JP2009041912A - Ultrasonic flow meter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain accurate measurement precision even in a thin tube with little influence of the tube shape. <P>SOLUTION: A tube 1 for measuring with the tube axis in the z-axis direction is a square tube, and a pair of ultrasonic transmission/reception devices 2, 3 are attached upstream and downstream of the upper face 1a of the tube 1. An ultrasonic reflector 4 with increased reflectance is arranged on the lower face 1b of the tube 1, and the reflectance of the lower face 1b of both sides of forward and backward of the ultrasonic reflector 4 is decreased enough. In general, transmission amplitude of ultrasonic beam does not distribute uniformly in the x-axis direction, namely, the width direction of the tube 1. The transmission amplitude is large in the central part of the piezo vibrator used for the ultrasonic transmission/reception devices 2, 3 and is small in the peripheral part thereof. By adjusting the length of the ultrasonic reflector 4 in the z-axis direction along the x-axis direction, the distribution of the maximum values of the receiving amplitude in the x-axis direction is uniformized, so that the wave form depending on the average value of a flow rate on a propagation path of the ultrasonic beam is received by the ultrasonic transmission/reception devices at the receiving side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ultrasonic flowmeter in which an ultrasonic reflector having a controlled ultrasonic reflectivity is provided in a measuring tube made of a square tube to enable accurate measurement.

  In general, in an ultrasonic flow meter, a so-called time difference method is used as a highly practical flow meter. Normally, ultrasonic transmitters / receivers are installed upstream and downstream of a circular pipe, and the flow rate in the pipe is measured from the difference in propagation time upstream and downstream. It is known that the configuration is affected by the viscosity of the fluid. As a special example, there is also used a type in which two ultrasonic beams are attached at a position where the cross-sectional radius is vertically divided into two. In this case, the flow velocity distribution error is small in the axially symmetric flow.

  Generally, in order to perform measurement with high accuracy, it is desirable to increase the propagation distance of the ultrasonic beam because the time difference increases. In a large-diameter fluid conduit, the propagation distance can be increased by arranging an ultrasonic reflector on the inner surface of the tube.

  However, it is difficult to arrange an ultrasonic reflector inside a small-diameter tube.

  An object of the present invention is to solve the above-described problems, and to provide an ultrasonic flowmeter that has a simple structure and can be applied to a thin tube.

  In order to achieve the above object, the technical feature of the ultrasonic flowmeter according to the present invention is that at least 1 is provided on the upstream side and the downstream side in the flow direction of one surface of a measurement tube body comprising a square tube through which a measurement fluid flows. A pair of ultrasonic transmitters / receivers, and an ultrasonic reflector having a higher ultrasonic reflectivity than the inner surface of the surrounding tube is disposed on a surface of the tube facing the mounting surface of the ultrasonic transmitter / receiver, An ultrasonic flowmeter in which an ultrasonic beam transmitted from an upstream or downstream ultrasonic transceiver is reflected by the ultrasonic reflector and propagates to the downstream or upstream ultrasonic transceiver, The distribution of the ultrasonic reflectance of the ultrasonic reflector in the direction orthogonal to the tube axis of the tube is adjusted so that the amplitude distribution of the ultrasonic beam is equalized in the tube.

  According to the ultrasonic flowmeter of the present invention, the ultrasonic beam transmitted / received by at least one pair of ultrasonic transmitter / receiver and passing through the ultrasonic reflector gives a propagation time difference according to the average value of the flow velocity on the propagation path, Furthermore, since the ultrasonic reflector reflects the reception amplitude evenly regardless of the transmission amplitude, the obtained time difference signal is obtained by averaging the flow velocity in the cross section.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 is a configuration diagram of the ultrasonic flowmeter according to the first embodiment. The tube 1 for measurement in which the tube axis is the z-axis direction and the measurement fluid flows is a rectangular tube having a rectangular or rectangular cross section, and a pair of ultrasonic transmission / reception is provided upstream and downstream of the upper surface 1a of the tube 1. Containers 2 and 3 are attached. The horizontal direction orthogonal to the z-axis direction of the tube axis is the x-axis and the vertical direction is the y-axis.

  On the inner surface of the lower surface 1b of the tube 1 between the ultrasonic transmitters / receivers 2 and 3, an ultrasonic reflector 4 having an increased ultrasonic reflectivity is disposed, and the surface around the ultrasonic reflector 4 is ultrasonic. The reflectivity is sufficiently low. The ultrasonic transceivers 2 and 3 are connected to lead wires 5, 5 ′ and 6, 6 ′ for connecting a drive measurement circuit (not shown).

  With such a configuration, ultrasonic beams transmitted from arbitrary points A and B in the upstream ultrasonic transceiver 2 are reflected at points A ′ and B ′ in the ultrasonic reflector 4, respectively. , The ultrasonic transmitter / receiver 3 on the downstream side is reached at the points A ″ and B ″. When an ultrasonic beam is sent from the downstream ultrasonic transmitter / receiver 3 to the upstream side, it propagates through the reverse path.

Although the ultrasonic beam is generally driven by a burst wave in the time difference method, it can be regarded as a sine wave if attention is paid to the received waveform in the vicinity of a specific time t, so the amplitude of the ultrasonic beam passing through the points A and B is Assuming that Va and Vb respectively, the following equations (1) and (2) can be obtained from the time difference operation equation. However, the attenuation of the ultrasonic beam in the fluid is ignored.
Va = a · ma · sin {2πf (t ± va · sin θ · T / 2C)} (1)
Vb = b · mb · sin {2πf (t ± vb · sin θ · T / 2C)} (2)

  Here, a and b are the maximum transmission amplitude values of the respective ultrasonic beams, ma and mb are the reflectances of the ultrasonic reflector 4 at the points A ′ and B ′, respectively, and f is the ultrasonic transceivers 2 and 3. , The sign of ± corresponds to − for the downstream and + for the upstream, va and vb are the average values of the flow velocity of the ultrasonic beam passing through the points A ′ and B ′, respectively, and θ is super The incident angle of the acoustic beam, T is the propagation time of the ultrasonic beam, and C is the speed of sound of the fluid.

  In general, the transmission amplitude of an ultrasonic beam is not uniformly distributed in the x-axis direction, that is, the width direction of the tube 1, and is the center of a piezoelectric vibrator used as an ultrasonic vibrator in the ultrasonic transceivers 2 and 3. The part has a large transmission amplitude and the peripheral part becomes small. Therefore, when the reflectance distribution in the x-axis direction of the ultrasonic reflector 4 is uniform, the reception amplitude of the ultrasonic transmitter / receiver on the receiving side is not uniform.

  Therefore, if the reflectance distribution in the x-axis direction of the ultrasonic reflector 4 is adjusted so that a · ma = b · mb≡p (constant) is always established, the maximum value of the reception amplitude in the x-axis direction The distribution of becomes uniform. That is, the ultrasonic transmitters / receivers 2 and 3 have the same frequency and the same amplitude in the x-axis direction, and the receiving ultrasonic transmitter / receiver has a phase that depends on the average value of the flow velocity on the propagation path of the ultrasonic beam. A waveform is received.

  FIG. 2 shows the distribution of the transmission amplitude of the ultrasonic beam from the ultrasonic transmitter / receiver in the x-axis direction. Usually, the maximum amplitude values a and b increase at the center of the tube 1. FIG. 3 shows the length in the z direction of the ultrasonic reflector 4 adjusted so that the amplitude received by the ultrasonic transmitter / receiver on the receiving side is uniform corresponding to the transmission amplitude of FIG.

  As described above, when the length of the ultrasonic reflector 4 in the z-axis direction is adjusted with respect to the transmission amplitude, the distribution of the ultrasonic beam received by the ultrasonic transmitter / receiver on the receiving side is equalized. Is done.

When the average amplitude V of the two ultrasonic beams of the formulas (1) and (2) is calculated using the sine sum formula of the following formula (3), the formula (4) is obtained.
sinE + sinF = 2 · sin (E + F) / 2 · cos (EF) / 2 (3)
V = 2 · p · sin [2πf {t ± (va + vb) / 2} · sin θ · T / 2C] · cos {2πf · (va−vb) sin θ · T / 2C} (4)

  Here, if the flow velocity is sufficiently smaller than the sound velocity C of the fluid, the cos term in the above equation can be regarded as 1, so if this is omitted, the average amplitude V is the average value of the two flow velocity va and vb. It is nothing but an operation formula of the time difference method when (va + vb) / 2.

  Since the above relationship holds for an arbitrary ultrasonic beam, the ultrasonic transceivers 2 and 3 can eventually detect the average value of the flow velocity on the plane determined by the direction of the ultrasonic beam and the x-axis.

  FIG. 4 shows an example in which the two pairs of ultrasonic transmitters / receivers 2, 3, 2 ′, 3 ′ of Example 2 are arranged on the upper surface 1b of the tubular body 1, and FIGS. 5 and 6 show the ultrasonic beam at this time. The transmission amplitude distribution and the length distribution of the ultrasonic reflector 4 are shown.

  For electrical connection of a plurality of pairs of ultrasonic transmitters / receivers 2, 3, 2 ′, 3 ′, electrodes having the same polarity are connected by lead wires 5, 5 ′ and lead wires 6, 6 ′ for each upstream side or downstream side. Are connected to each other.

  If the logarithm of the ultrasonic transceivers 2 and 3 to be used is increased as in the second embodiment, the transmission intensity approaches a more uniform distribution, but on the other hand, the mounting complexity increases.

  As a means for adjusting the reflectance of the ultrasonic reflector 4, the length of the ultrasonic reflector 4 in the z-axis direction is changed in FIGS. 3 and 6, but other methods are also conceivable.

  For example, FIG. 7 shows an example in which the x-axis direction distribution of the surface roughness of the ultrasonic reflector 4 when the pair of ultrasonic transceivers 2 and 3 is used as in the first embodiment is shown. Concavities and convexities are formed on the surface of the ultrasonic reflector 4 to scatter the ultrasonic beam with a size not smaller than the wavelength of the ultrasonic beam in the fluid. Since the portion with higher unevenness density has more scattering, as shown in FIG. 3, the unevenness density distribution is changed so that the scattering becomes larger at the center portion corresponding to the amplitude of the ultrasonic beam. The reflectivity can be adjusted.

  FIG. 8 shows another example of the ultrasonic reflector 4, and the x-axis direction distribution is adjusted by changing the inclination of the ultrasonic reflector 4 with respect to the mounting surface. As the inclination is larger, the reflection of the ultrasonic beam to the ultrasonic transmitter / receiver on the receiving side is reduced. Therefore, by increasing the inclination at the central portion in the x-axis direction, the ultrasonic reflectance at the central portion is reduced. Yes.

  As described above, the ultrasonic flowmeter of the present invention uses a square tube, but since a normal pipe line is a circular tube, a measuring tube 1 made of a square tube is provided before and after the measurement unit as a circular tube. It is preferable to connect the reducer pipes 7 deformed to the shape shown in FIG.

1 is a configuration diagram of Example 1. FIG. It is a transmission amplitude distribution map of the x-axis direction of an ultrasonic beam. It is the length distribution figure of the x-axis direction of an ultrasonic reflector. FIG. 6 is a configuration diagram of Example 2. It is a distribution map of the transmission amplitude of the ultrasonic beam in the x-axis direction. It is the length distribution figure of the x-axis direction of an ultrasonic reflector. It is a perspective view of the ultrasonic reflector which provided unevenness | corrugation in the surface and changed the ultrasonic reflectivity. It is the perspective view of the ultrasonic reflector which changed the inclination of the surface and changed the ultrasonic reflectivity. It is sectional drawing of the state which connected the reducer pipe | tube to the upstream and downstream of a tubular body.

Explanation of symbols

1 Measurement tube 2, 3, 2 ', 3' Ultrasonic transceiver 4 Ultrasonic reflector 5, 5 ', 6, 6' Lead wire 7 Reducer tube

Claims (6)

  At least one pair of ultrasonic transmitters / receivers is installed on the upstream side and the downstream side in the flow direction of one surface of a measurement tube body made of a square tube through which a measurement fluid flows, and the ultrasonic transmitter / receiver in the tube body An ultrasonic reflector having a higher ultrasonic reflectivity than the inner surface of the surrounding tube is disposed on the surface facing the mounting surface, and the ultrasonic beam transmitted from the upstream or downstream ultrasonic transceiver is reflected by the ultrasonic reflection. An ultrasonic flowmeter that is reflected by a body and propagates to the downstream side or upstream side ultrasonic transmitter / receiver, the ultrasonic flow rate of the ultrasonic reflector in a direction perpendicular to the tube axis of the tubular body An ultrasonic flowmeter, wherein the distribution is adjusted so that the amplitude distribution of the ultrasonic beam is equalized in the tube.   The ultrasonic reflectivity of the ultrasonic reflector is adjusted by changing a length of the ultrasonic reflector in the tube axis direction of the tube along a direction orthogonal to the tube axis. Item 2. The ultrasonic flowmeter according to Item 1.   The ultrasonic wave according to claim 1, wherein the ultrasonic wave reflectance of the ultrasonic wave reflector is adjusted by changing the surface roughness of the ultrasonic wave reflector along a direction orthogonal to the tube axis. Flowmeter.   The supersonic wave reflectance of the ultrasonic wave reflector is adjusted by changing an inclination of the ultrasonic wave reflector with respect to the mounting surface along a direction orthogonal to a tube axis. Sonic flow meter.   2. The ultrasonic flowmeter according to claim 1, wherein when a plurality of pairs of the ultrasonic transceivers are used, electrodes having the same polarity are connected to each other upstream or downstream.   The reducer pipe | tube which matches the cross-sectional shape of the said pipe body and external connection piping is connected to the upstream and downstream of the said measurement pipe body, The ultrasonic flowmeter of Claim 1 characterized by the above-mentioned.

Images