Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
1998-11-24
2003-01-21
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
C073S861290, C310S334000
Reexamination Certificate
active
06508133
ABSTRACT:
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP96/03629.
TECHNICAL FIELD
The present invention relates to an ultrasonic flowmeter for measuring the flow rate of a fluid and an ultrasonic transducer used therein, by disposing a pair of ultrasonic transducer sets at the upstream side and downstream side of the fluid each, transmitting an ultrasonic wave from one ultrasonic transducer, and receiving by other ultrasonic transducer.
BACKGROUND ART
Traditionally the technology for measuring the flow rate of a fluid flowing in a piping by using ultrasonic wave has been developed. An ultrasonic flowmeter is known in a constitution as disclosed as “Trial fabrication of ultrasonic flow meter for gas” in Measurement Research Report Vol. 26, No. 1, pp. 1-6, Japan.
Conventional ultrasonic flowmeter and ultrasonic transducer are described below.
FIG. 20
shows a constitution of a conventional ultrasonic flowmeter, and
FIG. 21
shows a constitution of a conventional ultrasonic transducer for gas. In
FIG. 20
, reference numeral
51
is a cylindrical tube,
52
is an ultrasonic transducer A,
53
is a mounting port A for mounting the ultrasonic transducer A
52
on the cylindrical tube
51
,
54
is an ultrasonic transducer B,
55
is a mounting port B for mounting the ultrasonic transducer B
54
on the cylindrical tube
51
, and
56
is a fluid to be measured flowing in the cylindrical tube
51
. In
FIG. 21
, reference numeral
57
is a cylindrical piezoelectric plate,
58
is a matching layer, and
59
is a lead wire.
In thus composed ultrasonic flowmeter, the constitution is described below.
Through the mounting port A
53
and mounting port B
55
, the ultrasonic transducer A
52
and ultrasonic transducer B
54
are mounted on the cylindrical tube
51
obliquely opposite to each other. Supposing the distance between the ultrasonic transducer A
52
and ultrasonic transducer B
54
to be L, the angle formed between the longitudinal direction of the cylindrical tube
51
and propagation direction of ultrasonic wave to be &thgr;, the sound velocity of ultrasonic wave propagating through the fluid
56
in windless state to be C, and the flow velocity of the fluid
56
to be V, the propagation time t
1
of the ultrasonic wave transmitted from the ultrasonic transducer A
52
propagating through the fluid
56
until received by the ultrasonic transducer B
54
is expressed as follows.
C
+
V
cos
θ
=
L
t1
(
Formula
1
)
Similarly, the propagation time t
2
of the ultrasonic wave transmitted from the ultrasonic transducer B
54
propagating through the fluid
56
until received by the ultrasonic transducer A
52
is expressed as follows.
c
-
V
cos
θ
=
L
t2
(
Formula
2
)
Canceling the sound velocity C of the fluid
56
from the two formulas, the following expression is obtained.
1
t1
-
1
t2
=
2
V
cos
θ
L
(
Formula
3
)
From the above formula, the flow velocity V of the fluid
56
is obtained as follows:
V
=
L
2
cos
θ
(
1
t1
-
1
t2
)
(
Formula
4
)
Since this expression does not include the sound velocity C of the fluid
56
, the flow velocity V is obtained regardless of the material of the fluid
56
, and the flow rate is deduced from the obtained flow velocity V and the sectional area of the cylindrical tube
51
. The ultrasonic transducer used when the fluid
56
is gas is cylindrical in shape as shown in
FIG. 21
, and comprises a cylindrical piezoelectric plate
57
and a single matching layer
58
.
Such conventional constitution, however, involves the following problems.
(1) In a first problem, since the piezoelectric plate used in the ultrasonic transducer is cylindrical, when the thickness vibration or radial vibration of a disk is utilized, if a low frequency is selected, the diameter becomes large, and the ultrasonic transducer is large in size, so that the ultrasonic flowmeter cannot be reduced in size. When using the ultrasonic transducer of small size, the frequency must be high, and effects of attenuation due to propagation of ultrasonic wave are significant, which causes to increase the cost of circuit of the ultrasonic flowmeter. Accordingly, when an ultrasonic transducer of a proper size suited to the ultrasonic flowmeter is selected, the selection of the frequency is limited. Moreover, the electromechanical coupling coefficient of thickness vibration of disk is Kt, and the electromechanical coupling coefficient of radial vibration is Kp, which were smaller than the electromechanical coupling coefficient of longitudinal vibration of K
33
, and hence the sensitivity was low. Yet, since the cylindrical piezoelectric plate
57
was not provided with constituent material such as backing layer for lowering the mechanical Q, only ultrasonic pulses of long ringing could be transmitted, and it was hard to shorten the flow rate measuring time.
(2) In a second problem, since the section of the cylindrical tube
51
is circular, in spite of the two-dimensional flow velocity distribution in which the flow velocity V near the center is fast and the flow velocity V of the outer side is slow, at the flow velocity V obtained by two confronting sets of ultrasonic transducer, it is hard to reflect the flow velocity distribution of the entire section of the cylindrical tube
51
, and the average flow velocity is only in the measuring region in the section of the cylindrical tube
51
. Since the flow rate in the cylindrical tube
51
is determined from the measured flow velocity V by using an approximate formula, it is hard to estimate the flow velocity distribution at high precision, and it is hard to obtain a high precision of measurement of flow rate.
OBJECT OF THE INVENTION
The invention is to solve the problems of the prior art, and it is an object thereof to present a compact ultrasonic flowmeter and ultrasonic transducer, advanced in degrees of freedom of selection of dimensions and frequency of ultrasonic transducer, high in sensitivity, and excellent in high speed response and precision.
DISCLOSURE OF THE INVENTION
The invention includes a flow passage, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface of the piezoelectric material is divided into plural sections, and all of electrodes disposed on the divided section are electrically connected through conductors.
An ultrasonic flowmeter according to a first aspect of the invention includes a flow passage, and an ultrasonic transducer disposed for measuring the flow rate of the fluid in this flow passage, in which the ultrasonic transducer comprises a piezoelectric material having electrodes on the opposed surfaces thereof, one of which is used as a transmitting/receiving surface, with this transmitting/receiving surface facing the flow passage, and at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface of the piezoelectric material is divided into plural sections, and all of electrodes disposed on the divided section are electrically connected through conductors, and the piezoelectric material, by dividing at least one of the transmitting/receiving surface and the surface confronting this transmitting/receiving surface into plural sections, is capable of separating the longitudinal vibration and undesired vibration mode, and therefore the ultrasonic transducer of high sensitivity, fast response, wide selection range of frequency and dimensions and small size is obtained, so that the ultrasonic flowmeter o
Adachi Akihisa
Azuma Naoko
Hashimoto Masahiko
Sato Toshiharu
Watanabe Atsushi
Matsushita Electric - Industrial Co., Ltd.
Patel Harshad
RatnerPrestia
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