U.S. patent application number 14/664468 was filed with the patent office on 2015-07-09 for single-probe mass flow meters.
The applicant listed for this patent is SIERRA INSTRUMENTS, INC.. Invention is credited to John G. Olin.
Application Number | 20150192444 14/664468 |
Document ID | / |
Family ID | 53494931 |
Filed Date | 2015-07-09 |
United States Patent
Application |
20150192444 |
Kind Code |
A1 |
Olin; John G. |
July 9, 2015 |
SINGLE-PROBE MASS FLOW METERS
Abstract
Microprocessor-based thermal dispersion mass flow meters (i.e.,
thermal anemometers) are described that use temperature sensing
elements in its flow sensor probe(s) in addition to the two
elements commonly used. Such systems allow for automatically
managing changes in gas selection, gas temperature, gas pressure,
and outside temperature. One mass flow meter described has a flow
sensor with four temperature sensing elements, wherein one pair is
provided in a temperature sensor probe and another pair in a
velocity sensor probe. Another variation operates without a
separate temperature sensor probe and integrates all function into
a single three-sensor probe. Such a device may also be used in
conjunction with a one- or two-sensor temperature probe.
Inventors: |
Olin; John G.; (Carmel
Valley, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIERRA INSTRUMENTS, INC. |
Monterey |
CA |
US |
|
|
Family ID: |
53494931 |
Appl. No.: |
14/664468 |
Filed: |
March 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/US12/56664 |
Sep 21, 2012 |
|
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14664468 |
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Current U.S.
Class: |
73/204.26 |
Current CPC
Class: |
G01F 1/698 20130101;
G01F 1/692 20130101; G01F 1/69 20130101 |
International
Class: |
G01F 1/692 20060101
G01F001/692 |
Claims
1. A mass flow meter apparatus for immersion in fluid flow
comprising: a probe including a Resistance Temperature Detector
(RTD) having a heated length and electrically coupled to a proximal
end of the probe; a second temperature sensor adjacent to a
proximal end of the heated length, an active region of the second
temperature sensor located a distance from the heated length equal
to or less than about three times a diameter of the velocity sensor
probe, and a third temperature sensor to determine fluid flow
temperature, wherein the apparatus includes no separate temperature
sensor probe.
2. The apparatus of claim 1, wherein the third temperature sensor
is located distal to the heated length.
3. The apparatus of claim 2, wherein the third sensor is located a
distance equal to or greater than a diameter of the probe from the
heated length.
4. The apparatus of claim 3, wherein the third temperature sensor
is located within about two and about three probe diameters
distance from the heated length.
5. The apparatus of claim 2, wherein a surface of the third
temperature sensor is located within about 0.1 inches of the heated
length.
6. The apparatus of claim 1, wherein a surface of the second
temperature sensor is located within about 0.1 inches of the heated
length.
7. The apparatus of claim 1, further comprising a computer
processor for outputting mass velocity measurements in real
time.
8. The apparatus of claim 7, further comprising a transmitter for
wireless communication of the measurements.
9. The apparatus of claim 1, wherein the RTD comprises a platinum
wire winding, the winding set upon a non-conductive spacer.
10. The apparatus of claim 9, wherein the spacer is adapted at a
proximal end to receive the second temperature sensor therein.
11. The apparatus of claim 9, wherein the spacer is adapted at a
distal end to receive the third temperature sensor therein.
12. The apparatus of claim 11, wherein the spacer is further
adapted at a proximal end of the spacer to receive the second
temperature sensor therein.
13. The apparatus of claim 11, wherein at least one of the second
and third temperature sensors comprises a thin-film RTD.
14. The apparatus of claim 11, wherein the spacer includes four
lumen with two lumen receiving electrical leads for the heated
sensor and two lumen receiving electrical leads for the third
temperature sensor.
15. The apparatus of claim 1, wherein at least one of the second
and third temperature sensors comprises a thin-film RTD.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of
International Application No. PCT/US2012/056664, filed Sep. 21,
2012, which is incorporated by reference herein in its entirety and
for all purposes.
FIELD OF THE INVENTION
[0002] This invention relates to mass flow meters, in
configurations identified to enable computational modeling for use
with different fluids and methods of use in connection with such
modeling.
BACKGROUND
[0003] Thermal dispersion mass flow meters directly measure the
mass flow rate of single-phase pure gases and gas mixtures of known
composition flowing through pipes or other flow conduits. They also
have application to single-phase liquids of known composition. In
most of the following, it is assumed that the fluid is a gas,
without the loss of applicability to liquids.
[0004] The mass flow rate of a fluid (defined by its average
velocity multiplied by its mass density multiplied by the
cross-sectional area of the channel through which the flow travels)
is a measured quantity of interest in the control or monitoring of
most practical and industrial applications, such as any chemical
reaction, combustion, heating, cooling, drying, mixing, fluid
power, etc. For such purposes, gases monitored by industrial
thermal dispersion mass flow meters typically include: air,
methane, natural gas, carbon dioxide, nitrogen, oxygen, argon,
helium, hydrogen, propane, and stack gases, as well as mixtures of
these gases and mixtures of hydrocarbon gases.
[0005] Generally speaking, a thermal anemometer (alternatively
referred to as a thermal dispersion mass flow meter or simply as a
mass flow meter) is used to measure the mass velocity at a point or
small area in a flowing fluid--be it liquid or gas. The mass
velocity of a flowing fluid is its velocity referenced to standard
(or normal) temperature and pressure. The mass velocity averaged
over the flow channel's cross-sectional area multiplied by the
cross-sectional area is the standard (or normal) volumetric flow
rate through the channel and is a common way of expressing the
total mass flow rate through the channel.
[0006] The thermal anemometer is sometimes referred to as an
immersible thermal mass flow meter because it can be immersed in a
flow stream or channel in contrast to other thermal mass flow meter
systems, such as those that sense the total mass flow rate by means
of a heated capillary tube mounted externally to the flow
channel.
[0007] The first general description of a thermal anemometer is
attributed to L. V. King who, in 1914, published "King's Law"
revealing how a heated wire immersed in a fluid flow measures the
mass velocity at a point in the flow: King, L. V. 1914, "On the
convection of heat from small cylinders in a stream of fluid:
Determination of the convection constants of small platinum wires
with application to hot-wire anemometry." Phil. Trans. Roy. Soc.
A214: 373-432. King called his instrument a "hot-wire
anemometer."
[0008] Early applications of this technology were hot-wire and
hot-film anemometers and other light-duty thermal dispersion flow
sensors used in fluid mechanics research and as light-duty mass
flow meters and point velocity instruments. It was not until the
1960s and 1970s that industrial-grade thermal dispersion mass flow
meters emerged that could solve the wide range of general
industry's more ruggedized needs for directly measuring the mass
flow rate of air, natural gas, and other gases in pipes and
ducts.
[0009] Thermal dispersion mass flow meters measure the heat
convected into the boundary layer of a fluid (e.g., liquid or gas)
flowing over the surface of a heated velocity sensor immersed in
the flow. Since it is the molecules of the gas that bear its mass
and carry away the heat, thermal dispersion mass flow meters
directly measure mass flow rate. In a constant-temperature mode of
operation, the "heated" sensor (as commonly known) incorporated in
the design is maintained at an average constant temperature above
the fluid temperature. The temperature difference between the
flowing fluid and the heated sensor results in an electrical power
demand in maintaining this constant temperature difference that
increases in proportion to the fluid mass flow rate that can be
calculated. In another approach, some thermal anemometers operate
in a constant-current mode in which a constant current or power is
applied to the heated sensor and the fluid mass flow rate is
calculated from the difference in the temperature of the heated
sensor and the fluid temperature sensor, which decreases as mass
flow rate increases.
[0010] Thermal anemometers may have greater application to gases,
rather than liquids, because their sensitivity in gases is higher
than in liquids. However certain examples described herein may be
equally applicable to mass flow meters for use with liquids.
[0011] Many of the mass flow meters currently known may have
shortcomings, some or all of which may be addressed by the present
disclosure. For example, because the parts of the heated sensor of
known thermal anemometers are not sufficiently reproducible (i.e.,
dimensionally or electrically), known thermal anemometers require
multi-point flow calibration of electrical output versus mass flow
rate, in the actual fluid with which they will be used and within
the actual ranges of fluid temperature and pressure of the
particular application. With such a multi-point flow calibration,
some level of flow measurement accuracy may be attainable, however
the accuracy is only be applicable to the particular fluid used for
calibration only within the narrow ranges of fluid temperature and
pressure within which the calibration was conducted.
[0012] For industrial applications, the separate heated velocity
and fluid temperature sensors are typically enclosed in a
protective housing shell. Sometimes, the heated sensor is inserted
into the tip of the housing shell and surrounded by a potting
compound, such as epoxy, ceramic cement, thermal grease, or alumina
powder. In such systems, "skin resistance" and stem conduction are
two major contributors to non-ideal behavior and measurement
errors. The so-called "skin resistance" is the electrical analog of
thermal resistance occurring between the encased heated sensor and
the external surface of the housing exposed to the fluid flow.
Hot-wire thermal anemometers have zero skin resistance, but thermal
anemometers with a housing shell do have some skin resistance. The
use of a potting compound substantially increases the skin
resistance because such potting compounds have a relatively low
thermal conductivity and are relatively thick.
[0013] Skin resistance (in units of degrees Kelvin per watt)
results in a temperature drop between the encased heated sensor and
the external surface of the housing that increases as the
electrical power supplied to the heated sensor increases. Skin
resistance creates a "droop" and decreased sensitivity in the power
versus fluid mass flow rate calibration curve, especially at higher
mass flow rates. The so-called droop is difficult to quantify and
usually varies from meter to meter because of variations in
manufacturing repeatability and in installation. The ultimate
result of these skin-resistance problems is reduced accuracy.
Furthermore, the use of a surrounding potting compound can create
long-term measurement errors caused by aging and by cracking due to
differential thermal expansion between the parts of the heated
sensor.
[0014] Accordingly, the highest quality heated sensors have a skin
resistance with a low numerical value that remains constant over
the long term. Of all known sensor configurations, the most
successful at managing these tradeoffs has been produced by the
assignee hereof, Sierra Instruments in U.S. Pat. Nos. 5,880,365;
6,971,274; 7,197,953 and/or U.S. Pat. No. 7,748,267, the
disclosures of which patents are incorporated herein by reference
in their entirety.
[0015] Velocity sensor probes constructed as such may be known as
"dry" sensors in contrast to velocity sensors fabricated with
potting cements or epoxies that are wet when mixed. As discussed,
these "wet" velocity-sensor systems suffer long-term stability and
other quality issues due to changes in the potting compound. With
regards to the temperature sensors, degradation of any potting
material incorporated in temperature sensor probes may only change
response time, which may be a relatively minor effect, and as such
temperature sensor probes may employ any convenient
construction.
[0016] A significant source of potential error in either the
temperature sensor probe and/or velocity sensor probe relates to
heat conduction along the probe stem. For example, stem conduction
causes a large fraction of the electrical power supplied to the
heated sensor to be lost through the stem of the heated sensor,
down the housing, lead wires, and other internal parts of the
heated sensor and ultimately to the exterior of the fluid flow
channel. Stem conduction couples the electrical power supplied to
the encased heated sensor to the ambient temperature outside the
channel. Typically, if the ambient temperature decreases, stem
conduction increases; if ambient temperature increases, the
conduction decreases. In either case, as ambient temperature
changes, stem conduction changes, and measurement errors occur.
Similarly, stem conduction is responsible for errors in the encased
fluid temperature sensor's measurement because the fluid
temperature sensor also is coupled to the ambient temperature in
this manner. Mass flow meters known in the art do not account for
stem conduction in sufficient manner to achieve the measurement
accuracy as may be desired in certain applications.
[0017] Accordingly, the examples described herein may provide
systems and methods for measuring mass flow of a fluid with
improved performance, including (but not limited to) the ability to
meter different fluids without requiring flow calibration specific
to the fluid or conditions being monitored, as well as the ability
to account for mode(s) of stem conduction heretofore unrecognized
and, thus, obtain measurements with increased accuracy.
SUMMARY
[0018] Examples of thermal dispersion mass flow meters
(interchangeably referred to herein as thermal anemometers or mass
flow meters) are described, which may include "secondary"
temperature sensing elements in one or more of their flow sensor
probe(s). Such "secondary" temperature sensing elements may be
provided in addition to the primary sensing elements. In some
examples, the primary sensing elements may include the heated
sensor in a velocity probe and the non-heated sensor in a
temperature probe, typically located distally with respect to the
velocity probe. Systems and methods according to the present
disclosure may allow for automatically managing changes in gas
selection, gas temperature, gas pressure, and outside temperature,
as will be further described.
[0019] The subject mass flow meters may include one or more flow
sensor probes with a plurality of Resistance Temperature Detector
(RTD) temperature sensing elements. In certain examples, each of
the velocity sensor probe and the temperature sensor probe, if
present, may include two or more RTD elements. As such, some
embodiments of the present invention may include four or more RTD
elements, which may be operatively configured to achieve a desired
measurement accuracy. Systems according to the present invention
may offer performance with accuracy as high as from about 1% to
about 2% of reading (as opposed to full scale) over mass flow rate
ranges from about 10% to about 100% of full scale (or larger range)
and over a wide range of fluid temperatures and pressures
encountered in field applications (e.g., about +/-10 to 25 deg. K
and +/-2 to 4 bar, respectively, generally referenced to their
values at flow calibration) and for any of a number of commonly
used fluids (e.g., most "clean" gases, including air, methane, Ar,
CO.sub.2, He, N.sub.2, O.sub.2, C.sub.3H.sub.8, and mixtures of
these components). Embodiments of the invention may offer high
accuracy performance for a gas or gas mixture even when flow
calibration is advantageously performed with a single inexpensive
surrogate gas operated at inexpensive conditions (e.g., air at
ambient conditions).
[0020] In one example, a first pair of RTD elements may be provided
in the velocity sensor probe of a mass flow meter, and a second
pair of RTD elements may be provided in the temperature sensor
probe of the mass flow meter. Each of the RTD elements in the first
pair and/or in the second pair may be arranged in a spaced apart
configuration, as will be further described, to facilitate
measurements according to the examples described. Another variation
may be configured without a separate temperature sensor probe, and
the functionality of the velocity probe and the fluid temperature
probe may be integrated into a single three-sensor probe. In yet
other examples, such integrated three-sensor probe may be used in
conjunction with an additional one- or two-sensor fluid temperature
probe.
[0021] In a coordinated system, mass flow meters according to the
present disclosure couple the flow sensor hardware with
microprocessor-based electronics programmed with algorithms that
manage changes in gas selection, gas temperature, gas pressure and
outside temperature. Multivariable versions provide analog and
digital outputs of mass flow rate, gas temperature, and
(optionally) gas pressure. A selection of sophisticated digital
communication protocols commonly used by industry may also be made
available.
[0022] In reference to the temperature sensor probe, the data
collected from the secondary sensor may be used to account
specifically for conduction of heat into or out of the probe. As
such, it is desirable that the distance between the temperature
sensors in the temperature probe is maximized (given all other fit
constraints) in order to offer the greatest temperature
spread/differential and thereby provide better data resolution and
accuracy.
[0023] In reference to the velocity sensor probe, in one embodiment
of the present invention, a thin-film RTD (TFRTD) sensor is not
used for the heated sensor. Instead, a wire-wound heated RTD sensor
is employed. Important aspect(s) regarding the use of a wire-wound
RTD in place of a thin-film RTD will become apparent in view of the
discussion of the computational models possible with such
configuration. Further, the secondary sensor of the velocity sensor
probe may be placed adjacent the proximal end of a heated length of
the wire-wound RTD sensor. The distance between the secondary
sensor and the heated length is advantageously minimized. The
separation between the secondary sensor and the heated length (e.g.
the distance between the two) may be less than about three
diameters of the probe to satisfy assumptions made for use of the
computational models described below. In certain examples, the
distance may be about two diameters of the probe, or in other
examples, the distance may be about one diameter of the probe.
Indeed, the active region of the secondary sensor may be in contact
with the heated length. Then, with such spacing options, the sensor
data is variously used according to methods described herein. As
such, the importance of the sensor spacing in the velocity sensor
probe will be appreciated in view of the computational models
adapted to be used in conjunction with the hardware (e.g. sensor
probes) described herein.
[0024] If the secondary sensor is positioned with its active area
in contact with the proximal end of the heated length, its
temperature data can be directly used as the boundary condition for
the proximal end in the solution for the differential equitation
shown below as Equation (1) used in system analysis. If separated
by a distance, or gap, the temperature measured provides this
boundary condition to the solution by means of nodal analysis
(included in such analysis are Finite Element Analysis (FEA) and
other known methods such as electrical analog models) or by
differential equation analysis (with ordinary or partial
differential equations linked together via their boundary
conditions).
[0025] A model is provided for the axial temperature distribution
T.sub.1(x) for a heated control volume (alternatively referred to
as the "heated length") of a velocity sensor comprising the heated
winding, its binder/coating and the insulating substrate upon which
it is wound (i.e., the mandrel or glans) per the following
equation:
2 T 1 ( x ) x 2 Conduction In - .pi. h e D [ T 1 ( x ) - T ]
Convention Out + ( I 1 2 R 1 , 0 L 1 ) [ 1 + .alpha. ( T 1 ( x ) -
T o ) ] = 0 Electrical Power In ( 1 ) ##EQU00001##
where x is the axial dimension of the heated length; .gamma. is the
overall axial conductance (kA); D is the outside diameter of the
velocity probe; T is the gas temperature; I.sub.1 is the measured
electrical current supplied to the winding; R.sub.1,0 is the
electrical resistance of the winding at reference temperature
T.sub.0; L.sub.1 is the length of the winding (and heated length);
and a is the temperature coefficient of resistance of the
winding.
[0026] Notably, Equation (1) is related to the differential
equation derived by Bruun (Bruun, H. H. 1995. Hot-Wire Anemometry:
Principles and Signal Analysis. Oxford: Oxford Univ. Press.) for a
hot-wire anemometer. However, in relation to the Bruun equation,
Equation (1) substitutes an "effective" film coefficient h.sub.e
for the classical film coefficient h in the original, expressed
as:
h e = h 1 + h .pi. DL 1 R skin ( 2 ) ##EQU00002##
where R.sub.skin is the electrical analog of thermal resistance for
various layers of "insulation" over the heated length. Further,
h.sub.e is derived from the convective heat transfer rate Q.sub.1
from the control volume, or heated length, as shown in the
following equation:
Q.sub.1=h(.pi.DL.sub.1)(T.sub.e-T)=h.sub.e(.pi.DL.sub.2)(T.sub.1-T)
(3)
where T.sub.e is the average temperature of the external surface of
the velocity sensor probe, and T.sub.1 is the average temperature
of T.sub.1(x) over length L.sub.1. Skin resistance R.sub.skin
lowers external temperature T.sub.e of the control volume according
to the equation:
T.sub.e=T.sub.1-Q.sub.1R.sub.skin (4)
Together, these equations are used to solve for mass flow rate as
further described.
[0027] In order to run the equation set as part of an effective
computation model, the subject hardware must conform to the
following assumptions: (a) that the temperature distribution is
relatively one-dimensional in the independent variable x; (b) that
a second differential equation for the temperature distribution of
the housing shell is not required; and (c) that .gamma., h.sub.e,
and R.sub.skin are constant at their average values over length
L.sub.1. As for assumption (a), this may hold true with hardware
where L.sub.1/D is sufficiently large (e.g., at least about 3:1 and
more preferably about 4:1 or more). However, the ratio can be less
than that normally required for the one-dimensionality assumption
to apply. Namely, in the constant temperature mode of operation,
the entire outside surface (e.g., a cylindrical surface) of the
control volume is maintained at constant average temperature
T.sub.1 and the RTD winding maintains the entire circumferential
surface of each differential slice (at a given axial location x) of
the control volume at essentially the same temperature (i.e.,
T.sub.1(x)). As such, the entire slice does not vary (or only
negligibly so) with the radial or azimuthal dimensions (in
cylindrical coordinates), varies only with the axial dimension x,
and has a temperature T.sub.1(x) throughout.
[0028] With these assumptions in mind, then the following
exponential solution for Equation (1) can be applied:
T 1 ( x ) - T = B 1 .beta. x + B 2 0 .beta. x + S .beta. 2 where :
.beta. = [ .pi. h e D - .alpha. I 1 2 R 1 , o L 1 ] 1 2 ( m - 1 ) S
= ( I 1 2 R 1 , o L 1 ) [ 1 + .alpha. ( T - T O ) ] ( K / m 2 ) ( 5
) ##EQU00003##
[0029] Associated with an analysis employing this solution, in
cases where a separate temperature sensor probe is included in the
system, the differential equation used in the analysis for the
classical case of heat transfer from fins may be employed. As such,
the performance of the temperature sensor probe may be
characterized according to:
2 T temp ( x ) x 2 - .beta. temp 2 [ T temp ( x ) - T ] = 0 ( 6 )
##EQU00004##
in which Equation (6) has a well known exponential solution
per:
T temp ( x ) - T = C 1 .beta. temp x + C 2 - .beta. temp x where :
.beta. temp = [ .pi. h temp D temp temp ] 1 2 ( m - 1 ) C 1 , C 2 =
Constants ( K ) ( 7 ) ##EQU00005##
and the constant coefficients are determined by boundary conditions
provided by temperature data where two temperature sensors are
included in the probe. As such, temperature sensor spacing is
advantageously maximized to offer greater temperature spread, and
thus, resolution in computed output.
[0030] So-optimized, one invention embodiment concerns a system
that is configured to run the equations and output any of gas
temperature and mass flow rate in response to sensor measurements
and/or input pressure for a given gas (after calibration with a
surrogate gas such as air) by reference to a library of properties
for others.
[0031] Typically, the equations are solved in an iterative,
converging method taking the closest approximation of gas
temperature (e.g., from the distal sensor in a temperature sensor
probe, or--if not available--from or related to the distal
temperature sensor measurement in a 3-sensor velocity sensor probe)
as the "seed" value in connection with other commonly-used formulae
describing Reynolds, Nusselt and Prandtl numbers. So that the
calculated solution offers sufficient accuracy, the hardware is
configured to conform to the assumptions required above and is also
preferably implemented in connection with "dry" sensor technology
as noted above. Accordingly, inventive aspects cover the requisite
hardware.
[0032] According to other embodiments hereof, computer readable
media with instructions stored thereon implementing the solution
method described herein may be provided. Such computer readable
media may be implemented on a general purpose computer (e.g. as
software or executable instructions stored on a recordable type
media such as a hard disk drive, digital tape, compact disc or the
like), or via Application-Specific Integrated Circuit (ASIC) or
other hardware means. Furthermore, the computer readable media
embodying aspects of the invention may advantageously be used in
conjunction with the sensor configurations in any suitable
combination and may be used to obtain flow measurements in real
time. By "real time", it is generally meant in the context of this
disclosure, that calculations performed by a chipset executing
instruction according to the present solution may involve
outputting and/or updating a result about every second, or in some
examples up to about 5 seconds. Moreover, to be of use in
monitoring an industrial process, the real time output should be
continuous (i.e., delivered over a duration without
interruption--on the order of hours and even days or more).
[0033] In a four-temperature sensor configuration as illustrated in
the drawings with spacing between the secondary temperature sensor
and the heated length in the velocity sensor probe, the mathematics
employed may solve the differential equation--Equation (1)--in
connection with one or more intermediate nodes. With another
configuration in which a secondary sensor is immediately adjacent
(i.e., touching) the proximal end of the heated length,
intermediate node(s) is/are eliminated and the secondary
temperature sensor may directly provide a proximal boundary
condition for the differential equation solution. With another
secondary sensor immediately adjacent the distal end of the heated
length, the other boundary condition may be directly provided for
that end of the heated length. Alternatively, a distal secondary
sensor may be provided in the velocity sensor probe and
calculations may optionally be made using one or more intermediate
nodes.
[0034] Interestingly (whether employed at some distance in
conjunction with nodal analysis modeling or located immediately
adjacent), use of the third temperature sensor (i.e., a second
non-heated sensor) in the velocity sensor probe permits the
elimination of the temperature sensor probe altogether. As alluded
to above regarding the discussion of gas temperature seed value(s),
given knowledge of the average temperature of the heated sensor and
its end/boundary conditions (via the secondary sensor(s)), the seed
values for the temperature of flowing gas can be inferred.
[0035] Notably, for such purposes, it may actually be preferred to
separate the distal secondary sensors some distance from the heated
sensor. By doing so, a greater temperature difference can be
measured, thereby improving the accuracy of the derived gas
temperature value. A distance between about two-to-three times the
diameter of the velocity sensor probe (or that of the heated sensor
windings) between the heated sensor and the distal secondary sensor
may be used for such purposes. Other distances exceeding two or
three times the diameter of the velocity sensor probe may be used
if desired, and the length of the velocity sensor probe may be so
configured as to accommodate such distances.
[0036] Any and all of these hardware configurations are intended as
embodiments of the present invention as well as the software
methodology associated with their use. Moreover, it is to be
appreciated that not all variations of the invention are practiced
with an outer housing shell.
[0037] Still further, the assemblies described above may be
configured in connection with relevant hardware for use as an
insertion or as an in-line type flow meters. In some embodiments,
complete mass flow meters include separate fluid temperature and
velocity sensor probe elements. In the three-sensor velocity probe
sensor variation, a complete mass flow meter assembly may utilize
only one probe (i.e., the velocity sensor probe).
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] The figures diagrammatically illustrate aspects of various
embodiments of different inventive variations.
[0039] FIGS. 1A and 1B are in-line and insertion type
configurations, respectively, with installed sensors as may be
employed in embodiments of the present invention.
[0040] FIGS. 2A and 2B are flow-axis/direction and end-view
details, respectively, of the same sensor hardware.
[0041] FIG. 3 is a partial section view of a known sensor
configuration.
[0042] FIG. 4A is a partial section view of a sensor configuration
according to one example of the present invention.
[0043] FIG. 4B is partial section view of sensor configurations
according to another example of the present invention.
[0044] FIG. 5 is an oblique construction view of a velocity sensor
probe corresponding to the embodiment shown in FIG. 4A.
[0045] FIGS. 6A-6C are side, distal and proximal views,
respectively, of a velocity sensor probe construction corresponding
to the embodiment in FIG. 4B.
[0046] FIGS. 7A-7C are partial side section, distal and proximal
views, respectively, of a velocity sensor probe construction
corresponding to the embodiment in FIG. 4B.
[0047] FIG. 8 is a block diagram of suitable electronics hardware
for carrying out software operations as variously described.
[0048] FIGS. 9A-9C are charts illustrating operation according to
embodiments of the invention.
[0049] FIGS. 10A-10C are charts illustrating measured vs. actual
mass velocity for air and methane, respectively, accomplished with
an embodiment of the present invention.
[0050] Variations of the embodiments shown in the figures are
contemplated, and shall be considered within the scope of the
claimed invention(s) explicitly, or under the Doctrine of
Equivalents.
DETAILED DESCRIPTION
[0051] Thermal dispersion mass flow meters may generally be
implemented in two primary configurations: in-line and insertion.
FIGS. 1A and 1B respectively, show examples of these two
configurations and their major components. In FIG. 1A, the mass
flow meter assembly 100 is shown connected with an adapter 10
extending from pipe 12. Because the velocity sensor probe element
20 and the temperature sensor probe element 30 are intended to be
enclosed within the pipe 12 as a delivered unit for in-line
placement within a system, the sensor probe elements do not require
a protective shield. The In-line mass flow meter assembly 100 is
typically attached to the process piping 14 by means of flanges 16,
16'. The mass flow meter assembly 100 may also include one or more
two perforated flow plates 18 provided in series and upstream of
the velocity and temperatures sensor probe elements to smooth out
disturbances and/or turbulence in the flow reaching the sensor
probe elements.
[0052] An insertion type mass flow meter assembly 100' may include
some of the same components as the mass flow meter assembly 100,
and in addition may include a shield element 40 as the meter 100'
is not delivered enclosed in a pipe but configured to be inserted
into the process pipe 14. Both the in-line and insertion mass flow
meters (e.g., 100 and 100' respectively) may also include
electronics enclosed in electronics housing 110, which may include
a digital readout display 112. The display 112 may be coupled to
one or more processor and/or other electronics and configured to
display signals corresponding to measurements and/or mass flow rate
results calculated by the one or more processors. The electronics
housing 110 may fully enclose the electronics necessary for
performing computations, as will be described, and may include a
variety of suitable electronic components, including but not
limited to processors, storage, communication devices, input/output
devices, and the like.
[0053] In many insertion-type and in-line configurations of mass
flow meters, the velocity sensor and temperature sensor probe
elements are aligned substantially perpendicular to the main fluid
flow stream (F) as shown FIGS. 1A and 1B. However, in-line mass
flow meter arrangements, as may be employed in connection with the
teaching herein, may alternatively have their sensor probe elements
arranged axially to the flow (e.g., with a longitudinal direction
of the sensor probe elements disposed substantially along the
direction of the flow).
[0054] In-line flow meters are typically applied to pipes and ducts
with diameters typically ranging from about 10 to 100 mm (0.25 to
4.0 inch pipe sizes), but some manufacturers offer sizes up to 300
mm (12.0 inch pipe size). Process connections include flanges, pipe
threads, and compression fittings. Insertion flow meters usually
are applied to larger pipes, ducts, and other flow conduits having
equivalent diameters typically ranging from approximately 75 mm to
5 m.
[0055] Because insertion meters are more economical than in-line
meters, they also have found wide use as flow switches. Compression
fittings and flanges are commonly used process connections.
Insertion meters measure the mass velocity at a point in the
conduit's cross-sectional area. For applications with smaller
conduits, they may be flow calibrated to measure the total mass
flow rate through the conduit.
[0056] Multipoint insertion meters measure the mass velocities at
the centroids of equal areas in the cross section of large pipes,
ducts, and stacks. The total mass flow rate through the entire
conduit is the average mass velocity of the several points
multiplied by the total cross-sectional area and the standard mass
density of the gas.
[0057] Any of such technologies/approaches may be employed in
connection with the flow meters described herein. More
specifically, FIGS. 2A and 2B show a flow sensor that is common to
both in-line and insertion configurations comprising a housing 50
with an extension region 52 from which velocity sensor and
temperature sensor probes 20, 30 extend along with shield "legs"
42--although in smaller in-line meters the flow sensor may not have
a shield. Notably, housing 50 incorporates an open-ended shield 40
design and a shoulder 54.
[0058] Traditional insertion meters have a shield with a closed end
that can cause the flow over the velocity sensor probe to be
non-uniform and turbulent. The open-ended shield shown still
protects the sensors but does not have this problem. In addition,
the length of reduced diameter of extension 52 and shoulder 54 just
above the flow sensor redirects and turns axial flow downwash so it
flows circumferentially around the probe before it can pass over
the velocity sensor probe, thereby minimizing another source of
inaccuracy.
[0059] The purpose of thermal dispersion mass flow meters is to
make an undistorted measurement of the free-stream velocity of a
fluid just upstream of its position. Thus, the flow sensor
components should not themselves create problematic flow
disturbances or turbulence in the velocity field before it has
passed over the velocity probe and is sensed. Features of the
design of the flow sensor in FIGS. 2A and 2B accomplish this
purpose. The aforementioned shoulder 54, open-ended shield 40 and
shielded legs 42 (with their aerodynamic cross section) mitigate
deleterious flow disturbances from the housing and shield. In
addition, the location of the velocity sensor probe 20 set forward
(relative to the flow) and relatively more centered within the
shield avoids flow interaction with the shield and/or temperature
sensor probe 30 (which is itself located downstream of, and offset
from, the velocity sensor probe).
[0060] Referring now to FIG. 3, a conventional thermal dispersion
flow sensor 200 is shown, which may be used in an in-line and/or an
insertion type mass flow meters intended for industrial-grade
applications. The flow sensor 200 includes a velocity sensor probe
220 and a temperature sensor probe 230. The velocity sensor probe
220 has an electrically self-heated (or heatable) temperature
sensor element 222 located in its tip that both heats the velocity
sensor probe and measures its own average temperature. The
temperature sensor probe 230 has a single non-heated temperature
sensor element 232 located in its tip that measures the temperature
of the gas in which the flow sensor 200 is immersed. Because flow
sensor 200 has a total of two temperature sensing elements (one in
each probe element 220,230), it is often called a "two-temperature"
flow sensor. However, as previously described and as will be
further discussed, the flow sensor 200 may suffer numerous
shortcomings, including problems associated with skin resistance
and stem conduction.
[0061] The velocity sensor and the temperature sensor probes are
mounted side-by-side in a sensor housing assembly 210. Each sensor
is enclosed in a rugged, sealed, single-ended, corrosion-resistant
metallic tube 212. In traditional velocity sensors of the kind
shown in FIG. 3, the temperature sensor element 222 is potted into
the tip of the tubular sheath. Typically, the potting, or filler
material (not shown) is ceramic cement or epoxy. Heat sink grease
also has been used for this purpose.
[0062] In use, the velocity sensor probe and the separate
temperature sensor probe of the flow sensors illustrated are
inserted or immersed in the flow stream. For that reason, thermal
dispersion mass flow meters are also often called "immersible"
thermal mass flow meters. Notably, the outside temperature external
to the flow sensor may be different than the gas temperature in the
flow conduit. For that reason, heat can be conducted in or out of
the stems of the velocity sensor and the temperature sensor probes.
In the field, the heat so-conducted through each stem may be
different from its value at the time of flow calibration, for
example if the outside temperatures or other parameters or
conditions in the field are different than during calibration.
Additionally, heat can be conducted from the hot velocity sensor
probe 220 to the cooler temperature sensor probe 230 via their
stems (i.e., the tubes 212 together with any internal components
therein including the housings, wires, ferrules/spacers, etc.).
These effects are further complicated because they depend on the
mass flow rate. Left uncorrected, the associated stem conduction
constitutes a major source of error in measuring mass flow
rate.
[0063] Mass flow meters according to embodiments of the present
invention may address some or all of these problems, for example
the problem of stem conduction. In this regard, mass flow meters
according to the present disclosure may include three or more
temperature sensing elements for improved accuracy and ease of use,
as will be further described. In some configurations a total of
four temperature sensing elements may be included, with two
elements positioned in the velocity probe and two elements in the
temperature probe. In other examples, the flow sensor may not
include a temperature probe, and instead three temperature sensing
elements may be arranged, as will be described, in a single probe
which are configured to perform all of the functionality of the
flow sensor. Specific relative arrangement of the temperature
sensing elements within each probe may be used so as to facilitate
the use of improved algorithms for calculating certain
measurements, also described herein.
[0064] An example of a thermal dispersion flow sensor 200' is shown
in FIG. 4A. The thermal dispersion flow sensor 200' includes a
velocity sensor probe 20 and a temperature probe 30 according to
examples of the present disclosure. The velocity sensor probe 20
may have a diameter D and the temperature sensor probe 30 may have
a diameter D.sub.T, which diameters may or may not be equal. Also,
each of the probes 20 and 30 may include a plurality of temperature
sensing elements (e.g. elements 22, 24 and 32, 34) therein. The
velocity probe 20 in the example in FIG. 4A includes two
temperature sensing elements 22, 24, and the temperature probe 30
includes two temperature sensing elements 32, 34. For higher
accuracy and higher stability, each of the temperature sensing
elements, 22, 24 and 32, 34 may be resistance temperature detectors
(e.g., platinum RTD sensors) that may be provided as thin film or
wire-wound RTDs and which may be protected by a thin insulation
layer of glass or ceramic. As may be known, the electrical
resistance of RTDs increases as temperature increases thus
providing a means for transducing/translating their electrical
output into temperature. Other types of temperature sensing
elements, such as thermistors, thermopiles, thermocouples, and
micro-electronic machined devices, may also be used in place of or
in combination with RTDs, for example for applications with lower
accuracy requirements.
[0065] Another example of a thermal dispersion flow sensor 200'' is
shown in FIG. 4B, which may offer additional functionality, as well
as certain additional flexibility in deployment configuration. The
flow sensor 200'' may include a velocity sensor probe 20' with a
diameter D and a temperature probe 30. The velocity sensor probe
20' in this example may include three separate temperature sensing
elements 22, 24, and 26 synergistically arranged as will be
described below.
[0066] In each of the examples depicted in FIGS. 4A and 4B, the
velocity sensor probes 20, 20' include a heated sensor 22 which is
preferably implemented using a platinum wire-wound RTD
construction. Used in either a constant current or constant
temperature mode, the temperature sensor 22 may be referred to as a
"heated" sensor to designate its physical and associated electrical
character, whether or not in use. That is, the term "heated" does
not imply that the sensor 22 is heated at all times, particularly
when not in use. The velocity sensor probes 20, 22' may also
include a second (or secondary) temperature sensor 24. The
secondary sensor 24 may be implemented using a thin-film platinum
RTD (TF RTD). Other ones of the temperatures sensing elements (e.g.
sensors 34, 32, and 26) may also be implemented using TFRTD
sensors. Such sensors are not only compact for deployment; they may
also be relatively inexpensive, while capable of holding excellent
tolerances. Secondary sensor 24 is typically not self-heated, but
may instead be used to measure temperature.
[0067] In the example in FIG. 4A, the heated sensor 22 (e.g.,
wire-wound RTD) may have a proximal end and a distal end, which
define a heated length (L.sub.1 as in FIG. 5) of the sensor 22. The
secondary sensor 24, which may be used for the purpose of
compensating for stem conduction, may be located near the proximal
end of the heated length in order to provide accurate boundary
condition for the algorithm described below. Specifically, the
distance x.sub.22,24 separating the active region of sensor 24 and
the proximal end should be less than or equal to about three times
the diameter of the velocity sensor probe D. In some examples, and
as shown in FIG. 4A, sensors 22, 24 may be set more closely than
three times the diameter D, including being directly adjacent
(i.e., touching, nearly touching or even overlapping) one another.
That is, in some examples, it may be advantageous to minimize the
distance x.sub.22,24 between heated sensor 22 and sensor 24. In
contrast, with respect to arrangement of sensors 32 and 34 in the
temperature probe 30, it may be advantageous, for example for
purpose of measured temperature range separation, to instead
maximize the distance between said probes x.sub.32,34. For example,
an active region of the distal sensor 32 and an active region of
the proximal sensor 34 may be separated by a distance (e.g.
distance x.sub.32,34) of at least 2 times the diameter of the
temperature probe D.sub.T. In other examples, a greater than two
times D.sub.T may be used, for example a distance of three times or
four times the diameter. Virtually any distance depending on the
length of the probe 30 may be used, provided the proximal sensor 34
is located within the flow within which the probe 30 is
immersed.
[0068] As shown in FIG. 4B, another temperature sensor 26, which
may be a thin-film RTD, may be included in the velocity sensor
probe 20'. The active region of sensor 26 may be separated from a
distal end of the wire-wound sensor 22 (e.g. heated sensor 22) by a
distance x.sub.22,26. The amount of separation of these sensors
(e.g. the distance x.sub.22,26 between heated sensor 22 and distal
sensor 26) may be selected to best serve the purposes described
herein. An example of one option is indicated by the dashed-line
extension of housing shell 28 and more distal location of sensor
26'.
[0069] As for the different purposes: when set directly adjacent to
one another (i.e., touching/overlapping) intermediate nodes (used
in conjunction with the aforementioned "nodal analysis") can be
eliminated in system analysis as described above; with marginally
more separation (e.g., about one diameter) such analysis may
utilize several nodes; set further apart (e.g., separated by about
2 to 3 diameters) additional computational intensity may be
required, but the "velocity" sensor probe 20' will be better able
to determine gas temperature with sensor 26--enabling the
elimination of a separate "temperature" sensor probe. In the last
instance, probe 20' might alternatively be referred to as a
"universal" or "independent" mass flow sensor probe.
[0070] However configured, in the examples shown in FIGS. 4A and
4B, the wire-wound platinum RTD sensors 22 according to the present
examples typically have a resistance ranging from about 10 to about
30 Ohms. The temperature sensing elements implemented as thin-film
RTDs (e.g. sensors 24, 26, 32, 34) may have resistances ranging
from about 500 to about 1000 Ohms.
[0071] FIG. 5 illustrates an example of a construction of velocity
probe 20. Here, housing shell 28 encases/encloses sensors 22 and 24
as illustrated before. Visible in more detail, is the manner in
which platinum RTD wire 60 is formed in multiple turns around a
mandrel (e.g., alumina) 62. The coiled length L.sub.1 of the heated
winding 60 is the length of the aforementioned "control volume" or
"heated length" discussed in connection with Equation (1) above.
The mandrel (alternatively referred to as a "glans" by those with
skill in the art) includes horizontal slots 64 (obscured slot not
shown) for Pt wire access into the center of the body. Electrical
leads A'' connected to the heated sensor wire 60 are also shown
(whereas those to/from "secondary" sensor 24 are not).
[0072] This configuration of the glans is well known. New, however
is the placement of a secondary temperature sensor 24 adjacent to
mandrel/glans 62. As shown, it is touching the body over which the
wire is wound. As such, a very predictable estimate to establish a
gap G between the position of a proximal end of heated sensor 22
and the active measurement area/point of sensor 24 can be
established using FEA analysis.
[0073] Still, the proximal extent of the mandrel separates the
active region of sensor 24 from the proximal end of windings 60
and--thus--the proximal end of the heated sensor 22. The
configuration in FIGS. 6A-6C and 7A-7C are adapted to enable closer
placement of the included sensors 22, 24 (in a two-sensor
variation, not shown) or 22, 24 and 26 (in the three-sensor
variations, shown) to enable elimination of FEA node(s) in system
analysis by directly using the temperature sensor measurement(s) as
boundary condition(s) in the aforementioned mathematical
modeling.
[0074] More specifically, the FIG. 6A-6C glans element 62'
incorporates one or more slots 70 cutting across the body. The
slot(s) can be machined or otherwise formed (e.g., water jet
cutting). In any case, it/they provide(s) clearance for the
secondary temperature sensor(s) 24, 26.
[0075] As an alternative, the approach in FIGS. 7A-7C includes
counter-bores or recesses 72 serving the same purpose. In such
systems, the closest surface of the temperature sensor body/bodies
may be touching or inserted within a region of the mandrel over
which the wire-wound heated sensor is formed.
[0076] Naturally, in three dimensions, there is radial separation
of the components. But with conformance to the hardware
configuration assumptions above, the one-dimensionality of the
mathematical analysis can be maintained. Thus, in relevant part
(i.e., x dimension along the length), the spacing is preferably
from about 0.05 inches to about zero x (projected) distance from
the last turn of the winding (with a small inset/overlap tolerance
of about 0.02 inches), or, even more moderately, about 0.10 inches
to about zero distance (with an inset/overlap of about 0.03
inches).
[0077] If using a distal secondary temperature sensor in the
velocity sensor (as shown in each of FIGS. 6A-6C and 7A-7C), glans
62'/62'' will typically include four lumen, providing insulated
clearance holes for the Pt winding (i.e., heated sensor 22) leads
"A" and distal TFRTD (i.e., secondary sensor 26) lead wires "B."
Electrical leads "C" for the proximal TFRTD (i.e., secondary sensor
24) extend proximally without need for clearance holes through the
mandrel/glans.
[0078] An overview of optional system-level constructional details
are presented in FIG. 8. The block diagram illustrates a
microprocessor-based thermal dispersion mass flow meter with the
four-temperature flow sensor configuration shown in FIG. 4A.
Adaptation to other sensor configurations as discussed herein
should be within the ability of those with ordinary skill in the
art.
[0079] In any case, the components shown may be set within housing
110, along with provision for wired connection or wireless data
transmission (such as though Bluetooth, WiFi, etc.). The voltage
sensing wires "D" make the measurement of the RTD resistances
independent of the length of the flow sensor cable, facilitating
remote location of the transmitter.
[0080] With the velocity sensor operated in the constant
temperature differential mode, heating current I.sub.1 depends on
the electrical resistance R.sub.1 of the velocity sensor 22 and the
electrical power input W required to maintain .DELTA.T constant
(i.e. the difference in temperature between the gas and average
temperature of the heated sensor). W typically ranges from about
0.1 to 5 watts depending on the "overheat" .DELTA.T, the mass flow
rate, and the size of the velocity sensor. The temperature sensing
current I.sub.2 is held constant and is less than 1 mA to avoid
self-heating sensor 24. The "Analog layer" shown includes precision
resistors for measuring the currents I.sub.1 and I.sub.2 but has no
bridge circuit. Analog-to-Digital conversion is provided with the
"A/D" converter between the Analog layer and a Microprocessor
(optionally with on-board ROM, EPROM or other computer readable
medium storing instructions). The system (i.e., by calculations
preformed by the Microprocessor in accordance with instructions)
digitally linearizes the mass flow rate q.sub.m output and
(optionally) T and P outputs, providing analog outputs for these
variables.
[0081] The system may further include algorithms based on the above
principle of operation that manage changes in gas selection, gas
temperature, and gas pressure in connection with measurements
received from the associated hardware. The system may also provides
a selection of digital communication protocols, including Hart,
Foundation Fieldbus, and Profibus (all trademarked). Likewise, the
systems described herein may enable a number of traditional digital
functions, such as: a multi-variable digital readout and user
interface; digital RS 232 and RS 485 communications; flow meter
diagnostics, validation, calibration adjustment, and
reconfiguration; flow totalization; and alarms.
[0082] Certainly, the thermal anemometers according to examples of
the invention retain advantageous performance if operated with
either digital or analog sensor-drive electronics, or with a
combination of both, in either the constant-temperature or
constant-current modes of operation. Digital electronics may be
preferred for reason of simplified computations based on
heat-transfer correlations and corrective algorithms, that
compensate for any changes (e.g., as referenced to flow calibration
conditions) in the fluid itself, fluid temperature, fluid pressure,
ambient temperature and other variables and influence parameters,
thereby yielding higher system accuracy. Said heat-transfer
correlations and corrective algorithms may be based on known
empirical heat transfer correlations, specific experimental data
for the thermal anemometer of the present invention, a gas property
library in electronic memory, physics-based heat transfer theory,
and other sources.
[0083] With a system as described in connection with the above,
examples of how a four-temperature microprocessor-based system
manages changes in gas selection, gas temperature and gas pressure
for air, methane, and argon are provided in FIGS. 9A-9C. These
figures are plotted in the conventional manner with the mass
velocity Vs shown as the independent variable and the electrical
power W shown as the dependent variable, whereas in the system they
have reversed roles. The three figures reflect the strong direct
dependence the electrical power W has on the thermal conductivity
of the gases. Thus, FIG. 9A results from the fact that
k.sub.methane>k.sub.air>k.sub.argon and FIGS. 9B and 9C
result from the fact that thermal conductivity increases as gas
temperature and pressure increase, respectively. The fact that
thermal conductivity, and therefore W, increases with gas pressure
as shown in FIG. 9C is a phenomenon that has heretofore been
ignored, but for higher accuracy applications should be
included.
[0084] FIGS. 9A-9C also reveal the non-linear, logarithmic nature
of the output. A log vs. log plot of these figures (not shown)
demonstrates a nearly straight line over approximately 1 to 150
standard m/s. This logarithmic property is responsible for the
exceptional rangeability and low-velocity sensitivity of thermal
dispersion mass flow meters. A rangeability as high as 100:1 is
common. Even higher rangeabilities are achieved with multi-range
flow calibration. Detectable minimum point mass velocities as low
as approximately 0.1 standard m/s (approximately 20 standard
ft/min) are reported by some manufacturers.
[0085] FIGS. 10A-10C show further results of the four-temperature
microprocessor based system. FIG. 10C reveals how the temperature
distribution T.sub.1(x) of the heated velocity sensor 22 (as shown
in FIG. 5) undergoes major changes as the mass velocity Vs
increases from 0 to 100 standard m/s. FIGS. 10A and 10B show, for
air and methane, the superb comparison between results calculated
using the four-temperature microprocessor-based system and actual
flow calibration data. Comparisons for other gases are likewise
excellent.
Variations
[0086] Exemplary aspects of the invention, together with details
regarding material selection and manufacture have been set forth
above. As for other details of the present invention, these may be
appreciated in connection with the above-referenced patents and
publications as well as is generally known or appreciated by those
with skill in the art. The same may hold true with respect to
method-based aspects of the invention in terms of additional acts
as commonly or logically employed. Regarding such methods,
including methods of manufacture and use, these may be carried out
in any order of the events which is logically possible, as well as
any recited order of events. Furthermore, where a range of values
is provided, it is understood that every intervening value, between
the upper and lower limit of that range and any other stated or
intervening value in the stated range is encompassed within the
invention. Also, it is contemplated that any optional feature of
the inventive variations described may be set forth and claimed
independently, or in combination with any one or more of the
features described herein.
[0087] Though the invention has been described in reference to
several examples, optionally incorporating various features, the
invention is not to be limited to that which is described or
indicated as contemplated with respect to each variation of the
invention. Various changes may be made to the invention described
and equivalents (whether recited herein or not included for the
sake of some brevity) may be substituted without departing from the
true spirit and scope of the invention.
[0088] Reference to a singular item includes the possibility that
there are a plurality of the same items present. More specifically,
as used herein and in the appended claims, the singular forms "a,"
"an," "said," and "the" include plural referents unless
specifically stated otherwise. In other words, use of the articles
allow for "at least one" of the subject item in the description
above as well as the claims below. It is further noted that the
claims may be drafted to exclude any optional element. As such,
this statement is intended to serve as antecedent basis for use of
such exclusive terminology as "solely," "only" and the like in
connection with the recitation of claim elements, or use of a
"negative" limitation.
[0089] Without the use of such exclusive terminology, the term
"comprising" in the claims shall allow for the inclusion of any
additional element--irrespective of whether a given number of
elements are enumerated in the claim, or the addition of a feature
could be regarded as transforming the nature of an element set
forth in the claims. Except as specifically defined herein, all
technical and scientific terms used herein are to be given as broad
a commonly understood meaning as possible while maintaining claim
validity. The breadth of the inventive variations is not to be
limited to the examples provided and/or the subject specification,
but rather only by the scope of the claim language.
* * * * *