic transducer 51 is fixed to an inclined surface 52a formed at the upper end portion thereof with an epoxy adhesive or the like. Further, 53 is a pipe through which the fluid 54 to be measured passes.

  Here, the material of the wedge 52 and the pipe 53 is a resin material having sound propagation properties such as polyvinyl chloride, acrylic, FRP, polyethylene, Teflon (registered trademark), tar epoxy, mortar, or iron, steel, tag tile cast iron, It is a metal material with sound propagation characteristics such as cast iron, stainless steel, copper, lead, aluminum, brass, etc. In any case, the wedge 52 and the pipe 53 are formed of a material having a similar acoustic impedance (including the same or almost the same). Has been. Preferably, the wedge 52 and the pipe 53 are formed of the same type of metal (for example, stainless steel) or resin.

Incidentally, the inclined surface 52a, as the inclination angle of the ultrasonic transducer 51 with respect to a direction perpendicular to the longitudinal direction of the pipe 53 (angle of incidence of the ultrasonic pulses at the interface between the wedge 52 and the pipe 53) is theta _in Inclined.
In FIG. 1, θ _pl is the refraction angle (outgoing angle) of the longitudinal wave in the pipe 53, and θ _fl is the refraction angle (outgoing angle) of the longitudinal wave in the measured fluid 54.

In the configuration of FIG. 1, the inclination angle θ _{in and the} like when the wedge 52 and the pipe 53 are made of stainless steel and the fluid 54 to be measured is water will be considered.
By the way, the sound speed of longitudinal waves in stainless steel is about 5750 [m / s], the speed of sound of shear waves is about 3250 [m / s], and the speed of sound in water is about 1490 [m / s].

As described above, when the sound waves from the medium 1 to the medium 2 is incident, since the acoustic velocity c ₂ in the medium 2 is a critical angle exists is larger than the sound velocity c ₁ at the medium 1 (c 1 _{<c 2),} In the example of FIG. 1, a critical angle exists when an ultrasonic echo enters the pipe 53 from the fluid to be measured 54. In addition, since the material of both is the same between the wedge 52 and the piping 53, a sound wave is propagated as it is.

As described above with reference to FIG. 5, when a sound wave propagates from the medium 1 to the medium 2, the propagation angle θ _in of the sound wave in the medium 1 and the medium 2 (incident angle at the boundary surface between both media) and θ _out (same The relationship with the refraction angle or the exit angle is as shown in Equation 3. The relationship of Equation 3 is between the inclination angle θ _in and the refraction angle θ _{pl in} FIG. 1 and the refraction angle θ _pl (that is, the pipe 53). This also applies between the angle of incidence at the boundary surface between the liquid and the fluid to be measured 54 and the refraction angle θ _fl .

When the sound wave is incident on the medium 2 from the medium 1 and the sound speed c ₂ in the medium ₂ is larger than the sound speed c ₁ in the medium 1 (c ₁ <c ₂ ), the critical angle θ _c is given by Street.

Therefore, when the critical angle θ _c when the ultrasonic echo enters the pipe 53 from the fluid to be measured 54 is calculated according to Equation 4, it is 15.5 degrees for the longitudinal wave and 23.4 degrees for the transverse wave. For this reason, the incident angle (this is θ _f . This θ _f is equal to θ _fl in FIG. 1) when the ultrasonic echo enters the pipe 53 from the measured fluid 54 is 15.5 degrees or more. Therefore, only the transverse wave propagates to the pipe 53, and the longitudinal wave does not propagate.
Therefore, when the inclination angle θ _in of the ultrasonic transducer 51 for setting θ _fl (= θ _f ) within the above range is obtained by the above equation 3, the inclination angle θ _in is 34.3 degrees or more and 60 degrees or less. Become.

For example, when the inclination angle θ _in of the ultrasonic transducer 51 is 45 degrees, the transverse sound wave generated from the ultrasonic transducer 51 enters the boundary surface between the wedge 52 and the pipe 53 made of the same material at an angle of 45 degrees. It exits and exits (enters) the fluid under measurement 54 at 18.9 degrees. That is, θ _in = θ _pl = 45 degrees and θ _fl = 18.9 degrees _in FIG. In FIG. 1, in consideration of the case where the wedge 52 and the pipe 53 are generally not the same material, the sound wave propagation paths inside the wedge 52 and the pipe 53 are not drawn in a straight line.

  The sound wave incident on the fluid under measurement 54 at 18.9 degrees is reflected by suspended particles or the like in the measurement region and enters the pipe 53 as an ultrasonic echo at an incident angle of 18.9 degrees. Since this incident angle is not less than the critical angle (15.5 degrees) of the longitudinal wave and not more than the critical angle (23.4 degrees) of the transverse wave, only the transverse wave is generated in the pipe 53 without generating the longitudinal wave. To propagate. When only the ultrasonic wave echo of the transverse wave is received by the ultrasonic transducer 51, the ultrasonic transducer due to the longitudinal wave is not received by the ultrasonic transducer, and the acoustic noise is reduced. For this reason, the measurement accuracy of the flow velocity distribution is improved, and the flow rate can be calculated with high accuracy.

  In addition, the measurement principle of the flow velocity distribution and the calculation method of the flow rate in the present embodiment are the same as those in the prior art, and thus the description thereof is omitted.

Next, FIG. 2 is a block diagram of the main part of the second embodiment corresponding to claim 2.
In this embodiment, as shown in detail in FIG. 2B, the inclination angle θ _in of the ultrasonic transducer 51 is equal to or less than the critical angle of the longitudinal wave when the ultrasonic echo enters the pipe 53 from the fluid to be measured 54. This value is an example.

When the inclination angle θ _in is set as described above, the incident angle θ _fl to the measured fluid 54 in FIG. 1 is always a value equal to or smaller than the critical angle of the longitudinal wave, and the ultrasonic wave from the measured fluid 54 to the pipe 53 is set. Since the incident angle θ _{f of the} echo is also equal to or less than the critical angle of the longitudinal wave, a longitudinal wave and a transverse wave are generated in the pipe 53. However, as shown in FIG. 2, by arranging the ultrasonic transducer 51 at a position where only the transverse wave can be received on the inclined surface 52a, the ultrasonic echo due to the longitudinal wave is not received and the acoustic noise is reduced. Thus, the same effect as that of the first embodiment can be obtained.
In FIG. 2, θ _ps is the refraction angle (outgoing angle) of the transverse wave at the boundary surface between the fluid 54 to be measured and the pipe 53.

Here, when the inclination angle θ _in of the ultrasonic transducer 51 is slightly larger than the critical angle of the longitudinal wave when the ultrasonic echo enters the pipe 53 from the fluid to be measured 54, the material of the wedge 52 and the pipe 53, and Depending on the type of the fluid 54 to be measured, the incident angle of the ultrasonic echo to the pipe 53 may be smaller than the critical angle of the longitudinal wave. In this case as well, the vertical angle within the pipe 53 as shown in FIG. Waves and shear waves are generated.
Therefore, in this embodiment, the ultrasonic transducer 51 is arranged so that the ultrasonic echo enters the pipe 53 at an angle equal to or smaller than the critical angle of the longitudinal wave when the ultrasonic echo enters the pipe 53 from the fluid to be measured 54. The ultrasonic transducer 51 may be arranged at a position where the inclination angle θ _in is set and only the transverse wave of the ultrasonic echo can be received via the pipe 53 and the wedge 52.

It is a block diagram of the principal part which shows 1st Embodiment of this invention. It is a block diagram of the principal part which shows 2nd Embodiment of this invention. It is a block diagram which shows a prior art. It is explanatory drawing of the principle of operation of a Doppler type ultrasonic flowmeter. It is a figure which shows the propagation state of the sound wave between different media. It is explanatory drawing of the measurement conditions described in the references 2 and 3. It is a figure which shows the relationship between the incident angle described in the reference document 4, and the transmittance | permeability and reflectance. It is a figure which shows the relationship between the incident angle described in the reference document 4, and the transmittance | permeability and reflectance. It is explanatory drawing of the behavior of the ultrasonic echo in FIG. It is the figure which expanded and showed FIG. It is explanatory drawing of the flow-velocity distribution for demonstrating the subject of this invention.

Explanation of symbols

51: Ultrasonic vibrator 52: Wedge 52a: Slope 53: Piping 54: Fluid to be measured

Claims (8)

Utilizes the fact that ultrasonic waves are incident on the fluid to be measured inside the tube from an ultrasonic transducer installed outside the tube, and the frequency of the ultrasonic waves reflected by the reflector present in the fluid to be measured changes due to the Doppler effect. A clamp-on type Doppler type ultrasonic flow velocity distribution meter for measuring a flow velocity distribution of a fluid to be measured, wherein a wedge of sound wave propagation is provided between a sound wave generation source of an ultrasonic transducer for generating an ultrasonic wave and the tube body. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter,
The wedge is made of a material having an acoustic impedance close to that of the tubular body,
The incident angle of the ultrasonic echo incident on the tube from the fluid to be measured is
A longitudinal wave that is equal to or greater than the critical angle of the longitudinal wave determined from the sound velocity in the fluid to be measured and the longitudinal wave in the tube, and the transverse wave determined from the sound velocity in the fluid to be measured and the sound velocity of the transverse wave in the tube. A clamp-on type Doppler type ultrasonic flow velocity distribution meter, wherein the sound wave generation source is tilted and fixed to the wedge so as to be equal to or less than a critical angle. Utilizes the fact that ultrasonic waves are incident on the fluid to be measured inside the tube from an ultrasonic transducer installed outside the tube, and the frequency of the ultrasonic waves reflected by the reflector present in the fluid to be measured changes due to the Doppler effect. A clamp-on type Doppler type ultrasonic flow velocity distribution meter for measuring a flow velocity distribution of a fluid to be measured, wherein a wedge of sound wave propagation is provided between a sound wave generation source of an ultrasonic transducer for generating an ultrasonic wave and the tube body. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter,
The wedge is made of a material having an acoustic impedance close to that of the tubular body,
The incident angle of the ultrasonic echo incident on the tube from the fluid to be measured is
The sound wave source is inclined and fixed to the wedge so as to be equal to or less than the critical angle of the longitudinal wave determined from the sound velocity in the fluid to be measured and the longitudinal wave velocity in the tube, and
A clamp-on type Doppler ultrasonic flow velocity distribution meter, wherein the sound wave generation source is disposed at a position where only the transverse wave of an ultrasonic echo propagated through the inside of the tube and the wedge can be received. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter according to claim 1 or 2,
A clamp-on type Doppler ultrasonic flow velocity distribution meter, wherein the wedge is made of a resin having sound propagation properties such as polyvinyl chloride, acrylic, FRP, polyethylene, Teflon (registered trademark), tar epoxy, mortar, or the like. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter according to any one of claims 1 to 3,
A clamp-on type Doppler ultrasonic flow velocity distribution meter characterized in that the tube body is made of a sound-propagating resin such as polyvinyl chloride, acrylic, FRP, polyethylene, Teflon (registered trademark), tar epoxy, or mortar. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter according to any one of claims 1 to 4,
A clamp-on type Doppler type ultrasonic flow velocity distribution meter, wherein the wedge and the tube are made of the same kind of sound propagation resin. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter according to claim 1 or 2,
A clamp-on type Doppler type ultrasonic flow velocity distribution meter, wherein the wedge is made of a metal having sound propagation properties such as iron, steel, tag tile cast iron, cast iron, stainless steel, copper, lead, aluminum, brass. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter according to claim 1, 2, or 6,
A clamp-on type Doppler type ultrasonic flow velocity distribution meter characterized in that the pipe body is made of a sound-propagating metal such as iron, steel, tag tile cast iron, cast iron, stainless steel, copper, lead, aluminum, or brass. In the clamp-on type Doppler type ultrasonic flow velocity distribution meter according to claim 1, 2, 6, or 7,
The clamp-on type Doppler ultrasonic flow velocity distribution meter, wherein the wedge and the tube are made of the same kind of sound-propagating metal.

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