JP5398377B2 - Ultrasonic flow meter - Google Patents

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, is formed in an annular shape, and is separated from the outer circumference of the measurement tube by a predetermined distance along the flow of the fluid. A plurality of transducers attached so that the inner peripheral surface thereof is in acoustic contact with the surface, and the transducers on the downstream side receive ultrasonic waves transmitted in the form of tone burst waves from the transducers on the upstream side To obtain the flow velocity of the fluid based on the time difference between the propagation time until the transducer on the upstream side receives the ultrasonic wave transmitted from the transducer on the downstream side in the form of a tone burst wave. And the computing means at the rising or falling timing of the first predetermined period predetermined according to the measurement tube among the received waves in the form of tone burst waves received by the vibrator. Propagation time The first time difference is obtained as the time difference when the fluid flow velocity is zero, and the second time difference of the propagation time at the rising or falling timing of the second predetermined period determined in advance according to the measurement tube is The flow velocity of the fluid is obtained based on the first time difference.

Moreover, in the ultrasonic flowmeter according to the present invention, the calculation means is determined according to the material and size of the measurement tube and the frequency of the ultrasonic wave among one received wave received by the vibrator. A cycle in which the flow velocity sensitivity, which is the amount of occurrence of the time difference in the propagation time, is set as the first predetermined cycle , and depends on the material and dimensions of the measuring tube and the frequency of the ultrasonic wave The period in which the flow velocity sensitivity that is the amount of occurrence of the time difference of the propagation time is maximized is set as the second predetermined period.

  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 relates to the first time difference in propagation time at the rising or falling timing of the first predetermined period, which is predetermined according to the measurement tube, among the received waves received by the vibrator, and the fluid flow velocity is zero. The flow rate of the fluid is determined based on the second time difference of the propagation time at the rising or falling timing of the second predetermined period determined in advance according to the measurement tube and the first time difference. Ask.
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. It is a figure explaining the waveform of the transmission wave and reception wave which concern on Embodiment 1, and the detection position of a reception wave. It is a figure explaining the waveform of the transmission wave and reception wave which concern on Embodiment 1, and the detection position of a reception wave. It is a figure which shows the relationship between the detection position of the received wave which concerns on Embodiment 1, and a flow velocity coefficient. FIG. 6 is a diagram illustrating a propagation time for each detection position of a received wave according to the first embodiment. It is the figure which expanded the vertical axis | shaft of FIG. It is a figure which shows the relationship between the detection position of the received wave which concerns on Embodiment 1, and propagation time difference (DELTA) t. It is a figure which shows the relationship between the detection position of the received wave which concerns on Embodiment 1, and a flow velocity coefficient. It is a figure which shows the relationship between the detection position of the received wave which concerns on Embodiment 1, and a flow velocity coefficient. 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.

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 the zero cross point of the received waveform.

  The arithmetic circuit 7 obtains the flow velocity from the comparison circuit 6 based on a plurality of zero cross points of the received wave input. 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.

Next, the relationship between the detection position of the received wave (hereinafter also referred to as “mountain position”) and the flow velocity sensitivity (the amount of time difference Δt corresponding to the flow velocity of the medium) will be described.
When the flow velocity sensitivity is measured by paying attention to the above-described peak position of the received wave, the value varies depending on the peak position of the received wave. That is, there is a phenomenon in which the flow velocity sensitivity varies depending on the peak position of the received wave.
In this embodiment, in order to quantify the peak position of the received wave, the received wave is passed through the comparison circuit 6 to obtain a “zero cross point”.
Hereinafter, the waveforms of the transmission wave and the reception wave and the detection position of the reception wave in the present embodiment will be described with reference to FIGS.

3 and 4 are diagrams for explaining the waveforms of the transmission wave and the reception wave and the detection position of the reception wave according to the first embodiment.
FIG. 3A is a diagram illustrating a waveform of a transmission signal of the ultrasonic transducer 2A.
FIG. 3B is a diagram illustrating a waveform of a reception signal of the ultrasonic transducer 2B.
FIG. 3C is a diagram illustrating a comparator output waveform obtained by extracting the zero cross of the received wave.
FIG. 3D is a diagram showing the relationship between the detection position of the received wave and the forward flow propagation time tu.
FIG. 4A is a diagram illustrating a waveform of a transmission signal of the ultrasonic transducer 2B.
FIG. 4B is a diagram illustrating a waveform of a reception signal of the ultrasonic transducer 2A.
FIG. 4C is a diagram showing a comparator output waveform obtained by extracting the zero cross of the received wave.
FIG. 4D is a diagram showing the relationship between the detection position of the received wave and the reverse flow propagation time td.

As shown in FIGS. 3A and 4A, transmission signals (tone bursts) of, for example, five peaks of Sin waves are electrically transmitted by the ultrasonic transducer 2 on the transmission side.
As shown in FIG. 3B and FIG. 4B, a reception waveform (Sin wave) propagated by a distance L between the transmission side and the reception side ultrasonic transducer 2 by the reception side ultrasonic transducer 2. Get.
When the zero cross point is detected via the comparison circuit 6, a rectangular wave signal as shown in FIGS. 3C and 4C is obtained.
Thereby, the rising or falling timing of each period of the received wave can be obtained.

In order to quantify the reception position of the received wave, when the received wave is passed through the comparison circuit 6 and the “zero cross point” is viewed, many reception positions are obtained.
For example, as the forward propagation time shown in FIG. 3D, the propagation time tu1 is obtained at the timing of the zero-cross point in the first cycle shown in FIG. 3C. In addition, for example, at the timing of the zero-cross point in the seventh cycle shown in (2) of FIG. 3C, the propagation time tu2 is obtained.
Similarly, for example, as the reverse flow propagation time shown in FIG. 4D, the propagation time td1 is obtained at the timing of the zero-cross point in the first cycle shown in FIG. 4C. Further, for example, at the timing of the zero-cross point in the seventh cycle shown in (2) of FIG. 4C, the propagation time td2 is obtained.

When the flow velocity sensitivity (the amount of occurrence of the time difference Δt corresponding to the flow velocity of the medium) is measured by paying attention to such a peak position of the received wave, it has been found that the value varies depending on the peak position of the received wave. That is, there is a phenomenon in which the flow velocity sensitivity varies depending on the peak position of the received wave.
Next, the relationship between the received wave detection position and the flow velocity sensitivity will be described with reference to FIG.

FIG. 5 is a diagram showing the relationship between the detection position of the received wave and the flow velocity coefficient according to the first embodiment.
In FIG. 5, when a predetermined flow velocity is given to the medium in the measuring tube 1, the peak position of the received wave in one received wave is shown on the horizontal axis, and the relative value of the flow velocity coefficient is shown on the vertical axis. That is, of the peak positions of one received wave, the maximum value of the flow velocity sensitivity (the amount of propagation time difference Δt) is set to “1”, and the relative value is indicated.
FIG. 5 shows measured values when PEEK (polyetheretherketone) is used as a material in the measuring tube 1 and predetermined dimensions (inner diameter and outer diameter) are obtained.

For example, in the example of FIG. 5, the flow velocity sensitivity is substantially “zero” at the timing of the zero-cross point in the first period shown in (1). In addition, at the timing of the zero cross point of the seventh cycle shown in (2), the flow velocity sensitivity becomes the maximum value.
In this way, by detecting simultaneously the detection position where the flow velocity sensitivity is almost “zero” and the detection position where the flow velocity sensitivity is “maximum” by the detection position that detects the propagation time in one received wave, The flow velocity can be obtained from the detection position where the flow velocity sensitivity is “maximum” while the “zero point” of the time difference Δt is determined.

  Next, the difference in flow velocity coefficient depending on the detection position of the received wave will be further described with reference to FIGS.

FIG. 6 is a diagram showing the propagation time for each detected position of the received wave according to the first embodiment.
In FIG. 6, the vertical axis represents the propagation time of the ultrasonic wave, and the horizontal axis represents the elapsed time.
In FIG. 6, a predetermined flow velocity v (for example, about 10 [cm / sec]) is given to the medium in the measuring tube 1 from around the 10th to around the 18th axis of the horizontal axis. At other times, the flow rate is “zero”. Then, the propagation time from the time of transmission in FIG. 4 and FIG. 5 (at the start of the waveform (a)) to the time of reception at each detection position (rectangular wave waveform (c)) is measured.
Further, in FIG. 6, as the detection position where the flow velocity sensitivity is substantially “zero” in the timing of the zero-cross point of the received wave, for example, the zero-cross point of the first period in FIGS. 4C and 5C is used. The timing is indicated by “1”. Further, as detection positions where the flow velocity sensitivity is increased, for example, the timings of the zero cross points in the seventh, eighth, and ninth cycles in FIGS. 4C and 5C are respectively “2”, “3”, and “4”. Show.

As shown in FIG. 6, at the timing “1” when the flow velocity sensitivity becomes “zero”, both the forward flow propagation time tu and the reverse flow propagation time td are obtained at the horizontal axis 10 to 18 where the flow velocity is given. There is no change and it is constant (overlapping).
On the other hand, at the timings “2”, “3”, and “4” where the flow velocity sensitivity is high, the propagation time is divided into two parts around 10 to 18 on the horizontal axis to which the flow velocity v is given.
For example, FIG. 7 shows an enlarged representation of the time axis (vertical axis) in the vicinity, focusing on “2” in FIG.

FIG. 7 is an enlarged view of the vertical axis of FIG.
As shown in FIG. 7, the forward flow propagation time tu and the reverse flow propagation time td are almost equal after 0 to 10 and 18 on the horizontal axis where the flow velocity of the medium in the measuring tube 1 is “zero”. It has reached the same time.
On the other hand, in the vicinity of 10 to 18 on the horizontal axis where the flow velocity v is given to the medium in the measuring tube 1, the forward flow propagation time tu arrives a little earlier (moves toward the time on the vertical axis less), and the reverse flow The propagation time td reaches later by the flow velocity (the direction of the time on the vertical axis is slower).
Next, FIG. 8 shows the timings “1” and “2” in FIG. 6 expressed by paying attention to the difference between the propagation times tu and td, that is, the time difference Δt.

FIG. 8 is a diagram showing the relationship between the detection position of the received wave and the propagation time difference Δt according to the first embodiment.
As shown in FIG. 8, at timing “2” where the flow velocity sensitivity is large, a difference in time occurs between the propagation times tu and td at the horizontal axis 10 to 18 where the flow velocity v is given, and the reaction time greatly reacts and is large. The value of Δt2 is obtained.
On the other hand, at the timing “1” when the flow velocity sensitivity is almost “zero”, there is almost no time difference between the propagation times tu and td on the horizontal axes 10 to 18 to which the flow velocity v is given. The value is a very small reaction and is almost “zero” for the flow rate.

Therefore, using the time difference Δt2 between the propagation times tu and td obtained at the detection position where the flow velocity sensitivity is high in one received wave, the flow velocity v is obtained by applying the above-described equation (4). Can do.
Further, among the same received waves, the “zero point” of the time difference Δt can be determined using the time difference Δt1 between the propagation times tu and td obtained at the detection position where the flow velocity sensitivity is substantially “zero”.

  Next, the difference in flow velocity sensitivity depending on conditions such as the material of the measuring tube 1 will be described.

9 and 10 are diagrams showing the relationship between the detection position of the received wave and the flow velocity coefficient according to the first embodiment.
FIG. 9 shows measured values when PFA (perfluoroalkoxyalkane: tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin) is used as the material of the measuring tube 1 and given dimensions (inner diameter and outer diameter). is there.
FIG. 10 shows measured values when PEEK (polyetheretherketone) is used as the material of the measuring tube 1 and the predetermined dimensions (inner diameter and outer diameter) are different from those in FIG. .
As shown in FIGS. 9 and 10, it can be seen that the flow velocity sensitivity at each detection peak position of the received wave varies depending on the material and size of the measuring tube 1 made of a pipe or a tube.

  Therefore, according to the conditions such as the material of the measuring tube 1, the detection position where the flow velocity sensitivity is minimum (almost zero) and the detection position where the flow velocity sensitivity is maximum among the detection positions of the received wave. By determining in advance, it is possible to obtain a time difference when the fluid flow velocity is zero and a time difference for obtaining the fluid flow velocity from one received wave.

For this reason, in the present embodiment, the arithmetic circuit 7 preliminarily determines a cycle in which the flow velocity sensitivity is minimum (substantially zero) among one received wave received by the ultrasonic transducer 2 according to the measurement tube 1. The first predetermined cycle is set, and the cycle in which the flow velocity sensitivity is maximized is set as the second predetermined cycle.
For example, in the example shown in FIGS. 3 to 5, the timing of the zero cross point in the first cycle where the flow velocity sensitivity is minimum (the flow velocity coefficient is substantially “zero”) is set as the first predetermined cycle. Further, the timing of the zero-cross point in the seventh cycle at which the flow velocity sensitivity is maximized (the flow velocity coefficient is “1”) is set as the second predetermined cycle.
Then, the arithmetic circuit 7 calculates the first propagation time at the rising or falling timing of the first predetermined period among the received waves received by the upstream ultrasonic transducer 2A and the downstream ultrasonic transducer 2B. A time difference Δt1 of 1 is obtained as a time difference when the fluid flow velocity is “zero”. Further, the flow velocity v of the medium (fluid) is obtained based on the second time difference Δt2 of the propagation time at the rising or falling timing of the second predetermined period 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. 11 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. 11 is a diagram showing a flow measurement result of the ultrasonic flowmeter according to the first embodiment.
In FIG. 11, the flow rate is shown on the vertical axis, and the elapsed time is shown on the horizontal axis. In FIG. 11, a predetermined flow rate (for example, about 20 [mL / min]) was applied to the medium in the measuring tube 1 from about 2800 scales to about 3300 scales (5 minutes) on the horizontal axis. At other times, the flow rate is “zero”.

FIG. 12 is a diagram showing a flow measurement result of a conventional ultrasonic flow meter.
In FIG. 12, the vertical axis represents the flow rate, and the horizontal axis represents the elapsed time. In FIG. 12, 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. 11, in the flow rate measurement result of the ultrasonic flowmeter according to 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. 12, in the flow rate 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 propagation time of the rising or falling timing of the first predetermined period that is predetermined according to the measurement tube 1 among the received waves received by the ultrasonic transducer 2 is determined. The first time difference Δt1 is obtained 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 of the propagation time at the rising or falling timing of the second predetermined period that is predetermined according to the measuring tube 1, and the first time difference Δt1. . 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, in one received wave, the time difference between the propagation times at the detection position where the flow velocity coefficient is maximum and the detection position where the flow velocity coefficient is substantially “zero” is detected simultaneously. That is, in the received wave under the same condition (physically the same signal transmission path), the fluid flow velocity v and the flow velocity “zero” are obtained simultaneously under the same condition.
For this reason, a signal transmission path having the same condition is formed, a condition that is extremely preferable for detecting the flow velocity v can be established, and the flow velocity v that always refers to the “zero point” can be determined. For this reason, the measurement accuracy of the flow velocity can be improved.

In addition, measurement of the flow velocity v given to the fluid and measurement of the “zero point” can be performed simultaneously within the same received wave on the same signal transmission path, eliminating environmental changes, especially temperature and fluctuations over time. Thus, zero drift can be reduced. 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.

The present invention is not limited to the flow meter using the annular ultrasonic transducer 2, but can be applied to a general ultrasonic flow meter. In actual application, the peak position of the reception point, It is important to measure the flow velocity coefficient and adopt a method for determining the “zero point” in the calculation formula. This needs to be designed in consideration that the relationship between the flow velocity coefficient and the peak position of the received signal differs depending on the material, dimensions, operating frequency, etc. of the measuring tube 1 (pipe or tube).
Depending on the peak position of the received wave, there is a peak position where the flow coefficient (flow speed dependency) is strong and a peak position that is extremely “zero”. ) And a number of ultrasonic wave propagation modes that propagate through the position of the flow velocity distribution where the flow velocity is maximized, and the frequency and propagation speed are different. Therefore, it varies depending on the material, dimensions, and frequency of the pipe or tube. This is because there exists a form.

Embodiment 2. FIG.
FIG. 13 is an operation principle system diagram of the ultrasonic flowmeter according to the second embodiment.
As shown in FIG. 13, 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, the arithmetic circuit 7 is based on the first time difference Δt1 and the second time difference Δt2 at a predetermined timing set in advance in one received wave. The fluid 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. 14 is an operation principle system diagram of the ultrasonic flowmeter according to the third embodiment.
As shown in FIG. 14, 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 angular 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, the high frequency component of the ultrasonic wave propagating through the measurement tube 1 itself is attenuated, so that noise caused by the ultrasonic wave propagating through the measurement tube 1 itself is reduced. Can be reduced. Therefore, the measurement accuracy of the flow velocity (flow rate) can be improved.

  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 (5)

In an ultrasonic flowmeter that calculates the flow velocity of fluid flowing in a measurement tube,
A plurality of transducers formed in an annular shape and attached to the outer peripheral surface of the measurement tube so that the inner peripheral surface thereof is in acoustic contact with the predetermined distance along the flow of the fluid;
And propagation time from the upstream side of the transducer until the outgoing ultrasound in the form of a tone-burst wave received by the transducer on the downstream side, originating in the form of a tone-burst wave from the vibrator downstream Computation means for obtaining the flow velocity of the fluid based on the time difference from the propagation time until the transducer on the upstream side receives the ultrasonic wave,
The computing means is
Of the received waves in the form of tone burst waves received by the vibrator,
A first time difference in propagation time at a rising or falling timing of a first predetermined period that is predetermined according to the measurement tube is obtained as a time difference when the fluid flow velocity is zero,
The flow velocity of the fluid is obtained based on the second time difference of the propagation time at the rising or falling timing of the second predetermined period that is predetermined according to the measuring tube, and the first time difference. Ultrasonic flow meter. The computing means is
Of one received wave received by the vibrator,
The period determined according to the material and size of the measurement tube and the frequency of the ultrasonic wave, and the period at which the flow velocity sensitivity, which is the amount of time difference between the propagation times, is minimized is set as the first predetermined period. And
The period determined according to the material and size of the measuring tube and the frequency of the ultrasonic wave, and the period at which the flow velocity sensitivity, which is the amount of time difference of the propagation time, is maximized is set as the second predetermined period. The ultrasonic flowmeter according to claim 1, wherein: The vibrator is provided at two locations on the upstream side and the downstream side of the measurement tube,
3. The ultrasonic wave transmitted by applying alternating electrical energy to one vibrator is received by the other vibrator, and the vibrator on the transmitting side and the receiving side are alternately switched. Ultrasonic flow meter. The vibrator is provided at three locations on the upstream side, the center, and the downstream side of the measurement tube,
The ultrasonic wave according to claim 1 or 2, wherein ultrasonic waves transmitted by applying alternating electrical energy to a vibrator provided in the center are received by the two vibrators located upstream and downstream. Flowmeter. 5. 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, wherein the acoustic filter cuts a high-frequency component of the ultrasonic wave propagating through the measurement tube. The described ultrasonic flowmeter.

Images