Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2001-02-27
2002-10-29
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
C073S861290
Reexamination Certificate
active
06470757
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is related to providing a method of measuring a flow velocity using a transit time difference of ultrasonic sine waves to calculate a flow rate of fluid in a large river or open sluice way channel and a flow rate of liquid or gas in a pipe having a large inner diameter.
PRIOR ARTS
The core portion of a recent well-known ultrasonic flow rate measuring system for a large open sluice way channel or a pipe having a large inner diameter is designed to measure a flow velocity of liquid or gas. The system is normally called “a flowmeter.”
Most of the flow rate measuring systems are supposed to measure the flow velocity based on a flow velocity measuring method utilizing an ultrasonic transit time difference.
As shown in
FIG. 1
, a flow velocity measuring system using an ultrasonic transit time difference operates as follows: ultrasonic transducers
1
and
2
for transmitting/receiving an ultrasonic wave are mounted at an angle &agr; to face each other. A switch circuit
3
functions to switch the ultrasonic transducers
1
and
2
in turns to the inputs of transmitting and receiving circuits. An example of a transmitting and receiving circuit is an ultrasonic pulse oscillator
4
and an ultrasonic receiving signal amplifier
5
. Next, a pulse shaping circuit
6
receives an amplified signal and shapes it into a pulse signal of a shorter period. A time interval measuring apparatus
7
measures transit times t
1
and t
2
at an interval distance L from the transmitting time till the receiving time. An arithmetic logic unit
8
computes a flow velocity based on expression (1).
That is to say, the transit time t
1
, which the ultrasonic pulse is transmitted from the transducer
1
to the transducer
2
(as shown in FIG.
1
), is measured. On the contrary, the transit time t
2
, which the ultrasonic pulse is transmitted from the transducer
2
to the transducer
1
, is measured. These times measured are made as follows:
t
1
=
L
C
+
V
cos
α
;
t
2
=
L
C
-
V
cos
α
Therefore, the transit time difference &Dgr;t that t
2
−t
1
can be presented as follows:
Δ
t
=
2
L
cos
α
V
C
2
(
1
)
Wherein, C is a sound velocity of liquid or gas, L is an interval between transducers
1
and
2
and V is an average flow velocity in the interval L.
The flow velocity V from the expression (1) is deduced as follows:
V
=
Δ
tC
2
2
L
cos
α
(
2
)
It may be called “A Transit Time Difference Flow Velocity Measuring Method,” because the flow velocity V is proportional to the transit time difference &Dgr;t. It seems that the transit time difference flow velocity measuring method is related to the sound velocity, because there is an item C
2
, which is the square of the sound velocity, in the expression (2). The item C
2
of the sound velocity must be simultaneously measured at the time of the flow velocity measurement. The square of the sound velocity is represented as follows:
C
2
=
L
2
t
1
·
t
2
The sound velocity item C
2
is substituted into the expression (2) to make the final flow velocity measuring expression as follows:
V
=
L
2
2
L
cos
α
·
t
2
-
t
1
t
1
·
t
2
=
L
2
2
d
t
2
-
t
1
t
1
·
t
2
(
3
)
Then, the flow velocity is obtainable by measuring only the ultrasonic transit times t
2
and t
1
and computing the expression (3), because L
2
/2d=const.
Typical prior arts are disclosed in U.S. Pat. No. 5,531,124 granted on Jul. 2, 1996, Japanese Patent No. 2,676,321 granted on Jul. 25, 1998, Manual of Ultrasonic flow Measuring and Apparatus thereof and Ultrasonic Flowmeter related to Model UF-2000C manufactured by the Ultra flux Co.
The transit time difference flow velocity measuring method has a great advantage in that the flow velocity measuring is simply performed as illustrated in the expression (3), even though the sound velocity is seriously changed in fluid. That is, although the expression (3) seems like being related to the square of the sound velocity according to a deliberative method of the flow velocity measuring expression, it is not principally related to the flow velocity.
For example, the difference between the reciprocal numbers with respect to the transit times t
1
and t
2
is obtained as follows:
1
t
1
-
1
t
2
=
2
V
cos
α
L
,
The items of the sound velocity C are offset to each other. Therefore, the flow velocity V is as follows:
V
=
L
cos
α
(
1
t
1
-
1
t
2
)
=
L
2
2
d
(
t
2
-
t
1
t
1
·
t
2
)
Wherein, d=Lcos&agr;.
As a result, the expression obtained is the same as the one (3).
It has a great advantage in that the transit time difference flow velocity measuring method has no relation with the change in the great range of the sound velocity C in fluid. But, the transit time difference flow velocity measuring method is limited to its using. For example, when the transit distance L is very small and/or the flow velocity V is very low, it is very difficult to measure the flow velocity, precisely. If L=0.05 m, V=0.1 m/s, &agr;=45° and C≈1500 m/s,&Dgr;t≈3.14×10
−9
s.
If it is intended to measure a very little time difference within the error range of 1%, the time difference absolute measuring error should not exceed the range of 3×10
−11
s. Measuring the time difference based on such a method needs a relative complex time interval measuring apparatus. Also, an apparatus for catching moments of transmitting/receiving the ultrasonic pulses must be very stable and precise. As mentioned below, the transit time difference flow velocity measuring method causes many problems, when the gas flow velocity is measured in a pipe, or the horizontal flow velocity is measured in a channel or river.
In addition to the transit time difference flow velocity measuring method, an ultrasonic phase difference flow velocity measuring method is also well known. For example, there are Dutch Patent Laid-Open Publication No. DE19722140 published on Nov. 12, 1997, and Japanese Patent Laid-Open Publication No. Hei 10-104039 published on Apr. 24, 1998, both of which are entitled: “A multi-channel flow rate measuring system.”
FIGS. 2A and 2B
show a typical configuration of a phase difference flow velocity measuring system. Ultrasonic transducers
1
,
1
′ and
2
,
2
′ are positioned to face each other. A sine wave oscillator
9
generates a sine wave having a frequency f. A phase shifter
10
adjusts the phase of received ultrasonic signals. An amplifier
11
amplifies the received signals from the phase shifter
10
and the transducer
1
′. A phase difference discriminator
12
measures the phase difference between the received phase signals. When the sine wave oscillator
9
is operated, the transducers
2
and
2
′ transmit ultrasonic waves at the same phase. At that time, the phase signals, which the receiving transducers
1
and
1
′ receive, are as follows:
&phgr;
1
=2&pgr;ƒ·t
1
+&phgr;
0
; &phgr;
2
=2&pgr;
ƒ
t
2
+&phgr;
0
Wherein,
t
1
=
L
C
-
V
cos
α
;
t
2
=
L
C
+
V
cos
α
&phgr;
0
is an initial phase that the ultrasonic wave is firstly transmitted. Therefore, the phase difference &Dgr;&phgr; between the received signals is as follows:
Δϕ
=
ϕ
1
-
ϕ
2
=
2
π
f
Δ
t
=
2
π
f
2
LV
cos
α
C
2
(
4
)
Herein, the flow velocity is as follows:
V
=
Δϕ
C
2
4
π
fL
cos
α
(
5
)
The phase differen
Chang Hak Soo
Lee & Sterba, P.C.
Patel Harshad
LandOfFree
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