JP2011007539A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flowmeter which can reduce zero-drift.SOLUTION: The ultrasonic flowmeter includes: a plurality of ultrasonic vibrators 2 separated by a prescribed distance along the flow of a fluid and attached to a measurement tube 1; and an operational circuit 7 obtaining the flow velocity of a fluid on the basis of the time difference between the propagation time until the ultrasonic vibrator 2 at the downstream side receives the ultrasonic wave transmitted from the ultrasonic vibrator 2 at the upstream side and the propagation time until the ultrasonic vibrator 2 at the upstream side receives the ultrasonic wave transmitted from the ultrasonic vibrator 2 at the downstream side. The ultrasonic vibrators 2 alternately transmit an ultrasonic wave at a first frequency and an ultrasonic wave at a second frequency predetermined in accordance with the measurement tube 1. The operational circuit 7 obtains the first time difference of the propagation time in the ultrasonic wave at the first frequency, as the time difference when the flow velocity of the fluid is zero, and obtains the flow velocity of the fluid on the basis of a second time difference of the propagation time in the ultrasonic wave at the second frequency and the first time difference.

Description

  The present invention relates to an ultrasonic flowmeter for obtaining a flow velocity of a fluid flowing in a measurement tube.

  In conventional ultrasonic flowmeters, for example, there have been proposed ones that provide two ultrasonic transducers on the upstream side and the downstream side of a measurement tube and obtain the flow velocity by measuring the propagation time of the transmission wave and the reception wave. (For example, refer to Patent Documents 1 to 3).

In this type of ultrasonic flowmeter, first, ultrasonic waves are transmitted from the upstream side and received at the downstream side. The propagation time at this time is assumed to be tu. Next, the transmission / reception direction is switched, ultrasonic waves are transmitted from the downstream side, and received at the upstream side. The propagation time at this time is assumed to be td.
At this time, if the distance between the two ultrasonic transducers is L, the sound velocity is C, and the flow velocity of the medium is v, the following equation is established.

tu = L / C + v (1)
td = L / Cv (2)
If the difference is obtained by taking the reciprocal of the equations (1) and (2), the following equation is obtained.
v = L / 2 ((tu-td) / tu · td) (3)
= L / 2 (Δt / tu · td) (4)
Here, the propagation time difference Δt = (tu−td).

  Therefore, the flow velocity v depends on the propagation time difference Δt. Thus, the flow velocity is detected from the propagation time difference Δt between the transmission wave and the reception wave. Then, the flow rate of the medium flowing through the measuring tube is measured by processing such as multiplying the flow velocity by the cross-sectional area.

Japanese Patent Laid-Open No. 10-9914 JP-A-10-122923 JP 2000-180228 A

  Here, since the flow velocity v is obtained from the propagation time difference Δt of the received wave from the above equation (4), the flow velocity of the medium (fluid) that actually flows in the measurement tube (hereinafter also referred to as “tube”). In theory, tu and td should be the same value.

However, in reality, the ultrasonic transducers are separate on the upstream side and the downstream side, and the transmission characteristics and reception characteristics of these ultrasonic transducers are not the same.
The propagation time tu obtained from the above equation (1) and the propagation time td obtained from the above equation (2) are measured values at different times.
Furthermore, it includes many uncertain factors such as temperature and pressure, including fields such as the propagation characteristics of a tube (pipe or tube) and an acoustic coupling material that joins an ultrasonic transducer to the tube.
That is, in an actual situation, when measuring tu and measuring td, the transmitting-side ultrasonic transducer, the receiving-side ultrasonic transducer, and their acoustic coupling materials are complicated in the signal transmission path. In reality, the reversibility at the time of transmission and reception is not always the same.
For this reason, when the flow velocity of the medium that actually flows through the tube is “zero”, the propagation times tu and td are not always exactly the same.

  In addition, even if the relationship between transmission and reception that should be considered that reversibility is not determined is obtained by using a theoretical calculation formula, the actual flow rate “ Determining the “zero point” of the measured flow velocity at “zero” is considered a difficult event.

As described above, in the conventional ultrasonic flowmeter, “fluctuation” due to environmental conditions or the like causes a zero point fluctuation (hereinafter referred to as “zero drift”) of a measured value, and the “zero point” in a long time. There was a problem of deteriorating stability.
For this reason, “zero” of the measurement value of the ultrasonic flowmeter is expressed as “relative zero” and cannot be obtained as “absolute zero”, resulting in a problem that the measurement accuracy is lowered.

The present invention has been made to solve the above-described problems, and provides an ultrasonic flowmeter capable of reducing zero drift.
Moreover, the ultrasonic flowmeter which can improve the measurement precision of the flow velocity is obtained.

  An ultrasonic flowmeter according to the present invention is an ultrasonic flowmeter for obtaining a flow velocity of a fluid flowing in a measurement tube, and a plurality of vibrators attached to the measurement tube at a predetermined distance along the flow of the fluid. The propagation time until the downstream transducer receives the ultrasonic wave transmitted from the upstream transducer, and the upstream transducer receives the ultrasonic wave transmitted from the downstream transducer. Calculating means for calculating a flow velocity of the fluid based on a time difference from the propagation time until the first time, and the vibrator has a first frequency ultrasonic wave and a second frequency predetermined according to the measurement tube. The ultrasonic wave is alternately transmitted, and the calculation means obtains the time difference of the propagation time in the ultrasonic wave of the first frequency as the time difference when the flow velocity of the fluid is zero. Based on the time difference in the propagation time of sound waves, And requests the flow rate.

  In the ultrasonic flowmeter according to the present invention, the vibrator has a frequency at which the attenuation amount of the ultrasonic wave propagating in the measurement tube is smaller than the attenuation amount of the ultrasonic wave propagating in the fluid. The frequency of the ultrasonic wave having a larger attenuation amount of the ultrasonic wave propagating in the measurement tube than the attenuation amount of the ultrasonic wave propagating in the fluid is set as the second frequency. .

  In the ultrasonic flowmeter according to the present invention, the vibrator is set such that the first frequency is lower than the second frequency.

  Further, in the ultrasonic flowmeter according to the present invention, the vibrator is provided at two locations on the upstream side and the downstream side of the measurement tube, and the ultrasonic wave transmitted by applying alternating electrical energy to one vibrator is provided. The sound wave is received by the other vibrator, and the vibrator on the transmitting side and the receiving side are switched alternately.

  In the ultrasonic flowmeter according to the present invention, the vibrator is provided at three locations on the upstream side, the center, and the downstream side of the measurement tube, and alternating electrical energy is applied to the vibrator provided at the center. The ultrasonic wave transmitted by this is received by the two vibrators located upstream and downstream.

  Moreover, the ultrasonic flowmeter according to the present invention is configured by a flange attached to the outer peripheral surface of the measurement tube, and includes an acoustic filter that cuts a high-frequency component of the ultrasonic wave propagating through the measurement tube. is there.

The present invention alternately transmits ultrasonic waves of the first frequency and ultrasonic waves of the second frequency, which are predetermined according to the measurement tube, and determines the time difference of the propagation time in the ultrasonic waves of the first frequency, Obtained as the time difference when the fluid flow velocity is zero, and the fluid flow velocity is obtained based on the time difference in the propagation time of the ultrasonic waves of the second frequency.
For this reason, the ultrasonic flowmeter which can reduce a zero drift can be obtained.
Moreover, the ultrasonic flowmeter which can improve the measurement precision of the flow velocity can be obtained.

FIG. 3 is a system diagram of the operation principle of the ultrasonic flowmeter according to the first embodiment. 3 is a perspective view showing the arrangement of ultrasonic transducers according to Embodiment 1. FIG. 4 is a diagram illustrating an ultrasonic wave propagation path according to Embodiment 1. FIG. FIG. 3 is a diagram showing a transmission wave and a reception wave according to the first embodiment. It is a figure which shows the flow measurement result of the ultrasonic flowmeter which concerns on Embodiment 1. FIG. It is a figure which shows the flow measurement result of the conventional ultrasonic flowmeter. FIG. 5 is an operation principle system diagram of the ultrasonic flowmeter according to the second embodiment. FIG. 6 is an operation principle system diagram of the ultrasonic flowmeter according to the third embodiment. It is a figure which shows the other structural example of an ultrasonic flowmeter. It is a figure which shows the other structural example of an ultrasonic flowmeter.

Embodiment 1 FIG.
FIG. 1 is an operation principle system diagram of the ultrasonic flowmeter according to the first embodiment.
FIG. 2 is a perspective view showing the arrangement of the ultrasonic transducers according to the first embodiment.
As shown in FIGS. 1 and 2, the ultrasonic flowmeter according to the present embodiment includes an ultrasonic transducer 2A, an ultrasonic transducer 2B, a power supply 4, an amplifier 5, a comparison circuit 6, and a calculation. A circuit 7.
This ultrasonic flow meter is for obtaining the flow velocity v of the medium flowing in the measuring tube 1.
In the first embodiment, a case where the flow velocity v is output as a measured value will be described, but the present invention is not limited to this. The flow rate can be obtained by multiplying the flow velocity v by the cross-sectional area in the pipe.

The “ultrasonic transducer 2A” and the “ultrasonic transducer 2B” correspond to the “vibrator” in the present invention.
The “comparison circuit 6” and the “arithmetic circuit 7” correspond to “arithmetic means” in the present invention.

  The measurement tube 1 is constituted by a pipe, a tube, or the like, and is, for example, a straight tube having a uniform outer diameter over the entire length.

The ultrasonic transducers 2A and 2B (hereinafter referred to as “ultrasonic transducer 2” when not distinguished from each other) are formed in an annular shape or a cylindrical shape having an inner diameter slightly larger than the outer diameter of the measurement tube 1. .
The ultrasonic transducer 2 is arranged at a predetermined distance along the fluid flow in the measurement tube 1.
In addition, the gap between the inner peripheral surface of the ultrasonic transducer 2 and the outer peripheral surface of the measuring tube 1 is filled with an acoustic coupling material 3 that is made of a semi-fluid or a semi-solid material such as grease and easily transmits ultrasonic waves. To do. As a result, the ultrasonic transducer 2 and the measuring tube 1 are brought into acoustic contact or joined to form a so-called acoustic coupling state.
The ultrasonic transducers 2A and 2B are connected to the power source 4 via the switch SW1 and to the amplifier 5 via the switch SW2.

  The comparison circuit 6 receives the received waveform signal amplified by the amplifier 5. The comparison circuit 6 is a comparator for detecting a point where the received wave exceeds a predetermined threshold value.

  The arithmetic circuit 7 obtains the flow velocity based on the received wave input from the comparison circuit 6. The arithmetic circuit 7 can set the frequency of alternating electrical energy generated by the power supply 4. Details will be described later.

In such a configuration, by switching the switches SW1 and SW2 to the a side, the ultrasonic transducer 2A is connected to the power source 4 to be a transmitter, and the ultrasonic transducer 2B is connected to the amplifier 5 to be a receiver. .
The upstream ultrasonic transducer 2A, when supplied with alternating electrical energy from the power source 4, vibrates in the radial direction with a reduced diameter and a larger diameter. When the inside of the measurement tube 1 is filled with a medium (fluid), the ultrasonic waves generated from the ultrasonic transducer 2A are transmitted to the fluid through the acoustic coupling material 3 and the tube wall of the measurement tube 1, and once the transducer After propagating toward the center (the center of the straight pipe), the direction is changed to a right angle and propagates in both the front and rear directions in parallel with the pipe. At this time, since ultrasonic waves are a kind of pressure vibration, pressure changes also occur in the radial direction of the tube during propagation.
The ultrasonic transducer 2B on the downstream side generates an electrical signal similar to the vibration waveform when a pressure change (vibration) in the radial direction is applied through the tube wall of the measurement tube 1 and the acoustic coupling material 3.
An electrical signal similar to the vibration waveform generated by the ultrasonic transducer 2B (hereinafter referred to as “received wave”) is amplified by the amplifier 5 and input to the arithmetic circuit 7 via the comparison circuit 6.
The arithmetic circuit 7 measures the forward flow propagation time tu until the downstream ultrasonic transducer 2B receives the ultrasonic wave transmitted from the upstream ultrasonic transducer 2A based on the input received wave. .

Further, by switching the switches SW1 and SW2 to the b side, the ultrasonic transducer 2A is connected to the amplifier 5 to be a receiver, and the ultrasonic transducer 2B is connected to the power source 4 to be a transmitter.
Accordingly, similarly, the arithmetic circuit 7 performs the reverse flow until the upstream ultrasonic transducer 2A receives the ultrasonic wave transmitted from the downstream ultrasonic transducer 2B based on the input received wave. The propagation time td is measured.
Then, the arithmetic circuit 7 obtains the flow velocity of the fluid based on the time difference Δt between the propagation time tu and the propagation time td.

  Here, the relationship between the ultrasonic propagation path and the frequency will be described with reference to FIG.

FIG. 3 is a diagram showing a propagation path of ultrasonic waves according to the first embodiment.
As described above, the ultrasonic transducer 2 on the transmission side vibrates when alternating electrical energy is applied. As shown in FIG. 3A, the ultrasonic waves from the transmission-side ultrasonic transducer 2 propagate through the medium (fluid) and reach the reception-side ultrasonic transducer 2. Hereinafter, this propagation path is referred to as “in-medium propagation”.
At this time, as shown in FIG. 3B, the ultrasonic wave from the ultrasonic transducer 2 on the transmission side propagates through the measurement tube 1 itself and reaches the ultrasonic transducer 2 on the reception side. Hereinafter, this propagation path is referred to as “intratubular propagation”.

Such an ultrasonic propagation path depends on the frequency characteristics of the measurement tube 1 and the medium (fluid). For this reason, by transmitting ultrasonic waves that are easy to propagate in the measurement tube 1 (the attenuation amount in the measurement tube 1 is small) and receiving the ultrasonic waves that have propagated through the measurement tube 1 itself, a propagation time that does not depend on the flow velocity is obtained. Obtainable. That is, it is possible to obtain a propagation time when the flow velocity is “zero”.
Further, by transmitting an ultrasonic wave that easily propagates in the medium (the attenuation amount in the measuring tube 1 is large) and receiving the ultrasonic wave propagated in the medium, a propagation time corresponding to the flow velocity can be obtained.

  For this reason, in the present embodiment, a frequency intended for propagation in the tube (hereinafter referred to as “first frequency”) and a frequency intended for propagation in the medium (hereinafter referred to as “second frequency”). )) Alternately in a short time, the time difference of the flow rate “zero” and the time difference of the flow rate “v” can be obtained almost simultaneously.

  Next, the operation of the first embodiment for measuring the flow velocity using such different frequencies will be described with reference to FIG.

FIG. 4 is a diagram showing a transmission wave and a reception wave according to the first embodiment.
First, the first frequency and the second frequency are set in advance in the arithmetic circuit 7 according to the measurement tube 1 and the medium (fluid).
As the first frequency, a frequency is set such that the attenuation amount of the ultrasonic wave propagating in the measuring tube 1 is smaller than the attenuation amount of the ultrasonic wave propagating in the fluid.
In addition, as the second frequency, an ultrasonic frequency in which the attenuation amount of the ultrasonic wave propagating in the measurement tube 1 is larger than the attenuation amount of the ultrasonic wave propagating in the fluid is set.
For example, a frequency lower than the cutoff frequency of the measuring tube 1 is set as the first frequency, and a frequency higher than this frequency is set as the second frequency.

As shown in FIG. 4, first, the upstream ultrasonic transducer 2A transmits an ultrasonic wave (f2) having a second frequency (transmitting A2). This ultrasonic wave (f2) propagates through the medium and is received by the ultrasonic transducer 2B on the downstream side (reception B2). Thereby, the arithmetic circuit 7 obtains the propagation time tu2.
Next, the upstream ultrasonic transducer 2A transmits an ultrasonic wave (f1) having a first frequency (transmitting A1). This ultrasonic wave (f1) propagates through the measurement tube 1 and is received by the ultrasonic transducer 2B on the downstream side (reception B1). Thereby, the arithmetic circuit 7 obtains the propagation time tu1.

Next, by switching the switches SW1 and SW2, the transmission-side and reception-side ultrasonic transducers 2 are switched.
First, the ultrasonic transducer 2B on the downstream side transmits an ultrasonic wave (f2) having the second frequency (transmitting B2). This ultrasonic wave (f2) propagates in the medium and is received by the ultrasonic vibrator 2A on the upstream side (reception A2). Thereby, the arithmetic circuit 7 obtains the propagation time td2.
Next, the ultrasonic transducer 2B on the downstream side transmits an ultrasonic wave (f1) having a first frequency (transmitting B1). The ultrasonic wave (f1) propagates through the measurement tube 1 and is received by the ultrasonic vibrator 2A on the upstream side (reception A1). Thereby, the arithmetic circuit 7 obtains the propagation time td1.
Thereafter, the same operation is repeated, and the propagation times by the first and second frequencies are obtained alternately. In order to reduce the influence of changes in environmental conditions as much as possible, it is desirable to switch the first and second frequencies in a short time.

Then, the arithmetic circuit 7 obtains the first time difference Δt1 between the propagation times tu1 and td1 in the ultrasonic waves of the first frequency as the time difference when the fluid flow velocity is “zero”. Further, the flow velocity v of the fluid is obtained based on the second time difference Δt2 between the propagation times tu2 and td2 in the ultrasonic waves of the second frequency and the first time difference Δt1. For example, the flow velocity v can be obtained by applying the second time difference Δt2 to the above equation (4).
The calculation of the flow velocity v is not limited to this. For example, the second time difference Δt2 is corrected by the first time difference Δt1 by a predetermined calculation process or the like, and the corrected second time difference Δt2 is calculated as (4 ) May be applied to the equation.

  When the flow rate of the medium is obtained, the flow rate can be obtained by processing such as multiplying the flow velocity v obtained by the arithmetic circuit 7 by the inner cross-sectional area of the measuring tube 1.

  FIG. 5 shows the flow rate measurement result in the present embodiment by such an operation. Moreover, the flow measurement result in a prior art is shown in FIG.

FIG. 5 is a diagram showing a flow measurement result of the ultrasonic flowmeter according to the first embodiment.
In FIG. 5, the vertical axis indicates the flow rate, and the horizontal axis indicates the elapsed time. In FIG. 5, a predetermined flow rate (for example, about 20 [mL / min]) was applied to the medium in the measuring tube 1 from about 2800 to 3300 on the horizontal axis (5 minutes). At other times, the flow rate is “zero”.

FIG. 6 is a diagram showing a flow measurement result of a conventional ultrasonic flow meter.
In FIG. 6, the vertical axis represents the flow rate, and the horizontal axis represents the elapsed time. In FIG. 6, a predetermined flow rate (for example, about 15 [mL / min]) was given to the medium in the measuring tube for 10 minutes around the 17000 scale on the horizontal axis. At other times, the flow rate is “zero”.

As shown in FIG. 5, in the flow rate measurement result of the ultrasonic flowmeter in the first embodiment, when the flow rate of the medium is “zero”, the flow rate measurement value is also “zero” and stable. Further, when a predetermined flow rate is given to the medium, the flow rate of the medium can be measured.
On the other hand, as shown in FIG. 6, in the flow measurement result of the ultrasonic flowmeter in the prior art, even when the flow rate of the medium is “zero”, the flow rate measurement value fluctuates as time passes, Drift has occurred.

  As described above, in the present embodiment, the ultrasonic transducer 2 alternately transmits ultrasonic waves of the first frequency and ultrasonic waves of the second frequency, which are predetermined according to the measurement tube 1, The arithmetic circuit 7 obtains the first time difference of the propagation time in the first frequency ultrasonic wave as the time difference when the fluid flow velocity is zero, and calculates the second propagation time in the second frequency ultrasonic wave. Based on the time difference and the first time difference, the flow velocity of the fluid is obtained. For this reason, zero drift can be reduced. Moreover, the measurement accuracy of the flow velocity can be improved.

  As described above, in the present embodiment, the flow velocity “v” always referring to the “zero point” is obtained by obtaining the flow velocity “zero” of the fluid by the time difference of the propagation time in the propagation in the tube independent of the flow velocity of the medium (fluid). Can be determined. For this reason, the measurement accuracy of the flow velocity can be improved.

  In addition, since the first frequency and the second frequency are alternately switched and transmitted, the fluid flow velocity v and the flow velocity “zero” are obtained almost simultaneously under the same conditions. For this reason, it is possible to reduce the zero drift by eliminating environmental changes, particularly fluctuations in temperature and long time. For this reason, the measurement accuracy of the flow velocity v can be improved.

  In addition, since the flow velocity v is measured while constantly referring to (recognizing) the “zero point”, there is no need to calibrate to determine the “zero point” by stopping the flow velocity. This means that even in the case of environmental changes over a long period of time, even if the flow velocity is continuously measured, the “zero point” of the measured flow velocity can be determined, and the flow velocity can be accurately measured. It is.

Embodiment 2. FIG.
FIG. 7 is an operation principle system diagram of the ultrasonic flowmeter according to the second embodiment.
As shown in FIG. 7, in the second embodiment, ultrasonic transducers 2A, 2B, and 2C are provided at three locations on the upstream side, the center, and the downstream side of the measurement tube 1.
The ultrasonic transducers 2 </ b> A, 2 </ b> B, and 2 </ b> C are formed in an annular shape as in the first embodiment, and are acoustically coupled to the measurement tube 1 by the acoustic coupling material 3.

  The ultrasonic transducer 2B is connected to the power source 4. And when alternating electrical energy is given from the power supply 4, it will reduce in diameter and expand and vibrate in the radial direction. When the inside of the measurement tube 1 is filled with a medium (fluid), the ultrasonic waves generated from the ultrasonic transducer 2B are transmitted to the fluid through the acoustic coupling material 3 and the tube wall of the measurement tube 1, and once the transducer After propagating toward the center (the center of the straight pipe), the direction is changed to a right angle and propagates in both the front and rear directions in parallel with the pipe. At this time, since ultrasonic waves are a kind of pressure vibration, pressure changes also occur in the radial direction of the tube during propagation.

The ultrasonic transducer 2A on the upstream side and the ultrasonic transducer 2C on the downstream side are similar to the vibration waveform when a pressure change (vibration) in the radial direction is applied through the tube wall of the measurement tube 1 and the acoustic coupling material 3. The electrical signal is generated.
Electric signals (received waves) similar to the vibration waveforms generated by the ultrasonic transducers 2A and 2B are amplified by the amplifiers 5A and 5C, respectively, and input to the arithmetic circuit 7 via the comparison circuits 6A and 6C.
Based on the received wave input from the comparison circuit 6A, the arithmetic circuit 7 performs a reverse flow until the upstream ultrasonic transducer 2A receives the ultrasonic wave transmitted from the ultrasonic transducer 2B provided at the center. The propagation time td is measured.
Further, based on the received wave input from the comparison circuit 6C, the forward flow propagation time tu until the ultrasonic transducer 2C on the downstream side receives the ultrasonic wave transmitted from the ultrasonic transducer 2B provided in the center. Measure.
Then, similarly to the first embodiment, ultrasonic waves of the first and second frequencies are alternately transmitted, and the arithmetic circuit 7 determines the fluid based on the first time difference Δt1 and the second time difference Δt2. The flow velocity “zero” and the fluid flow velocity v are obtained.

As described above, also in the present embodiment, the same effect as in the first embodiment can be obtained.
Furthermore, in the second embodiment, it is not necessary to switch between the ultrasonic transducers 2 on the transmission side and the reception side by a switch. That is, the forward flow propagation delay time tu and the reverse flow propagation delay time td can be obtained simultaneously.
For this reason, it is possible to further reduce the influence on the propagation time due to environmental changes such as propagation characteristics due to differences in measurement time. Thereby, the measurement accuracy of the flow velocity can be improved.

Embodiment 3 FIG.
FIG. 8 is an operation principle system diagram of the ultrasonic flowmeter according to the third embodiment.
As shown in FIG. 8, in the third embodiment, acoustic filters 21 and 22 are provided on the outer peripheral surface of the measuring tube 1.
Other configurations are the same as those of the first embodiment, and the same reference numerals are given to the same portions.

The acoustic filters 21 and 22 are configured by flanges attached to the outer peripheral surface of the measurement tube 1, and cut high frequency components of ultrasonic waves propagating through the measurement tube 1.
That is, if the measurement tube 1 is considered as an ultrasonic wave propagation path, the acoustic filters 21 and 22 are low-pass filters, that is, high-frequency cut filters. At this time, a frequency higher than a predetermined cutoff frequency is attenuated by the shape of the acoustic filters 21 and 22 and the like.
In addition, since what is equipped with such an acoustic filter is well-known (for example, refer patent document 3), detailed description is abbreviate | omitted.

As described above, also in the present embodiment, the same effect as in the first embodiment can be obtained.
Furthermore, in the third embodiment, since the acoustic filters 21 and 22 are provided, when transmitting the ultrasonic wave of the first frequency for the purpose of propagation in the tube, the high frequency component is attenuated to reduce noise and the like. The delay time due to propagation in the tube can be measured by ultrasonic waves having a frequency lower than the frequency. Thereby, the noise etc. by an ultrasonic wave can be reduced and the measurement precision of a flow velocity (flow rate) can be improved.

In the first to third embodiments, the ultrasonic flowmeter using the annular ultrasonic transducer 2 has been described. However, the present invention is not limited to this.
For example, as shown in FIG. 9, two pairs of ultrasonic transducers are fixed to the tube wall of the measurement tube 1 while being displaced in the axial direction, and the generated ultrasonic waves are slanted in the fluid with respect to the fluid flow. The present invention can be applied even to a flow meter of a propagation type.
For example, as shown in FIG. 10, two pairs of ultrasonic transducers are provided at both ends of the measurement tube 1 that are closed, and the ultrasonic waves generated by the ultrasonic transducers flow in the fluid flowing through the measurement tube. The present invention can be applied even to a flow meter that propagates in parallel.
That is, as long as the ultrasonic wave is propagated in the medium and in the measurement tube 1, it can be applied to an ultrasonic flowmeter having an arbitrary structure.
In actual application, depending on the material, dimensions, etc. of the measuring tube 1 (pipe or tube) and the type of medium, the sound frequency in the material of the pipe or tube and the sound speed in the medium are taken into consideration. It is necessary to determine.

  1 measurement tube, 2A ultrasonic transducer, 2B ultrasonic transducer, 2C ultrasonic transducer, 3 acoustic coupling material, 4 power supply, 5 amplifier, 5A amplifier, 5C amplifier, 6 comparison circuit, 6A comparison circuit, 6C comparison circuit 7 arithmetic circuit, 21 acoustic filter, 22 acoustic filter, SW1 switch, SW2 switch.

Claims (6)

In an ultrasonic flowmeter that calculates the flow velocity of fluid flowing in a measurement tube,
A plurality of vibrators attached to the measurement tube at a predetermined distance along the flow of the fluid;
The propagation time until the downstream transducer receives the ultrasonic wave transmitted from the upstream transducer, and the upstream transducer receives the ultrasonic wave transmitted from the downstream transducer. Calculating means for obtaining the flow velocity of the fluid based on the time difference from the propagation time until
The vibrator is
Predetermining according to the measurement tube, the first frequency ultrasonic wave and the second frequency ultrasonic wave are alternately transmitted,
The computing means is
Obtaining a first time difference of propagation time in the ultrasonic wave of the first frequency as a time difference when the flow velocity of the fluid is zero;
An ultrasonic flowmeter, wherein a flow velocity of the fluid is obtained based on a second time difference of propagation time in the ultrasonic wave of the second frequency and the first time difference. The vibrator is
The frequency at which the attenuation amount of the ultrasonic wave propagating in the measurement tube is smaller than the attenuation amount of the ultrasonic wave propagating in the fluid is set as the first frequency,
2. The frequency of an ultrasonic wave having a larger attenuation amount of the ultrasonic wave propagating in the measurement tube than the attenuation amount of the ultrasonic wave propagating in the fluid is set as the second frequency. Ultrasonic flow meter. The vibrator is
The ultrasonic flowmeter according to claim 1, wherein the first frequency is set lower than the second frequency. The vibrator is provided at two locations on the upstream side and the downstream side of the measurement tube,
The ultrasonic wave transmitted when alternating electrical energy is given to one vibrator is received by the other vibrator, and the vibrator on the transmitting side and the receiving side are switched alternately. The ultrasonic flowmeter according to any one of the above. The vibrator is provided at three locations on the upstream side, the center, and the downstream side of the measurement tube,
The ultrasonic wave transmitted when alternating electrical energy is given to the vibrator provided in the center is received by the two vibrators located upstream and downstream. The described ultrasonic flowmeter. 6. The acoustic filter according to claim 1, further comprising an acoustic filter configured by a flange attached to an outer peripheral surface of the measurement tube and configured to cut a high-frequency component of an ultrasonic wave propagating through the measurement tube. The described ultrasonic flowmeter.

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