Abstrict A method of correcting reading of a noncontact solids flow meter
measuring solid particulate flow where the solid particulate product
enters the flow tube at one end and flows past a sensor and then
exits the flow tube. The sensor for the flow meter is very sensitive
and not only can sense particulate flow, but can also pick up system
machinery motion such as the rotation of a screw conveyor or other
moving machinery parts as product flow and provide a system output
reading in excess of the actual flow rate. In addition, if the product
flow creates dust during the initial calibration process, and the
dust is controlled at the actual installation, the system output
reading may indicate a flow rate substantially less than the actual
flow. The calibration method of this invention uses the original
calibration or performance curves to accurately correct the output
readings.
Claims What is claimed is:
1. In a system for moving particulate matter and using a flow meter
for measuring the mass flow rate of particulate matter as a parameter
(F) by radiating the entire flow path through a conduit portion
with electromagnetic energy such that substantially all of the particulate
matter contributes to the generation of backscatter energy and receiving
said backscatter energy to generate an electrical signal as a parameter
(E) proportional to the concentration of particulate matter flowing
in said conduit a method of correcting motion sensed by said flow
meter not caused by the actual flow of particulate matter being)
measured to obtain a corrected flow rate comprising the steps of:
generating data points for said flow meter showing the value of
said electrical signal parameter at different values of said mass
flow rate parameter of selected particulate materials between "0"
flow rate and a selected upper limit flow rate;
determining an initial algorithm representative of at least a portion
of said generated data points wherein said initial algorithm defines
a flow rate parameter (F) as a function of said electrical signal
parameter (F);
determining constant coefficients and exponents of said function;
installing said flow meter into its working environment;
operating said system with said installed flow meter at a known
flow rate of said particulate material through said conduit and
determining a corresponding electrical signal;
computing a correction factor for a selected one of said flow rate
or said electrical signal from said determined corresponding electrical
signal and said initial algorithm; and
subtracting said correction factor from the corresponding selected
flow rate or electrical signal in said initial algorithm to obtain
an adjusted algorithm representing said flow rate as a function
of said electrical signal in said working environment.
2. A method of correcting for sensed machinery motion in said system
according to the method of claim 1 wherein said known flow rate
is zero, said step of determining a corresponding electrical signal
comprises the step of reading the value of said electrical signal
from said flow meter at said zero flow rate and said step of computing
said correction factor comprises the step of setting the electrical
signal (E) to said corresponding electrical signal value read from
said flow meter and computing said flow rate (F) from said initial
algorithm as said correction factor.
3. A method of correcting a flow meter for dust and particulate
movement beyond said conduit portion according to the method of
claim 1 wherein said step of determining a corresponding electrical
signal and said step of computing said correction factor are a single
step comprising setting flow rate (F) of said initial algorithm
to said known flow rate and computing the electrical signal (E)
as said correction factor from said initial algorithm.
4. The method of claim 1 wherein said solid particulate matter
flows past said sensor at a substantially constant velocity.
5. The method of claim 4 wherein said method further comprises
the step of providing a source of pneumatic pressure coupled to
said first conduit for conveying said particulate matter past said
sensor at said substantially constant velocity.
6. The method of claim 1 wherein said generated electrical signal
is nonlinear and provided in milliamps.
7. The method of claim 2 wherein said step of operating said system
includes operating machinery having motion at the discharge end
of said flow meter and said sensed machinery motion is the operation
of said machinery.
8. The method of claim 7 wherein said operating machinery is a
rotating screw conveyor.
9. The method of claim 1 wherein said function is of the form Y=aX.sup.b
where Y=flow rate (F) and X=electrical signal (E).
10. The method of claim 1 wherein said function is of the form
Y=a.sub.0 +a.sub.1 X+a.sub.2 X.sup.2 +a.sub.3 X.sup.3 +a.sub.4 X.sup.4
where Y=flow rate (F) and X=electrical signal (E).
11. The method of claim 1 wherein a first portion of said generated
data points are defined by a first function and a second portion
of said generated data points are defined by a second function.
12. The method of claim 11 wherein said first function has the
same form as said second function but at least one of said constant
coefficients and said exponents are different.
13. In a system for moving particulate matter and using a flow
meter for measuring the mass flow rate of particulate matter as
a parameter (F) by radiating the entire flow path through a conduit
with electromagnetic energy such that substantially all of the particulate
matter contributes to the generation of backscatter energy and receiving
said backscatter energy to generate an electrical signal as a parameter
(E) proportional to the concentration of particulate matter flowing
in said conduit, a method of correcting motion sensed by said flow
meter not caused by the actual flow of particulate matter being
measured to obtain a corrected flow rate comprising the steps of:
generating an initial algorithm or performance curve for said flow
meter showing the value of said electrical signals at different
values of said mass flow rates of particulate materials between
"0" flow rate and a selected upper limit flow rate;
installing said flow meter into its working environment;
operating said system at a known flow rate of said particulate
material through said conduit to obtain a corresponding electrical
signal;
determining from said initial algorithm or performance curve and
said corresponding electrical signal a correction factor; and
subtracting said correction factor from a corresponding value in
said initial algorithm to obtain an adjusted flow rate.
14. The method of claim 13 wherein said solid particulate matter
flows past said sensor at a substantially constant velocity.
15. The method of claim 14 wherein said method further comprises
the step of providing a source of pneumatic pressure coupled to
said first conduit for conveying said particulate matter past said
sensor at said substantially constant velocity.
16. The method of claim 13 wherein the electrical signal generated
by said receiver is generated as a nonlinear signal.
17. The method of claim 16 wherein said generated nonlinear electrical
signal is provided in milliamps.
18. In a system for moving particulate matter and using a flow
meter for measuring the mass flow rate of particulate matter by
radiating the entire flow path through a conduit with electromagnetic
energy such that substantially all of the particulate matter contributes
to the generation of backscatter energy and receiving said backscatter
energy to generate an electrical signal proportional to the concentration
of particulate matter flowing in said conduit, a method of correcting
motion sensed by said flow meter not caused by the actual flow of
particulate matter being measured to obtain a corrected flow rate
comprising the steps of:
generating a performance curve showing the value of said generated
electrical signals at different mass flow rates of particulate materials
between "0" flow rate and a selected upper limit flow
rate;
installing said flow meter into its working environment;
operating said system at operating conditions at a zero flow rate
of said particulate material through said conduit to obtain a first
generated electrical signal;
determining from said performance curve a first flow rate represented
by said first generated electrical signal; and
subtracting said first flow rate from a flow rate indicated by
said flow meter during actual operation for each electrical signal
value to obtain an adjusted algorithm or performance curve to provide
corrected flow rate values.
19. The method of claim 18 wherein said step of operating said
system includes operating a screw conveyor at discharge end of said
flow meter.
20. The method of claim 19 wherein said flow rate indicated by
said flow meter during actual operation represents particulate flow
plus motion from said screw conveyor.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to flow measurement of particulate
streams and in particular to methods for correcting erroneous measurements
of particulate streams due to motion other than the motion of particulate
matter being measured.
2. Description of Related Art Including Information Disclosed Under
37 CFR 1.97 and 1.98
Flow measurement of particulate streams such as wet cakes, grains,
cereals, dry powders, minerals, pharmaceuticals, dairy powders,
chemicals, spices, snack foods, cement, resins, plastics, fibrous
materials, and others is critical to the operation and optimization
of a given process. A noncontact flow meter is of great importance
since measurements are obtained without interfering with the flow
of product through the process transfer line. For flow measurement
of some products through transfer lines, this is critical since
any obstruction in the line can cause buildup and eventual pluggage.
In addition, no degradation of the material occurs since the flow
is unobstructed. Also, the integrity of the process is maintained
with a noncontact flow meter. For example, with food and pharmaceutical
manufacturing, a truly noncontact solids flow meter obtains measurements
without any contamination of the process since, being a noncontact
device, the integrity of the process is never compromised. This
factor is important when considering food, pharmaceutical, mineral,
and chemical manufacturing.
Some typical applications for flow/quantity measurements are: feed
to dryers, discharge from dryers, feed to milling operations, flow
to mixers, flow from dust collectors, flow from conveyors, loading/unloading
of railcars, loading/unloading of trucks, loading/unloading of barges,
flow of grains through ducts, cement loading/unloading, flow of
plastic granules, flow from cyclones, flow in pneumatic transfer
lines, loading/unloading of silos, and feed to reactors to mention
a few applications.
In U.S. Pat. No. 4091385 a Doppler radar flow meter is disclosed
in which the flow meter comprises a radar transmitter and receiver
that respectively radiates radio waves at a predetermined microwave
frequency at least partially through a fluid and receive at least
a portion of the radio waves backscattered by at least some of the
particulate matter in the path of the radiated radio waves. A signal
processor connected to the receiver produces a signal related to
the Doppler's shift in frequency between the backscattered radio
waves and the radiated radio waves and, thus, the frequency is related
to the velocity of flow of the particulate matter being measured.
In particular in this case, the flow meter is used for velocity
of flow of fluids such as blood in conduits such as blood vessels.
U.S. Pat. No. 5550537 discloses an apparatus for measuring mass
flow rate of a moving medium using Doppler radar. The patent discloses
a nonintrusive mass flow rate meter that includes a transceiver
that transmits an electromagnetic signal of known frequency and
power to illuminate a portion of moving material. The transceiver
detects the magnitude and the Doppler shift of the electromagnetic
signal that is reflected by material moving along the process flow
as it passes through the electromagnetic field established by the
signal. The transceiver then combines the magnitude of the reflected
electromagnetic signal along with the Doppler shift between the
frequency of the transmitted and reflected electromagnetic signals
to generate an output signal related to the mass flow rate of the
material. The problem with the 5550537 patent is that only a portion
of the moving material is illuminated. This creates errors in the
mass flow rate and thus in the quantity of material that is passing
through the conduit.
U.S. Pat. No. 5986553 issued to the same inventor as the present
invention discloses an improved flow meter for measuring solid particulate
flow rates by radiating the particulate flow path through a conduit
such that substantially all of the particulate matter contributes
to and forms backscatter energy. The backscatter energy is used
to generate an electrical signal that is proportional to the consolidation
of solid particulate matter flowing through the conduit. The flow
meter described in U.S. Pat. No. '553 is quite sensitive to motion
and normally very accurate. However, because of its sensitivity
to particulate motion it is also sensitive to various "motions",
other than the particulate material motion, which are often present
in a particulate matter distribution system. For example, the motion
of a rotating screw conveyor or product dust can be sensed by the
system and result in an erroneous indication of the output particulate
flow rate.
SUMMARY OF THE INVENTION
The present invention discloses a method of compensating and correcting
a noncontact mass flow meter which measures the flow of particulate
streams through ducts, chutes, or pipes utilizing a Dopplerradar
sensor, a unique flow tube, a flow rate and totalizer indicator,
and an algorithm to convert the sensor output signal to mass flow
rate. For example, in the unique flow meter disclosed in U.S. Pat.
No. 5986553 the solid particulate matter flows along a first
hollow conduit with a second hollow conduit having at least the
same diameter as the first conduit and being joined to the first
conduit at an angle. At least one sensor is associated with the
second hollow conduit and includes a transmitter of electromagnetic
energy for radiating the entire particulate matter flow path formed
by the first conduit such that substantially all of the particulate
matter contributes to and forms backscattered energy. A receiver
receives the backscattered energy and generates an electrical signal
that is proportional to the concentration of solid particulate matter
flowing in the first hollow conduit. A processor is coupled to at
least one sensor for generating an output signal representative
of the concentration of the solid particulate matter.
In one embodiment described in U.S. Pat. No. 5986553 the solid
particulate matter flows past the sensor at a substantially constant
velocity that is achieved by placing a source of the particulate
matter a predetermined distance above the sensor for achieving the
substantially constant velocity by gravity flow. In another embodiment
described in the '553 patent, a source of pneumatic pressure is
coupled to the first conduit for conveying the particulate matter
past the sensor at the substantially constant velocity.
A sightglass is preferably interposed in the second hollow conduit
between the sensor and the particulate matter. The electrical signal
generated by the receiver is typically a nonlinear signal measured
in either milliamps or volts. The processor converts the milliamp
or volt signal into a poundsperhour mass flow rate. A totalizer
generates a total quantity value of the material delivered.
The processor includes a memory for storing at least one algorithm
for converting the signal generated by the receiver into a continuous
range of values to a poundsperhour mass flow rate. In the described
embodiment, the memory stores a first algorithm for converting a
signal generated by the receiver in a first range of values to a
poundsperhour mass flow rate and stores a second algorithm for
converting the signal generated by the receiver in a second continuous
range of values to a poundsperhour mass flow rate to enhance accuracy
of the flow meter.
In the preferred embodiment, the first algorithm has the form of
F=aE.sup.b (Y=aX.sup.b), where F=pounds/hour, E=electrical signals
as milliamps or volts, and a and b are constants and the second
algorithm has the form of F=a.sub.0 +a.sub.1 E+a.sub.2 E.sup.2 +a.sub.3
E.sup.3 +a.sub.4 E.sup.4 (Y=a.sub.0 +a.sub.1 X+a.sub.2 X.sup.2 +a.sub.3
X.sup.3 +a.sub.4 X.sup.4) were F=pounds/hour, E=milliamps, and a.sub.0
a.sub.1 a.sub.2 a.sub.3 and a.sub.4 are constants.
Further, a central processing unit is coupled between the receiver
and the industrial computer for calculating constants for the first
and second algorithms for use by the industrial computer or smart
indicator. Alternatively, the processor itself may include a central
processing unit for calculating the constants for the first and
second algorithms and generating mass flow rate in poundperhour.
It further may have a converting means in the central processing
unit for converting the mass flow rate to total pounds.
The present invention relates to a method of correcting or compensating
for erroneous readings of a flow meter of the type disclosed in
U.S. Pat. No. '553 resulting from sensing motion in the system other
than motion or movement of the particulate matter.
According to the invention the correction is achieved by generating
data points represented by an initial performance curve or initial
algorithm under controlled conditions such as in a laboratory. The
initial algorithm or performance curve will typically show a relationship
between the electrical output signal (typically in milliamps or
volts) for different known flow rates. After the flow meter is installed
into its working environment the system is operated in its normal
manner and at a known flow rate to determine a corresponding electrical
signal.
A correction factor is then computed for either the mass flow rate
parameter (F) or the electrical signal parameter (E) by using the
electrical signal determined at the known flow rate and the initial
algorithm.
An adjusted algorithm is then developed by subtracting the correction
factor in the initial algorithm. Thus it is seen that sensing motion
not actually representing the flow of particulate material may result
in a corrected value that can be less than the indicated flow rate
such as a situation where the motion of a screw conveyor is the
source of error. The corrected value could also be greater than
the indicated flow rate as could be the case if the laboratory calibrating
process was subjected to backscatter due to grain dust and the grain
dust was not present in the final installation. However, the important
consideration for either situation is that the laboratory calibration
procedure develops an algorithm or a performance curve that represents
the flow meter and may be readily adjusted for the particular environment
at the final installation. Thus, extensive recalibration is not
required even though the individual values of flow rate per unit
of sensor output as represented by the initial algorithm or performance
curve are substantially different from the flow rate per unit of
sensor output as determined from the adjusted algorithm or performance
curve.
According to an embodiment for correcting the machinery motion,
the system is operated at a zero flow rate to determine a flow rate
correction factor at a specific electrical signal value, and according
to a preferred embodiment for correcting for dust, etc., the system
is operated at a known positive flow rate to obtain an electrical
signal correction factor at a specific flow rate.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the present invention will be more
fully disclosed when taken in conjunction with the following DETAILED
DESCRIPTION OF THE PREFERRED EMBODIMENT(S) in which like numerals
represent like elements and in which:
FIG. 1 is a prior art diagrammatic representation of a typical
flow meter application for the noncontact mass flow meter in a
gravity flow application;
FIG. 2A is a side view of a prior art flow tube and attached sensor
tube;
FIG. 2B is a top view of a prior art rectangular flow tube with
the sensor tube attached;
FIG. 2C is a top view of a prior art circular flow tube with a
sensor tube attached;
FIG. 3 is a crosssectional view of a typical sightglass that could
be used with the flow meter shown in FIG. 1;
FIG. 4 illustrates the equipment necessary to calibrate the solids
flow meter of the flow meter of FIG. 1;
FIG. 5 is a graph of mass rate through the meter in FIG. 1 in poundsperhour
versus sensor output in milliamps illustrating the original nonlinear
calibration data used to create an algorithm;
FIG. 6 is a graph illustrating the accuracy of the calibrated flow
meter utilizing rolled oats;
FIG. 7 illustrates the accuracy of the calibrated flow meter for
a "Certa" product;
FIG. 8 is a graph illustrating the accuracy of the calibrated meter
for use with a berry type cereal;
FIG. 9 illustrates the accuracy of the calibrated meter utilizing
a Life.RTM. Cereal product, remill stream;
FIG. 10 is a diagrammatic representation of a typical prior art
pneumatic conveying noncontact solids flow meter; and
FIG. 11A is a side view of a flow tube utilizing at least two sensors;
FIG. 11B is a top view of a rectangular flow tube utilizing two
sensors;
FIG. 11C is a top view of a circular flow tube utilizing two sensors;
FIG. 12 is a flow diagram for determining the mass flow rate with
a mass flow meter of the type shown in FIG. 1;
FIG. 13 is a flow diagram of the method of the present invention
for correcting the readings of a mass flow meter due to errors caused
by sensed motion other than motion of the particulate material being
measured;
FIG. 14 is an example of a performance curve or algorithm of a
mass flow meter developed in a laboratory or at the factory;
FIG. 15 is an example of the performance curve of FIG. 14 after
correction according to the teachings of this invention;
FIG. 16 is a chart showing the total weight per day of Green Oats
flowing through a flow meter and the total weight as indicated by
the flow meter;
FIG. 17 shows the close correlation of the actual total weight
as illustrated in FIG. 16 and the total weight indicated by the
flow meter after being corrected according to the teachings of this
invention; and
FIG. 18 shows the initial performance curve or algorithm of the
flow meter used to obtain the charts of FIGS. 16 and 17 and the
performance curve after beings corrected according to the teachings
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
FIG. 1 is a prior art view showing a typical flow meter application
for the noncontact mass flow meter 10 in a gravity flow application.
A product such as a cereal flows into a product bin 14 and a rotary
air lock 16 at the bottom of the bin discharges the cereal to a
flow meter 12. The flow meter 12 measures mass rate (pounds/hour)
and quantity (pounds). The product discharged from the bottom of
the flow meter 12 passes through a manual divert valve 18 which
enables the product to follow either path 20 or path 22.
It will be noted that the distance from the solids feed equipment
(in this case the rotary air lock 16) to the flow meter 12 would
be kept the same for calibration and the actual application or installation
into an industrial plant. This would ensure that the initial particulate
velocities would be nearly identical at the flow meter both during
the calibration conditions and the end use conditions under which
the meter would finally operate.
The flow tube design is one of the important attributes of the
present invention. It is important that the lowenergy microwave
beam emitted from the sensor 32 shown in FIG. 1 and prior art view
FIGS. 2A, 2B, and 2C cover the entire crosssectional area of the
flow tube 24. In this manner, substantially all particulate materials
flowing through the flow tube 24 come in contact with the beam and
thus the reflected Dopplershifted energy picked up by the sensor
32 will be a signal truly representative of the solids flow through
the flow tube 24.
Thus as can be seen in FIG. 2A the noncontact solids flow meter
flow tube and sensor arrangement 12 comprises the material flow
tube 24 having a product inlet 27 and a product outlet 28 and is
attached at an angle 30 to a sensor tube 26 that has a sensor 32
mounted thereon for transmitting the lowenergy microwave beam 34
through a sightglass 36 and across the entire crosssectional area
of the flow tube 24. The angle 30 may vary from about 10.degree.
to 90.degree.. Further the flow tube 24 may be vertical as shown
or at an angle to the horizontal. For example only, the flow tube
24 may be at an angle of 60.degree. to the horizontal. As shown
in the top views 2B and 2C, the top view of a rectangular flow tube
24 and a circular flow tube 24 respectively, the beam 34 from sensor
32 in each case covers the entire crosssectional area of the flow
tube. Thus, the tube 26 holding the sensor 32 is of the same diameter
as the flow tube 24. Note that the sensor 32 in both FIGS. 2B and
2C is located at a distance from the flow tube path such that the
beam width covers the entire diameter or crosssectional area of
the flow tube. In such case, a backreflected Dopplershifted energy
signal is representative of the entire solids flow. It can be seen
then that the sensor 32 must be properly positioned at the right
distance from the centerline of flow tube 24 or the beam 34 will
be too narrow to cover all of the material in the flow tube or will
be so far away that the maximum energy would not be received from
the reflected energy from the flowing material. In each case, the
beam 34 passes through a sightglass 36 to form a noncontact flow
meter.
FIG. 3 discloses a typical sightglass 36 that can be positioned
as shown in FIGS. 2A, 2B and 2C in the sensor tube 26.
FIG. 4 illustrates a calibration circuit 48 containing equipment
set up to calibrate the solids flow meter 52 illustrated in dashed
lines. This flow meter is of the type disclosed in U.S. Pat. No.
5986553 wherein substantially all of the particulate matter can
be illuminated by the radar or high frequency beam. As can be seen
in prior art FIG. 4 solids feed equipment 50 supplies the particulate
solid (mass flow at a constant mass rate to meter 52) through a
duct 51. The flow meter 52 is comprised of the flow tube 12 sensor
32 and industrial computer or smart indicator 58 with the mass
flow from the flow meter 52 passing through duct 60 and weigh scale
62 for measuring the mass rate through the flow meter 52. Sensor
32 output on line 55 is connected to computer 56 that is typically
used to analyze the calibration data and compute an algorithm for
the industrial computer or smart indicator 58 via computer output
57. Usually two, and preferably more than two, mass flow rates and
associated sensor output data are collected and used to determine
an algorithm. Once the calibration procedures have been completed
and the algorithm placed into industrial computer or smart indicator
58 the sensor 32 output is connected at 59 to industrial computer
or smart indicator 58 that contains the algorithm and communication
connections 55 and 57 are not used.
The sensor 32 could be a Granuflow GMR130 microwave solids flow
indicator made by Endress+Hauser or a Model SSI microwave solids
flow indicator by Monitor Manufacturing Company or equivalent. Computer
56 could be a personal computer such as a Gateway 2000 Pentium computer
or equivalent. Industrial computer 58 could be an Allen Bradley
PLC (programmable logic controller) or leukhardt Systems, Inc. industrial
computer or a Contec Microelectronics, Inc. industrial computer
or equivalent. If a smart indicator 58 is used, it could be an Apollo
Intelligent Meter Red Lion Model IMP23107 or equivalent. The weigh
scale 62 could be any typical load cell weight scale or equivalent.
The solids feed equipment 50 could be a hopper with a vibratory
feeder or volumetric feeder by KTrion America used with a rotary
air lock or equivalent. The flow tube 12 has an input that is kept
at a constant distance from the solids feed equipment 50 during
the calibration procedure and is maintained at a fixed or equivalent
value for the final commercial installation.
Thus, after calibration, any particulate solid fed to the flow
meter are indicated by sensor 32 and the sensor output on line 59
is sent to the industrial computer or smart indicator 58 displaying
mass rate (sensor output is converted to mass rate via an algorithm
determined from calibration) and the mass quantity is displayed
by integrating the mass flow rate over time. The sensor 32 has a
keypad 54 connected thereto for entering calibration data. The keypad
is described in U.S. Pat. No. 5550537 which is incorporated herein
by reference in its entirety.
With the equipment of the type as indicated earlier and with the
sensor tube being at a 35.degree. angle from the vertical with respect
to the flow tube as illustrated in FIG. 2A, a vibratory feeder with
variable speed controls may be used to keep a constant mass rate
through the meter 52. The product, as an example only, may be regular
table rolled oats No. 5 ConAgra, Inc., with a bulk density of 25.3828.84
pounds per cubic foot.
The solids feed equipment 50 should be adjusted until a known pounds/hour
of particulate matter such as rolled oats is fed to the flow meter
52 at a constant mass rate such as, for example only, 745.9 pounds/hour.
Sensor 32 is set for amplification by pressing "H" key
on keypad 54 and then the amplification set at coarse adjustment
2 and then the fine adjustments made through keyboard 54 as well
known in the art, until an LED indicates 100% or the maximum of
20 milliamps output from the sensor 32. The sensor is then advanced
to the calibration mode through keypad 54.
With the sensor 32 in the calibration mode, the particulate matter
in flow path 52 is stopped, and with no material flowing to the
flow meter 52 the +/keys on the keypad 54 are adjusted until an
LED on the sensor 32 indicates 0% output or 4.0 milliamps. The "E"
key on the keypad 54 is pressed once and the LED flashes for about
five seconds to accept zero point. Any previous points are also
cleared by pressing the plus (+) and minus () keys simultaneously
and holding for 3seconds.
Next, the feed through conduit 51 is set at the selected pounds/hour
and the plus/minus keys on keypad 54 are adjusted until the LED
displays 100% or 20 milliamps. The "E" key is then pressed
once and the LED flashes for about five seconds. Next, the "H"
key on the keypad 54 is depressed until at damping mode. Then (+)
or () keys are depressed until damping mode is set at two seconds.
Then, the "H" key is pressed until the unit returns to
the run mode. The mass flow through the conduit 51 is then set by
adjusting the solids feed equipment 50 to 727.4 pounds/hour (weigh
scale 62 will indicate pounds collected over the time interval measured
using a stop watch) and the sensor 32 output (milliamps) is measured
on connection 55 to computer 56 for several minutes. This calibration
data point is used to begin a table such as that shown in Table
I. This calibration data point is shown as the first two columns
where the average output from the sensor 32 was 19.21 milliamps
at the constant mass rate of 727.4 pounds/hour. Thus there is a
data pair (mass rate and corresponding sensor output) which in this
case is 727.4/hour and 19.21/milliamps.
This procedure is repeated for another different mass flow rate
to obtain the average output from the sensor 32 corresponding to
the new mass flow rate. Again, a table can be created shown in the
first two columns in Table I for as many data pairs as necessary
to obtain the accuracy desired.
TABLE I Sensor Mass Output Flow (milli Rate amps) (lbs/hr) (mA)
(lbs/hr) 3.90 0. 3.90 0.0 Eq(2) 6.30 62.5 6.00 55.0 Eq(2) 9.34 141.8
8.00 98.6 Eq(1) 11.32 213.7 10.00 161.9 Eq(1) 14.51 357.8 12.00
242.8 Eq(1) 15.08 403.1 14.00 341.9 Eq(1) 16.94 501.8 16.00 460.0
Eq(1) 19.08 681.8 18.00 597.6 Eq(1) 19.21 727.4 20.00 755.2 Eq(1)
20.00 745.9
With that information in the first two columns of Table I, the
data pairs are available (mass rate, sensor output) as necessary
to obtain an accurate function (algorithm) for obtaining data pairs
between these experimental data pairs (interpolation) and beyond
these data pairs (extrapolation). A regression analysis is used
to analyze these data pairs and find a model or algorithm to predict
new values of the dependent variable (mass flow rate) for other
values of the independent variable (milliamps).
From the first two columns, using data pairs with milliamps from
9.34 through 20.00 the value of the constants a and b for the algorithm
or power equation F=aE.sup.b (Y=aX.sup.b) can be determined by simple
regression analysis, which is a wellknown procedure for relating
one dependent variable to one independent variable by minimizing
the sum of the squares of the residuals for the fitted equation
or line. The value for "a" was determined to be a=0.97247476
and "b" was determined to be b=2.22144851. The coefficient
of determination (COD), which is the measure of the fraction of
the total variance accounted for by the model equation was 0.99731366.
Thus, using the power equation (1) F=aE.sup.b with the values of
the constants a and b as described above, a close tit between the
predicted data pairs and the experimental data pairs was found as
shown in Table I between 8 milliamps through 20 milliamps. These
data pairs were then placed into the smart indicator 58 (FIG. 4)
as equation (1) in a manner well known in the art.
Similarly, data pairs including 3.9 milliamps and 11.32 milliamps
(first two columns in Table I) were used with regression analysis
to obtain the constants for algorithm or polynomial equation (2)
F=a.sub.0 +a.sub.1 E+a.sub.2 E .sup.2 +a.sub.3 E.sup.3 +a.sub.4
E.sup.4 (Y=a.sub.0 +a.sub.1 X+a.sub.2 X.sup.2 +a.sub.3 X.sup.3 +a
.sub.4 X.sup.4). The coefficient of determination (COD), which is
the measure of the fraction of the total variance account for by
the equation or model was 1.00000000. This is an excellent fit of
the predicted data pairs and the experimental data pairs as shown
in the third and fourth columns of Table I between 3.9 mA through
6 mA. These data pairs are then placed into the smart indicator
58 (FIG. 4) as equation (2) in a manner well known in the art. The
constants that are determined for equation (2) are as follows: a.sub.0
=110.683736; a.sub.1 =26.1049689; a.sub.2 =1.6799281; a.sub.3 =0.36137862;
and a.sub.4 =0.0205726.
It should be noted that if industrial computer 58 is used in place
of a smart indicator, the actual algorithm (one or more equations
such as equations (1) and (2) derived by linear regression) could
be used directly as a formula by the industrial computer 58 and
not as discrete (separate pairs of data) pairs as required by the
smart indicator. The end result would be a greater degree of accuracy
to be expected from using an industrial computer 58.
In summary, the data pairs in the first two columns of Table I
and obtained from sensor 32 are coupled on line 55 to computer 56
for regression analysis and development of the algorithm, which
is then stored in the industrial computer or smart indicator 58.
The nonlinear results of the sensor output in these tests are shown
in the graph of FIG. 5 that plots sensor output versus mass rate
through the meter. Note that the sensor output is nonlinear.
Once the meter has been calibrated as indicated previously, a test
result utilizing rolled oats is illustrated in the graph of FIG.
6 which compares the meter totalizer reading in pounds versus the
scale reading in pounds. Notice the accuracy of the meter is within
+/0.5% over the entire range.
FIG. 7 is a graph illustrating the results from the calibrated
mass flow meter for "Certa" Product from General Mills,
Inc. The accuracy is +/1.9%. The material being measured had poor
flowability characteristics and it was difficult to maintain constant
mass rates. Thus, the accuracy of +/1.9%.
FIG. 8 is a graph illustrating the accuracy of the calibrated flow
meter measuring Crunch Berries.RTM. from Quaker Oats Company. An
accuracy of +/1.63% was obtained in the upper range and +/2.24%
in the overall range. Only one equation was used to make up the
algorithm, equation (1), and it provided the best fit over a portion
of the range. If more than one equation had been utilized, the accuracy
would have been improved substantially for this case.
FIG. 9 is a graph setting forth the accuracy of the calibrated
flow meter for measuring Life.RTM. Cereal from Quaker Oats Company.
As can be seen, an accuracy of +/0.68% was obtained in the upper
range and +/2.86% in the overall range. Again, only one equation
was used to make up the algorithm. The use of both algorithms (1)
and (2) would provide a much greater accuracy.
Thus, in the flow meter disclosed in U.S. Pat. No. 5986553 the
sensor tube has a diameter at least equal to the flow tube. This
allows the beam to contact the entire crosssectional area of the
flow tube and thus all particulate materials flowing through the
flow tube will come in contact with the beam and cause reflected
energy. The flow tube may be a round, square, or rectangular crosssectional
shape. The signal from the sensor is conditioned by at least one
algorithm to relate the sensor output to mass rate and quantity
(totalizer). The first algorithm is of the power function type F.sub.1
=aE.sup.b (Y.sub.1 =aX.sup.b) where E is the independent variable
(e.g., sensor output in mA), F is the dependent variable (mass rate),
and "a" and "b" are constants obtained from
statistical analysis. The second algorithm or equation is of a polynomial
function of the type F.sub.2 =a.sub.0 +a.sub.1 E+a.sub.2 E.sup.2
+a.sub.3 E .sup.3 +a.sub.4 E.sup.4 (Y.sub.2 =a.sub.0 +a.sub.1 X+a.sub.2
X.sup.2 +a.sub.3 X.sup.3 +a.sub.4 X.sup.4) where, again, E is the
independent variable, F.sub.2 is the dependent variable, and a.sub.0
a.sub.1 a.sub.2 a.sub.3 and a.sub.4 are constants obtained from
statistical analysis. Thus, in one embodiment the algorithm is a
combination of a polynomial function and a power function in order
to correlate the sensor output with the matching mass rates over
the entire range so as to obtain accurate indications of mass rate
and quantity. It is to be understood, of course, that even greater
accuracy could be obtained by utilizing further equations such as
F.sub.3 =ae.sup.bE (Y.sub.3 =ae.sup.bX), where a and b are constants,
F.sub.3 is the mass rate, and E is sensor output in milliamps for
some specific range between 4 to 20 milliamps. Again, the constants
would be determined by regression analysis. Further, an equation
such as F.sub.4 =e.sup.a+bE (Y.sub.4 =e.sup.a+bX), where a and b
are constants, F.sub.4 is the mass rate, and E is the sensor output
in milliamps for some specific range between 4 and 20 milliamps
with the constants being determined by regression analysis from
specific points as set forth earlier. Also F=a+bE (Y=a+bX) could
also be used where E, F, a, and b have the definitions set forth
above.
In the laboratory calibration of a meter of the type discussed
in U.S. Pat. No. 5986553 for a specific material, a fixed or
constant particulate solid rate (mass rate) is passed through the
meter and corresponding sensor output is recorded. This step is
repeated until the mass rates corresponding to the sensor's output
range from 4 to 20 milliamps is determined.
Second, the total output sensor data from 420 milliamps and the
corresponding mass rate data are analyzed mathematically (typically
by regression analysis such as the method of least squares) to determine
which of the mathematical equations (F.sub.1 F.sub.2 F.sub.3
or F.sub.4) best fit the data. One equation may fit the date over
the entire 420 milliamp range accurately or two or more may equations
may be needed to accurately fit the data over the entire range.
Thus, again, as an example, using three equations, the mass rate
F and the sensor output E could be represented over the entire sensor
output range of 420 milliamps by the following algorithm which
uses three equations:
It is understood in the above example that the constants a.sub.01
a.sub.11 a.sub.21 a.sub.31 and a.sub.41 are determined by
mathematical methods such as regression analysis using the mass
rate data and corresponding sensor output data for the sensor output
range from 4.ltoreq.5.6 milliamps: the constants a.sub.12 and b.sub.12
are determined by mathematical methods such as regression analysis
using the mass rate data and corresponding sensor output data for
the sensor output range from >5.6 to .ltoreq.18 milliamps; and
the constants a.sub.13 and b.sub.13 are determined by mathematical
methods such as regression analysis using the mass rate data and
corresponding sensor output data for the sensor output range from
>18.1 to .ltoreq.20.00 milliamps.
The above, of course, is just an example. Many different equations
may be used to obtain a desired algorithm for better accuracy.
Prior art FIG. 10 is a variation of the flow meter disclosed in
U.S. Pat. No. 5986553 that utilizes pneumatic conveying of the
flowable material. In this case, the materials are provided from
hopper 66 through a rotary air lock 68 to a flow tube 70. The pneumatic
conveying gas or vapor inlet at 72 conveys the material through
tube 70 the solids flow meter 12 and the output line 74 to a product
receiver 76. The material in the receiver may be conveyed through
air lock 78 to a product outflow line 80. The pneumatic conveying
gas or vapor may flow out at 82. The sensor 32 in the solids flow
meter 12 operates as described previously. The gas or vapor velocity
used to transport the particulate solid material through a duct
should be nearly the same during the calibration of the flow meter
as it will be for induced conditions under which the meter will
finally operate.
Prior art FIGS. 11A, 11B and 11C disclose the use of two or more
side by side sensors used with the concept disclosed in U.S. Pat.
No. 5986553. In FIG. 11A, a side view of the flow tube is shown
with the beams 8890 being illustrated as one beam inasmuch as they
are parallel and are provided by sensors 84 and 86 only one of
which can be seen in the side view in FIG. 11A.
FIG. 11B is a top view of a rectangular flow tube 24 with two sensors
84 and 86 positioned on the sensor tube 26. Sensor 84 generates
beam 88 and sensor 86 generates beam 90. It will be noted that the
beams 88 and 90 include and overlap area 92. This same overlap area
is illustrated in FIG. 11C which is a top view of a circular flow
tube. Note that the distance of the sensors 84 and 86 from flow
tube 24 is adjusted such that their beams 88 and 90 intersect at
the outer periphery of the flow tube to ensure that the entire flow
tube is covered by the beams 88 and 90. The two sensors 8486 send
out beams 88 and 90 of low microwave energy at the same fixed frequency.
The moving particles reflect the energy beams and thereby the receivers
at the sensors measure the total reflected Dopplershifted energy.
Since the moving particles create a Dopplershifted energy that
is reflected back to the sensors 84 and 86 the sensors 84 and 86
measure the intensity of the total signal reflected back. An average
of the two sensor signals is taken. Thus, the average of the sensors'
output signals is the "E" in equations (1) and (2) (algorithms
1 and 2). Then the two equations F.sub.1 and F.sub.2 could be used
to represent the algorithm. Thus, the average output from the sensors
is mathematically correlated with the total mass rate through the
meter. This is the typical calibration method described earlier
herein using only one sensor output signal. With two or more sensor
outputs, an average value is used or some weighted average mathematical
value of the sensor output signal is used and is correlated with
the mass rate. The onsite adjustment technique discussed above
with respect to FIG. 1 is equally applicable to the embodiment discussed
in FIGS. 10 through 11C.
The calibration technique discussed above with respect to FIGS.
1 and 2A provides an illustration of the excellent and superior
results for most applications and installations. However, it has
been discovered that sensor 32 is extremely sensitive. Further,
some onsite installations require the use of various types of equipment
to move the particulate material away from the flow meter after
being measured. As an example, a screw conveyor may be present at
the bottom of the discharge end of flow tube 24 to move the particulate
material away from flow meter 12. In such installations, the rotational
motion of the screw conveyor may be sensed by sensor 32 as additional
flow of the solid particulate material if the distance 91 between
the sensor tube 26 and discharge end or outlet 28 of flow tube 24
is not of sufficient length. Other types of "machinery motion"
located at the discharge end of the mass flow meter and which may
cause erroneous readings include, but are not limited to, agitators,
rotating shafts and the operation of valves such as slidegate valves,
ballvalves, etc. Although the preferred correction or remedy may
be to increase distance 91 in many installations the physical constraints
of the equipment simply will not permit this. It might be possible
to recalibrate the meter on site rather than at the factory or in
a laboratory, but this would require disrupting the installation
and undesired movement and connection of heavy and expensive equipment
such as scales, etc. A simpler and better method is desirable.
Therefore, according to the present invention, it has been discovered
that although the mass flow rate indicated by a newly installed
meter may be very much in error and appear to be of no value, the
basic algorithm or the basic shape of the performance curve as calibrated
or obtained in the laboratory or at the factory in the manner discussed
heretofore still represents the relative performance of the flow
meter. This means that when the algorithm is adjusted according
to the teachings of this invention a full recalibration is not necessary.
For example, referring now to FIG. 13 and assuming a sensor 32
having a nominal 4 milliamps to 20 milliamps output, there is shown
a flow diagram for an onsite adjustment or recalibration of a mass
flow meter, according to the teachings of this invention. In FIG.
13 data points are obtained during calibration at the laboratory
or at the manufacturing location as indicated at 91. Then, as shown
at step 92 the data points obtained in the laboratory are used
to develop or determine the initial algorithm or performance curve
where flow rate (F) is a function of an electrical signal (E) as
was discussed heretofore. Then, as shown at step 94 the calibrated
flow meter is installed in its working environment. The system is
then operated under working conditions and at a known flow rate
as indicated at step 96. The value of a corresponding electrical
signal corresponding to the known flow rate is then obtained as
shown in step 98. According to various embodiments and as will be
discussed later, the value of the electrical signal may be obtained
by simply reading the flow meter at the known flow rate of zero
to adjust for machinery motion. Alternately in an embodiment for
adjusting due to error caused by dust the correction factor is calculated
from the initial algorithm by using a known positive flow rate (F)
and the previously determined constant coefficients and exponents
to calculate a corresponding electrical signal E. Then a correction
factor is determined by using the obtained electrical signal in
step 98 whether by simply reading the sensor in the case of correcting
for machinery motion or by calculating the electrical signal value
as in the case of correcting for particulate dust, etc. In the embodiment
for correcting for machinery motion and as indicated in step 100
a flow rate correction factor is computed or calculated from the
initial algorithm and the electrical reading obtained in step 98.
In the embodiment for correcting for excessive dust, steps 98 and
100 are essentially the same step, and the correction factor is
the electrical signal E calculated in step 98. Then as shown at
step 102 the adjusted algorithm or performance curve is developed
by subtracting the correction factor from the appropriate parameter
F (for machinery motion correction) or E (for dust correction).
In the embodiment for correcting for machinery motion, the flow
rate correction factor F is subtracted from the indicated flow rate
for each electrical signal value. In the embodiment for correcting
for excessive dust, the obtained electrical signal correction factor
is subtracted from the electrical signal value of the initial algorithm
for each sensor reading and the flow rate for the corrected electrical
signal as indicated by the initial algorithm is used to determine
the correct flow rate.
More specifically and for purposes of explanation, to adjust or
correct the initial algorithm or performance curve for machinery
motion. Table II shows typical calibration points that might be
obtained for a flow meter having a maximum flow rate at some value
somewhat in excess of 5000 lb/hour.
TABLE II Sensor Output Mass Flow Rate (mA) lbs/hour 3.986 0.0 6
585.4 8 1037.3 10 1489.2 12 1976.5 14 2656.0 16 3430.9 18 4299.9
20 5262.3
In the example shown, 20 milliamps was calibrated to represent
about 5262.3 lbs/hour. FIG. 14 is the performance curve or algorithm
developed from the laboratory calibration points. The calibrated
flow meter is then installed in its working location as discussed
above with respect to step 94 of FIG. 13. The system machinery used
to move the solid particulate material away from the flow meter
is then turned on as shown in step 96 of FIG. 13. However, the flow
of particulate material through the meter is blocked, diverted or
simply no material is available. That is, the "known"
flow rate through the flow meter shown at step 96 is zero ("0").
A reading is taken from the flow meter as the machinery, which moves
the particulate material away from the discharge end of the flow
meter, continues to operate with the known zero flow rate and is
the obtained corresponding electrical signal of step 98 of FIG.
13. Then at step 100 a flow rate (F) correction factor is determined
by referring to the initial algorithm. At step 102 an adjusted algorithm
or performance curve is developed using the correction factor performance
curve of FIG. 14. In this embodiment or as also indicated in Table
II, the flow rite indicated for 14 milliamps corresponds to a 2656.1
lbs/hour correction factor as indicated by the intersection of line
102 of FIG. 14 with the vertical (or mass flow rate lbs/hour) coordinate
104. This flow rate value is then used to develop a corrected performance
curve or algorithm by subtracting the correction factor 2656.1 lbs/hour
from the mass flow rate indicated by the original algorithm or performance
curve shown in FIG. 14 at each milliamp value. Table III shows the
milliamp readings and the corresponding adjusted mass flow rate,
and FIG. 15 illustrates the resulting or adjusted performance curve
as developed at block 102 of FIG. 13.
TABLE III Sensor Output Mass Flow Rate (mA) (lbs/hour) 3.986 0.0
14000 0.0 14500 184.8 15000 375.6 16000 774.8 17000 1197.6
18000 1643.9 19000 2413.4 20000 2606.2
In addition to correcting for erroneous mass flow readings due
to the motion of machinery, the present method has also been found
to be effective in correcting for errors resulting from other "motion"
sensed by the sensor 32 which is not from the flow of the solid
particulate material being measured. For example, it has also been
discovered that the basic shape of the performance curve or algorithm
generated under laboratory conditions is representative of the actual
performance of the flow meter of FIGS. 1 and 10 even though the
absolute values of the indicated mass flow rates are not even close
to being accurate. More specifically, during the laboratory calibration
of a flow meter to be used with Green Oats, there was a significant
amount of oats dust. This dust was sensed as motion and resulted
in an erroneous calibration of the mass flow rate as indicated by
the milliamp output reading of sensor 32. Thus, the mass flow rate
indicated by a particular milliamp reading on the calibrated performance
curve was significantly greater than the actual mass flow rate occurring
during calibration. This error was discovered when the flow meter
was installed in its working environment and tested under operating
conditions. The working environment included equipment which eliminated
or reduced the oats dust to a level substantially less than was
experience at the laboratory. Consequently, the actual mass flow
rate was substantially greater than that indicated by the initial
algorithm or performance curve when referenced against a specific
milliamp reading from sensor 32.
Referring now to FIG. 16 there is shown (by circles) the indicated
total weight of Green Oats delivered per day by a system using the
"calibrated" mass flow meter. The square data points indicate
the actual total weight per day. The indicated values from the flow
meter are seen to be less than 1/4 of the actual values. Such erroneous
readings without correction would of course be unacceptable. Thus,
as was discussed above, one of the data points indicating actual
flow rate per hour was used in the original algorithm to calculate
the corresponding electrical signal used as the correction factor.
The adjusted or correction procedure discussed above with respect
to FIG. 13 when applied to the oats dust situation also provided
an extremely accurate adjustment. FIG. 17 shows how closely the
readings correspond to the actual readings once the adjustment procedure
of the present invention is applied to the original (although erroneous)
calibration curve. FIG. 18 shows the performance curve 116 representing
the initial algorithm and the performance curve 118 after being
adjusted according to the teachings of this invention.
Thus, there has been disclosed a compensation technique for correcting
readings from a Dopplerradar flow meter wherein the sensor beam
covers the entire crosssectional area of the flow tube in order
that all particulate materials flowing through the flow tube will
come in contact with the beam and provide reflected Dopplershifted
energy.
The corresponding structures, materials, acts, and equivalents
of all means or step plus function elements in the claims below
are intended to include any structure, material, or act for performing
the function in combination with other claimed elements as specifically
claimed.
