JPH11230799A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flowmeter for accurately measuring the flowrate of a fluid flowing in a pipeline with an extremely small diameter. SOLUTION: An ultrasonic flowmeter is set to a value where the dimensions of transducers 1a and 1b are, for example, ten times or more as large as the diameter of a pipeline T. Preferably, vibration transfer means 2a and 2b being formed between the transducers 1a and 1b convert vibration in the diameter direction of the transducers 1a and 1b to vibration in the direction of a pipe axis of the pipeline T for transferring to a fluid in the pipeline. Attenuation mechanisms 7a-7b and 8 for attenuating an ultrasonic wave being transferred in the pipe wall are formed on the pipe wall of the pipeline T.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flowmeter for measuring a flow rate and a flow velocity of a fluid from a difference in propagation time of an ultrasonic wave.

[0002]

2. Description of the Related Art Ultrasonic waves are propagated in a fluid to be measured,
Ultrasonic flowmeters that measure the flow rate and flow velocity from the difference in propagation time in the downstream and upstream directions are widely used. In an ultrasonic flow meter having the simplest configuration, a pair of transducers (electric / acoustic transducers or ultrasonic transducers) are installed so as to face the upstream side and the downstream side in the fluid. However, in order to avoid problems such as disturbances in the flow velocity caused by installing the transducer in the flow path, contamination of the fluid due to contact of the transducer with the fluid, and corrosion of the transducer, the flow of the fluid through the transducer is usually avoided. It is often installed outside the pipeline. As described above, in the ultrasonic flowmeter in which the transducer is installed outside the pipeline, the transducer is disposed outside the pipeline so as to be oblique and opposed to the pipeline.
A pair of transducers is provided to form an ultrasonic wave propagation path inclined at a predetermined angle with respect to the flow velocity.

[0003]

In recent years, it has become necessary to measure the flow rate of a fluid flowing through an extremely thin tube or to measure an extremely small flow rate in the fields of semiconductor device manufacturing processes and medical fields. ing. However, in the above-described conventional ultrasonic flowmeter, the diameter of the transducer is larger than the diameter of the pipe, even when the transducer is installed inside the pipe, as well as when the transducer is installed inside the pipe. It has been taken for granted that it is also small. This is because even if the transducer is mounted outside the pipeline, if the diameter of the transducer is larger than the diameter of the pipeline, not only is it difficult to mount such a transducer in the pipeline, but also This is because it becomes difficult to transmit the ultrasonic wave between the fluid flowing inside and the transducer outside the tube, and the transmission efficiency is extremely reduced.

Therefore, in an ultrasonic flowmeter for measuring the flow rate of a fluid flowing through a small-diameter thin tube, it is necessary to obtain a specially small-sized transducer as a custom-ordered product. There has been a problem that the required measurement accuracy cannot be ensured due to a decrease in the ultrasonic output accompanying the miniaturization. It is also conceivable to increase the diameter of the thin tube so that it becomes the same as the diameter of the transducer only in the short section of the measuring object.However, as the diameter of the tube increases, the flow velocity decreases. The problem is that the measurement error for small flow rates is even greater.

For this reason, conventionally, the flow rate of a fluid flowing through a small-diameter pipe is counted by dropping the fluid as a fixed amount of droplets without using an ultrasonic flowmeter and counting the number of the droplets. Measurements based on other principles.

[0006]

SUMMARY OF THE INVENTION An ultrasonic flowmeter of the present invention emits ultrasonic waves generated by a transducer outside a pipeline into a fluid flowing through the pipeline, and measures the flow velocity or flow rate of the fluid. The size of the transducer is set to a value larger than the diameter of the pipeline.

[0007]

According to a preferred embodiment of the present invention, the size of the transducer is set to be at least ten times the diameter of the conduit through which the fluid flows.

According to another preferred embodiment of the present invention,
Vibration transmitting means is formed between the transducer and the pipeline. According to another preferred embodiment of the present invention,
The transducer generates vibration including a radial vibration component, and the vibration transmitting means converts the radial vibration component of the transducer into a vibration component in the pipe axis direction of the pipe while the fluid in the pipe is being moved. It is configured to transmit to.

According to still another preferred embodiment of the present invention, an attenuating mechanism for attenuating an ultrasonic wave propagating in the tube wall is formed on the tube wall of the conduit between the transducers.

According to a further preferred embodiment of the present invention,
This ultrasonic flowmeter has a plate-like transducer that generates vibration in the lateral direction, and a fixed-transducer, and a fluid passage having a diameter smaller than the size of the transducer. Plate-shaped vibration transmission means in which an L-shaped flow path to be connected is formed is installed on the upstream side and the downstream side of the pipeline.

[0011]

FIG. 1 is a block diagram showing the construction of an ultrasonic flowmeter according to an embodiment of the present invention, wherein 1a and 1b are transducers, 2a and 2b are vibration transducers, 3 is a transceiver, and 4 is data. Processor, 5 a display, 6 an operation panel, 7,
8 is a vibration damper, and T is a conduit for the fluid whose flow rate is to be measured.

The conduit T is made of glass, metal, resin, or the like, and has a typical diameter of 1 mm to 0.2 mm. Inside the pipe T, a fluid composed of a liquid or gas to be measured for flow flows in the direction of the arrow shown in the figure. A transducer (electric / acoustic transducer or vibrator) 1a is mounted on the upstream side of the pipe T via a vibration transmitter 2a, and a transducer 2b is mounted on the downstream side via a vibration transmitter 2b. I have.

FIG. 2 is an enlarged sectional view showing a state in which the transducer 1a is attached to the conduit T with the vibration transmitter 2a interposed therebetween. Disc-shaped transducer 1a
Are fixed on the disk-shaped vibration transmitter 2a via an adhesive layer or a bolting mechanism (not shown). The vibration transmitter 2a is made of metal or resin, and its typical dimensions are 15 mm in diameter and 2 m in thickness.
m. Inside the vibration transmitter 2a, an L-shaped internal conduit S extending from the peripheral portion to the central portion while being bent near the center is formed. Internal pipeline S
The pipeline T is connected to the end of the peripheral portion and the end of the central portion by press fitting, welding, or the like.

The disk-shaped transducer 1a fixed to the surface of the vibration transmitter 2a generates ultrasonic vibration mainly including radial-mode vibration components that expand and contract in the radial direction. The vibration component in the radial mode is transmitted to the disk-shaped vibration transmitter 2a, which expands and contracts in the radial direction. Here, attention is paid to a rectangular cross section R surrounded by a dotted line between the bent portion of the L-shaped internal conduit S and the surface to which the transducer 1a is fixed. The deformation depending on the components will be described with reference to FIG.

The shape of the cross-sectional portion R is such that in the state where expansion and contraction in the radial direction due to the vibration component of the radial mode does not occur,
As shown in (A), the shape is kept rectangular. next,
As shown in (B), when the cross-sectional portion R extends in the radial direction with the vibration component in the radial mode, the central portion of the long side shrinks in the axial direction perpendicular to the radial direction. Conversely, as shown in (C), when the cross-sectional portion R shrinks in the radial direction due to the radial mode vibration component, the central portion of the long side extends in the axial direction perpendicular to the radial direction. The expansion and contraction in the axial direction due to the expansion and contraction in the radial direction
Also called longitudinal strain, the ratio of both is Poisson's ratio ε (<
1).

As described above, the vibration transmitter 2a converts the radial mode vibration component transmitted from the transducer 1a into an axial vibration component reduced by Poisson's ratio, and at the same time, at right angles near its center. By bending, the vibration component in the axial direction is transmitted to the fluid in the internal conduit S that is extended in the axial direction. Specifically, when the lower side of the cross-sectional portion R surrounded by the dotted line in FIG. Is transmitted.

Referring again to FIG. 1, the transceiver 3 drives the transducer 1a in accordance with a command from the data processor 4 so that the transducer 1a transmits a burst-like ultrasonic signal having an appropriate frequency, for example, 200 to 300 kHz. Generate. As described above, the ultrasonic signal is transmitted to the fluid in the pipe T via the vibration transmitter 2a, and the ultrasonic signal is transmitted to the transducer 1a at a fixed distance and the vibration transmitter 2b is transmitted to the transducer 1a. The signal is received by the transducer 1b installed opposite thereto.

The reception of the ultrasonic signal by the transducer 1b is performed by the data processor 4 via the transmission / reception unit 3.
Will be notified. The data processor 4 determines the time between the time when the ultrasonic wave is instructed to the transducer 1a via the transceiver 3 and the time when the notification of the reception of the ultrasonic signal is received from the transducer 1b.
Is stored as the propagation time required for the ultrasonic waves to propagate in the same direction (downstream direction) as the flow of the fluid between the fluids 1 and 1b.

Similarly, the data processor 4 causes the transducer 1b to generate ultrasonic waves via the transceiver 3,
A notification of reception of an ultrasonic signal in the transducer 1a is received via the transceiver 3. Data processor 4
Is the time between the time when the ultrasonic wave is instructed to the transducer 1b via the transceiver 3 and the time when the notification of the reception of the ultrasonic signal is received from the transducer 1a. The propagation time required for the ultrasonic wave to propagate in the fluid in the opposite direction (upstream direction) to the flow of the fluid is stored.

The data processor 4 calculates the flow velocity of the fluid from the reciprocal difference between the transmission times of the ultrasonic waves in the downstream direction and the upstream direction, and the propagation velocity of the ultrasonic waves in the stationary fluid. The flow rate of the fluid is calculated by multiplying the cross-sectional area of the road by the correction coefficient relating to the flow velocity distribution. The calculated flow velocity and flow rate are displayed on the display panel 5. A series of processing by the data processor 4 is performed according to a command input from the operation panel 6.

In this ultrasonic flowmeter, since the inner diameter of the pipe T is considerably smaller than the dimensions of the disk-shaped transducers 1a and 1b and the vibration transmitters 2a and 2b, the ultrasonic vibration generated by the transducer is considerably large. Is transmitted not to the internal fluid, but to the conduit itself. Moreover, since the diameter of the pipe T is extremely smaller than that of the conventional one, the ratio of the cross-sectional area of the pipe wall to the cross-sectional area of the flow path formed inside the pipe T is increased. As a result, an ultrasonic wave having a considerably larger energy than the ultrasonic wave propagating in the fluid in the pipe T propagates in the pipe wall of the pipe T.

Since the material of the conduit T is a solid such as glass, metal or resin, it has a very high density as compared with a fluid composed of a liquid or a gas. Therefore, the propagation speed of the ultrasonic wave is much higher than that of the fluid. Big. As a result, of the ultrasonic waves generated by the transmitting-side transducer, the component that has propagated through the tube wall arrives at the receiving-side transducer sooner than the component that has propagated through the fluid, and is reflected there and transmitted to the transmitting-side transducer. The light propagates, is further reflected and arrives at the receiving transducer again. As described above, the ultrasonic wave propagating in the tube wall reciprocates many times between the transmitter and the receiver on the transmitting side and interferes with the transmission and reception of the ultrasonic wave propagating in the fluid.

In order to attenuate the undesired ultrasonic waves which cause interference, the vibration attenuators 7a to 7d made of silicone rubber are formed by coating on the pipeline. Also, the vibration damper 8
Is formed by winding a porous rubber (sponge) around the outer peripheral surface of the pipe and then crushing the same.

FIG. 4 is a view showing experimental data of the above embodiment. In FIG. 1, an ultrasonic wave is transmitted from one transducer 1a, and a waveform received by the other transducer 1b is output from an oscilloscope to a printer. The diameter of the pipe T is 0.53 mm, and the distance between the transducers 1a and 1b is 265 mm. The upper part (A) shows the reception waveform when the water in the pipeline T is stationary, the middle part (B) shows the reception waveform when the water flows in the ultrasonic wave propagation direction, and the lower part (C) shows the reception waveform. It is a reception waveform at the time of flowing water in the direction opposite to the propagation direction of a sound wave. When the water flows in the propagation direction of the ultrasonic wave around the stationary state, the reception waveform appears earlier, and when the water flows in the opposite direction, the reception waveform appears later. By calculating the difference in the propagation speed from the difference in the propagation time, the speed of the water flow can be measured.

As described above, in order to increase the transmission efficiency of ultrasonic waves,
The configuration in which the transducer mainly generates a vibration component in the radial direction has been exemplified. However, when the inner diameter of the conduit is relatively large, or when the transmission efficiency of the ultrasonic wave can be slightly sacrificed, the transducer generates vibration in the axial direction, which is directly subjected to the vibration component in the axial direction (longitudinal vibration). It can also be configured to transmit to the fluid as a component).

Also, an example has been described in which a pair of vibrators are installed to face each other on the upstream side and the downstream side of the fluid, and the flow rate is measured from the difference in the propagation time of the ultrasonic wave in each direction. However, the present invention can also be applied to a Doppler type flow meter that emits ultrasonic waves into a fluid from one transducer and measures the flow velocity and the flow rate from the Doppler shift amount of the frequency of the reflected wave from the inside of the fluid.

[0027]

As described above in detail, in the ultrasonic flowmeter of the present invention, since the size of the transducer is set to a value larger than the diameter of the pipe, the flow rate of the fluid flowing through the narrow pipe is Can be easily and accurately measured using ultrasonic waves.

According to another preferred embodiment of the present invention,
The transducer contains a radial vibration component,
Vibration transmitting means is formed between the transducer and the pipe for transmitting a vibration component in the radial direction of the transducer to a vibration component in the pipe axis direction of the pipe while transmitting the vibration component to the fluid in the pipe. Therefore, efficient transmission of vibration between the transducer and the fluid in the pipeline is realized.

The ultrasonic flowmeter of the present invention is used for increasing the flow rate of a fluid flowing at a small flow rate in a pipe having a large diameter by flowing the fluid at a small flow rate in the pipe having a small diameter. Also applicable to

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an ultrasonic flowmeter according to one embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing, in an enlarged manner, a portion of a transducer, a vibration transmitter, and a pipeline in FIG. 1;

FIG. 3 is a conceptual diagram for explaining how a radial mode vibration component is converted into an axial vibration component inside a vibration transmission unit.

FIG. 4 is a diagram showing experimental data of the above embodiment.

[Explanation of symbols]

 1a, 1b Transducer 2a, 2b Vibration transducer 3 Transceiver 4 Data processor 5 Display 6 Operation panel 7,8 Vibration attenuator T Pipe for fluid to be measured

Claims (8)

[Claims] 1. An ultrasonic flowmeter for emitting ultrasonic waves generated by a transducer outside a pipeline into a fluid flowing through the pipeline and measuring the flow velocity or flow rate of the fluid, wherein the size of the transducer is equal to that of the pipeline. An ultrasonic flowmeter characterized by being set to a value larger than the diameter of the ultrasonic flowmeter. 2. The ultrasonic flowmeter according to claim 1, wherein the size of the transducer is set to a value that is at least ten times the diameter of the conduit. 3. The ultrasonic flowmeter according to claim 1, wherein a vibration transmitting unit is formed between the transducer and the pipeline. 4. The transducer according to claim 3, wherein the transducer generates a vibration including a vibration component in a radial direction, and the vibration transmission unit transmits the vibration component in a radial direction of the transducer in a pipe axis direction of the conduit. An ultrasonic flowmeter for transmitting a vibration component to a fluid in the conduit while converting the vibration component into a fluid. 5. The apparatus according to claim 1, wherein the transducers are arranged so as to face each other on an upstream side and a downstream side of the pipeline, and the propagation speed of the upstream side and the propagation speed of the downstream side are different from each other. An ultrasonic flowmeter, wherein the flow rate and the flow rate of the fluid are measured from the difference. 6. The ultrasonic flowmeter according to claim 5, wherein an attenuation mechanism for attenuating an ultrasonic wave propagating in the tube wall is formed on a tube wall of the conduit between the transducers. . 7. A plate-like transducer for generating ultrasonic vibrations, and an L fixed to the transducer and connected at a peripheral portion and a central portion to a fluid conduit having a diameter smaller than the size of the transducer. An ultrasonic flowmeter comprising: a flat-plate-like vibration transmission means having a U-shaped flow path formed therein. 8. The ultrasonic flowmeter according to claim 7, wherein the transducer generates an ultrasonic vibration including a lateral vibration component.