Patent Application
20140109688
This application is based on Japanese Patent Application No. 2012-234889, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an ultrasonic flowmeter for use in fluid transportation in various industries such as chemical works, semiconductor manufacture field, food processing field and biotechnology field, which propagates an ultrasonic vibration through a fluid and measures a flow velocity or flow rate of the fluid from a difference between the ultrasonic wave propagation time from the upstream side of the flow and the ultrasonic wave propagation time from the downstream side of the flow, and also to a fluid controller having such an ultrasonic flowmeter. The present invention particularly relates to an ultrasonic flowmeter suitable for measuring a micro flow rate and the flow rate of a slurry fluid or especially the CMP slurry fluid used in the semiconductor field, and also to a fluid controller having such an ultrasonic flowmeter.
2. Description of the Related Art
Ultrasonic flowmeters for measuring a flow velocity or flow rate of a fluid flowing in a measurement pipe from a difference in ultrasonic wave propagation time are generally classified into two types.
In a first type of ultrasonic flowmeter, flow passages are connected to both ends of a liner measurement pipe so that the flow passages are at generally right angle to the measurement pipe, and ultrasonic transceivers are disposed on an upstream side and a downstream side of the measurement pipe so that the ultrasonic transceivers face each other across the measurement pipe. In the ultrasonic flowmeter, an ultrasonic wave transmitted from the upstream ultrasonic transceiver is propagated through a fluid in the measurement pipe and received by the downstream ultrasonic transceiver. Instantaneously after that, an ultrasonic wave transmitted from the downstream ultrasonic transceiver is propagated into the fluid in the measurement pipe and received by the upstream ultrasonic transceiver (see Japanese Unexamined Patent Publication Nos. 2000-146645, 2006-337059, 2007-58352, etc.). In the process, a difference between the ultrasonic wave propagation time from the upstream ultrasonic transceiver to the downstream ultrasonic transceiver and the ultrasonic wave propagation time from the downstream ultrasonic transceiver to the upstream ultrasonic transceiver is used to determine the flow velocity of the fluid in the measurement pipe and measure the flow rate.
In a second type of ultrasonic flowmeter, two ultrasonic transceivers are disposed on transmitting bodies mounted on outer peripheral portions of a liner measurement pipe, respectively. In the ultrasonic flowmeter, an ultrasonic wave transmitted from one of the ultrasonic transceivers is propagated into a fluid in the measurement pipe through the transmitting body and a wall of the measurement pipe, propagated obliquely with respect to a flowing direction of the fluid in the measurement pipe while being reflected on the pipe wall of the measurement pipe, and received by the other ultrasonic transceiver. Instantaneously after that, the transmitting side and the receiving side are switched, and, similarly to above, an ultrasonic wave transmitted from one of the ultrasonic transceivers is received by the other ultrasonic transceiver (see Japanese Unexamined Patent Publication Nos. 2005-188974, 2008-275607, 2011-112499, etc.). In the process, like the first type of the ultrasonic flowmeter, a difference between the ultrasonic wave propagation time from the upstream ultrasonic transceiver to the downstream ultrasonic transceiver and the ultrasonic wave propagation time from the downstream ultrasonic transceiver to the upstream ultrasonic transceiver is used to determine the flow velocity of the fluid in the measurement pipe and measure the flow rate.
In the first type of the ultrasonic flowmeter, bent portions are formed on both end portions of the measurement pipe. Therefore, especially in a case where a fluid flowing in the measurement pipe is a slurry, the slurry is deposited and fixed to the bent portions, and propagation of the ultrasonic vibration is hindered, thus causing a problem that accurate measurement of the flow rate is not possible. On the contrary, the second type of the ultrasonic flowmeter has an advantage that the above-mentioned problem is unlikely to be posed since it is not necessary to form bent portions on both end portions of the measurement pipe.
However, in the second type of the ultrasonic flowmeter, it is necessary to provide the transmitting bodies on the outer peripheral portion of the measurement pipe. In a case where the transmitting bodies fabricated in a process different from the measurement pipe fabricating process are later mounted to the measurement pipe by an adhesive, welding, etc., it is likely that positions of the transmitting bodies with respect to the measurement pipe and a distance between the transmission bodies vary depending on proficiency of an operator, thus causing deterioration of measurement accuracy. Further, factors such as an amount of adhesive applied, drying time of the adhesive, uniformity of application of the adhesive, etc., cause variation in performance of the ultrasonic flowmeter, and therefore need to be controlled in order to ensure performance of the ultrasonic flowmeter. In addition, in a case where a small-diameter measurement pipe is used, a problem occurs that it is difficult to assemble the measurement pipe and the transmitting bodies. It is not necessary to use an adhesive when the measurement pipe and the transmitting bodies are formed integrally with each other by injection molding. However, it is necessary to provide a draft in an inner diameter of the measurement pipe, which makes a flow velocity of a fluid in the measurement pipe non-constant. Therefore, forming the measurement pipe and the transmitting bodies integrally with each other is not suitable especially for fabricating a small-diameter measurement pipe. As a result, when fabricating the transmitting bodies and the measurement pipe integrally with each other, cutting work is often used.
However, with the cutting work, it is especially difficult to fabricate a measurement pipe having a small pipe diameter, and it is also difficult to control quality of an inner peripheral surface of the measurement pipe. Further, microasperity is formed on the inner peripheral surface of the measurement pipe, and microscopic bubbles are thus easily adhered to the inner peripheral surface of the measurement pipe. Surfaces of the microscopic bubbles reflect an ultrasonic vibration, thereby causing a decrease in output signal strength and deterioration of measurement accuracy especially in the second type of the ultrasonic flowmeter in which the ultrasonic vibration is propagated while being reflected within the measurement pipe.
In order to solve the problem of the microscopic bubbles inside the measurement pipe, Japanese Unexamined Patent Publication No. 2012-42243 suggests a straight-pipe type ultrasonic flowmeter in which, as shown in
Accordingly, it is an object of the present invention to solve the problems of the prior art and to provide an ultrasonic flowmeter in which transmitting bodies for ultrasonic transceivers to be mounted thereon are formed integrally with a measurement pipe and microscopic bubbles are unlikely to be adhered to an inner peripheral surface of the measurement pipe of the ultrasonic flowmeter.
In a first aspect, according to the present invention, there is provided an ultrasonic flowmeter including a measurement pipe through which a fluid flows, and two ultrasonic transceivers mounted on two transmitting bodies, respectively, the transmitting bodies being provided on outer side portions of the measurement pipe so as to be spaced apart from each other in an axis direction, the measurement pipe and the two transmitting bodies being formed integrally with each other, the ultrasonic flowmeter determining a flow velocity of the fluid by receiving an ultrasonic vibration transmitted from one of the two ultrasonic transceivers through the fluid in the measurement pipe with the other ultrasonic transceiver, alternately switching between the ultrasonic transceiver on the transmitting side and the ultrasonic transceiver on the receiving side, and measuring the ultrasonic wave propagation time between the two ultrasonic transceivers, wherein the measurement pipe has a length, an inner diameter uniform in a length direction, and an arithmetic mean roughness Ra of an inner peripheral surface, the inner diameter being equal to or less than 5 mm, the length of the measurement pipe being equal to or more than 30 mm, and the arithmetic mean roughness Ra satisfying a relation of 0 μm<Ra≦0.2 μm.
In the ultrasonic flowmeter having the measurement pipe and the transmitting bodies formed integrally with each other, when the measurement pipe has a length of 30 mm or more and an inner diameter of 5 mm or less being uniform in a length direction, it is difficult to fabricate the measurement pipe by injection molding, and a draft in an inner hole of the measurement pipe largely affects measurement accuracy. Therefore, the measurement pipe is generally fabricated by cutting work. In this case, a microasperity (having arithmetic mean roughness of approximately 0.4 μm) is formed on the inner peripheral surface of the measurement pipe, and microscopic bubbles are easily adhered to the microasperity on the inner peripheral surface of the measurement pipe. As a result, microscopic bubbles adhered to the inner peripheral surface of the measurement pipe adversely affects propagation of an ultrasonic wave, and causes signal strength reduction and deterioration of measurement accuracy. The present inventors have found the fact that the arithmetic mean roughness Ra of the inner peripheral surface satisfying the relation of 0μm<Ra≦0.2 μm makes it possible to prevent microscopic bubbles from being adhered to the inner periphery of the measurement pipe. By making the arithmetic mean roughness Ra of the inner peripheral surface of the measurement pipe satisfy the relation of 0 μm<Ra≦0.2 μm, an influence of microscopic bubbles on propagation of an ultrasonic vibration is suppressed to enhance signal strength of an output signal, and measurement accuracy is improved.
In the ultrasonic flowmeter, the arithmetic mean roughness Ra of the inner peripheral surface of the measurement pipe more preferably satisfies the relation of 0 μm<Ra≦0.02 μm. When the arithmetic mean roughness Ra of the inner peripheral surface of the measurement pipe is within the above range, adhesion of microscopic bubbles can be prevented more effectively.
Preferably, the measurement pipe and the transmitting bodies are made of a same kind of fluorine resin.
In a second aspect, according to the present invention, there is provided a fluid controller including the ultrasonic flowmeter described above, and a control part controlling an instrument in accordance with an output from the ultrasonic flowmeter.
In the ultrasonic flowmeter according to the present invention, the measurement pipe has the smooth inner peripheral surface and therefore it is unlikely that microscopic bubbles are adhered to the inner peripheral surface of the measurement pipe. This makes it possible to suppress an influence of microscopic bubbles on propagation of ultrasonic vibration, thereby improving measurement accuracy. As a result, an ultrasonic flowmeter with high measurement accuracy can be provided.
The above and other objects, features and advantages of the present invention will be described below in more detail based on embodiments thereof with reference to the accompanying drawings, in which:
While embodiments of an ultrasonic flowmeter according to the present invention and a fluid controller having such an ultrasonic flowmeter will be described with reference to the drawings, the present invention should not, of course, be limited thereto.
First, an overall configuration of an ultrasonic flowmeter 10 according to the present invention will be described with reference to
The ultrasonic flowmeter 10 includes a measurement pipe 1 through which a fluid to be measured flows in a filled state, a pair of transmitting bodies 2 constituted by a first transmitting body 2a and a second transmitting body 2b, and ultrasonic transducers 3 serving as ultrasonic transceivers that are mounted on the pair of transmitting bodies 2, respectively.
A length of the measurement pipe 1 is equal to or more than 30 mm. An inner diameter of the measurement pipe 1 is uniform in a length direction and is equal to or less than 5 mm and uniform in a length direction. If such a measurement pipe 1 is fabricated by injection molding, a draft in an inner hole of the measurement pipe 1 changes flow velocity of a fluid flowing through the measurement pipe 1, and largely affects measurement accuracy. Further, there is a problem that it is difficult to design molds and control molding conditions. Therefore, such a measurement pipe 1 is generally fabricated by cutting work, thereby forming a microasperity (normally, arithmetic mean roughness Ra of 0.4 μm or more) on an inner peripheral surface 1a of the measurement pipe 1. As a result, microscopic bubbles are easily adhered to the inner peripheral surface 1a of the measurement pipe 1. In the ultrasonic flowmeter 10, the inner peripheral surface 1a of the measurement pipe 1 is smoothed more than a surface formed by cutting work so that microscopic bubbles are less likely to be adhered to the inner peripheral surface 1a of the measurement pipe 1. More specifically, methods such as polishing and melting described later are used so that arithmetic mean roughness Ra of the inner peripheral surface 1a of the measurement pipe 1 is within a range of 0 μm<Ra≦0.2 μm, more preferably, within a range of 0 μm<Ra≦0.02 μm.
Preferably, the measurement pipe 1 is made of a synthetic resin material such as perfluoroalkoxy fluorocarbon resin (PFA), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) or polypropylene (PP), etc. However, the material for the measurement pipe 1 is not particularly limited as long as the measurement pipe 1 can propagate an ultrasonic wave, and the measurement pipe 1 may be made from metal such as duralumin, aluminum, aluminum alloy, titanium, hastelloy or stainless steel (SUS), glass, or quartz. An outer diameter of the measurement pipe 1 is not particularly limited. However, a thin pipe wall of the measurement pipe 1 is preferred in order to facilitate propagation of an ultrasonic vibration.
The first transmitting body 2a and the second transmitting body 2b of the pair of transmitting bodies 2 are provided on outer side portions of the measurement pipe 1 so as to be spaced apart from each other in an axis direction of the measurement pipe 1, and are formed integrally with the measurement pipe 1. Preferably, as in the embodiment shown in
However, a shape of the transmitting body 2 is not limited to the shape described in the embodiment shown in
A material for the transmitting bodies 2 is not particularly limited. For example, the transmitting bodies 2 may be made of a synthetic resin such as perfluoroalkoxy fluorocarbon resin (PFA), polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC) or polypropylene (PP), or may be made of metal such as duralumin, aluminum, aluminum alloy, titanium, hastelloy or stainless steel (SUS), glass, quartz, and so on. However, the transmitting bodies 2 are preferably made of the same material as the measurement pipe 1 in order to realize good propagation capability of an ultrasonic vibration.
The ultrasonic transducers 3 used as ultrasonic transceivers are not particularly limited as long as the ultrasonic transducers 3 can generate ultrasonic waves. For example, the ultrasonic transducer 3 may be an ultrasonic transducer which is fabricated by using a piezoelectric material such as lead zirconate titanate (PZT) and generates an ultrasonic wave by extending and contracting in an axis direction when voltage is applied. The ultrasonic transducers 3 are mounted on the transmitting bodies 2, respectively, so that an ultrasonic wave generated by one of the ultrasonic transducers 3 is propagated to the other ultrasonic transducer 3 through a fluid in the measurement pipe 1. In the embodiment shown in
The inner peripheral surface 1a of the measurement pipe 1 may be smoothed by a method such as polishing and melting as described below.
The methods described above are merely examples, and a method for smoothing the inner peripheral surface 1a of the measurement pipe 1 is not limited to the methods described above as long as the arithmetic mean roughness Ra of the inner peripheral surface 1a of the measurement pipe 1 can be within the range of 0 μm<Ra≦0.2 μm. For example, after fabricating the measurement pipe 1 by extrusion molding so that the arithmetic mean roughness Ra of the inner peripheral surface 1a is within the range of 0 μm<Ra≦0.2 μm, the pair of transmitting bodies 2 may be formed on the outer side portions of the measurement pipe 1 so as to be integral with each other, by insert molding, while using the fabricated measurement pipe 1 as an insert, thereby fabricating the ultrasonic flowmeter 10 having the measurement pipe 1 and the pair of transmitting bodies 2 formed to be integral with each other.
Next, the operation of the ultrasonic flowmeter 10 will be described.
In the ultrasonic flowmeter 10, when a voltage pulse or a voltage having no frequency component is applied from a converter (not shown) to the ultrasonic transducer 3 located on the upstream side along the fluid flow direction, the ultrasonic transducer 3 generates a vibration in a direction along the thickness (i.e., in a direction of voltage application) and in a diameter direction (i.e., in a direction perpendicular to the direction of the voltage application) of the ultrasonic transducer 3. The end face on the bottom face side, i.e., the axial end face, of the transmitting body 2 is fixedly secured to the axial end face of the ultrasonic transducer 3 and a voltage is applied between both axial end faces of the ultrasonic transducers 3, so that the ultrasonic vibration in the direction along the thickness, which has a large energy of the ultrasonic vibration, is propagated to the end face of the transmitting body 2 on the bottom face side. The ultrasonic vibration thus propagated to the transmitting body 2 is further transmitted to the fluid in the measurement pipe 1 through the transmitting body 2 and the pipe wall of the measurement pipe 1 and is propagated in the fluid inside the measurement pipe 1 while being repeatedly reflected on the outer peripheral surface of the measurement pipe 1. Thereafter, ultrasonic vibration is propagated, through the transmitting body 2 located on the downstream side in opposed relation, to the ultrasonic transducer 3 fixed to the transmitting body 2 located on the downstream side, and is converted into an electric signal, which is outputted to the converter.
When the ultrasonic vibration is transmitted from the upstream ultrasonic transducer 3 to the downstream ultrasonic transducer 3 and received by it, the transmitting and receiving sides are instantaneously switched in the converter, and a voltage pulse or a voltage having no frequency component is applied from the converted to the downstream ultrasonic transducer 3. Then, similarly to the upstream ultrasonic transducer 3, the ultrasonic vibration is generated and propagated to the fluid in the measurement pipe 1 through the transmitting body 2. This ultrasonic vibration is again received by the ultrasonic transducer 3 fixed to the transmitting body located on the upstream side in opposed relation and is then converted into an electric signal, which is outputted to the converter. In the process, the ultrasonic vibration is propagated against the flow of the fluid in the measurement pipe 1. Therefore, the propagation velocity of the ultrasonic vibration in the fluid is lower than when the ultrasonic vibration transmitted from the upstream ultrasonic transducer 3 is received by the downstream ultrasonic transducer 3, and the propagation time is longer.
In the converter, the propagation time of the ultrasonic vibration from the upstream ultrasonic transducer 3 to the downstream ultrasonic transducer 3 and the propagation time of the ultrasonic vibration from the downstream ultrasonic transducer 3 to the upstream ultrasonic transducer 3 are measured, and a flow velocity and a flow rate are computed based on a difference between the propagation times. Thus, highly accurate measurement of a flow rate can be achieved.
Microscopic bubbles adhered to the inner peripheral surface 1a of the measurement pipe 1 of the ultrasonic flowmeter 10 reflect ultrasonic waves on the surfaces of the microscopic bubbles. As shown by an arrow A in
In the ultrasonic flowmeter 10 according to the present invention, the inner peripheral surface 1a of the measurement pipe 1 of the ultrasonic flowmeter 10 is smoothed by reducing surface roughness of the inner peripheral surface 1a, thereby restraining microscopic bubbles from being adhered to the inner peripheral surface 1a of the measurement pipe 1. Therefore, it is unlikely that ultrasonic vibration is reflected on the microscopic bubbles and that reduction of signal strength and deterioration of measurement accuracy due to the microscopic bubbles may be restrained.
The ultrasonic flowmeter 26 used has the same configuration as the ultrasonic flowmeter 10, and includes a measurement pipe having a length of 40 mm, an outer diameter of 3 mm, and an inner diameter of 2 mm. When a square-wave voltage pulse having a frequency of 600 kHz and an amplitude of ±5 V was applied to the ultrasonic transducer on the transmitting side, a peak-to-peak voltage Vp-p of an output signal from the ultrasonic transducer on the receiving side was measured by using the oscilloscope 27.
The fluid controller 30 includes the ultrasonic flowmeter 10, a fluidic element 31 for adjusting a flow rate, a flow velocity, a pressure and so on of a fluid, and an electric component 34 that processes an output signal from the ultrasonic flowmeter 10 and performs control.
For example, an electric-driven or air-driven pinch valve may be used as the fluidic element 31. However, the fluidic element 31 is not limited to the electric-driven or air-driven pinch valve as long as the fluidic element 31 is an instrument for adjusting a flow rate, a flow velocity, a pressure and so on of a fluid.
The electric component 34 includes an amplifier part 32 that amplifies an output signal from the ultrasonic transducer 3 of the ultrasonic flowmeter 10, and a control part 33 that performs control based on the signal amplified by the amplifier part 32, so that the electric component 34 can control the operation of the fluidic element 31 based on a control signal from the control part 33 and perform fluid control.
Since the ultrasonic flowmeter 10 according to the present invention is used in the fluid controller 30, it is possible to measure a flow rate of a fluid with high accuracy, thereby achieving accurate fluid control.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-234889 | Oct 2012 | JP | national |
