Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
1998-12-18
2001-04-17
Noori, Max (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06216544
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ultrasonic flowmeter for measuring the flow of a fluid by use of an ultrasonic wave.
BACKGROUND ART
One of conventional ultrasonic flowmeters of the type described above is disclosed, for example, in Japanese Laid-Open Publication No. 8-233628. In this ultrasonic flowmeter, as shown in
FIGS. 27A and 27B
, ultrasonic oscillators
2
and
3
are disposed facing each other in a portion of a flow path
1
which is a rectangle in section
4
. The speed of a fluid is calculated by a flow calculation means
5
using the difference between the propagation time in which an ultrasonic wave transmitted from the ultrasonic oscillator
2
is received by the ultrasonic oscillator
3
and the propagation time in which an ultrasonic wave transmitted from the ultrasonic oscillator
3
is received by the ultrasonic oscillator
2
. At the same time, the flow rate distribution in the flow path
1
is presumed from the Reynolds number of the fluid, to obtain a correction coefficient and thus calculate the flow.
The conventional ultrasonic flowmeter, however, has the following problem. The propagation distance of a reflected wave which is reflected from the inside walls of the flow path is different from the propagation distance of a direct wave which propagates without being reflected. A phase difference is therefore generated between the reflected wave and the direct wave. Since a synthetic wave of the reflected wave and the direct wave is observed as a received wave, the amplitude of the received wave increases or decreases, and the period thereof varies, depending on the phase difference between the reflected wave and the direct wave. This narrows the measurement precision as well as the measurable flow range.
DISCLOSURE OF THE INVENTION
In order to solve the above problem, the present invention includes a flow measurement section and a pair of ultrasonic oscillators constructed so that the influence of the phase difference between the direct wave and the reflected wave on the measurement results is reduced.
According to the above present invention, since the influence of the reflected wave in the measurement section of the flow path can be reduced, the measurement precision can be improved over a wide range.
The ultrasonic flowmeter of the first embodiment according to the present invention includes: a pair of ultrasonic oscillators; a measurement section for measuring a time in which an ultrasonic wave propagates between the pair of ultrasonic oscillators; and a calculation section for calculating the flow of the fluid flowing in a flow measurement section based on an output from the measurement section, wherein the flow measurement section and the pair of ultrasonic oscillators are configured so that an influence of a reflected wave reflected from a wall of the flow measurement section on a measurement result is reduced. Accordingly, the influence of the reflected wave in the flow measurement section can be reduced, to obtain a high-precision ultrasonic flowmeter.
The ultrasonic flowmeter of the second embodiment according to the present invention, for measuring a flow of a fluid by use of an ultrasonic wave, includes: a pair of ultrasonic oscillators; a measurement section for measuring a time in which an ultrasonic wave propagates between the pair of ultrasonic oscillators; and a calculation section for calculating the flow of the fluid flowing in a flow measurement section based on an output from the measurement section, wherein, in a configuration where a phase difference between a direct wave which propagates in the fluid flowing in the flow measurement section without being reflected from a wall of the flow measurement section and a reflected wave which is reflected from a wall of the flow measurement section influences a measurement result, the flow measurement section and the pair of ultrasonic oscillators are configured so that an influence of the phase difference between the direct wave and the reflected wave on the measurement result can be reduced. Accordingly, the influence of the reflected wave in the flow measurement section can be reduced, to obtain a high-precision ultrasonic flowmeter.
The ultrasonic flowmeter of the third embodiment according to the present invention, for measuring a flow of a fluid by use of ultrasonic wave, includes: a pair of ultrasonic oscillators; a measurement section for measuring a time in which an ultrasonic wave propagates between the pair of ultrasonic oscillators; and a calculation section for calculating the flow of the fluid flowing in a flow measurement section based on an output from the measurement section, wherein, in a configuration where a phase difference between a direct wave which propagates in the fluid flowing in the flow measurement section without being reflected from a wall of the flow measurement section and a reflected wave which is reflected from a wall of the flow measurement section influences a measurement result, parameters relating to a frequency of the pair of ultrasonic oscillators, a distance between the pair of ultrasonic oscillators, and a cross section shape of the flow measurement section are combined and characterized so that an influence of the phase difference between the direct wave and the reflected wave on the measurement result can be reduced. Accordingly, the influence of the reflected wave in the flow measurement section can be reduced with a simple structure, to obtain a high-precision ultrasonic flowmeter.
In the ultrasonic flowmeter of the fourth embodiment according to the present invention, based on the ultrasonic flowmeter of the third embodiment, the direct wave is a wave which propagates along a straight line connecting centers of the pair of ultrasonic oscillators, the reflected wave is a wave which propagates along two equal sides of an isosceles triangle formed by connecting the centers of the pair of ultrasonic oscillators and a point on a wall of the flow measurement section, and a propagation phase difference caused by a difference between a propagation distance of the direct wave and a propagation distance of the reflected wave is 3&pgr;/2 or more. Accordingly, the influence of the reflected wave in the flow measurement section can be reduced with a simple structure, to obtain a high-precision ultrasonic flowmeter.
In the ultrasonic flowmeter of the fifth embodiment according to the present invention, based on the ultrasonic flowmeter of the third embodiment, the direct wave is a wave which propagates along a straight line connecting centers of the pair of ultrasonic oscillators, the reflected wave is a wave which is reflected only once from a wall of the flow measurement section, and one side or a diameter of effective radiation surfaces of the pair of ultrasonic oscillators is shorter than a height of the flow measurement section so that a shortest propagation time of the reflected wave is longer than a propagation time of the direct wave. Accordingly, the influence of the reflected wave in the flow measurement section can be reduced with a simple structure, to obtain a high-precision ultrasonic flowmeter.
In the ultrasonic flowmeter of the sixth embodiment according to the present invention, based on the ultrasonic flowmeter of the fourth or fifth embodiment, a frequency of the pair of ultrasonic oscillators is set at a predetermined value or greater. Accordingly, the influence of the reflected wave in the flow measurement section can be reduced and the time resolution can be improved, to obtain a higher-precision ultrasonic flowmeter.
In the ultrasonic flowmeter of the seventh embodiment according to the present invention, based on the ultrasonic flowmeter of the third embodiment, the direct wave is a wave which propagates along a straight line connecting centers of the pair of ultrasonic oscillators, the reflected wave is a wave which propagates along two equal sides of an isosceles triangle formed by connecting the centers of the pair of ultrasonic oscillators and a point on a wall of the flow measurement section, and a propagation
Adachi Akihisa
Hashimoto Masahiko
Iwanaga Shigeru
Nakabayashi Yuji
Sato Toshiharu
Kelly Michael K.
Matsushita Electric - Industrial Co., Ltd.
Noori Max
Patel Jagdish
Snell & Wilmer LLP
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