JP2005189003A - Integration system capable of flow rate measurement and bubble detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To share an oscillator in flow rate measurement and bubble detection regarding an integration system capable of measuring the speed of fluid (flow rate) flowing in a tube and detecting bubbles in the fluid. <P>SOLUTION: By utilizing a resonance of a radial directional oscillation or a lateral oscillation of the oscillators 14u, 14d, an axial directional plate wave is made to generate in a tube 12. By utilizing the resonance of the radial directional oscillation or the lateral oscillation, the oscillators 14u, 14d are made smaller than the case utilizing a thickness directional oscillation or a lateral oscillation. The oscillators 14au, 14ad for detecting bubbles are provided at the positions opposite to the oscillators 14u, 14d across the tube 12. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an integrated system capable of measuring a velocity (flow rate) of a fluid flowing in a tube using a vibrator and detecting bubbles in the fluid.

  Conventionally, there is a flow rate measurement system that measures the flow rate in a tube using a vibrator such as an ultrasonic vibrator. In this flow measurement system, vibrators are installed at two locations, upstream and downstream, and the time required for the wave to propagate from the upstream side to the downstream side and the time required for propagation from the downstream side to the upstream side. From the time difference between and the propagation distance of the wave, the flow velocity in the tube is measured.

  In Patent Document 1, a wave that is obliquely transmitted into the tube using a vibrator that is in contact with the outer wall of the tube in a posture inclined with respect to the axial direction of the tube, and the wave reflected by the inner wall of the tube is another. A configuration in which waves are received by two inclined transducers is disclosed. However, this method has a problem that when the tube is thin, the propagation distance becomes short, so that it is difficult to accurately measure the propagation time shortened thereby.

  Patent Document 2 discloses a configuration in which a tube is inserted into a central hole of an annular plate-like vibrator. According to this method, even when the flow rate in a thin tube is measured, the problem of time measurement accuracy that occurs in the method of Patent Document 1 does not occur.

  On the other hand, there is a bubble detection system that detects the presence or absence of bubbles in a fluid in a tube using a vibrator such as an ultrasonic vibrator. In such a bubble detection system, detection of bubbles is performed by utilizing the fact that the signal intensity decreases when ultrasonic waves pass through the bubbles (for example, Patent Document 3).

JP 2002-22505 A JP 2003-83787 A JP-A-9-99062

  However, with an annular ultrasonic transducer, it is difficult to bring the inner wall of the center hole and the outer wall of the tube into close contact with each other, and the vibration may be attenuated by a gap or the like, resulting in a decrease in flow rate measurement accuracy. It was. In addition, the annular ultrasonic transducer has a problem that it takes time and effort to manufacture compared to a plate-shaped transducer without holes.

  In addition, when using both the flow measurement system and the bubble detection system, it was necessary to prepare them separately for measurement, but if they could be integrated, installation space, measurement effort, cost, etc. There is a big merit in terms of.

  The flow measurement and bubble detection system according to the present invention is a plate-like vibration in which an electrode-formed surface is in direct or indirect contact with the outer wall in a posture along the outer wall of the tube to be flow-measured. A pair of child elements, each of which is a pair of plate-like vibrators for flow rate measurement arranged on the upstream side and downstream side of the tube, and a plate-like vibrator forming the above-mentioned pair for flow rate measurement A drive circuit for flow rate measurement that vibrates at one of the wave transmitting elements at a radial or lateral resonance frequency, and an axial plane wave generated in the fluid in the tube by the vibration of the flow rate measuring element. A propagation time acquisition unit that acquires a propagation time until it is detected by the other vibrator, and at least one of the plate-like vibrators and a plate that is disposed opposite to the plate-like vibrator with the tube interposed therebetween Vibrator A bubble detection drive circuit configured to vibrate using one of a pair of bubble-detecting plate-shaped vibrators and a plate-shaped vibrator forming the bubble-detecting pair as a wave-transmitting element; and And a bubble detection unit that detects bubbles based on the result of detection of the wave generated in the fluid in the tube by the vibration of the wave transmission element by the other detection element.

  Further, in the system capable of measuring the flow rate and detecting the bubble according to the present invention, it is preferable that the bubble detection drive circuit vibrate the transmitting element at the resonance frequency in the thickness direction.

  In the system capable of measuring flow rate and detecting bubbles according to the present invention, it is preferable that the plate-like vibrator is attached to a clamp having a holding portion for holding the tube so as to be detachable.

  In the system capable of measuring flow rate and detecting bubbles according to the present invention, it is preferable that the plate-like vibrator has two arms that can be opened and closed and is attached to a clip that sandwiches the tube by the arms. is there.

  Moreover, the clamp for a system capable of measuring a flow rate and detecting a bubble according to the present invention has a clamping portion for detachably clamping the tube, and the plate-like vibrator is directly or indirectly attached to the outer wall of the tube. So that they are in contact with each other.

  The clip for a system capable of measuring flow rate and detecting bubbles according to the present invention includes two arms for sandwiching the tube, and directly or indirectly abuts the plate-like vibrator on the outer wall of the tube. To hold.

とする必要があることが知られている（ここに、ｃ：流体中の音速、ｄ：チューブの内径）。ここで、内径ｄが小さいほど右辺の値が大きくなり、式（１）の不等式の関係が得られやすいことがわかる。すなわち、この方式は、比較的細いチューブ内の流量を計測するのに適していることがわかる。 In the present embodiment, at the time of flow rate measurement, the tube functions as an acoustic tube, that is, the wave generated by the vibration of the vibrator propagates in the fluid mainly as a plane wave in the tube axis direction. A plane wave can propagate over a relatively long distance and is less attenuated by bending of the pipeline. In order to obtain such a plane wave, the vibration frequency must be sufficiently lower than the lowest resonance frequency in the radial direction of the fluid in the tube, and the tube is a rigid tube having an annular cross section. Assuming that the frequency f of vibration is

(Where c is the speed of sound in the fluid and d is the inner diameter of the tube). Here, it can be seen that the smaller the inner diameter d is, the larger the value on the right side is, and it is easier to obtain the inequality relationship of Equation (1). That is, this method is suitable for measuring the flow rate in a relatively thin tube.

となる。また、表裏面に電極が形成される矩形板状の振動子の横方向基本振動の共振周波数ｆは、

となる。ただし、η：係数（＝２．０８；ただし、ポアソン比σ^E＝０．３５のとき）、Ｄ：円板状振動子の直径、Y₁₁ ^E：弾性係数、ρ：密度である。なお、添え字₁₁は、面方向（拡がり方向）を意味し、添え字^Eは電界Ｅ＝一定の条件にあることを意味する。 However, in order to obtain a low frequency as the resonance frequency in the thickness direction vibration or longitudinal vibration of the vibrator, the vibrator must be enlarged. Therefore, in the present embodiment, as shown in FIG. 4, it is utilized that the resonance frequency f of radial vibration or lateral vibration of the plate-like vibrator 14 is lower than the resonance frequency f _{0 of} thickness vibration or longitudinal vibration. To do. In this way, a low resonance frequency can be obtained even if a relatively small vibrator is used. The resonance frequency f of the fundamental vibration in the radial direction of the disk-shaped vibrator in which the electrodes 14a are formed on the front and back surfaces is

It becomes. In addition, the resonance frequency f of the fundamental vibration in the lateral direction of the rectangular plate-shaped vibrator in which electrodes are formed on the front and back surfaces is

It becomes. Where η is a coefficient (= 2.08; Poisson's ratio σ ^E = 0.35), D is the diameter of the disk-shaped vibrator, Y ₁₁ ^{E is the} elastic coefficient, and ρ is the density. Note that the subscript ₁₁ means a surface direction (expansion direction), and the subscript ^E means that the electric field E = a constant condition.

となり、この式（４）の右辺は、流体中の音速ｃを１５００［ｍ／ｓｅｃ］とすると、０．５８６×１５００［ｍ／ｓｅｃ］／（２２０×１０³［Ｈｚ］）×１０³≒４［ｍｍ］となる。すなわち、一辺の長さａが８［ｍｍ］の矩形状の振動子の径方向振動を利用する場合、式（４）より、内径ｄが４［ｍｍ］以下のチューブに対しては、管軸方向に伝搬する平面波が得られることがわかる。なお、内径ｄが６［ｍｍ］以下のチューブについては、他の内径ｄの場合についても同様に、矩形状の振動子については、その一辺の長さａを、チューブの内径ｄ［ｍｍ］の２倍程度とすれば良いことが判明した。 That is, in the system according to the present embodiment, the vibration of the frequency satisfying the above equation (1) is obtained as the resonance of the radial vibration or the transverse vibration, and thereby the flow rate of the thin tube is reduced using a relatively small vibrator. This makes it possible to measure with higher accuracy. As an example, the resonance frequency of the radial vibration of a rectangular vibrator having a side length a = 8 [mm] is f = 220 × 10 ³ [Hz] from the equation (3). Here, when the equation (1) is transformed,

Thus, the right side of the equation (4) is 0.586 × 1500 [m / sec] / (220 × 10 ³ [Hz]) × 10 ³ ≈ if the sound velocity c in the fluid is 1500 [m / sec]. 4 [mm]. That is, when the radial vibration of a rectangular vibrator having a side length a of 8 [mm] is used, the tube axis is determined for the tube having an inner diameter d of 4 [mm] or less from the equation (4). It can be seen that a plane wave propagating in the direction is obtained. For tubes having an inner diameter d of 6 [mm] or less, similarly to other inner diameters d, the length a of one side of the rectangular vibrator is set to the inner diameter d [mm] of the tube. It was found that it should be about 2 times.

  FIG. 1 is a diagram illustrating an example of a main configuration of an integrated system 10 capable of both flow rate measurement and bubble detection according to the present embodiment. The integrated system 10 includes a pair of flow rate measurement plate-like vibrators 14 (14u, 14d) provided upstream and downstream of the tube 12 and a drive provided in each vibrator 14 as a device configuration for flow rate measurement. The circuit / detection circuit 16, the control unit 18 that controls the drive circuit / detection circuit 16, the propagation time acquisition unit 20 that acquires the propagation time of the wave between the vibrators 14, and the flow rate of the fluid in the tube 12 from the propagation time And a flow rate calculation unit 22 for calculating.

  The vibrator 14 has electrodes 14a formed on the front and back surfaces thereof, and is configured as a polarized piezoelectric element (piezo element).

  The two drive circuits / detection circuits 16 are controlled by the control unit 18 and are switched so that one of them functions as a drive circuit and the other as a detection circuit. The vibrator 14 connected to the drive circuit becomes a wave transmitting element, and the vibrator 14 connected to the detection circuit becomes a wave receiving element. The drive circuit vibrates the vibrator 14 at a radial or lateral resonance frequency.

  The propagation time acquisition unit 20 is based on the information acquired from the two drive circuits / detection circuits 16 or the control unit 18, and a vibrator in which a wave output from the vibrator 14 functioning as a wave transmitting element functions as a wave receiving element. 14, the time T (Tu, Td) until reception is measured.

から、流量Ｑを取得する（ここに、Ｌ：二つの振動子１４間の距離、Ａ（＝π・ｄ²／４）：チューブの流路面積）。 For example, the flow rate calculation unit 22 includes a time Td in which a wave propagates from the upstream vibrator 14u to the downstream vibrator 14d, and a time Tu in which a wave propagates from the downstream vibrator 14d to the upstream vibrator 14u. Based on the difference ΔT (= | Tu−Td |) with

From obtains the flow rate Q (here, L: the distance between the two transducers 14, A (= π · d 2/4): flow area of the tube).

  Further, the integrated system 10 of FIG. 1 has plate-shaped vibrators 14au and 14ad and vibrators 14u provided so as to face the vibrators 14u and 14d with the tube 12 interposed therebetween as a device configuration for detecting bubbles. , 14d, a vibration detection circuit 46 for detecting vibrations of the vibrators 14au, 14ad, and a bubble detector 48 for detecting bubbles. The drive circuit 44 and the vibration detection circuit 46 (operation start / stop) are controlled by the control unit 18, for example. As shown in FIG. 1, it is preferable that bubble detection can be performed at two locations, upstream and downstream.

となる。ただし、ｔ：振動子の厚さ、Y₃₃ ^E：弾性係数である。なお、添え字₃₃は、縦方向（厚み方向）を意味する。波動の周波数が高いほど小さい気泡を検出できるようになる。本実施形態では、気泡検出において、厚み方向振動あるいは縦振動の共振周波数を利用することで、比較的高い周波数の強い波動を生じさせ、微小な気泡をより精度良く検出することができるようにしている。 The drive circuit 44 drives the vibrators 14u and 14d at the resonance frequency f ₀ of the thickness direction vibration or the longitudinal vibration. The resonance frequency f ₀ of the fundamental vibration in the thickness direction of the disc-like and rectangular plate-like vibrators on which the electrodes 14a are formed on the front and back surfaces is:

It becomes. Where t: thickness of vibrator, Y ₃₃ ^E : elastic modulus. The subscript ₃₃ means the vertical direction (thickness direction). The higher the wave frequency, the smaller bubbles can be detected. In the present embodiment, in the bubble detection, by using the resonance frequency of the thickness direction vibration or the longitudinal vibration, a strong wave with a relatively high frequency is generated so that a minute bubble can be detected with higher accuracy. Yes.

  The bubble detection unit 48 detects bubbles by a decrease in the signal level (reception level) of vibration detected by the vibration detection circuit 46. As an example, bubbles are present when the signal level is less than or equal to a predetermined threshold, and bubbles are absent when the signal level is greater than the threshold. However, this is merely an example, and bubble detection may be performed by other known methods.

  As described above, according to the integrated system 10 according to the present embodiment, the vibrators 14u and 14d can be shared by the flow rate measurement and the bubble detection. If it is sufficient to detect a relatively large bubble, the bubble detection may be performed using vibration at a resonance frequency of radial vibration or lateral vibration. In that case, there is a merit that the drive circuit can be shared for the flow rate measurement and the bubble detection.

  FIG. 2 is a diagram (diameter cross-sectional view) showing a configuration example of the clamp 24 for bringing the vibrator 14 into contact with the outer wall of the tube 12. The clamp 24 includes an inner plate 26, a main body 28, and the vibrator 14.

  The cross section of the inner plate 26 is U-shaped. The distance δ between the opposing wall surfaces of the inner plate 26 is formed to be slightly smaller than the outer diameter of the tube 12, so that the tube 12 is detachably held inside the U-shape. . That is, in this example, the inner plate 26 functions as a holding portion.

  The front surface (or back surface) of the vibrator 14 and the back surface of the inner plate 26 (back surface of the surface contacting the tube 12) are bonded, for example, so that the vibrator 14 is fixed to the inner plate 26. At this time, the vibrator 14 has a posture in which the front surface (or back surface) is along the outer wall of the tube 12. In such a configuration, the vibrator 14 is indirectly in contact with the outer wall of the tube 12 via the inner plate 26, and the inner plate 26 and the tube 12 are interposed between the vibrator 14 and the fluid in the tube 12. Will intervene. Therefore, the thickness and material of the inner plate 26 are preferably determined so that the inner plate 26 and the tube 12 function as a matching layer. The clamp 24 of FIG. 2 is provided with two vibrators 14 facing each other with the tube 12 interposed therebetween. When air bubbles are detected, one of them is a wave transmitting element and the other is a detecting element. On the other hand, when performing flow rate measurement, one or both becomes a wave transmitting element or a detecting element.

  The main body 28 includes an outer plate portion 30 and a support plate portion 32 that fixes the inner plate 26 to the tip thereof by, for example, adhesion. With this configuration, the clamp 24 has a hollow structure to reduce the weight.

  As described above, the clamp 24 can be attached to and removed from the tube 12 very easily. That is, according to this example, the vibrator 14 can be more easily and reliably brought into contact with and separated from the outer wall of the tube 12.

  FIG. 3 is a view (side view) showing a configuration example of the clip 34 for bringing the vibrator 14 into contact with the outer wall of the tube 12. The clip 34 includes two arms 36 and 38, a shaft 40, a spring 42 as an elastic member, and the vibrator 14.

  At least one of the two arms 36 and 38 is rotatably supported by the shaft 40, and the tube 12 is sandwiched between the arms 36 and 38. In this example, the tube 12 is pinched by the urging force of the spring 42 on the side where the arms 36 and 38 are close to each other. However, in this case, care should be taken not to crush the tube 12 due to excessive biasing force. That is, as in the example of FIG. 3, it is preferable to prevent the arms 36 and 38 from approaching a distance δ or less slightly smaller than the outer diameter of the tube 12 by providing stoppers 36 a and 38 a.

  Each of the arms 36 and 38 includes inner plates 36b and 38b and main bodies 36c and 38c having a hollow structure (not shown) similar to that of the clamp 24.

  The front surface (or back surface) of the vibrator 14 is bonded to, for example, the back face of the inner plates 36b and 38b of either one of the arms 36 and 38, whereby the vibrator 14 is fixed to the inner plate 26. Also in this example, the vibrator 14 is in contact with the outer wall indirectly in a posture in which the front surface (or the back surface) is along the outer wall of the tube 12. Also in this example, the thicknesses and materials of the inner plates 36b and 38b are preferably determined so that the inner plates 36b and 38b and the tube 12 function as a matching layer. Similarly to the clamp 24, the clip 34 of FIG. 3 is also provided with two vibrators 14 facing each other with the tube 12 interposed therebetween. When performing bubble detection, one of them becomes a wave transmitting element and the other becomes a detecting element. On the other hand, when performing flow rate measurement, one or both becomes a wave transmitting element or a detecting element.

  As described above, the clip 34 can be attached to and removed from the tube 12 very easily. That is, according to this example, the vibrator 14 can be more easily and reliably brought into contact with and separated from the outer wall of the tube 12.

  As described above, according to the system according to the present embodiment, the flow rate of the fluid flowing in a relatively thin tube of about φ6 [mm] or less can be measured with higher accuracy using a smaller vibrator. become able to. Since the vibrator and the drive circuit can be shared for the flow rate measurement and the bubble detection, it is advantageous in terms of installation space, measurement effort, cost, and the like, compared to the case where they are provided separately and not shared.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above-described embodiment, the case where one oscillator is attached to each clip or clamp is illustrated, but the present invention is not limited to this, and a plurality of oscillators may be provided in each clip or clamp. In the above embodiment, the case where the vibrator is brought into contact with the outer wall of the tube via the inner plate is illustrated, but the present invention is not limited to this, and the surface of the vibrator is brought into direct contact with the outer wall of the tube. You may comprise as follows. However, a configuration in which some member such as an inner plate is interposed is advantageous from the viewpoint of protecting the vibrator. In a situation where foreign matter may be mixed in the tube, foreign matter can also be detected with the same or modified configuration. Further, the drive circuit for measuring flow rate and the drive circuit for detecting bubbles may be integrated into one drive circuit.

It is a figure which shows an example of the principal part structure of the integrated system which can perform flow volume measurement and bubble detection concerning embodiment of this invention. It is sectional drawing which shows an example of the clamp for attaching the vibrator | oscillator contained in the integrated system concerning embodiment of this invention to a tube. It is a side view showing an example of a clip for attaching a vibrator included in an integrated system concerning an embodiment of the present invention to a tube. It is explanatory drawing which shows radial direction vibration (lateral direction vibration) and thickness direction vibration (longitudinal direction vibration) of a vibrator | oscillator (however, (a): Circular vibrator, (b): Rectangular vibrator).

Explanation of symbols

  10 Integrated system capable of flow rate measurement and bubble detection, 12 tube, 14 (14u, 14d) vibrator, 14a electrode, 16 drive circuit / detection circuit, 18 control unit, 20 propagation time acquisition unit, 22 flow rate calculation unit, 24 Clamp, 26 Inner plate, 28 Main body, 30 Outer plate portion, 32 Support plate portion, 34 Clip, 36, 38 Arm, 36a, 38a Stopper, 36b, 38b Inner plate, 36c, 38c Main body, 40 Shaft, 42 Spring, 44 Drive circuit, 46 vibration detection circuit, 48 bubble detection unit.

Claims (6)

A pair of plate-like vibrators in which the surface on which the electrode is formed is in contact with the outer wall in a posture along the outer wall of the tube whose flow rate is to be measured, each of which is upstream of the tube And a pair of plate-like vibrators for flow rate measurement arranged on the downstream side,
A drive circuit for flow measurement that vibrates at a radial or lateral resonance frequency using either one of the plate-like vibrators forming a pair for flow measurement as a transmitting element;
A propagation time acquisition unit for acquiring a propagation time until an axial plane wave generated in the fluid in the tube by the vibration of the flow measuring element for flow rate detection is detected by the other vibrator as a detection element;
A pair of plate-like vibrators for detecting bubbles, comprising at least one of the plate-like vibrators and a plate-like vibrator disposed opposite to the plate-like vibrator with the tube interposed therebetween;
A bubble detection drive circuit that vibrates any one of the pair of plate-like vibrators for detecting the bubble as a wave transmitting element;
A bubble detection unit that detects bubbles based on the result of detection of the wave generated in the fluid in the tube by vibration of the wave detection element for detecting bubbles with the other detection element;
Including flow measurement and bubble detection system.   The system according to claim 1, wherein the bubble detection drive circuit vibrates the transmitting element at a resonance frequency in a thickness direction thereof.   The system according to claim 1, wherein the plate-like vibrator is attached to a clamp having a holding portion that holds the tube in a detachable manner.   The system according to claim 1, wherein the plate-like vibrator has two arms that can be opened and closed, and is attached to a clip that sandwiches the tube by the arms.   A clamp for mounting a vibrator used in the system according to claim 3, wherein the clamp has a holding portion for holding the tube so as to be detachable, and the plate-like vibrator is directly or indirectly attached to an outer wall of the tube. A clamp characterized in that it is held so as to abut against it. 5. A clip for mounting a vibrator used in the system according to claim 4, comprising two arms for sandwiching the tube, wherein the plate-like vibrator is brought into direct or indirect contact with the outer wall of the tube. A clip characterized by holding on.

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