Surgery – Blood drawn and replaced or treated and returned to body
Reexamination Certificate
1997-06-26
2002-05-21
Bockelman, Mark (Department: 3762)
Surgery
Blood drawn and replaced or treated and returned to body
C073S861290
Reexamination Certificate
active
06390999
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to the measurement of fluid flow in a conduit, with compensation for variations in the temperature and density of the fluid. The invention has a wide range of specific applications, including, for example, monitoring of blood flowing outside the body of a patient through tubing during medical procedures, measurement of the velocity of a ship or other vessel traveling through water, monitoring of the flow of petroleum materials to a flare stack in a petroleum production or refining facility, measurement of the flow of air or fuel to an engine, measurement of the flow of hydrocarbon fluids from a well head, storage tank or pump, and measurement of fluid flow in a chemical-carrying conduit. In addition, the invention has general applicability in many fields, including, for example, medicine, biology, automobiles, aerospace, the military, oceanography, meteorology, cryogenics, pharmacology, chemical production and processing, agriculture, and the oil and gas industry.
2. State of the Art
With reference to
FIG. 1A
, a well-known technique for measuring the flow (denoted by arrows) of a fluid
8
through a conduit
10
is commonly referred to as “transit time” flow metering. In this technique, transducer driving signals
12
and
14
cause a downstream ultrasonic transducer
16
to emit an ultrasonic signal
18
that traverses the conduit
10
and the fluid
8
and is received by an upstream ultrasonic transducer
20
. Because the ultrasonic signal
18
takes time to pass through the conduit
10
and the fluid
8
, transducer output signals
22
and
24
indicative of the received ultrasonic signal
18
lag behind the transducer driving signals
12
and
14
by an upstream phase shift &Dgr;&phgr;
upstream
.
As shown in
FIG. 1B
, every few milliseconds, the roles of the upstream and downstream transducers
20
and
16
are reversed so that the transducer driving signals
12
and
14
cause the upstream transducer
20
to emit an ultrasonic signal
28
that traverses the conduit
10
and the fluid
8
and is received by the downstream transducer
16
. Because the ultrasonic signal
28
takes time to pass through the conduit
10
and the fluid
8
, transducer output signals
30
and
32
indicative of the received ultrasonic signal
28
lag behind the transducer driving signals
12
and
14
by a downstream phase shift &Dgr;&phgr;
downstream
.
When the fluid
8
is not flowing, the upstream and downstream phase shifts &Dgr;&phgr;
upstream
and &Dgr;&phgr;
downstream
equal one another and are attributable solely to properties of the fluid
8
other than flow (primarily temperature, density, and compressibility). Thus, under this condition,
&Dgr;&phgr;
upstream
=&Dgr;&phgr;
downstream
=&Dgr;&phgr;
fluid
(1)
where &Dgr;&phgr;
fluid
is the phase shift attributable to properties of the fluid
8
other than flow.
When, instead, the fluid
8
is flowing, the upstream and downstream phase shifts &Dgr;&phgr;
upstream
and &Dgr;&phgr;
downstream
do not equal one another. Rather, the upstream phase shift &Dgr;&phgr;
upstream
includes an additional component &Dgr;&phgr;
up
—
flow
attributable to the additional time the ultrasonic signal
18
takes to traverse upstream against the flowing fluid
8
, while the downstream phase shift &Dgr;&phgr;
downstream
is reduced by a component &Dgr;&phgr;
down
—
flow
attributable to the ultrasonic signal
28
being aided by traversing downstream with the flowing fluid
8
. Thus,
&Dgr;&phgr;
upstream
=&Dgr;&phgr;
fluid
+&Dgr;&phgr;
up
—
flow
(2)
&Dgr;&phgr;
downstream
=&Dgr;&phgr;
fluid
−&Dgr;&phgr;
down
—
flow
(3)
The components &Dgr;&phgr;
up
—
flow
and &Dgr;&phgr;
down
—
flow
may be defined as follows:
&Dgr;&phgr;
up
—
flow
=(2
&pgr;f×s
)/(
c
+(
r
f
×cos(&thgr;))) (4)
&Dgr;&phgr;
down
—
flow
=(2
&pgr;f×s
)/(
c
−(
r
f
×cos(&thgr;))) (5)
where f is the frequency of the ultrasonic signals
18
and
28
, s is the distance shown in
FIGS. 1A and 1B
between the transducers
16
and
20
, c is the speed of sound in the fluid
8
, r
f
is the rate of flow of the fluid
8
in the conduit
10
, and the angle &thgr; is the angle shown in
FIGS. 1A and 1B
between the axis of transmission of the ultrasonic signals
18
and
28
and the longitudinal axis of the conduit
10
.
As shown in
FIG. 1C
, taking the difference between the downstream phase shift &Dgr;&phgr;
downstream
and the upstream phase shift &Dgr;&phgr;
upstream
using a differential amplifier
34
cancels out the phase shift &Dgr;&phgr;
fluid
and yields the sum of the phase shift components &Dgr;&phgr;
up
—
flow
and &Dgr;&phgr;
down
—
flow
as the output &Dgr;&phgr;
flow
of the amplifier
34
. Thus,
&Dgr;&phgr;
upstream
−&Dgr;&phgr;
downstream
=&Dgr;&phgr;
fluid
+&Dgr;&phgr;
up
—
flow
−(&Dgr;&phgr;
fluid
−&Dgr;&phgr;
down
—
flow
)=&Dgr;&phgr;
flow
(6)
=&Dgr;&phgr;
up
—
flow
+&Dgr;&phgr;
down
—
flow
=&Dgr;&phgr;
flow
(7)
Since the phase shift components &Dgr;&phgr;
up
—
flow
and &Dgr;&phgr;
down
—
flow
are related to fluid flow r
f
(see equations (4) and (5) above), it may be said that
r
f
=ƒ(&Dgr;&phgr;
flow
, f, s, c, &thgr;)
(8)
Thus, with appropriate correlation of the output &Dgr;&phgr;
flow
of the differential amplifier
34
to the fluid flow r
f
using calibrated circuitry, the fluid flow r
f
may be determined.
A conventional transit time flow metering system like that discussed above is described in more detail in U.S. Pat. No. 4,227,407 to Drost. Also, applications for conventional transit time flow metering systems like that described above are found in a wide variety of contexts, including measuring petroleum materials flowing to a flare stack, as described in U.S. Pat. No. 4,596,133 to Smalling et al., measuring air flowing to an automobile engine, as described in U.S. Pat. No. 4,488,428 to Taniuchi, and monitoring blood flowing outside the body of a patient (“extracorporeal blood flow”) through tubing during medical procedures to actuate a clamp on the tubing, if necessary, to prevent back-flow flow of the blood, as described in U.S. Pat. No. 5,445,613 to Orth (assigned to the Assignee of the present invention, Rocky Mountain Research, Inc. of Salt Lake City, Utah).
While conventional transit time flow metering systems are useful in a variety of contexts, they traditionally lack the accuracy necessary or desirable in some instances. For example, while state-of-the-art transit time flow metering systems can be accurate to within ±2%, some applications, like extracorporeal blood flow monitoring, would benefit from accuracies within ±1%. Transit time flow metering systems traditionally lack greater accuracy because the above-described process of correlating the value &Dgr;&phgr;
flow
to fluid flow is subject to errors resulting primarily from variations in the temperature and density of the fluid being measured.
Therefore, there is a need in the art for a transit time ultrasonic fluid flow metering apparatus and method with compensation for variations in the temperature and density of the fluid for enhanced accuracy. Such an apparatus and method should have applicability in a wide variety of flow metering contexts.
SUMMARY OF THE INVENTION
An inventive transit time flow meter includes an assembly for transmitting an ultrasonic signal through fluid in a conduit and for receiving the transmitted ultrasonic signal. The assembly may comprise a pair of ultrasonic transducers. Circuitry coupleable to the transmitting and receiving assembly detects phase shifts in the received ultrasonic signal relative to the transmitted ultrasonic signal, and circuitry coupled to the phase shift detecting circuitry adjusts future detection of such phase shifts in response to already-detected phase shifts to enhance the accuracy of such future detection. Thus, the
Eidens Richard S.
Puckett Jeffrey F.
Zscheile John
Bockelman Mark
Rocky Mountain Research, Inc.
TraskBritt
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