Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-09-07
2001-12-25
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S861250, C073S861270
Reexamination Certificate
active
06332360
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an apparatus for measuring the vertical average flow velocity and the depth of water to measure the flow quantity of an open channel, e.g., a river. The invention also relates to a measuring apparatus for measuring the depth of water, water velocity and water temperature of a lake, dam, reservoir, river and the like.
As a typical method for measuring the flow quantity of a point of an open channel such as river, it is know that a cross section of the point and the flow quantity of the point are to be measured. It's specific method is as follows. First, an open channel is divided into a number of sections along a imaginary line drawn along the width of the channel. Then, in each section, the flow velocities are measured at various vertical depths along the vertical center line thereof using a propeller flow-meter, e.g. Based on this, the average flow quantity of each section is calculated. Then, the flow quantity of each point is calculated by multiplying the average flow velocity by the cross section. Finally, the open channel's flow quantity is obtained by summing the all flow quantities of the points.
This conventional method is disclosed in Japanese patent provisional publication No. 9-196727, entitled “Apparatus and method for measuring the river flow quantity”, and Japanese patent application No. 9-340875, entitled “Apparatus for measuring the flow velocity” which is not published yet.
The accuracy in the conventional method for measuring the flow quantity becomes higher when many vertical lines are provided to divide the cross section of the water. The vertical lines should be prepared at least 10. In order to measure the average vertical flow velocity along a vertical line, a local flow velocity should be measured at various depths utilizing a local flow velocity gauge (for instance, a propeller-type gauge). The average vertical flow velocity is calculated by substituting the values obtained by the measurement into a formula. When an accuracy in a measurement is required, each vertical line should be divided into 5 to 10, and the local flow velocity is to be measured at each point.
However, since the flow velocity roughly varies at each local point, it takes more than 60 seconds in a measurement operation in each point. When there are provided 10 vertical lines , and the flow velocity is measured at 5 points on each vertical line, it requires more than 3000 seconds to complete the measurement operation. Further, considering the time period needed for moving a measuring apparatus or a gauge, a lot of time is required for a measurement of the flow quantity. Besides, a lot of manpower is needed.
To ease the heavy work needed in the conventional method, there is a permanent river flow quantity measurement post, which automatically measures the local flow velocities along the vertical lines by moving a local flow measuring gauge with, for example, a carrier. However, this method also requires a lot of time to complete the measurement. This problem remain unchanged. Further, in case the flow quantity varies shortly, the obtained flow quantity which has been measured a while ago differ from the flow quantity flowing right now.
In order to solve such drawback, there is a consideration of reducing a number in the local flow velocity measuring points or reducing a time period used in measuring the flow velocity at each local point. However, in doing so, the errors in the local flow quantity and the flow variation are generated. Subsequently, the error in the flow quantity measurement becomes larger.
In order to solve the drawback in the conventional method, a new apparatus for measuring the flow velocity has been developed. The apparatus basis a principle that the propagation velocity of an ultrasonic wave and the frequency of the reflected wave vary in water depending on the flow velocity. This type of apparatus for measuring the flow velocity is superior to the aforementioned mechanical-type measuring method which has commonly been used. That is, it does not disturb the flow velocity of an open channel; it is stable in measurement through the dead flow velocity to the high flow velocity, so that a line showing the measured velocities in a graph is linear; it can measure the directional element of the flow velocity; it can be used in real time measurement; it performs continuous automatic measurement; it is easily maintained since it includes no parts which are mechanically operated.
The method for measuring the flow velocity using the ultrasonic wave includes a propagation time difference method, a phase difference method, a sing around method, Doppler effect method and a beam displacement method. Among these methods, an apparatus using the propagation time difference method is disclosed in the aforementioned Japanese patent provisional publication No. 9-196727 and Japanese patent application No. 9-340875. The apparatus measures the vertical average flow velocity from the water bed to the water surface of an open channel by use of the ultrasonic wave.
The method for measuring the flow velocity utilizing the propagation time difference will be described below referring to an apparatus disclosed in Japanese provisional publication No. 9-196727. As illustrated in
FIG. 5
, a pair of transducers
1
,
1
′ for measuring the flow velocity is positioned just below the water surface as it is fixed to a catamaran float
4
which is floating on the water surface. Each transducer is positioned at an equal distance D from the center of the float
4
in the same level. A transducer
2
for measuring the water depth is positioned just below the water surface along the center of the catamaran float
4
. Another transducer
2
′ for measuring the water depth is positioned below the transducer
2
with a vertical distance l. Further, an ultrasonic reflecting device
3
is positioned on the river bed as needed.
In
FIG. 5
, the distance L is a space between the transducer
2
for measuring the water depth and the upper surface of the ultrasonic reflecting device
3
. When a distance between the surface of the river and the transducer
2
is a, the water depth H=L+(a+b). The vertical distance l is arranged to a length which is less than ½ of the water depth H.
The propagation time periods t
2
and t
2′
are calculated by the equations (a) as shown below. The propagation time period t
2
is a time period between the time an ultrasonic wave is transmitted from the transducer
2
and the time it returns to the transducer
2
after reflecting at the reflecting device
3
. The propagation time period t
2′
is a time period between the time an ultrasonic wave is transmitted from the transducer
2
′ and the time it returns to the transducer
2
′ after reflecting at the reflecting device
3
.
t
2
=
2
L
c
2
,
t
2
′
=
2
(
L
-
l
)
c
2
′
(a)
In explaining the same point of the prior art disclosed in Japanese provisional publication No. 9-196727 in a different expression, when the ultrasonic velocity measured at a point on the vertical distance l is Cl, the ultrasonic velocity Cl is obtained by equation (b). And, when the total average ultrasonic velocity in the distance L is CL, the distance L is obtained by equation (c). Therefore, supposing the distance L is a distance L′, the distance L is obtained by equation (d) which is formulated by substituting the equation (c) into the equation (b). (The rightmost side formula in the equation (d) is the same expression as that described in the above-mentioned prior invention.)
c
l
=
2
l
t
2
-
t
2
′
(b)
L
=
c
L
·
t
2
2
(c)
L
′
=
t
2
2
c
l
=
t
2
t
2
-
t
2
′
l
(d)
Further, the time difference &Dgr;t is measured, which is a time difference between a first time period and a second time period. The first time period is a time in that an ultrasonic wave is transmitted from the transducer
1
and is received by the transducer
1
′ after reflecting at the reflectin
Oliff & Berridg,e PLC
Saint-Surin Jacques
Toho Keisoku Institute
Williams Hezron
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