Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2000-07-17
2002-08-20
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
C073S861280, C073S861290
Reexamination Certificate
active
06435038
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to apparatus for measuring the flow velocity of fluid using an ultrasonic beam. More particularly, it relates to ultrasonic flow velocity measuring apparatus which generates or receives ultrasonic beam whose frequency is modulated according to PN (Pseudo Noise) code of a diffusion band of a transit side, and precisely measures a flow velocity of a pipe conduit or sluice open channel.
2. Description of the Prior Art
Conventionally, it is well known to use an ultrasonic flowmeter using ultrasonic beam in order to measure a flow quantity a large-sized pipe conduit or a larger river.
The conventional ultrasonic flowmeter widely uses a flow velocity measuring method using a ultrasonic transit time difference.
FIG. 1
illustrates an example that ultrasonic transducers
1
and
2
are installed to be separately from each other in a conventional ultrasonic flowmeter. The ultrasonic transducers
1
and
2
alternately generate or receive ultrasonic beam, and measures a flow velocity by using the following equation (1).
V=&Dgr;t·C
2
/2
·L
·cos &phgr;=(
L
2
/2
d
)·[(
t
21
−t
12
)/(
t
12
·t
21
)] [Eq. 1]
Herein, &Dgr;t is equal to t
12
and t
21
are times that ultrasonic beam is transmitted in fluid at an angle &phgr; or on the contrary to a flow velocity direction. L is an interval between tow ultrasonic transducers, d is equal to L cos &phgr; and C is a sound velocity in fluid (called instead of an ultrasonic transit velocity below).
The flow velocity measuring method using the ultrasonic transit time difference previously inputs a predetermined constant L
2
/2d, and computes a time difference between a time t
12
and a time t
21
, wherein the time t
12
is measured when the ultrasonic beam is emitted in a flow velocity direction, and the time t
21
is measured when the ultrasonic beam is emitted in opposite direction of the flow velocity direction of the time t
12
. Such a flow velocity measuring method is well known to those skilled in the art by U.S. Pat. No. 5,531,124(Jul. 2, 1996) and Japanese Patent No. 2676321(Jul. 26, 1998).
However, according to the aforementioned prior method, if an interval L between the ultrasonic transducers is relatively longer, or various sizes of vortexes or eddies occur in the fluid flow, or the suspension concentration of fluid and a temperature distribution change in a natural river, a sound pressure of an ultrasonic beam is severely pulsated at an ultrasonic receiving place because the ultrasonic beam is refracted or diffused, or the absorbing damping factor is changed.
Furthermore, even if an ideal ultrasonic beam having a short wave length is transmitted, the receiving signal becomes a bell-shaped pulse, because the higher harmonic component of the ultrasonic beam is severely damped. For it, a receiving error corresponding to a few periods of the ultrasonic beam usually happens in checking out the moment that the ultrasonic beam is received, and the receiving failure case is not quite less.
In order not to distort the shape of the received pulse in transmitting and receiving the ultrasonic beam, a wideband amplifier is used, but various noises are amplified. Especially, it causes the confusion in measuring the ultrasonic transmitting time due to the pulse noises.
In considering the above problems, another prior art which measures an ultrasonic transit time by emitting or receiving a frequency-modulated ultrasonic beam and obtains a flow velocity is disclosed in U.S. Pat. No. 6,012,338 which is shown in FIG.
2
.
As shown in
FIG. 2
, a frequency modulation oscillator
3
is connected to a transducer switching part
14
through an output amplifier
6
. A pair of ultrasonic transducers
1
and
2
are connected to the transducer switching part
14
. The ultrasonic modulation oscillator (
3
) connected to an input terminal of the output amplifier
6
successively outputs an oscillation frequency f when there is no pulse input from an one-shot multivibrator
4
, and outputs a frequency fo (shown in
FIG. 3
c
) which is modulated according to a short pulse (shown in
FIG. 3
b
) generated from the one-shot multivibrator
4
by a long pulse (shown in
FIG. 3
a
) generated from a control square pulse oscillator
5
with a given period.
The frequencies f and fo generated from the frequency modulation oscillator
3
pass through the output amplifier
6
, and are input to the transducer switching part
14
. The transducer switching part
14
inputs the amplified frequencies f and fo into the ultrasonic transmitting transducer
1
. The ultrasonic transmitting transducer
1
successively emits the oscillation frequency f and a frequency-modulated frequency fo as shown in
FIG. 3
d
. The ultrasonic receiving transducer
2
installed to a lower place of the ultrasonic transmitting transducer
1
receives the oscillation frequency f and the frequency-modulated frequency fo.
At this time, the output signal of the output amplifier
6
is transmitted to a frequency discriminator
9
through an attenuator
13
and the output switching part
8
. The frequency discriminator
9
generates an output voltage (shown in
FIG. 3
e
) during a duration time of the frequency fo. The output voltage of
FIG. 3
e
is changed to a square pulse by a pulse shaping part
10
, as shown in
FIG. 3
f
. A time interval measuring part
11
starts a counting operation from a moment at which the square pulse is received. After that, at the moment of a pulse trailing edge, an output switching part
8
and the transducer switching part
14
are switched according to a control of the control square pulse oscillator
5
, an output signal (shown in
FIG. 3
g
) of the receiving amplifier
7
is input to the frequency discriminator
9
, and an output voltage (shown in
FIG. 3
h
) are changed to a square pulse (shown in
FIG. 3
i
) by the pulse shaping part
10
and is then transmitted to the time interval measuring part
11
. At this time, the time interval measuring part
11
stops a counting operation. In addition, the time interval measuring apparatus outputs the counted ultrasonic transit time t
12
to a flow velocity arithmetic-logic processing unit
12
.
After that, the transducer switching part
14
transmits an output signal of the output amplifier
6
to the ultrasonic receiving transducer
2
by a control of the control square pulse oscillator
5
, and emits the ultrasonic beam having a modulated frequency to the ultrasonic transmitting transducer
1
. By the aforementioned operation steps, a ultrasonic transit time t
21
are measured. The flow velocity arithmetic-logic processing unit
12
receives a time t
21
having an opposite direction of the time t
21
from the time interval measuring part
11
, and calculates a flow velocity by using the above equation (1).
The aforementioned prior art of U.S. Pat. No. 6,012,338 measures an ultrasonic transit time by catching a moment at which a frequency of a receiving signal is changed, and thus measures it even in a condition of a sound pressure of ultrasonic beam is pulsated.
However, the ultrasonic beam generated from the ultrasonic transmitting transducer
1
is reflected from a surface or a bottom, and is transmitted to the ultrasonic receiving transducer
2
after a delay operation, so that it is difficult to capture accurate frequency modulation time point. In other words, as shown in
FIG. 4
, when the ultrasonic transmitting transducer
1
emits an ultrasonic beam to the ultrasonic receiving transducer
2
, the ultrasonic beam is transmitted to the ultrasonic receiving transducer
2
via a multiple-path. For example, the ultrasonic beam through first to third path P
1
, P
2
and P
3
has a predetermined phase difference (shown in
FIGS. 5
a
-
5
c
) according to a path difference. At this time, as shown in
FIG. 5
d
, there are many output voltages Vo
1
, Vo
2
and Vo
3
in the frequency discriminator
9
. Due to Vo
1
, Vo
2
and Vo
3
, at a receiving side, the moment at which an oscillation fr
Chang Min Tech Co., Ltd.
Fuller Benjamin R.
Ladas & Parry
Mack Corey D.
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