Note: Descriptions are shown in the official language in which they were submitted.
BUBBLE SIZE DETERMINATION BASED ON BUBBLE STIFFNESS
BACKGROUND OF THE INVENTION
I. Field of Invention
The present invention relates to a technique for bubble size determination in
wet concrete; more particularly related to a technique for bubble size
determination
in wet concrete in order to control the amount of air in a mixture of
concrete.
2. Description of Related Art
In the manufacturing process of many materials, gas is often required to
achieve the optimum performance of the material. A primary example would be in
the manufacture of concrete, where not only is a specific amount of air
required in
the product but also the bubble size of the gas component is critical. The
assignee
of the instant patent application has developed gas void fraction (GVF)
measurement
systems that perform well at determining the gas content however there are no
readily available system for measurement of the bubble size.
In one implementation of a known GVF measurement system in concrete, the
speed of sound of acoustic signals may be determined by injecting a signal
into the
concrete and measuring how long it takes for that acoustic signal to travel
over a set
distance. As shown in Figure 1a, a piston may be used to cause a pressure
fluctuation in the concrete and generate an acoustic signal. A pressure
transducer
arranged a set distance away is used to measure the arrival of the acoustic
wave
and then the speed of sound (SOS) in the concrete is determined. The GVF is
then
calculated using Wood's equation based on the SOS measurement.
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One characteristic of bubbles is that the internal pressure is dependent on
the
bubble size, as shown by the Young-Laplace equation, which describes the
difference between the inside and outside pressure of a bubble due to surface
tension. As shown in Figure 1 b, as the bubble radius decreases the pressure
and
therefore the stiffness of the bubble increases (as referenced in "Influence
of bubble
size distribution on the echogenicity of ultrasound contrast agents: a study
of
SonoVue", Gorce JM, Arditi M, Schneider M., Invest Radiol. 2000 Nov;35(11):661-
71).
Known SONAR-based GVF Meters
In the prior art, a number of techniques have been developed that rely on
measuring the speed of sound through a material flowing through a pipe. These
techniques include using a known SONAR-based GVF meter, density meter and
potential mass fraction meter. In these techniques, a passive array-based
sensor
system is used to detect the presence and speed of acoustics traveling through
the
materials contained within a pipe. These materials can range from single phase
homogeneous fluids to two or three phase mixtures of gases, liquids and
solids.
Since the measurements system is passive it relies on acoustics produced
externally
for the measurement. These acoustics can often times come from other equipment
in or attached to the pipe such as pumps or valves.
Moreover, in these known techniques many times chemical additives may be
added, including to a known flotation process in mineral processing to aid in
the
separation of the ore. The chemicals, known as frothers, control the
efficiency of the
flotation process by enhancing the properties of the air bubbles. An important
parameter in flotation optimization is the gas volume fraction within a
flotation cell.
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United States Patent No. 7,426,852 B1, discloses approaches to make this
measurement, and discloses a technique whereby the speed of sound in the
aerated
fluid is locally measured using a waveguide (pipe) in conjunction with a SONAR-
based array. From the speed of sound measurement, the gas volume fraction can
be calculated.
By way of example, see other techniques related to the use of such SONAR-
based technology disclosed, e.g., in whole or in part in United States Patent
Nos.
7,165,464; 7,134,320; 7,363,800; 7,367,240; and 7,343,820.
Moreover, air is a very important component of many materials, such as
viscous liquids, slurries or solids, and mixtures of concrete. In particular,
air is a
critical ingredient when making concrete because it greatly improves the cured
product damage resistance to freeze/thaw cycles. Chemical admixtures are
typically
added during mixing to create, entrain and stabilize billions of small air
bubbles
within the concrete. However, the entrained air in concrete has the
disadvantage of
reducing strength so there is always a trade-off to determine the right amount
of air
for a particular application. In order to optimize certain properties of
concrete, it is
important to control the entrained air present in the wet (pre-cured)
concrete. Current
methods for measuring the entrained air can sometimes be slow and cumbersome
and additionally can be prone to errors. Moreover, the durability of concrete
may be
enhanced by entraining air in the fresh mix. This is typically accomplished
through
the addition of chemical admixes. The amount of admix is usually determined
through empirical data by which a "recipe" is determined. Too little entrained
air
reduces the durability of the concrete and too much entrained air decreases
the
strength. Typically the nominal range of entrained air is about 5-8% by
volume, and
can be between 4% and 6% entrained air by volume in many applications. After
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being mixed in the mixer box, the concrete is then released to the truck. The
level of
entrained air is then measured upon delivery of the mix to the site. The draw
back of
the current method is that the mix is committed to the truck without
verification of that
the air level in the mix is within specification.
The aforementioned United States patent application serial no. 13/583,062
(WFVA/CiDRA file nos. 712-2.338-1/CCS-0033, 35,40, and 45-49) discloses
techniques for real time air measurement in wet concrete in concrete a rotary
drum
mixer, including implementing sensing technology in a hatch cover, as well as
a
stationary concrete mixer using an integrated sound source and two receivers,
using
SONAR-based technology developed and patented by the assignee of the instant
patent application as well as that application.
SUMMARY OF THE INVENTION
The Basic Invention
In this application, a technique is set forth so that the bubble size can be
determined in conjunction with the GVF.
One can use this phenomenon to deduce the mean or average bubble size
using a system like that detailed in Figure la, with some modifications.
Essentially,
a measurement of the stiffness of the concrete or concrete mixture will be
substantially directly proportional to the mean bubble size. To determine the
stiffness of the concrete or concrete mixture a simple combination of a force
probe
connected to an acoustic piston and a displacement sensor may be used to
provide
a stiffness factor. Alternate sensor configurations can also be used to
determine the
stiffness such as a combination of a drive current sent to the piston,
acceleration of
the piston's motion, and the force imparted into the concrete mixture.
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An alternative method to determine the concrete stiffness is to check the
displacement of the piston when an impulsive force is applied. A measure of
the
displacement, force and subsequent dampening of the piston's motion will lead
to an
understanding of the stiffness of the concrete mixture.
As described above, once the stiffness and GVF of the concrete is
determined, the pressure inside the air bubbles can be calculated, which in
turn will
give a measurement of the mean bubble size.
Particular Embodiments
The present application provides new techniques or ways of real time
measurement of entrained air in wet concrete, consistent with, and further
building
on that set forth in, the aforementioned PCT/US12/60822, filed 10 October 2012
(WFVA/CiDRA file nos. 712-2.365-1/CCS-0075), as well as United States patent
application serial no. 13/583,062, filed 12 September 2012 (WFVA/CiDRA file
nos.
712-2.338-1/CCS-0033, 35, 40, and 45-49).
By way of example, the present invention provides new measurement devices
that may include, or take the form of, apparatus featuring: a signal
processing
module configured with at least one processor and at least one memory
including
computer program code, the at least one memory and computer program code
configured, with the at least one processor, to cause the apparatus at least
to:
receive signaling containing information about a stiffness of concrete or
a concrete mixture; and
determine an average bubble size of gas contained in the concrete or
concrete mixture, based at least partly on the signaling received.
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According to some embodiments, the present invention may include one or
more of the following features:
The signal processing module may be configured to provide corresponding
signaling containing information about the average bubble size of gas
contained in
the concrete mixture.
The signal processing module may be configured to determine the pressure
inside air bubbles and determine an average air bubble size of the gas
contained in
the concrete mixture, based at least partly on the pressure determined inside
the air
bubbles.
According to some embodiments of the present invention, the apparatus may
include a combination of a force probe connected to an acoustic piston and a
displacement sensor that is configured to provide associated signaling
containing
information about the stiffness of the concrete mixture. The signal processing
module may be configured to receive the associated signaling containing
information
about a force applied by the acoustic piston to the concrete mixture and
sensed by
the force probe, and information about a displacement of the acoustic piston
in
relation to the concrete mixture sensed by the displacement sensor, and
configured
to determine the stiffness factor of the concrete mixture, based at least
partly the
associated signaling received.
According to some embodiments of the present invention, the apparatus may
include a combination configured with a piston to impart a force into the
concrete
mixture, a drive current sensor to sense a drive current sent to the piston,
and a
piston accelerometer to sense an acceleration of the piston's motion, and also
configured to provide associated signaling containing information about the
stiffness
of the concrete mixture. The signal processing module may be configured to
receive
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the associated signaling containing information about the drive current sent
to the
piston and sensed by the drive current sensor, about the acceleration of the
piston's
motion sensed by the piston accelerometer, and configured to determine the
stiffness of the concrete mixture based at least partly on the associated
signaling
received.
According to some embodiments of the present invention, the apparatus may
include a combination configured with a piston to apply an impulsive force to
the
concrete mixture and at least one sensor to sense or determine a displacement
of
the piston when the impulsive force is applied to the concrete mixture, the
impulsive
force applied to the concrete mixture and subsequent dampening of the piston's
motion, and also configured to provide associated signaling containing
information
about the stiffness of the concrete mixture. The signal processing module may
be
configured to receive the associated signaling information about the
displacement of
the piston when the impulsive force is applied to the concrete mixture, the
impulsive
force applied to the concrete mixture, and subsequent dampening of the
piston's
motion, and configured to determine the stiffness of the concrete mixture
based at
least partly on the associated signaling received.
According to some embodiments of the present invention, the signal
processing module may be configured to determine the average bubble size of
the
gas contained in the concrete mixture, based at least partly on a measurement
of the
stiffness of the concrete mixture being substantially directly proportional to
the
average bubble size.
According to some embodiments of the present invention, the apparatus may
include a pressure transducer configured to sense at least one acoustic signal
injected into the concrete mixture and provide associated signaling containing
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information about the information about the at least one acoustic signal
sensed. The
signal processing module may be configured to receive the associated signaling
and
to determine a gas volume fraction (GVF) of the concrete mixture, based at
least
partly on the associated signaling received.
According to some embodiments of the present invention, the signal
processing module may be configured to receive in the signaling information
about at
least one acoustic signal injected into the concrete mixture, and to determine
a gas
volume fraction (GVF) of the concrete mixture, based at least partly on the
signaling
received. The signal processing module may be configured to determine the GVF
of
the concrete mixture, based at least partly on determining the speed of sound
of the
at least one acoustic signal injected in the concrete mixture, including by
injecting the
at least one acoustic signal into the concrete mixture and measuring how long
the at
least one acoustic signal takes to travel over a set distance. The apparatus
may
include a combination having a piston and an actuator configured to cause a
pressure fluctuation in the concrete mixture and generate the at least one
acoustic
signal; a pressure transducer configured the set distance away from the
piston,
configured to sense the at least one acoustic signal, and to provide
associated
signaling containing information about the arrival of the at least one
acoustic wave;
and the signal processing module being configured to receive the associated
signaling and to determine a speed of sound (SOS) in the concrete mixture and
the
GVF of the concrete mixture, including by using a Wood's equation based on a
SOS
measurement.
The stiffness of the concrete mixture may be based on, or may be understood
to include, or may take the form of, or may be understood to be, the rigidity
of the
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concrete mixture as an object, including the extent to which the concrete
mixture
resists deformation in response to an applied force.
Methods
According to some embodiments of the present invention, the present
invention may take the form of a method that may include, or take the form of,
steps
for receiving in a signal processor module signaling containing information
about the
stiffness and a gas volume fraction (GVF) of a concrete mixture; and
determining in
the signal processor module an average bubble size of gas contained in the
concrete
mixture, based at least partly on the signaling received.
This method may also include some combination of the aforementioned
features set forth herein.
The present invention makes important contributions to this current state of
the art for bubble size determination in wet concrete, as well as techniques
to control
the amount of air in a mixture of concrete.
BRIEF DESCRIPTION OF THE DRAWING
The drawing includes Figures 1 ¨ 2b, which are not necessarily drawn to
scale, as follows:
Figure la is a diagram of an arrangement known in the art for determining the
entrained air in concrete or a concrete mixture, including a SONAR-based
arrangement using a SOS measurement
Figure lb is a graph of partial pressure versus bubble radius consistent with
that known in the art.
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Figure 2a shows a diagram of apparatus, e.g., including a signal processing
module, according to some embodiments of the present invention.
Figure 2b shows a diagram of apparatus, e.g., including a combination of a
signal processing module, an actuator, a piston and a transducer, according to
some
embodiments of the present invention.
DETAILED DESCRIPTION OF BEST MODE OF THE INVENTION
Figures 2a, 2b
Figures 2a and 2b show, by way of example, the present invention that may
include, or take the form of, apparatus 10 featuring: a signal processing
module 10a
configured with at least one processor or signal processor and at least one
memory
including computer program code, the at least one memory and computer program
code configured, with the at least one processor or signal processor, to cause
the
apparatus at least to:
receive signaling containing information about a stiffness of concrete or
a concrete mixture C; and
determine an average bubble size of gas contained in the concrete or
concrete mixture C, based at least partly on the signaling received.
In Figure 2a, the signaling may including first signaling Si, e.g., provided
by a
combination 12 having an actuator 12a and a piston 12b, and may also include
second signaling S2, e.g., provided by a pressure transducer 14, consistent
with that
shown in Figure 2b.
The signal processing module 10a may be configured to provide
corresponding signaling S3, e.g., containing information about the average
bubble
size of gas contained in the concrete or concrete mixture C. By way of
example, the
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corresponding signaling S3 may be further processed, e.g., to display the
average
bubble size in the concrete or concrete mixture C, or to control the
manufacturing
process of the concrete or concrete mixture C, such as by dosing the concrete
mixture with some agent to adjust the average bubble size in the concrete or
concrete mixture.
By way of example, the signal processing module 10a may be configured to
determine the pressure inside air bubbles and determine an average air bubble
size
of the gas contained in the concrete or concrete mixture C, based at least
partly on
the pressure determined inside the air bubbles. This determination process may
be
used in relation to other types of kinds of gases other than air.
According to some embodiments of the present invention, the apparatus 10
may include a force probe connected or coupled to the acoustic piston 12b and
a
displacement sensor that is configured to provide associated signaling
containing
information about the stiffness of the concrete mixture. By way of example,
the force
probe and displacement sensor may forms part of the actuator 12a, or
alternatively
be separate stand alone elements, all within the spirit of the present
invention. The
signal processing module 10a may be configured to receive the associated
signaling
containing information about a force applied, e.g., by the acoustic piston 12b
to the
concrete or concrete mixture C and sensed by the force probe, and information
about a displacement of the acoustic piston 12b in relation to the concrete or
concrete mixture C sensed by the displacement sensor, and to determine the
stiffness factor of the concrete or concrete mixture C, based at least partly
the
associated signaling received.
According to some embodiments of the present invention, the apparatus 10
may include a combination, e.g., configured with a piston like element 12b to
impart
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a force into the concrete or concrete mixture C, a drive current sensor to
sense a
drive current sent to the piston 12b, and a piston accelerometer to sense an
acceleration of the piston's motion, and also configured to provide associated
signaling containing information about the stiffness of the concrete mixture.
The
signal processing module may be configured to receive the associated signaling
containing information about the drive current sent to the piston 12b and
sensed by
the drive current sensor, about the acceleration of the piston's motion sensed
by the
piston accelerometer, and to determine the stiffness of the concrete mixture
based at
least partly on the associated signaling received. By way of example, the
drive
current sensor and the piston accelerometer may form part of the actuator 12a,
or
alternatively be separate stand alone elements, all within the spirit of the
present
invention.
According to some embodiments of the present invention, the apparatus 10
may include a combination, e.g., configured with a piston like element 12b to
apply
an impulsive force to the concrete or concrete mixture C and at least one
sensor to
sense or determine a displacement of the piston 12b when the impulsive force
is
applied to the concrete or concrete mixture C, the impulsive force applied to
the
concrete or concrete mixture C and subsequent dampening of the piston's
motion.
Such a combination may also be configured to provide associated signaling
containing information about the stiffness of the concrete or concrete mixture
C. By
way of example, the at least one sensor may form part of the actuator 12a, or
alternatively be a separate stand alone element, all within the spirit of the
present
invention. The signal processing module 10a may be configured to receive the
associated signaling information about the displacement of the piston when the
impulsive force is applied to the concrete mixture, the impulsive force
applied to the
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concrete mixture, and subsequent dampening of the piston's motion, and to
determine the stiffness of the concrete or concrete mixture C based at least
partly on
the associated signaling received.
The signal processing module 10a may be configured to determine the
average bubble size of the gas contained in the concrete mixture C, based at
least
partly on a measurement of the stiffness of the concrete or concrete mixture C
being
substantially directly proportional to the average bubble size.
According to some embodiments of the present invention, the apparatus 10
may include the pressure transducer 14 configured to sense at least one
acoustic
signal injected into the concrete mixture and provide associated signaling
containing
information about the at least one acoustic signal sensed. The signal
processing
module 10a may be configured to receive the associated signaling and to
determine
a gas volume fraction (GVF) of the concrete or concrete mixture C, based at
least
partly on the associated signaling received.
According to some embodiments of the present invention, the signal
processing module 10a may be configured to receive in the signaling
information
about at least one acoustic signal injected into the concrete or concrete
mixture, and
to determine a gas volume fraction (GVF) of the concrete mixture, based at
least
partly on the signaling received. By way of example, the signal processing
module
10a may be configured to determine the GVF of the concrete or concrete mixture
C,
based at least partly on determining the speed of sound of the at least one
acoustic
signal injected in the concrete or concrete mixture C, including by injecting
the at
least one acoustic signal into the concrete or concrete mixture C and
measuring how
long the at least one acoustic signal takes to travel over a set distance. The
apparatus 10 may include a combination 12 having the actuator 12a and the
piston
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12b configured to cause a pressure fluctuation in the concrete or concrete
mixture C
and generate the at least one acoustic signal; the pressure transducer 14
configured
the set distance away from the piston 12b configured to sense the at least one
acoustic signal, and to provide associated signaling containing information
about the
arrival of the at least one acoustic wave. The signal processing module 10a
may be
configured to receive the associated signaling and to determine the SOS in the
concrete or concrete mixture C and the GVF of the concrete or concrete mixture
C,
including by using a Wood's equation based on a SOS measurement.
Signal Processing or Signal Processing Module 10a
By way of example, and consistent with that described herein, the
functionality
of the signal processing or signal processing module 10a may be implemented
using
hardware, software, firmware, or a combination thereof, although the scope of
the
invention is not intended to be limited to any particular embodiment thereof.
In a
typical software implementation, the signal processor would be one or more
microprocessor-based architectures having a microprocessor, a random access
memory (RAM), a read only memory (ROM), input/output devices and control, data
and address buses connecting the same. A person skilled in the art would be
able to
program such a microprocessor-based implementation to perform the
functionality
set forth in the signal processing block 10a, such as determining the gas
volume
fraction of the aerated fluid based at least partly on the speed of sound
measurement of the acoustic signal that travels through the aerated fluid in
the
container, as well as other functionality described herein without undue
experimentation. The scope of the invention is not intended to be limited to
any
particular implementation using technology now known or later developed in the
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future. Moreover, the scope of the invention is intended to include the signal
processor being a stand alone module, as shown, or in the combination with
other
circuitry for implementing another module.
It is also understood that the apparatus 10 may include one or more other
modules, components, circuits, or circuitry 10b for implementing other
functionality
associated with the apparatus that does not form part of the underlying
invention,
and thus is not described in detail herein. By way of example, the one or more
other
modules, components, circuits, or circuitry 10b may include random access
memory,
read only memory, input/output circuitry and data and address buses for use in
relation to implementing the signal processing functionality of the signal
processor
10a, or devices or components related to mixing or pouring concrete in a ready-
mix
concrete truck or adding chemical additives, etc.
The Dual Frequency Techniques for Determining Entrained Air
The scope of the invention may include, by way of example, using dual
frequency techniques to determine the entrained air in the concrete or
concrete
mixture C, according to some embodiments of the present invention. For
example, a
signal processor 10a may be configured to receive signaling containing
information
about an acoustic signal injected into a mixture of concrete; and determine a
measurement of air percentage in the mixture of concrete based at least partly
on a
dual frequency technique that depends on a relationship between the acoustic
signal
injected and the signaling received.
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Phase Sensitive Dual Frequency Lock-in Measurement
for Concrete Air Content with Quality Factor
The scope of the invention may include using other techniques to determine
the entrained air in the concrete or concrete mixture C, according to some
embodiments of the present invention. By way of example, another approach for
the
measurement of air percentage in concrete, e.g., is to measure the speed of
sound
(SOS) in the mixture and then through the use of the Wood's equation to
calculate
the amount of gas present. Various acoustic speed of sound measurements used
in
relation to SONAR-based technology as well as other sound receiving technology
are set forth below with numerous patents disclosing this technology. This
measurement of air percentage in concrete can be very difficult in materials
like
concrete where acoustic waves will quickly die out in strength due to the
material's
constituents along with other factors. This can be overcome by injecting a
strong
acoustic signal into the mixture at one point and then timing the signal
propagation
through a representative section of the material. However, this approach
requires
significant amounts of energy to produce a large compression wave in the
concrete.
According to some embodiments of the present invention, a variation of this
approach may be implemented that would require a modest acoustic signal to be
injected but a very sensitive detection technique that can pull the injected
signal out
of the other acoustic "noise" that is present in the system. One detection
technique
that is well suited for this is a phase sensitive lock-in approach.
In a lock-in approach, a reference signal may be injected into the mixture and
that same signal may be mixed with a resultant detected signal from the
mixture.
After a low pass filter is used to get the DC component of the result, a value
may be
obtained that is proportional to the amplitude and phase of the detected
signal at the
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reference frequency. If the same calculation is made with the reference
shifted by
90 deg, the phase and amplitude components can be separately determined. If
one
takes Gref as the reference phase, edet as the detected phase, Adet as the
detected signal amplitude at the frequency of interest, then the signal
amplitude and
the signal phase difference may be determined using the following set of
equations:
e = Ode - eref,
X ¨ Adet cos(e),
Y Adet cos(G + 90deg) = Adet sin(e),
Signal amplitude = Adet = (X2* Y2)112, and
Signal phase difference = e = tan-1(Y/X).
The signal phase difference calculated along with the frequency can then be
used to
determine the time of propagation of the signal in the material and then the
SOS.
Ambiguity in the Detected Acoustic Signal
However, an ambiguity exists once the detected signal has gone through a
propagation time equal to 2*pi of the injected signal (or any multiple). This
can be
somewhat prevented by assuring that the frequency used for injection is low
enough
that the time delay cannot introduce the ambiguity, however this will severely
restrict
the operational range of the measurement. Variations in the air content along
with
the attenuation characteristic of the materials may force the system to
operate in a
region where the ambiguity will exist. This can be prevented by injecting two
slightly
different frequencies into the material and then detecting each to determine
the
relative phase between the two injected signals, e.g., using the acoustic
probe that
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include two dynamic transducers. An ambiguity can still exist but it will be a
function
of the difference of the two injected signals rather than just the single
injected
frequency.
An additional issue with a system such as this which calculates a SOS is the
reliability of the calculation. The lock-in scheme above will always give a
number for
the phase delay and therefore the SOS but an indication or quality factor is
needed
to be able to gauge the reliability of that calculation. Since from the phase
calculation the amplitude of the signal may also be obtained, this can be used
for
calculation of a quality metric. If one takes the amplitude of the signal at
the injected
frequency and compares that to several amplitudes of signals around that
frequency,
then one can get an indication of how the signal of interest is, or relates,
to the
surrounding "noise". If one takes the amplitude of the signal of interest at
Asig and
also take a sample of four other signals spaced adjacent to the original of
AO, Al, A2
and A3, then one can average the four comparison signals and consider this the
adjacent noise Anoise= (AO + Al + A2 + A3)14. A difference over sum
normalization
will give one a quality signal, Q, that varies between -Ito 1. With 1
representing a
good quality, a 0 indicating same signal strength at frequency of interest as
other
frequencies and a -1 as a very weak signal of interest.
Q = (Asig ¨ Anoise) / (Asig + Anoise).
Examples of Known SONAR-based technology
Techniques are known for impact and coherent noise sources for acoustic
speed of sound measurements, including such acoustic speed of sound
measurements used in relation to SONAR-based technology as well as other sound
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receiving technology as shown and described herein. By way of example, the
SONAR-based entrained air meter may take the form of SONAR-based meter and
metering technology disclosed, e.g., in whole or in part, in United States
Patent Nos.
7,165,464; 7,134,320; 7,363,800; 7,367,240; and 7,343,820.
A. Introduction
The known SONAR-based technology includes a gas volume fraction meter
(known in the industry as a GVF-100 meter) that directly measures the low-
frequency sonic speed (SOS) of the liquid or slurry flowing through a pipe. By
way of
example, the SONAR-based entrained air meter may take the form of SONAR-based
meter and metering technology disclosed, e.g., in whole or in part, in United
States
Patent Nos. 7,165,464; 7,134,320; 7,363,800; 7,367,240; and 7,343,820. Using
the
Wood's equation, the volume percent of any gas bubbles or the gas void
fraction
(GVF) is determined from the measured SOS. The Wood's equation requires
several
other inputs in addition to the measured SOS of liquid/gas mixture. One of the
additional inputs in particular, the static pressure of the liquid/gas
mixture, can be
very important for an accurate calculation of the GVF. To a first order, if
the static
pressure used for the GVF calculation differs from the actual static pressure
of the
liquid/gas mixture, then the calculated GVF may typically differ from the
actual GVF
by 1% as well. For example:
Static Pressure used for GVF calculation = 20 psia
Calculated GVF = 2%
Actual Static Pressure = 22 psia
Static pressure error = 22/20-1 = 0.1 = 10%
Actual GVF = 2% x (1+0.1) = 2.2% (10 c/0 error)
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In many cases, the static pressure of the liquid/gas mixture is available
through existing process plant instrumentation. In this case, the measured
static
pressure can be input directly to the GVF calculation through, e.g., an analog
4-20
mA input in the SONAR-based gas volume fraction transmitter (e.g. GVF-100
meter).
Alternatively, a correction to the calculated GVF can be made in the customer
DCS
for any variation from the fixed pressure that was used to originally
calculate the
GVF.
In other cases, a static pressure transmitter can be added to the process
plant
specifically to measure the static pressure used for the GVF calculation. The
measured pressure can either be input to the SONAR-based gas volume fraction
transmitter (e.g., GVF-1200) or correction made in the DCS as described above.
Occasionally, a the SONAR-based gas volume fraction meter (e.g., GVF-100)
may be installed at a location in the process that does not already have a
static
pressure gauge installed and it is impractical to add one. This could be a
location
where there is no existing penetration of the pipe to sense the pressure and
it would
be difficult or expensive to add one. In the case, where a traditional
pressure gauge
is not available and it is desirable to have a static pressure measurement the
following description of a non-intrusive (clamp on) static pressure
measurement
could be used.
B. Description
For example, according to some embodiments of the present invention, a
non-intrusive static pressure measurement may be sensed using traditional
strain
gauges integrated into the sensor band of the SONAR-based gas volume fraction
sensing technology (e.g. the known GVF-100 meter). As the static pressure
inside
CA 2876463 2018-06-12
the pipe changes, the static strain on the outside of the pipe also changes.
Using a
thin-wall assumption for simplicity (t/R < 10, where t is the wall thickness
and R is the
pR
radius) the tangential strain due to internal static pressure is: s = ,
where c is the
Et
tangential strain (inch/inch), R is the radius (inch), E is the modulus of
elasticity
(Ib/in2) and t is the wall thickness (inch). The radius, wall thickness and
modulus is
generally known, or at least constant and so if the tangential strain is
measured the
internal static pressure can be determined.
By way of example, according to one embodiment of the present invention,
four strain gauges could be arranged on the sensor band of the SONAR-based gas
volume fraction sensing technology (e.g. the known GVF-100 meter) in a
Wheatstone bridge configuration to maximize strain sensitivity and minimize
temperature effects. In this case, the sensitivity assuming a strain gauge
factor of 2,
the sensitivity is approximately 131M E, where V is volts. Assuming a 4-inch
schedule 40 carbon steel pipe, a one psi change in pressure would cause a 4 V
change in Wheatstone bridge output. This sensitivity would increase for larger
diameter pipes which generally have a smaller t/R.
The integrated pressure gauge could be calibrated in-situ for best accuracy,
but it may be sufficient to normalize the pressure output to a certain know
state then
use the tangential strain formula above with know pipe parameters to calculate
the
pressure from the measured strain.
The SONAR-based entrained air meter and metering technology are known in
the art and may take the form of a SONAR-based meter disclosed, e.g., in whole
or
in part in United States Patent Nos. 7,165,464; 7,134,320; 7,363,800;
7,367,240; and
7,343,820. The SONAR-based entrained air meter and metering technology is
capable of providing a variety of information, including the pure phase
density and
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pure phase liquid sound speed is known, such that the GVF can be determined by
measuring the speed of sound and then applying the Woods Equation.
Determining the GVF by measuring the speed of sound can provide fast an
accurate data. Also the SOS measurement system can be very flexible and can
easily be configured to work with different concrete containers and sample
particular
volumes.
Consistent with that described above, the SONAR-based entrained air meter
and metering technology are known in the art and may take the form of a SONAR-
based meter disclosed, e.g., in whole or in part in United States Patent Nos.
7,165,464; 7,134,320; 7,363,800; 7,367,240; and 7,343,820.
Other Known Technology
The pistons, acoustic transmitters, actuators, the acoustic receiver or
receiver
probes, pressure transducers, and/or transponders are devices that are known
in the
art, and the scope of the invention is not intended to be limited to any
particular type
or kind either now known or later developed in the future.
The Scope of the Invention
While the invention has been described with reference to an exemplary
embodiment, it will be understood by those skilled in the art that various
changes
may be made and equivalents may be substituted for elements thereof without
departing from the scope of the invention. In addition, may modifications may
be
made to adapt a particular situation or material to the teachings of the
invention
without departing from the essential scope thereof. Therefore, it is intended
that the
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invention not be limited to the particular embodiment(s) disclosed herein as
the best
mode contemplated for carrying out this invention.
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