JPH06103206B2 - Ultrasonic velocity measuring method and apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to an ultrasonic velocity measuring method and apparatus,
In particular, the present invention relates to an ultrasonic flow velocity measuring method and apparatus for mounting an ultrasonic wave transmitter / receiver on the outer surface of a pipe to measure the internal flow velocity.

[Conventional technology]

A conventional example is shown in FIG. In the conventional example of FIG. 9,
The ultrasonic waves output from the ultrasonic transducer 51 of one ultrasonic wave transmitter / receiver 50 toward the downstream side are propagation paths l ₁ , l ₂ , l ₃ , l ₄ ,
And l ₅ and the ultrasonic transducer 61 of the other ultrasonic transducer 60.
Leading to. The propagation time in this case is t _d .

In addition, the ultrasonic waves output from the ultrasonic transducer 61 of the other ultrasonic transducer 60 toward the upstream side are propagated through the propagation paths l ₅ , l ₄ ,
The ultrasonic transducer 51 of one ultrasonic wave transmitter / receiver 50 reaches the ultrasonic transducer 51 via l ₃ , l ₂ , and l ₁ . The propagation time in this case is t _u .

In this case, the flow velocity in the pipe 3 is calculated by the following equation.

^{V = (C 2 / 2Dtanθ)} · (t u -t d) ... (a) where, D is the inner diameter of the pipe 3, theta is the angle of refraction in the fluid, C
Indicates the speed of sound of the fluid.

As a result, if the sonic velocity of the fluid is fixed in advance, the flow velocity of the fluid in the pipe 3 can be measured relatively easily based on the above equation, and at the same time, the inner diameter of the pipe 3 becomes clear. Therefore, the flow rate of the fluid in the pipe 3 can be obtained very easily.

[Problems to be solved by the invention]

However, the directivity of ultrasonic waves, that is, the spread in the propagation direction, changes significantly depending on the size of the vibration source (vibrator or vibration surface). On the other hand, the possible value of the incident angle Φ largely depends on this directivity. That is, when the vibration source becomes smaller, the incident angle Φ becomes wider. Therefore, in the flow measurement using ultrasonic waves, many errors are likely to be included in the measurement value depending on the measurement conditions.

The directivity angle β of the first zero-width glancing angle that indicates the magnitude of this directivity
Is generally represented by β≈57 · λ / b (degrees) (b). Here, b represents the width of the vibration source, and λ represents the wavelength of the ultrasonic wave in the propagation medium.

On the other hand, in the ultrasonic transducer for the flow meter which is usually used most often, the dimension of the contact surface with respect to the pipe is b≈
Many are 5λ to 8λ. Those with b≈10λ are extremely rare. Therefore, the directivity angle β is β even if b≈10λ.
≈5.7 °. Therefore, in a normal ultrasonic transducer,
It always has a divergence angle of ± 3 ° or more.

As described above, the conventional ultrasonic transducer has a wide directivity, which is because the spread of the refraction angle θ is a direct cause of the fluid velocity error, as shown in the equation (b). It takes a lot of time and effort on the receiving side to specify the center position of the ultrasonic wave propagating at an appropriate angle from the beam with a wide angle width so that the refraction angle is set correctly. There was an inherent drawback.

At the same time, the spread of the directivity angle of the propagating ultrasonic wave depends on one or more excitation conditions (determined by the incident angle) of a plurality of resonance modes (A mode or S mode of plate wave) peculiar to the thickness of the pipe. Approach and include.

For this reason, on the receiving side, the receiving position is set so as to always detect the maximum value, so that other resonance modes with large energy transmittance are often detected, and a significant error occurs in the measured value. That is, the directivity angle of the ultrasonic wave is wide, and the ultrasonic beam cannot be regarded as a parallel beam.
In addition, because the propagation mode of the ultrasonic waves cannot be accurately specified in the wedge, in the pipe wall, and in the fluid in the pipe because it propagates in an unexpected direction due to the harmful mode, it was measured. It becomes difficult to capture how much of the propagation time t _u , t _d it took to pass through the pipe fluid, and the principle of measurement is based on the Doppler effect. In total, there was a drawback that the accuracy was essentially unreliable.

[Object of the Invention]

The present invention improves the inconvenience of the conventional example, and particularly measures the flow velocity of the fluid in the pipe with high accuracy even if the distance between the pair of ultrasonic transducers mounted on the pipe is roughly set. It is an object of the present invention to provide an ultrasonic flow velocity measuring method and an apparatus therefor capable of good workability.

[Means for solving problems]

Therefore, in the present invention, two ultrasonic wave transmitters / receivers each having a remarkably small directivity angle are arranged at appropriate intervals on the upstream side and the downstream side of the pipe to be measured, respectively, and the ultrasonic wave from the outer wall of the pipe is Measure the sound velocity C ₁ of the wedge part in the ultrasonic transducer at the time of measuring by alternately injecting sound waves obliquely, and before or after these measurements, from the upstream side to the downstream side, or from the downstream side to the upstream side. The ultrasonic waves are oscillated to the respective sides, and the times t _d and t _u until each of the oscillated ultrasonic waves propagates through the pipe wall and the pipe fluid and is received are sequentially measured, and these measured values C ₁ , T _d , t _u and the interval L _X between the ultrasonic transducers are substituted into a predetermined function, that is, V = F (C ₁ , t _u , t _d , L _X ) Is calculated along with the necessary constants for calculating the flow velocity V of the fluid in the pipe. Serial is intended to achieve the objectives.

Example of Invention

An embodiment of the present invention will be described below with reference to FIGS. 1 to 8.

In FIG. 1, reference numeral 1 denotes one ultrasonic wave transmitter / receiver installed on the upstream side of the pipe 3, and reference numeral 2 denotes the other ultrasonic wave transmitter / receiver installed on the downstream side of the pipe 3. Among them, the ultrasonic transmitter / receiver 1 on one side includes a wedge member 1A and a vibrator for causing ultrasonic waves to obliquely enter the pipe 3 as shown in FIG.
Equipped with 1B. The wedge member 1A is made of acrylic resin or the like, has a trapezoidal cross section, and one of the slopes 1a
The ultrasonic transducer 1B is fixed to the. Also, the other slope
1c constitutes an ultrasonic reflection surface orthogonal to the propagation path when the ultrasonic wave transmitted from the ultrasonic transducer 1B is reflected by the incident surface 1b as an ultrasonic wave emission surface and propagates in the wedge member 1A. ing. Therefore, the internal reflected wave propagating through the wedge member 1A returns to the ultrasonic transducer 1B side. Furthermore, the incident surface that becomes the opening surface when leaking and radiating ultrasonic waves into the tube
The length b of 1b is about 18 wavelengths or more with respect to the center frequency used.

As shown in FIG. 4, when the opening of the transducer 1B is longer than a certain length and the length b of the incident surface 1b is about 18 waves or more, the directivity angle becomes very small. Therefore, the ultrasonic transducer The ultrasonic beam that sequentially propagates through the wedge portion, the pipe wall portion, and the fluid portion inside the pipe can be regarded as a substantially parallel beam.

As shown in FIG. 1, each of these ultrasonic wave transmitters / receivers 1 and 2 is separately connected to a transmission circuit section 11 and a reception circuit section 12 via a transmission / reception switching section 10. In FIG. 1, the case where the liquid in the pipe 3 flows from the left side to the right side of the drawing is shown.

In each of the ultrasonic wave transmitters / receivers 1 and 2, a repetitive signal as shown in FIG. 2 is received according to the flow velocity in the pipe 3. That is, as shown in FIG. 1, the ultrasonic wave output from the ultrasonic transducer 1 on the upstream side propagates in the pipe wall of the pipe 3 and the propagating wave A in the pipe 3 via the pipe wall of the pipe 3. Of the propagation wave B into the liquid.

This will be described in more detail. First, when the ultrasonic waves are output from the upstream side to the downstream side, the received signal of the incoming ultrasonic wave shown in FIG. 2 (1) is sent to the time measuring means 13 via the receiving circuit section 12 and the signal selecting means 13A. The transmission time t _d is timed and stored in the first memory 14 temporarily.

Next, when the transmission / reception switching unit 10 operates and an ultrasonic wave is output from the downstream side to the upstream side, the received signal of the incoming ultrasonic wave shown in FIG. It is sent to the time measuring means 13 via the propagation time t _{u, and} is temporarily stored in the first memory 14.

Next, before and after the above operation, the sound velocity C ₁ in the wedge in the ultrasonic transducer is measured. This does not have to be performed for each flow velocity measurement, and can be appropriately performed when necessary. good. When measuring the speed of sound in wedges, either one of the ultrasonic wave transmitters / receivers 1 or 2 is connected to the transmission circuit unit 11 and the reception circuit unit 12 via the transmission / reception switching unit 10 shown in FIG. For example, when the ultrasonic wave transmitter / receiver 1 is connected, the ultrasonic wave output from the transducer 1B shown in FIG. 2 passes through the path l _{1 in} FIG.
It propagates back and forth through l ₁ ′ and is received by the oscillator 1B. This signal is sent to the time measuring means 13 via the receiving circuit section 12 and the signal selecting means 13A, where the propagation time thereof, for example, t _w, is timed and temporarily stored in the first memory 14.

The data of the propagation times t _d , t _u and t _w stored in the first memory 14 are immediately sent to the calculating means 17. Then, the flow velocity V calculated and specified by the calculating means 17 based on the equation is displayed by the displaying means 18. Further, the flow rate is calculated by the flow velocity V and the cross-sectional area in the pipe.
It is calculated in 17, and this is also displayed on the display means 18. 19 is
A main control unit that controls a series of operations of each of these components is shown.

Next, a theoretical process of obtaining the flow velocity V using the measured propagation times t _w , t _u , and t _d will be described.

First, the speed of sound C ₁ in the wedge in the ultrasonic transducers 1 and 2 is obtained by the following equation.

_{C 1 = 2 (l 1 +} l 1 ') / t w ...... However, where l _1, l _1' is the path length of the path l _1, l ₁ 'shown in Figure 3.

This will be described below with reference to FIG.

The total propagation time t _o when the flow velocity V = 0 is given by the following equation.

T _o = [2 {(L _x −L _o ) / 2} · sin θ ₁ / C ₁ ] + {2 (d / co
_{sθ 2) / C 2} +} {N (D / cosθ 3) / C 3 + τ c ...... Here, L _o is the distance between incident point 1P and 2P center-path g _o, L _x is the vibration Sub-junction surfaces 1a and 2a and ultrasonic radiation surface 1b and
The intersection with 2b, the distance between 1R and 2R. θ ₁ , θ ₂ , and θ ₃ are the incident angles of ultrasonic waves inside the wedge, inside the wall, and inside the fluid, and C ₁ , C ₂ , and C ₃ are the respective sound velocities. However, since these have a narrow ultrasonic directivity angle, they satisfy Snell's law. d is the plate thickness of the tube, and D is the tube inner diameter. N is the number of ultrasonic fluid inner diameter paths, and in the case of FIGS. 1 and 4, N = 2
Becomes τ _c indicates an electrical delay time in the cable or the like.

Next, when the flow velocity V is not 0, the propagation times t _w , t that can be obtained
_d is as follows.

t _u = [{(L- _Lo ) sin θ ₁ } / C ₁ ] + {(2d / cos θ ₂ )
_{/ C 2} + {(ND} / cosθ 3) / (C 3 -Vsinθ 3)} + τ c ...
... t _d = [{(L- _Lo ) sin θ ₁ } / C ₁ ] + {(2d / cos θ ₂ ).
_{/ C 2} + {(ND} / cosθ 3) / (C 3 + Vsinθ 3)} + τ c ...
… Normally C ₃ >> V (For example, if the fluid is water, C ₃ ≈ 1500 m /
Since the maximum values of s and V are also 20 m / s, approximately t _o = (t _u + t _d ) / 2 ...... Therefore, the flow velocity V is V = (by Snell's law and the approximation of C ₃ >> V C ₁ ³ / sin θ ₁ ) ・ [{(t _u + t _d -2τ) (t _u −
t _d )} / {C ₁ ² (t _u + t _d -2τ) ² + (2NDsin θ ₁ ) ² }]
…… However, τ = {(Lsinθ ₁ ) / C ₁ } + {(2dcosθ ₂ ) /
C ₂ } + τ _c …… As a result, the first memory 14 stores the wedge inner path length (l ₁ +
l ₁ ′), installation interval L _x , angle of incidence in wedge θ ₁ , sound velocity in tube wall C ₂ , delay time in cable τ C, number of paths in fluid N,
If the tube thickness d and the tube inner diameter D are stored, the equation and the following equation cos θ ₂ / C ₂ = (1 / C ₂ ) ² − (sin θ ₁ / C ₁ ) ² ... Can be used to calculate the flow velocity V. According to this method, the sound velocity C ₃ in the fluid is As a result, the sonic velocity C _{3 of the} fluid is unnecessary in the equation of the flow velocity V. That is, even if the sound velocity C _{3 of the} fluid is unknown, it can be sufficiently obtained by this method.

The distance L _o between the incident point 1P and 2P are also no longer needed in the expression, thus resulting in eliminating the need to strictly identify those that point of incidence of the ultrasonic transducer at all, mounting It only needs to know the distance L _x . Therefore, the accuracy of the mounting device of the ultrasonic wave transmitter / receiver is almost unnecessary, and a considerable allowable range is expected.

The above two points are that in the conventional ultrasonic flowmeter, the sound velocity C ₃ of the fluid becomes unknown due to the temperature change of the fluid,
It also means that the problem that the incident points 1P, 2P or the propagation route was unknown was overcome.

From the above points of view, the predetermined function specified in the claim (1) of the patent refers to the entire function group including the expression, centering on the expression.

Here, the error of the measurement value in the ultrasonic flowmeter is significantly changed by the directivity of the ultrasonic transducers 1 and 2,
A description will be given based on the relationship with the conventional example and the experimental results.

In FIG. 5, in the conventional case, the ultrasonic wave incident on the pipe 3 from the ultrasonic wave transmitter / receiver 1 at the incident angle Φ ₀ is generally ± 3 ° or more with respect to the central refraction angle θ ₀ as described above. It propagates in the pipe 3 with a spread, is reflected or re-radiated by the inner wall on the opposite side, and propagates to the ultrasonic wave transmitter / receiver 2 on the receiving side.

Furthermore, if the incident angle with this spread is near the excitation condition of the resonance mode (plate wave) of the pipe described above, the plate wave of V _po will be generated in the tube wall part of the ultrasonic transducer 1. Is the fifth
The leakage waves are generated as shown in the figure, and at the same time, with the propagation of the plate wave V _po , a leaky wave tends to be radiated toward a specific direction in the pipe 3, for example, θ ₁ . The leaky propagating wave is reflected or re-radiated on the opposite wall surface. As a result, the receiving pipe 3
In the pipe wall portion of, the ultrasonic wave of the component propagating in the fluid in the pipe 3 from the direction of θ ₁ is also received, and the refraction angle of the received wave is initially Snell's law. It differs from the expected direction of θ ₀ .

When this is further illustrated with a specific example, in FIG. 3, the wedge member 1A, the 2A and acrylic resin, 1 using ultrasound [MH _z], to form the pipe 3 in steel thickness 3.2 mm. , Consider the case where water flows inside. In this case, the energy transmittance is as shown in FIG.

Now, if the incident angle Φ ₀ is set to Φ ₀ = 47 °, then θ ₀ = 23 ° into the flowing water of the pipe 3 according to Snell's law of refraction.
The ultrasonic waves are radiated into the liquid with a spread of 20 ° to 26 ° in the direction of, and the reflected leaky waves are reflected and propagated to the ultrasonic transducer 2 side. In the ultrasonic wave transmitter / receiver 2 part, when converted from Snell's law, reflected waves in this range will receive ultrasonic waves obtained by exciting the pipe 3 in the range of the incident angle of 38 ° to the incident angle of 61 °. . In this range, the S ₀ mode exists as shown in FIG.

Therefore, in the specific example described with reference to FIG. 6, although the ultrasonic wave obtained at the incident angle Φ ₁ = 47 ° is output, the receiving side has the incident angle Φ ₁ = 56 ° and the S ₀ mode As the ultrasonic wave of the resonance wave is output, the ultrasonic wave component of the refraction angle different from the originally planned refraction angle is strongly received. As a result, the measured value is less reliable.

Next, consider the case of the present invention in which b = 18λ is set in FIG. In this case, according to the equation (b), β≈3.2 °, and the directivity is ± 1.6 °. In this case, as shown in FIG. 7, the incident angle Φ ₀ = 47 °, while the receiving side is 38 ° to 5 °.
Receives propagating waves in the direction of 2 °. Therefore, in such a case S
_{Since the 0} mode is hardly generated and harmful waves having different refraction angles are hardly generated, it is possible to effectively receive the ultrasonic waves on the transmission side with the refraction angle θ ₀ originally planned.

Fig. 8 shows the relationship between the size (length) of the radiating apertures of the ultrasonic transducers 1 and 2 and the error in the measured values in terms of flow velocity in the case of specific flow rate measurement, in addition to this series of examinations. Was experimentally investigated. As a result of this experiment, it was obtained that the size of the radiation aperture surface is b ≧ 15λ and the error is 1.5% or less.

Therefore, from the formula (b) and the experimental result of FIG. 8, b ≧ 18λ
If so, the directivity is within ± 1.6 °, and the characteristics are close to those of a parallel beam. Therefore, it is possible to obtain the proof that the measurement error can be sufficiently reduced.

Therefore, in the above embodiment, the ultrasonic waves emitted from the transducer 1B of the ultrasonic wave transmitter / receiver 1 are the dotted lines g ₁ and g _{3 in} FIG.
Is propagated as a parallel beam, reflected by the bottom surface of the tube, and finally received by the transducer 2B of the ultrasonic wave transmitter / receiver 2. However, in this case, only the ultrasonic beam passing through the shaded area in the figure, that is, the area sandwiched between the dotted lines g ₁ and g ₂ , is effectively received, and the other area, that is, the dotted line g ₂ The ultrasonic beam passing through the region sandwiched by g ₃ is not received. The central path at this time is shown by the solid line g ₀ .

Therefore, even if the other ultrasonic transmitter / receiver 2 is arranged at a different position x as shown in FIG. 4, for example, it must receive the ultrasonic beam in the range surrounded by g ₂ and g ₃ . Becomes In this respect, the change in the mounting position of the ultrasonic wave transmitter / receiver 2 does not hinder the measurement.

〔The invention's effect〕

Since the present invention is configured and functions as described above, according to this, it becomes extremely easy to adjust the set position of the ultrasonic transmitter / receiver, and it is necessary to perform highly accurate positioning of the ultrasonic transmitter / receiver as in the conventional case. If the relative distance between the ultrasonic transducers and the size of the opening length of the ultrasonic transducers are clear, the values can be used as the basic data for calculating the flow velocity. It can be performed with high accuracy, and if the sound speeds of the parts exposed to the outside, that is, the wedge members of the ultrasonic transducer and the pipe to be measured are accurately measured beforehand, the sound velocity of the fluid in the pipe is unknown. However, it is possible to provide an unprecedented excellent ultrasonic flow velocity measuring method and its device, which can perform highly accurate flow velocity measurement without temperature correction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of the measurement data of FIG. 1, and FIG. 3 is an ultrasonic wave used in the embodiment of FIG. FIG. 4 is an explanatory view showing an example of a wave transmitter / receiver, FIG. 4 is an explanatory view showing the operation of the ultrasonic wave transmitter / receiver portion at the time of measurement in FIG. 1, and FIG. 5 is an ultrasonic wave transmitter / receiver showing the spread of ultrasonic waves. FIG. 6 is an explanatory diagram showing the operation of the received wave when the directivity angle is wide and the acoustic resonance point of the pipe to be measured. FIG. 7 is the received wave spread when the directivity angle is narrow. And FIG. 8 is an explanatory diagram showing acoustic resonance points of the pipe to be measured, FIG. 8 is a diagram showing how the received wave spreads when the spread angle of the directional characteristic is small in this embodiment, and FIG. 9 is a conventional example. FIG. 1,2 …… Ultrasonic transducers, 1A, 2A …… Wedge members, 3 ……
Piping, 10 …… Transmission / reception switching section, 11 …… Transmission circuit section, 12 ……
Reception circuit section, 13 ... Clocking means, 14 ... First memory as storage means, 17 ... Computing means, 19 ... Main control section.

Claims (2)

[Claims] 1. An ultrasonic wave transmitter / receiver formed with a remarkably small directivity angle is arranged at appropriate intervals on an upstream side and a downstream side of a pipe to be measured, and ultrasonic waves are transmitted from an outer wall of the pipe. Alternately obliquely incident to measure the sound velocity C ₁ of the wedge part in the ultrasonic transducer at the time of measurement, and before and after these measurements, from the upstream side to the downstream side,
Or, while oscillating ultrasonic waves from the downstream side to the upstream side respectively, sequentially measuring the time t _d , t _u until each of the oscillated ultrasonic waves propagates through the pipe wall and the pipe fluid and is received, The measured values C ₁ , t _d , t _u and the distance L _X between the ultrasonic transducers are defined by a predetermined function, that is, V = F (C ₁ , t _u , t _d , L _X ). The ultrasonic flow velocity measuring method is characterized in that the flow velocity V of the fluid in the pipe is calculated by substituting into the above formula and other necessary constants. 2. An ultrasonic wave transmitter / receiver, which is arranged on the upstream side and the downstream side of a pipe along the propagation line of the ultrasonic wave and has a significantly small directivity angle, and these two ultrasonic wave transmitters / receivers. The oscillator circuit unit and the receiver circuit unit is provided with a transmitter / receiver switching unit that is alternately switched and connected as necessary, and the receiver circuit unit outputs from the ultrasonic transmitter / receiver from the upstream side to the downstream side or Time measuring means for measuring the propagation times t _d , t _u until the ultrasonic waves transmitted from the downstream side to the upstream side are respectively propagated and received in the pipe wall and the fluid inside the pipe, and the propagation times t _d , t _u. And a storage means for storing the value of the mounting interval L _X of the ultrasonic transmitter / receiver, and in this storage means, the measured value of the sound velocity C ₁ of the wedge portion in the ultrasonic transmitter / receiver at the time of measuring the flow velocity, etc. The necessary constants are stored in memory, and each output of this storage means is stored. An ultrasonic flow velocity measuring device, comprising: a flow velocity calculation means for performing a predetermined calculation based on force information to identify a flow velocity of a fluid in a pipe.