JP2005195372A - Ultrasonic flowmeter, and wedge used for ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a measuring error caused by a transverse wave in an ultrasonic wave emitted from an ultrasonic transmission means to measure an accurate flow rate. <P>SOLUTION: This ultrasonic flowmeter is provided with an ultrasonic transmission means 20 for making an ultrasonic pulse get incident into a measured fluid 11 inside a fluid pipe 10 along a measuring line from an ultrasonic transducer, a fluid velocity distribution measuring means for receiving an ultrasonic echo reflected from a measuring area out of the ultrasonic pulses incident into the measuring fluid 11 to measure a flow velocity distribution of the measured fluid in the measuring area, and a flow rate computing means for computing the flow rate of the measuring fluid in the measuring area, based on the flow velocity distribution of the measured fluid. The ultrasonic flowmeter is provided also with a wedge 30 for fixing the ultrasonic transmission means 20 onto an outer wall face of the fluid pipe 10 concerned in the measured fluid 11, and a material of a portion in the wedge 30 ranging over from the ultrasonic transmission means 20 to the outer wall face of the fluid pipe 10 comprises a material to make an acoustic impedance equivalent to that of the fluid pipe 10. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an ultrasonic flowmeter capable of instantaneously measuring a flow rate of a fluid to be measured from a flow velocity distribution in a measurement region in a time-dependent manner and a technique related thereto.

  Various techniques have been provided for Doppler ultrasonic flowmeters capable of measuring the flow rate without contact. (For example, JP 2000-97742 A)

JP 2000-97742 A

  The above technique will be specifically described. The Doppler type ultrasonic flowmeter disclosed in the above document is an ultrasonic transmission that causes an ultrasonic pulse of a required frequency to enter a measured fluid in a fluid (for example, water) pipe along a measurement line from an ultrasonic transducer. Means, a fluid velocity distribution measuring means for receiving an ultrasonic echo reflected from the measurement area among ultrasonic pulses incident on the measurement fluid, and measuring a flow velocity distribution of the measurement fluid in the measurement area; and the measurement A flow rate calculation means for calculating the flow rate of the fluid under measurement in the measurement region is provided based on the flow velocity distribution of the fluid, and the flow rate of the fluid under measurement is measured.

  This technique measures the flow velocity distribution of the fluid to be measured flowing in the pipe, and is excellent in responsiveness to the transient flow rate that varies with time. In addition, the flow rate of the fluid to be measured even in places where the flow of the fluid is not sufficiently developed or where the flow is three-dimensional, such as an elbow pipe or a bent pipe such as a U-shaped inverted pipe Can be measured efficiently and instantaneously. Compared to the ultrasonic flowmeters provided before that, there is a feature that accurate measurement is possible without the "flow rate correction coefficient" calculated from experimental values and experience values, etc. Has been.

  Although not limited to the Doppler type ultrasonic flowmeter, in the ultrasonic flowmeter, when the fluid to be measured is a liquid, a “clamp-on type” that fixes the ultrasonic transmission means to the pipe through a wedge is often used. . This is because there is an advantage that “retrofitting” is possible for the piping. The first condition for the wedge is that the material is easy to pass ultrasonic waves. On the other hand, a synthetic resin (for example, an acrylic resin) is generally employed for the convenience of fixing the ultrasonic transmission means after determining the incident angle of the ultrasonic waves.

The above-mentioned “clamp-on type” ultrasonic flowmeter was aimed at further improvement in measurement accuracy, and the following problems emerged.
This will be described with reference to FIG. The ultrasonic wave transmitted by the ultrasonic wave transmission means (transducer 20) is intended to use a reflected wave ("longitudinal wave A" in the figure) reflected by bubbles or the like in the fluid 11 to be measured. When the material (acoustic impedance) is different from that of the ultrasonic wave 10, the ultrasonic wave is divided into a longitudinal wave and a transverse wave (“lateral wave B” in the figure) at the interface between the two. The presence of this transverse wave B is one of the causes of measurement errors.

The problem to be solved by the present invention is to provide a technique for measuring a more accurate flow rate by reducing a measurement error caused by a transverse wave with respect to an ultrasonic wave emitted from an ultrasonic wave transmitting means.
An object of the invention described in claim 1 is to provide an ultrasonic flowmeter for measuring a more accurate flow rate by reducing a measurement error caused by a transverse wave with respect to an ultrasonic wave emitted from an ultrasonic transmission means. It is in.
The object of the invention described in claim 2 is to provide a wedge for an ultrasonic flowmeter for measuring a more accurate flow rate by reducing a measurement error caused by a transverse wave with respect to an ultrasonic wave emitted from an ultrasonic transmission means. It is to provide.

(Claim 1)
The invention according to claim 1 is an ultrasonic transmission means (20) for causing an ultrasonic pulse of a required frequency to enter a measured fluid (11) in a fluid pipe (10) along a measurement line from an ultrasonic transducer; A fluid velocity distribution measuring means for receiving an ultrasonic echo reflected from the measurement region among the ultrasonic pulses incident on the fluid to be measured (11) and measuring a flow velocity distribution of the fluid to be measured in the measurement region; The present invention relates to an ultrasonic flowmeter that includes a flow rate calculation unit that calculates a flow rate of a fluid to be measured in the measurement region based on a flow velocity distribution of the fluid and that measures a flow rate of the fluid to be measured.
A wedge (30) is provided for fixing the ultrasonic transmission means (20) to the outer wall surface of the fluid pipe (10) related to the fluid to be measured (11), and the ultrasonic wave in the wedge (30) is provided. The material of the part from the transmitting means (20) to the outer wall surface of the fluid pipe (10) is characterized in that the acoustic impedance of the fluid pipe (10) is equivalent.

(Glossary)
The ultrasonic flow meter includes a general Doppler ultrasonic flow meter and an ultrasonic flow meter using a correlation method. The ultrasonic flow meter using the correlation method is, for example, an ultrasonic flow meter as disclosed in JP-A-2003-344131.
In both cases, an ultrasonic transmission means for injecting an ultrasonic pulse of a required frequency from an ultrasonic transducer along a measurement line into a fluid to be measured in a fluid pipe, and a measurement region of the ultrasonic pulses incident on the fluid to be measured A fluid velocity distribution measuring means for receiving the ultrasonic echo reflected from the measurement region and measuring a flow velocity distribution of the fluid under measurement in the measurement region; and a flow rate of the fluid under measurement in the measurement region based on the flow velocity distribution of the fluid under measurement. The flow rate of the fluid to be measured is measured.

の演算を行う手段である。 The “flow rate calculation means” has a flow rate of m (t),

It is a means to perform the calculation.

Further, from the above equation (1), the flow rate m (t) of the time t flowing through the fluid piping can be rewritten as the following equation.

ここで、αとは、超音波トランスジューサから発振される超音波の入射角度、すなわち管壁への垂線に対してなす角度である。 If the flow of the fluid to be measured flowing in the pipe is a flow in the tube axis direction and the flows vr and vθ in the radial direction and the angle θ can be ignored, vx >> vr = vθ, and the flow rate measurement is simplified. It is expressed by the following formula.

Here, α is an incident angle of the ultrasonic wave oscillated from the ultrasonic transducer, that is, an angle formed with respect to a perpendicular to the tube wall.

  The incident angle α of the ultrasonic wave oscillated from the ultrasonic transducer (20) is determined by specifying variable conditions such as the material of the pipe, the inner and outer diameters or thickness of the pipe, and the type of fluid to be measured. .

  For example, if the fluid piping (10) is made of stainless steel, the material that makes the acoustic impedance of the fluid piping (10) equivalent is the fluid piping (20) from the ultrasonic transmission means (20) in the wedge (30). The part reaching the outer wall in 10) is also made of stainless steel, or a mixture of epoxy resin and tungsten powder. Of course, it is possible to use the same material for the entire wedge (30). In the previous example, when the fluid pipe (10) is stainless steel, the wedge (30) itself may be stainless steel.

“Equal acoustic impedance” is, for example, about plus or minus about 10%, more preferably about plus or minus about 5%.
The material with the same acoustic impedance as the fluid piping, which is often made of stainless steel or aluminum alloy, is the same material, as well as a mixture of epoxy resin and tungsten powder as described above, and instead of tungsten. In some cases, molybdenum, chromium, lead, or the like may be employed.

(Function)
First, an ultrasonic pulse of a required frequency is made incident from the ultrasonic transducer (20) along the measurement line toward the fluid to be measured (11) in the fluid pipe (10). Then, the ultrasonic wave reaches the outer wall surface of the fluid pipe (10) from the ultrasonic transducer (20) through the wedge (30). In the interface of the wedge (30) and the fluid pipe (10), when the acoustic impedance is different due to different materials or the like, a transverse wave is generated, but in the present invention, the ultrasonic transmission means in the wedge (30) ( Since the material of the part from 20) to the outer wall surface of the fluid pipe (10) has the same acoustic impedance as the fluid pipe (10), the generation of transverse waves can be suppressed.
Therefore, the ultrasonic wave incident on the fluid to be measured (11) is only a longitudinal wave, and the occurrence of a measurement error due to a transverse wave can be suppressed. The fluid velocity distribution measuring means (ultrasonic transducer 20) receives ultrasonic echoes due to longitudinal waves and measures the flow velocity distribution of the fluid to be measured (11) in the measurement region. Based on the flow velocity distribution of the fluid to be measured (11), the flow rate calculation means calculates the flow rate of the fluid to be measured (11) in the measurement region.

(Claim 2)
The invention according to claim 2 is an ultrasonic transmission means (20) for causing an ultrasonic pulse of a required frequency to enter the measured fluid (11) in the fluid pipe (10) along the measurement line from the ultrasonic transducer; A fluid velocity distribution measuring means for receiving an ultrasonic echo reflected from the measurement region among the ultrasonic pulses incident on the fluid to be measured (11) and measuring a flow velocity distribution of the fluid to be measured in the measurement region; The present invention relates to a wedge (30) used in an ultrasonic flowmeter that includes a flow rate calculation unit that calculates a flow rate of a fluid to be measured in the measurement region based on a flow velocity distribution of the fluid.
The wedge (30) includes a fixing portion (31) for fixing the ultrasonic transmission means (20) to the fluid pipe (10) related to the fluid to be measured (11), and a fixing portion (31). An ultrasonic transmission section (32) extending from the fixed ultrasonic transmission means (20) to the outer wall surface of the fluid pipe (10), and the material of the ultrasonic transmission section (32) is that of the fluid pipe (10). It is characterized in that the material has the same acoustic impedance.

  At least, the material of the ultrasonic transmission part (32) may be a material in which the acoustic impedance of the fluid pipe (10) is equivalent, and the entire material of the wedge (30) including the fixing part (31) is the fluid pipe (10 ) May be the same material.

(Function)
With the configuration described above, it is possible to suppress the occurrence of a transverse wave in the ultrasonic wave oscillated by the ultrasonic transducer (20) at the interface between the wedge (30) and the fluid pipe (10). Therefore, the ultrasonic wave incident on the fluid to be measured (11) is only a longitudinal wave, and the occurrence of a measurement error due to a transverse wave can be suppressed.

According to the first aspect of the present invention, there is provided an ultrasonic flowmeter for measuring a more accurate flow rate by reducing a measurement error caused by a transverse wave with respect to an ultrasonic wave emitted from an ultrasonic transmission unit. I was able to.
According to the second aspect of the present invention, there is provided a wedge for an ultrasonic flowmeter for measuring a more accurate flow rate by reducing a measurement error caused by a transverse wave with respect to an ultrasonic wave emitted from an ultrasonic transmission unit. Could be provided.

Hereinafter, the present invention will be described in more detail based on embodiments and drawings. The drawings used here are FIGS. 1 and 2.
(Figure 1)
FIG. 1 shows an ultrasonic flowmeter for measuring the flow rate of a fluid pipe 10 through which a fluid under measurement 11 flows, and receives an ultrasonic echo reflected from a measurement region of an ultrasonic pulse incident on the fluid under measurement 11. An ultrasonic transmission / reception means (transducer 20) also serving as a receiver is provided. The transducer 20 is fixed to a predetermined portion of the pipe 10 by a resin wedge 30. The material of the wedge 30 will be described later.

  The transducer 20 transmits ultrasonic pulses having a required frequency (fundamental frequency) along the measurement line to the fluid 11 to be measured, and reflects from the measurement region of the ultrasonic pulses incident on the fluid to be measured. It also serves as fluid velocity distribution measuring means for receiving the ultrasonic echo and measuring the flow velocity distribution of the fluid to be measured in the measurement region. Although not shown in the drawing, a computer such as a microcomputer, CPU, MPU or the like as a flow rate calculation means for obtaining the flow rate of the fluid to be measured in a time-dependent manner based on the flow velocity distribution, and outputs from the computer are displayed in time series. Connected with possible display devices.

  Further, the transducer 20 is provided with a vibration amplifier as a signal generator for vibrating the transducer 20, so that a pulse electric signal having a required fundamental frequency is input from the vibration amplifier to the ultrasonic transducer. It has become. Then, an ultrasonic pulse having a fundamental frequency is oscillated along the measurement line by applying the pulse electric signal. The ultrasonic pulse is a straight beam having a pulse width of about 5 mm and hardly spreading.

  The transducer 20 receives an ultrasonic echo that is reflected when an oscillated ultrasonic pulse hits a reflector (bubble) 12 in the fluid 11. What is to be received and measured is the longitudinal wave of the oscillated ultrasonic pulse. In addition, the reflector 12 must be a foreign substance having an acoustic impedance different from that of the fluid to be measured 11.

The wedge 30 is formed of the same material as the fluid pipe 10 through which the fluid 11 to be measured flows, that is, stainless steel. For this reason, ultrasonic waves are not refracted even at the interface between the wedge 30 and the outer wall surface of the fluid pipe 10, and the occurrence of transverse waves can be suppressed. Therefore, the ultrasonic wave incident on the fluid to be measured 11 is only a longitudinal wave, and the occurrence of measurement errors due to the transverse wave can be suppressed.
The ultrasonic echo by the longitudinal wave received by the transducer 20 is received by a reflected wave receiver that also serves as the transducer 20 and converted into an echo electric signal by the reflected wave receiver. The echo electric signal is amplified by an amplifier and then digitized through an AD converter. Then, the digitized digital echo signal is input to a flow velocity calculation device provided with a flow velocity distribution measuring circuit.

  The flow velocity calculation device receives the digital signal of the fundamental frequency from the oscillation amplifier and measures the flow velocity using the change in flow velocity based on the Doppler shift or the cross-correlation value of both signals from the frequency difference between the two signals. The flow velocity distribution in the measurement area along the measurement line is calculated. By calibrating the flow velocity distribution in the measurement region with the incident angle α of the ultrasonic wave, the flow velocity distribution in the cross section of the fluid piping can be measured.

  When the dimensions of the fluid pipe 10 (two or more of the outer diameter, the wall thickness, and the inner diameter), the material of the fluid pipe 10 and the type of the fluid 11 are known in advance, the incidence of the ultrasonic wave described above is performed. The angle α can be specified. Based on the specified incident angle α of the ultrasonic wave, the mounting angle of the transducer 20 with respect to the wedge 30 is specified, and the wedge 30 is formed so as to obtain the mounting angle.

(Figure 2)
In the embodiment shown in FIG. 2, the material of each part is made different based on two functions required for the wedge 30. The two functions are a function for fixing the transducer 20 to the fluid pipe 10 related to the fluid to be measured 11 and a function for causing the ultrasonic wave oscillated from the transducer 20 to reach the outer wall surface of the fluid pipe 10. A part that achieves the former function is a fixing part 31, and a part that achieves the latter function is an ultrasonic transmission part 32. And the material of the ultrasonic transmission part 32 shall be the material in which the acoustic impedance of the fluid piping 10 becomes equivalent, and the material of the fixing | fixed part 31 employs materials, such as resin which is easy to process.
Specifically, the material of the ultrasonic transmission part 32 is the same material as the fluid pipe 10, for example, stainless steel, and the material of the fixing part 31 is, for example, an epoxy resin.

If the material of the ultrasonic transmission part 32 is a material in which the acoustic impedance of the fluid piping 10 is equivalent, the generation of transverse waves can be suppressed even at the interface between the wedge 30 and the outer wall surface of the fluid piping 10. Therefore, the ultrasonic wave incident on the fluid to be measured 11 is only a longitudinal wave, and the occurrence of measurement errors due to the transverse wave can be suppressed.
On the other hand, the fixing portion 31 is configured so that the ultrasonic incident angle α can be obtained by grasping the dimensions of the fluid pipe 10 (two or more of the outer diameter, the wall thickness, and the inner diameter) and the type of the fluid 11. Is advantageous compared to the case where the fixing part 31 is made of stainless steel (for example, in the case of FIG. 1).

  The wedge 30 includes a fixing portion 31 and an ultrasonic transmission portion 32, and the fixing portion 31 is provided in a shape that holds the ultrasonic transmission portion 32 as shown in FIG. It is also possible to employ a liquid or gel-like material as the material.

The present invention is not limited to the Doppler type ultrasonic flowmeter, but can also be adopted in a flowmeter belonging to a general ultrasonic flowmeter.
In addition to the manufacturing industry of ultrasonic flowmeters, it is also used in the installation and maintenance industries of ultrasonic flowmeters.

It is a conceptual diagram which shows 1st embodiment. It is a conceptual diagram which shows 2nd embodiment. It is a conceptual diagram for showing the problem of the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fluid piping 11 Fluid 12 to be measured Bubble 20 in fluid Ultrasonic transmission / reception means (transducer)
30 Wedge 31 Fixing part 32 Ultrasonic transmission part

Claims (4)

Ultrasonic transmission means for injecting ultrasonic pulses of the required frequency from the ultrasonic transducer along the measurement line into the fluid to be measured in the fluid piping, and reflected from the measurement area among the ultrasonic pulses incident on the fluid to be measured. A fluid velocity distribution measuring means for receiving the measured ultrasonic echo and measuring the flow velocity distribution of the fluid under measurement in the measurement region; and calculating the flow rate of the fluid under measurement in the measurement region based on the flow velocity distribution of the fluid under measurement. An ultrasonic flowmeter comprising a flow rate calculation means for measuring the flow rate of a fluid to be measured,
Provide a wedge for fixing the ultrasonic transmission means to the outer wall surface of the fluid piping related to the fluid to be measured,
The ultrasonic flowmeter according to claim 1, wherein a material of a portion of the wedge extending from the ultrasonic transmission means to an outer wall surface of the fluid piping is a material having an equivalent acoustic impedance of the fluid piping. Ultrasonic transmission means for injecting ultrasonic pulses of the required frequency from the ultrasonic transducer along the measurement line into the fluid to be measured in the fluid piping, and reflected from the measurement area among the ultrasonic pulses incident on the fluid to be measured. A fluid velocity distribution measuring means for receiving the measured ultrasonic echo and measuring the flow velocity distribution of the fluid under measurement in the measurement region; and calculating the flow rate of the fluid under measurement in the measurement region based on the flow velocity distribution of the fluid under measurement. A wedge for use in an ultrasonic flowmeter comprising a flow rate calculation means for measuring a flow rate of a fluid to be measured,
A fixing portion for fixing the ultrasonic transmission means to a fluid pipe related to the fluid to be measured;
An ultrasonic transmission unit extending from the ultrasonic transmission means fixed to the fixed portion to the outer wall surface of the fluid pipe,
A wedge for an ultrasonic flowmeter, characterized in that the material of the ultrasonic transmission part is made of a material with the same acoustic impedance of the fluid piping.   The distance from the ultrasonic transmission means to the outer wall surface of the fluid pipe in the wedge is larger than the distance calculated by multiplying the speed at which the ultrasonic wave passes through the wedge by the dead zone time of the ultrasonic transducer. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter is formed as described above. The distance calculated from the ultrasonic transmission means in the ultrasonic transmission section of the wedge to the outer wall surface of the fluid pipe is calculated by multiplying the speed at which the ultrasonic wave passes through the wedge by the dead zone of the ultrasonic transducer. The wedge for an ultrasonic flowmeter according to claim 2, wherein the wedge is formed so as to be larger.

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