Note: Descriptions are shown in the official language in which they were submitted.
CA 02776481 2013-05-31
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APPARATUS AND METHOD FOR CALCULATING THE TEMPERATURE OF
A MATERIAL FLOW WITHIN A CORIOLIS FLOW METER
This application is a divisional application of co-pending application Serial
No. 2,539,204, filed September 29, 2003.
Background of the Invention
1. Field of the Invention
The present invention relates to diagnostic apparatus and methods for a
Coriolis
flow meter.
2. Statement of the Problem
It is known to use Coriolis mass flow meters to measure mass flow and other
information of materials flowing through a pipeline as disclosed in U.S.
Patent No.
4,491,025 issued to J.E. Smith, et al. of January 1, 1985 and Re. 31,450 to
J.E. Smith of
February 11, 1982. These flow meters have one or more flow tubes of different
configurations. Each conduit configuration may be viewed as having a set of
natural
vibration modes including, for example, simple bending, torsional, radial and
coupled
modes. In a typical Coriolis mass flow measurement application, a conduit
configuration is excited in one or more vibration modes as a material flows
through the
conduit, and motion of the conduit is measured at points spaced along the
conduit.
The vibrational modes of the material filled systems are defined in part by
the
combined mass of the flow tubes and the material within the flow tubes.
Material flows
into the flow meter from a connected pipeline on the inlet side of the flow
meter. The
material is then directed through the flow tube or flow tubes and exits the
flow meter to
a pipeline connected on the outlet side.
A driver applies a force to the flow tube. The force causes the flow tube to
oscillate. When there is no material flowing through the flow meter, all
points along a
flow tube oscillate with an identical phase. As a material begins to flow
through the
flow tube, Coriolis accelerations cause each point along the flow tube to have
a different
phase with respect to other points along the flow tube. The phase on the inlet
side of the
flow tube lags the driver, while the phase on the outlet side leads the
driver. Sensors are
placed at different points on the flow tube to produce sinusoidal signals
representative of
the motion of the flow tube at the different points. A phase difference of the
signals
received from the sensors is calculated in units of time.
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The phase difference between the sensor signals is proportional to the mass
flow
rate of the material flowing through the flow tube or flow tubes. The mass
flow rate of
the material is determined by multiplying the phase difference by a flow
calibration
factor. The flow calibration factor is determined by a calibration process. In
the
calibration process, a known fluid is passed through the flow tube at a given
flow rate
and the proportion between the phase difference and the flow rate is
calculated.
One advantage of a Coriolis flow meter is that there are no moving components
in the vibrating flow tube. The flow rate is determined by multiplying the
phase
difference between two points on the flow tube and the flow calibration
factor. The
phase difference is calculated from sinusoidal signals received from the
sensors
indicating the oscillation of two points on the flow tube. The flow
calibration factor is
proportional to the material and cross sectional properties of the flow tube.
Therefore,
the measurement of the phase difference and the flow calibration factor are
not affected
by wear of moving components in the flow meter.
However, it is a problem that material properties, cross sectional properties
and
the stiffness of a flow tube can change during operation of the Coriolis flow
meter. The
changes in the material properties, cross sectional properties and stiffness
of the flow
tube can be caused by erosion, corrosion, and coating of the flow tube by
material
flowing through the flow tube, changing pipeline mountings and temperature.
One
example of the change in cross-sectional properties of the flow tube is the
change in the
moment of inertia caused by corrosion of the flow tube. A second example of a
change
in the material and cross-sectional properties of the flow tube is an increase
of the mass
of the flow tube and a decrease in cross-sectional areas caused by coating of
the flow
tube by materials flowing through the tube. A change in the material
properties, cross
sectional properties and stiffness of the flow tube can change the flow and
density
calibration factors of the flow meter. If the flow calibration factor of the
flow meter
changes, flow rates that are calculated using the original flow calibration
factor are
inaccurate. Therefore, there is a need in the art for a system that detects a
possible
change in the material properties, cross sectional properties and/or stiffness
of a flow
tube indicating that the mass flow rates measured by the Coriolis flow meter
may be
inaccurate.
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Summary of the Solution
The above and other problems are solved and an advance in the art is achieved
through the provision of a system for validating the integrity of a Coriolis
flow meter
through the determination and comparison of various parameters, including mass
flow
and density. For example, mass flow and density are determined based on the
mass flow
effect on frequency, as disclosed in the U.S. Pat. No. 5,687,100 to Buttler
etal. of Nov.
11, 1997.
A method for calculating a flow rate of a flow meter using multiple modes is
provided according to an embodiment of the invention. The method for
calculating a
flow rate of a flow meter using multiple modes comprises calibrating the flow
meter for
a number of desired modes. The method for calculating a flow rate of a flow
meter
using multiple modes includes determining a density of a material flowing
through the
flow meter associated with each mode. The method for calculating a flow rate
of a flow
meter using multiple modes further includes determining the flow rate effect
on density
for each desired mode. The method for calculating a flow rate of a flow meter
using
multiple modes further includes calculating a flow rate based on the density
and flow
rate effect on density values for each desired mode.
A method for validating a flow meter using multiple modes is provided
according to an embodiment of the invention. The method for validating a flow
meter
using multiple modes comprises the determination of a flow rate associated
with each
desired mode. The method for validating a flow meter using multiple modes
includes
comparing the flow rates and detecting an error condition responsive to the
comparison.
A method for validating a flow meter using multiple modes is provided
according to an embodiment of the invention. The method for validating a flow
meter
using multiple modes comprises determining a density of a material flow
associated
with each desired mode. The method for validating a flow meter using multiple
modes
includes comparing the density values associated with each mode and detecting
an error
condition responsive to the comparison.
A method for validating a flow meter using multiple modes is provided
according to an embodiment of the invention. The method for validating a flow
meter
using multiple modes comprises calibrating the flow meter for a number of
desired
modes. The method for validating a flow meter using multiple modes includes
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determining a density of a material flowing through the flow meter associated
with each
mode. The method for validating a flow meter using multiple modes further
includes
determining the flow rate effect on density for each desired mode. The method
for
validating a flow meter using multiple modes further includes calculating a
flow rate for
each desired mode from the density and flow rate effect on density values for
each
desired mode. The method for validating a flow meter using multiple modes
further
includes comparing the flow rates and detecting an error condition responsive
to the
comparison.
A method for validating a flow meter using multiple modes is provided
according to an embodiment of the invention. The method comprises calibrating
the
flow meter for a number of desired modes. After calibration, a flow rate
effect on
density for each desired mode is determined. Knowing the flow rate effect on
density
value for each desired mode a flow rate compensated density for each desired
mode can
then be calculated. A comparison of the density values is then made and an
error
condition responsive to the comparison is detected.
A method for determining a temperature of a material flow using multiple modes
is provided according to an embodiment of the invention. The method comprises
calibrating the flow meter for a number of desired modes to ascertain
calibration
constants. After calibration, a tube period is calculated for each of the
desired modes.
Using the calibration constants and tube periods for each mode, a temperature
of a
material flow can be determined.
A system for calculating a flow rate of a flow meter using multiple modes is
provided according to an embodiment of the invention. The system for
calculating a
flow rate of a flow meter using multiple modes comprises a means for
calibrating the
flow meter for a number of desired modes. The system for calculating a flow
rate of a
flow meter using multiple modes includes a means for determining a density of
a
material flowing through the flow meter associated with each mode. The system
for
calculating a flow rate of a flow meter using multiple modes further includes
a means
for determining the flow rate effect on density for each desired mode. The
system for
calculating a flow rate of a flow meter using multiple modes further includes
a means
for calculating a flow rate based on the density and flow rate effect on
density values for
each desired mode.
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A system for validating a flow meter using multiple modes is provided
according
to an embodiment of the invention. The system for validating a flow meter
using
multiple modes comprises a means for determining a flow rate associated with
each
desired mode. The system for validating a flow meter using multiple modes
further
comprises a means for comparing the flow rates determined for each mode and a
means
for means for detecting an error condition responsive to compared density
values
associated with each desired mode.
A system for validating a flow meter using multiple modes is provided
according
to an embodiment of the invention. The system for validating a flow meter
using
multiple modes comprises a means for determining a density of a material flow
associated with each desired mode. The system for validating a flow meter
using
multiple modes includes a means for comparing the density values. The system
for
validating a flow meter using multiple modes further includes a means for
detecting an
error condition responsive to the compared density values.
A system for validating a flow meter using multiple modes is provided
according
to an embodiment of the invention. The system for validating a flow meter
using
multiple modes comprises a means for calibrating a flow meter for a number of
desired
modes. The system for validating a flow meter using multiple modes further
comprises
a means for determining a density of a material flowing through the flow meter
associated with each mode. The system for validating a flow meter using
multiple
modes further comprises a means for determining the flow rate effect on
density for
each desired mode. The system for validating a flow meter using multiple modes
further
comprises a means for calculating a flow rate for each desired mode. The
system for
validating a flow meter using multiple modes further comprises a means for
comparing
the flow rates and a means for detecting an error condition responsive to the
compared
flow rate values.
A system for validating a flow meter using multiple modes is provided
according
to an embodiment of the invention. The system for validating a flow meter
using
multiple modes comprises a means for calibrating the flow meter for a number
of
desired modes. The system for validating a flow meter using multiple modes
includes a
means for determining a flow rate effect on density for each desired mode. The
system
for validating a flow meter using multiple modes further comprises a means for
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calculating a flow rate compensated density for each desired mode. The system
for
validating a flow meter using multiple modes further comprises a means for
comparing
the density values and a means for detecting an error condition responsive to
the
compared density values.
A system for determining a temperature of a material flow using multiple modes
is provided according to an embodiment of the invention. The system for
determining a
temperature of a material flow using multiple modes comprises a means for
calibrating
the flow meter for a number of desired modes to ascertain calibration
constants. The
system for determining a temperature of a material flow using multiple modes
includes a
means for determining a tube period for each of the desired modes. The system
for
determining a temperature of a material flow using multiple modes further
includes a
means for determining a material flow temperature using the calibration
constants and
tube periods for each mode.
Description of the Drawings
FIG. 1 illustrates a Coriolis flow meter in an example of the invention;
FIG. 2 illustrates a validation system in an example of the invention;
FIG. 3 illustrates a validation system in an example of the invention;
FIG. 4 illustrates a process for determining flow rate in an example of the
invention;
FIG. 5 illustrates a validation system in an example of the invention;
FIG. 6 illustrates a validation system in an example of the invention; and
FIG. 7 illustrates a process for temperature in an example of the invention.
Detailed Description of the Invention
FIGS. 1-7 and the following description depict specific examples to teach
those
skilled in the art how to make and use the best mode of the invention. For the
purpose
of teaching inventive principles, some conventional aspects have been
simplified or
omitted. Those skilled in the art will appreciate variations from these
examples that fall
within the scope of the invention. The examples below have been expressed
using two
modes for brevity. It is to be understood that more than two modes can be
used. Those
skilled in the art will appreciate that the features described below can be
combined in
various ways to form multiple variations of the invention. As a result, the
invention is
not limited to the specific examples described below, but only by the claims
and their
equivalents.
CA 02776481 2011-10-24
FIG. 1 shows a Coriolis flow meter 5 comprising a meter assembly 10 and meter
electronics 20. Meter assembly 10 responds to mass flow rate and density of a
process
material. Meter electronics 20 is connected to meter assembly 10 via leads 100
to
provide density, mass flow rate, and temperature information over path 26, as
well as
other information not relevant to the present invention. A Coriolis flow meter
structure
is described although it is apparent to those skilled in the art that the
present invention
could be practiced as a vibrating tube densitometer without the additional
measurement
capability provided by a Coriolis mass flow meter.
Meter assembly 10 includes a pair of manifolds 150 and 150', flanges 103 and
103' having flange necks 110 and 110', a pair of parallel flow tubes 130 and
130', drive
mechanism 180, temperature sensor 190, and a pair of velocity sensors 170L and
170R.
Flow tubes 130 and 130' have two essentially straight inlet legs 131 and 131'
and outlet
legs 134 and 134' which converge towards each other at flow tube mounting
blocks 120
and 120'. Flow tubes 130 and 130' bend at two symmetrical locations along
their length
and are essentially parallel throughout their length. Brace bars 140 and 140'
serve to
define the axis W and W' about which each flow tube oscillates.
The side legs 131, 131' and 134, 134' of flow tubes 130 and 130' are fixedly
attached to flow tube mounting blocks 120 and 120' and these blocks, in turn,
are fixedly
attached to manifolds 150 and 150'. This provides a continuous closed material
path
through Coriolis meter assembly 10.
When flanges 103 and 103', having holes 102 and 102' are connected, via inlet
end 104 and outlet end 104' into a process line (not shown) which carries the
process
material that is being measured, material enters end 104 of the meter through
an orifice
101 in flange 103 is conducted through manifold 150 to flow tube mounting
block 120
having a surface 121. Within manifold 150 the material is divided and routed
through
flow tubes 130 and 130'. Upon exiting flow tubes 130 and 130', the process
material is
recombined in a single stream within manifold 150' and is thereafter routed to
exit end
104' connected by flange 103' having bolt holes 102' to the process line (not
shown).
Flow tubes 130 and 130' are selected and appropriately mounted to the flow
tube
mounting blocks 120 and 120' so as to have substantially the same mass
distribution,
moments of inertia and Young's modulus about bending axes W--W and W'--W',
respectively. These bending axes go through brace bars 140 and 140'. Inasmuch
as the
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Young's modulus of the flow tubes change with temperature, and this change
affects the
calculation of flow and density, resistive temperature detector (RTD) 190 is
mounted to
flow tube 130', to continuously measure the temperature of the flow tube. The
temperature of the flow tube and hence the voltage appearing across the RTD
for a
given current passing therethrough is governed by the temperature of the
material
passing through the flow tube. The temperature dependent voltage appearing
across the
RTD is used in a well known method by meter electronics 20 to compensate for
the
change in elastic modulus of flow tubes 130 and 130' due to any changes in
flow tube
temperature. The RTD is connected to meter electronics 20 by lead 195.
Both flow tubes 130 and 130' are driven by driver 180 in opposite directions
about their respective bending axes W and W' and at what is termed the first
out-of-
phase bending mode of the flow meter. This drive mechanism 180 may comprise
any
one of many well known arrangements, such as a magnet mounted to flow tube
130' and
an opposing coil mounted to flow tube 130 and through which an alternating
current is
passed for vibrating both flow tubes. A suitable drive signal is applied by
meter
electronics 20, via lead 185, to drive mechanism 180.
Meter electronics 20 receives the RTD temperature signal on lead 195, and the
left and right velocity signals appearing on leads 165L and 165R,
respectively. Meter
electronics 20 produces the drive signal appearing on lead 185 to drive
element 180 and
vibrate tubes 130 and 130'. Meter electronics 20 processes the left and right
velocity
signals and the RTD signal to compute the mass flow rate and the density of
the material
passing through meter assembly 10. This information, along with other
information, is
applied by meter electronics 20 over path 26 to utilization means 29.
Coriolis flow meter 5 is vibrated at its resonant frequency so as to enable
flow
meter 5 to measure mass and density. The mass measurement is based on the
following
equation:
m FCF * [At ¨ Atoi (1)
Where:
in is the mass flow rate;
FCF is the flow calibration factor;
At is the time delay; and
Ato is the time delay at zero flow.
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The FCF term is proportional to the stiffness of the flow meter. Stiffness is
the
predominate parameter that affects the flow meter's performance. In other
words, if the
stiffness of the flow meter changes the meter's FCF will change. A change in
the flow
meters performance can be caused by corrosion, erosion and coating.
Equation (1) can be rewritten to reflect the stiffness:
m = G * (E/)* [At ¨ Ato] (2)
Where:
G is a geometric constant associated with a particular sensor;
E is Young's Modulus; and
I is the moment of inertia.
The area moment of inertia, I, changes when the meter's flow tube changes. For
example, if the tube corrodes reducing the wall thickness, the area moment of
inertia is
decreased.
FIG. 2 shows a process 200 for detecting and differentiating flow meter
structure
changes from indicated changes in flow rate. Process 200 starts with the
determination
of mass flow rate, r n, using multiple modes in steps 210 and 220 from the
following
equation:
( \
!//1 'At' \
m
2 E G2 At2 ¨ A t20 (3)
mn n Atn jAtno ,/
When multiple modes are excited, either from flow noise or forced vibration,
the
vibration of the mode will couple with the mass flow passing through the flow
tube
causing a Coriolis response for each mode. The Coriolis response results in an
associated At which is used to calculate a mass flow reading for each mode.
Step 230 compares the mass flow reading for each mode. The resulting mass
flow rate must be the same for each mode. If the mass flow readings are equal,
step 250
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generates a "proper operation" signal and the process restarts at step 210.
The "proper
operation" signal can be in the form of a visible or audible signal to a user.
When a deviation occurs between the mass flow rates, which are outside of
acceptable limits, an error signal is generated in step 240. The error signal
generated in
step 240 can cause various actions to occur. For instance, the error signal
may cause the
process to be shut down or may signal a visible or audible warning to an
operator who
then takes appropriate action.
The density measurements of Coriolis meter 5 are based on the following
equation:
_r 2;r lirr
27-g = (4)
r m
Where:
k is the stiffness of an assembly;
m is the mass of the assembly;
f is the frequency of oscillation; and
T is the period of oscillation
Equation (4) is the solution of the equation of motion for a single degree-of-
freedom
system. A Coriolis flow meter at zero flow is represented by an expansion of
equation
(4) yielding:
2n- EIG
(5)
z- pe4f
Where:
E is Young's modulus;
is the cross-sectional moment of inertia;
Gp is a geometric constant;
A is the cross-sectional area;
p is the density
f represents the fluid in the flow meter; and
t represents the material of the flow tube(s).
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By rearranging terms, equation (5) can be re-written as:
(6)
Where:
El 5 and (7)
4;r2Af
C2 =E! (8)
The geometric constant, Gp, accounts for geometric parameters such as tube
length and
shape. The constants, CI and C2, are determined as part of the normal
calibration
process at zero flow on two different fluids.
FIG. 3 shows a process 300 for detecting and differentiating flow meter
structure
changes from changes in indicated density. Process 300 starts with the
determination of
density, p, using multiple modes in steps 310 and 320. Multiple modes can be
excited
either from flow noise or forced vibration.
Step 330 compares the density reading for each mode. The resulting density
reading must be the same for each mode. If the density readings are equal,
step 350
generates a "proper operation" signal and the process restarts at step 310.
The "proper
operation" signal can be in the form of a visible or audible signal to a user.
When a deviation occurs between the density readings, which are outside of
acceptable limits, an error signal is generated in step 340. The error signal
generated in
step 340 can cause various actions to occur. For instance, the error signal
may cause the
process to be shut down or may signal a visible or audible warning to an
operator who
then takes appropriate action.
In addition to the method described in equation (1) for determining mass flow,
density can also be used to calculate mass flow. As described more fully in
U.S. Pat. No.
5,687,100 to Buttler et al. of Nov. 11, 1997, a second-order flow effect on
density term
is added to equation (6) resulting in:
2
= [CI r 2 ¨C2]--(n 1) FD (9)
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Where:
0
in is the mass flow rate; and
FD is the flow effect on density constant.
The FD term is a constant for all flow rates and at all densities for a given
mode shape,
however, the FD term differs for each mode shape and tube geometry.
When flow meter 5 is driven in multiple modes or multiple modes are measured,
multiple equations and multiple unknowns can be derived. For example, in the
case of
flow meter 5 being driven in two modes, the density equations are written as
follows:
2
1 o
p .[C,õzõ2 ¨ j¨(m.) FDa (10)
Pfb= [Cibrb2 ¨ C,b1¨(4b FD (11)
Where:
a is a first mode shape;
b is a second mode shape;
C,õzõ ¨ C2a is pa, the true density using mode a;
Cihrb2 ¨C21, is Pb, the true density using mode b;
pfa is the true density corrected for the flow effect on density measurement;
and
pfb is the true density corrected for the flow effect on density measurement.
Equations (10) and (11) are two independent density readings, at zero flow,
corrected
for the flow effect, using two modes. Since pfa and pfb are equal, equations
(10) and (11)
can be combined to form:
2 1 o )2
F
õ Czb I¨ (Mb A, (12)
[Cia ra 2 ¨ C2a1¨(4o FD
For a single flow path, ma = nib, resulting in a solution for mass flow as
follows:
Pa Pb
nt ¨ (13)
FD0 ¨ FDb
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FIG. 4 shows a process 400 for determining mass flow based on density. Process
400 starts with calibration of flow meter 5 using modes "a" and "b" in step
410. The
calibration process establishes constants Ca and Ch and Cib and C2b using two
different
fluid densities, i.e. air and water.
Step 420 determines the density values, pa and pb, from equation (6) above.
Step
430 compares pa and Pb to determine if the density values agree. If the
density values do
not agree calibration must be performed again in step 410. lithe density
values agree,
steps 440 and 450 determine the associated FD values for modes "a" and "b".
Once the
FD values are determined, mass flow is calculated in step 460 using equation
(13).
a
The M rd value determined above can also be used to determine when changes
have occurred in the flow meter. FIG. 5 shows a process 500 for detecting and
differentiating flow meter structure changes from indicated changes in flow
rate.
Process 500 starts with the determination of mass flow rate, mfa , from step
460 of FIG.
4 in step 510.
Step 520 calculates a traditional mass flow rate, mr, from equation (1) and
a a
compares mfd and mr in step 530. If the mass flow readings are equal, step 550
generates a "proper operation" signal and the process restarts at step 510.
The "proper
operation" signal can be in the form of a visible or audible signal to a user.
When a deviation occurs between the mass flow readings, which are outside of
acceptable limits, an error signal is generated in step 540. The error signal
generated in
step 540 can cause various actions to occur. For instance, the error signal
may cause the
process to be shut down or may signal a visible or audible warning to an
operator who
then takes appropriate action.
The pa and pfb values determined above can also be used to determine when
changes have occurred in the flow meter. FIG. 6 shows a process 600 for
detecting and
differentiating flow meter structure changes from indicated changes in density
corrected
for the flow rate effect.
Process 600 starts with calibration of flow meter 5 using modes "a" and "b" in
step 610. The calibration process establishes constants Cia and C23 and Cib
and C2b
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using two different fluid densities, i.e. air and water. It is to be
understood that multiple
modes can be used and that the use of two modes in this example are for
illustrative
purposes only.
Step 620 determines the associated FD values for modes "a" and "b". Once the
FD values are determined, pfa and pfb are calculated in step 630 using
equations (10) and
(11).
Step 640 compares the density readings, pfb and pfb. The density readings must
be
the same for each mode. If the density readings are equal, step 660 generates
a "proper
operation" signal and the process restarts at step 620. The "proper operation"
signal can
be in the form of a visible or audible signal to a user.
When a deviation occurs between the density readings, which are outside of
acceptable limits, an error signal is generated in step 650. The error signal
generated in
step 650 can cause various actions to occur. For instance, the error signal
may cause the
process to be shut down or may signal a visible or audible warning to an
operator who
then takes appropriate action.
Multiple mode density determination can also be used to ascertain the
temperature of the material flow. Density, as a function of temperature, is
expressed
from the following:
põ =c *r2(1 ¨ 0.0004T)+ C2n (14)
Where:
põ is a temperature compensated density using mode n;
Cln is a first constant using mode n;
C2n is a second constant using mode n;
is the tube period; and
T is the temperature of' the material flow.
Using multiple modes, the temperature of the material flow can be ascertained
using
equation (14). For example, using two modes of operation, equation (14) can be
expressed as two equations:
p,= C11*r2 ¨ 0.000479 + C21 (15)
P2 7= c12 * r2(1-0.0004T)+ C22 (16)
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Since pi and p2 are equal, equations (15) and (16) written as:
2
- 0.000411= C; - C21 2 (17)
, r2 ¨ C,2r2
Solving for T yields:
( C,2- C21 1
T= 1 (18)
C r2 C2 r2,/' 0 0004
t 2
FIG. 7 shows a process 700 for ascertaining material flow temperature based on
multiple mode density determination. Process 700 starts with calibration of
flow meter 5
using modes "1" and "2" in step 710. The calibration process establishes
constants C11
and C21 and C12 and C22 using two different fluid densities, i.e. air and
water.
Step 720 determines the density values, pi and p2, from equation (15) and (16)
above. Step 730 compares pj and p2 to determine if the density values agree.
If the
density values do not agree calibration must be performed again in step 710.
If the
density values agree, step 740 determines the associated tube period values
for modes
"1" and "2". Once the tube period values are determined, temperature is
calculated in
step 750 using equation (18).
