Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2002-06-05
2004-02-24
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06694824
ABSTRACT:
The present invention relates to a flow meter, and specifically to a flow meter for measuring a flow rate of a fluid utilizing ultrasonic waves.
BACKGROUND ART
Flow meters utilizing ultrasonic waves are in wide use in order to measure flow rates of town gas and LPG (liquefied petroleum gas). Japanese Laid-Open Publication No. 9-189589 discloses a conventional flow meter for measuring a flow rate utilizing ultrasonic waves.
FIG. 40
is a longitudinal and vertical cross-sectional view of a conventional flow meter
900
, and
FIG. 41
is a height direction cross-sectional view of the conventional flow meter
900
.
FIG. 41
shows a flow path structure of the flow meter
900
.
FIG. 42
is a cross-sectional view of the flow meter
900
seen in the direction of arrow A shown in FIG.
40
.
FIG. 42
shows a flow path structure of the flow meter
900
when the flow rate is high. The flow meter
900
includes a flow path wall
105
defining a flow path
101
, through which a fluid as a measuring target flows. As shown in
FIG. 41
, the flow path wall
105
defines a quadrangular flow path cross-section
108
having a pair of longer sides
108
A and a pair of shorter sides
108
B. A pair of generally quadrangular parallelepiped transceivers
131
for sending and receiving ultrasonic waves propagating across the flow path
101
are provided in the flow path wall
105
. One of the transceivers
131
is provided in an upstream part of the flow path wall
105
, and the other of the transceivers
131
is provided in a downstream part of the flow path wall
105
. Each transceiver
131
has a quadrangular transceiving surface
132
for sending and receiving ultrasonic waves propagating across the flow path
101
. The length of the transceiving surface
132
along the shorter sides
108
B of the flow path wall
105
is substantially the same as the length of the shorter side
108
B of the flow path wall
105
. Each transceiver
131
is provided so as to be aligned with the shorter sides
108
B.
The flow meter
900
includes a flow rate calculation section
123
for calculating a flow rate of a fluid flowing through the flow path
101
based on a result of the sent and received ultrasonic waves obtained by the pair of transceivers
131
. The flow rate calculation section
123
includes a measurement control section
124
connected to each of the pair of transceivers
131
, and a calculation section
125
connected to the measurement control section
124
.
The flow meter
900
having the above-described structure operates as follows. When a fluid as a measuring target flows through the flow path
101
, an ultrasonic wave sent from the upstream transceiver
131
propagates so as to cross the flow path
101
obliquely with respect to a fluid flow direction, and reaches the downstream transceiver
131
. An ultrasonic wave sent from the downstream transceiver
131
oppositely propagates so as to cross the flow path
101
obliquely with respect to the fluid flow direction, and reaches the upstream transceiver
131
. The measuring control section
124
measures a first propagation time period required for the ultrasonic wave sent from the upstream transceiver
131
to reach the downstream transceiver
131
and a second propagation time period required for the ultrasonic wave sent from the downstream transceiver
131
to reach the upstream transceiver
131
. When the fluid flows through the flow path
101
, the first propagation time period and the second propagation time period are different from each other. The calculation section
125
calculates the flow rate of the fluid flowing through the flow path
101
based on the first propagation time period and the second propagation time period measured by the measuring control section
124
.
When a fluid flows through the flow path
101
at a high flow rate, a high flow rate flow speed distribution R along the flow path cross-section
108
shown in
FIG. 42
is obtained. As shown in
FIG. 42
, the flow rate is substantially uniform along the flow path cross-section
108
. When a fluid flows through the flow path
101
at a low flow rate, a low flow rate flow speed distribution S along the flow path cross-section
108
shown in
FIG. 40
is obtained. As shown in
FIG. 40
, the flow rate is lower as it is closer to the flow path wall
105
, and the flow rate is maximum at the center. Thus, the flow rate exhibits a parabolic curve distribution. The length of the transceiving surface
132
of each transceiver
131
along the shorter sides
108
B of the flow path wall
105
is substantially the same as the length of the shorter side
108
B of the flow path wall
105
. Each transceiver
131
is provided so as to be aligned with the shorter sides
108
B. Therefore, two sides of the surface of each transceiver
131
which receives the ultrasonic wave corresponds to the shorter sides
108
B of the flow path
1
, and each transceiver
131
receives the ultrasonic wave on the entirety of this surface. As a result, the high flow rate flow speed distribution R and the low flow rate flow speed distribution S can entirely be measured.
However, when the fluid flows through the flow path
101
at a higher flow rate as a result of the measurable flow rate range is enlarged, the flow path cross-section
108
needs to be enlarged. The transceiving surface
132
of each transceiver
131
also needs to be enlarged. This requires production of transceivers
131
having a larger transceiving surface
132
, which raises the cost.
When the length of the transceiving surface
132
along the shorter sides
108
B of the flow path cross-section
108
is smaller the length of the shorter sides
108
B, the flow speed of the entirety of the low flow rate flow speed distribution S cannot be measured. In order to obtain a true flow rate measurement (average flow rate) based on the low flow rate flow speed distribution S, the flow rate of the fluid calculated based on the first propagation time period and the second propagation time period needs to be corrected based on a correction coefficient in accordance with the flow rate. Nor can the high flow rate flow speed distribution R entirely be measured. In order to obtain an average flow rate, the calculated flow rate needs to be corrected based on a correction coefficient in accordance with the flow rate. The correction coefficients are significantly different for a high flow rate area and a low flow rate area. The correction coefficient significantly changes in a transition area between the high flow rate area and the low flow rate area. Therefore, in the case where there is even a slight error in the measured value of the flow rate in the transition area, the slight error is magnified by the correction coefficient which significantly changes in the transition area. As a result, the measurement precision of the flow rate in the transition area is deteriorated.
The present invention, for solving this problem, has an objective of providing a flow meter for measuring a wide flow rate range with high precision.
Another objective of the present invention is to provide a flow meter for reducing a change in the correction coefficient in a transition area between a high flow rate area and a low flow rate area.
DISCLOSURE OF THE INVENTION
A flow meter according to the present invention includes a flow path through which a fluid flows; a pair of transceivers for sending and receiving an ultrasonic wave propagating across the flow path; and a flow calculation section for calculating a flow rate of the fluid flowing through the flow path based on a result of the ultrasonic wave being sent and received by the pair of transceivers. The flow path has an equal flow speed area in which the fluid flows at a substantially equal flow speed over an entire flow rate area ranging from a high flow rate area to a low flow rate area. The pair of transceivers send and receive the ultrasonic wave so that the ultrasonic wave propagates in the equal flow speed area. Thus, the above-described objectives are achieved.
The equal flow speed area may be provided at a posi
Iwanaga Shigeru
Nagaoka Yukio
Shinmura Norio
Lefkowitz Edward
Matsushita Electric - Industrial Co., Ltd.
Snell & Wilmer LLP
Thompson Jewel V.
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