Abstrict A non-contact solids flow meter for measuring solid particulate
flow is comprised of a flow tube, a sensor, and an indicator. The
product enters the flow tube at one end and flows downward by gravity
past the sensor and then exits the flow tube at the bottom. The
sensor is placed in a sensor tube at an angle to the flow of particulate
solids. As the product passes the sensor signal (low microwave energy),
this energy upon contacting the particulates undergoes a Doppler
shift which is detected by the sensor. The width of the sensor beam
has to be at least the diameter of the flow tube so that it covers
the entire cross-sectional area of the flow tube. In this manner,
all particulate materials flowing through the flow tube come in
contact with the beam and are thus reflected. The instrument is
calibrated and algorithms determined from the calibration to cause
the indicator to provide a best fit function over the output range
of the indicator.
Claims What is claimed is:
1. A flow meter for measurement of the mass flow rate of solid
particulate matter comprising:
a first hollow conduit forming a flow path along which the solid
particulate matter moves;
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 associated with said second hollow conduit,
said at least one sensor including:
a transmitter of electromagnetic energy for radiating the entire
particulate matter flow path formed by said first conduit such that
substantially all of the particulate matter contributes to and forms
back scattered energy;
a receiver for receiving said backscattered energy and generating
an electrical signal that is proportional to the concentration of
solid particulate matter flowing in said first hollow conduit; and
processor means coupled to said at least one sensor for generating
an output signal representative of said concentration of solid particulate
matter.
2. A flow meter as in claim 1 wherein said solid particulate matter
flows past said sensor at a substantially constant velocity for
purpose of calibration.
3. A flow meter as in claim 2 further comprising a source of said
particulate matter located a predetermined distance above said sensor
for achieving said substantially constant velocity by gravity flow.
4. A flow meter as in claim 2 further comprising a source of pneumatic
pressure coupled to said first conduit for conveying said particulate
matter past said sensor at said substantially constant velocity.
5. A flow meter as in claim 1 further comprising a sightglass interposed
in said second hollow conduit between said sensor and said particulate
matter to form a non-contact flow meter.
6. A flow meter as in claim 1 wherein said second conduit is joined
to said first conduit at an angle from the vertical in the range
of about 10.degree. to about 90.degree..
7. A flow meter as in claim 6 wherein the preferred angle between
said first and second conduits is in the range of about 10.degree.to
about 35.degree..
8. A flow meter as in claim 1 wherein the receiver is a Doppler
receiver that measures the frequency difference between the transmitted
energy and that scattered energy received from the moving particulate
matter.
9. A flow meter as in claim 1 wherein the electrical signal generated
by said receiver is a non-linear signal.
10. A flow meter as in claim 9 wherein said non-linear electrical
signal generated by said receiver is in milliamps.
11. A flow meter as in claim 9 wherein said non-linear electrical
signal generated by said receiver is in volts.
12. A flow meter as in claim 10 wherein said processor means converts
said milliamps signal into a pounds/hour mass flow rate.
13. A flow meter as in claim 1 wherein said processor means includes
memory means for storing a first algorithm for converting the signal
generated by said receiver in a first range of values to a pounds/hour
mass flow rate and storing a second algorithm for converting the
signal generated by said receiver in a second continuous range of
values to a pounds/hour mass flow rate to enhance accuracy of the
flow meter.
14. A flow meter as in claim 13 wherein said first algorithm has
the form of Y=aX.sup.b, where Y=pounds/hour, X=milliamps, and a
and b are constants and said second algorithm has the form of 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=pounds/hour, X=milliamps, and a.sub.0 a.sub.1 a.sub.2 a.sub.3
and a.sub.4 are constants.
15. A flow meter as in claim 14 wherein said processor means is
an industrial computer.
16. A flow meter as in claim 15 further including a central processing
unit coupled between said receiver and said industrial computer
for calculating said constants for said first and second algorithms
for use by said industrial computer.
17. A flow meter as in claim 14 wherein said processor means comprises:
a central processing unit for calculating said constants for said
first and second algorithms and generating said mass flow rate in
pounds/hour; and
converting means in said central processing unit for converting
said mass flow rate to total pounds.
18. The flow meter of claim 1 wherein said at least one sensor
includes:
first and second sensors associated with said second conduit, each
of said sensors comprising:
a transmitter of electromagnetic energy for radiating at least
a first portion of the particulate matter flow path to cause backscattered
energy;
an associated receiver for receiving the backscattered energy from
its associated transmitter; and
said processor means being coupled to both said first and second
sensors for generating an output signal representative of the concentration
of said particulate matter.
19. The flow meter as in claim 1 wherein said processor means includes
memory means for storing at least one algorithm for converting the
signal generated by said receiver into a continuous range of values
to a pounds-per-hour mass flow rate.
20. A method of measuring mass flow rate of a solid particulate
matter comprising the steps of:
conveying the particulate matter through a first hollow conduit;
transmitting electromagnetic energy through a second hollow conduit
attached to said first hollow conduit at an angle;
said second hollow conduit having at least the same diameter as
the first hollow conduit;
radiating substantially all of said particulate matter in said
first conduit as it passes said second hollow conduit to form a
signal from backscattered electromagnetic energy;
receiving said backscattered energy signal from said particulate
matter; and
converting said received backscattered energy signal to mass flow
rate in pounds/hour.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to flow measurement of particulate
streams and in particular to a Dopplar flow meter and method for
flow measurement of particulate streams.
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 non-contact 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 non-contact flow meter. For example, with food and pharmaceutical
manufacturing, a truly non-contact solids flow meter obtains measurements
without any contamination of the process since, being a non-contact
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 non-intrusive 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 U.S. Pat. No. 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.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of the prior
art by providing a non-contact mass flow meter for measuring the
flow of particulate streams through ducts, chutes, or pipes utilizing
a Doppler-radar sensor, a unique flow tube, a flow rate and totalizer
indicator, and an algorithm to convert the mass flow rate signal
to total mass flow rate. In the present invention, 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 the preferred embodiment, 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, a source of pneumatic pressure
is coupled to the first conduit for conveying the particulate matter
past the sensor at the substantially constant velocity.
In order to form a non-contact flow meter, a sightglass is interposed
in the second hollow conduit between the sensor and the particulate
matter. The electrical signal generated by the receiver is a non-linear
signal measured in either milliamps or volts. The processor converts
the milliamp or volt signal into a pounds-per-hour 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 pounds-per-hour mass flow rate. In the preferred
embodiment, the memory stores a first algorithm for converting a
signal generated by the receiver in a first range of values to a
pounds-per-hour 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 pounds-per-hour mass flow rate to enhance accuracy
of the flow meter.
In the preferred embodiment, the first algorithm has the form of
Y=aX.sup.b, where Y=pounds/hour, X=mllliamps (volts), and a and
b are constants and the second algorithm has the form of 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=pounds/hour, X=milliamps, and a.sub.0 a.sub.1 a.sub.2 a.sub.3
and a.sub.4 are constants.
The processor may be an industrial computer or a smart indicator.
Further, a central processing unit, which may be a personal computer
or equivalent, 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 pound-per-hour. It further may have a converting
means in the central processing unit for converting the mass flow
rate to total pounds.
In still another embodiment, first and second sensors may be associated
with the second conduit with the processor being coupled to both
the first and second sensors for generating an output signal that
is representative of the concentration of the particulate matter
and, therefore, that is related to mass flow rate.
Thus, the present invention relates to a flow meter for measurement
of the mass flow rate of solid particulate matter comprising a first
hollow conduit forming a flow path along which the solid particulate
matter flows, a second hollow conduit having at least the same diameter
as the first conduit, one of the conduits being joined to the other
conduit at an angle, at least one sensor associated with the second
hollow conduit, at least one sensor including 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
for receiving the backscattered energy and generating an electrical
signal that is proportional to the concentration of solid particulate
matter flowing in the first hollow conduit, and a processor coupled
to the at least one sensor for generating an output signal representative
of the concentration of the solid particulate matter.
The invention also relates to a method of measuring mass flow rate
of a solid particulate matter comprising the steps of conveying
the particulate matter through a first hollow conduit, transmitting
electromagnetic energy through a second hollow conduit attached
to the first hollow conduit at an angle, and having at least the
same diameter as the first hollow conduit, radiating substantially
all of the particulate matter in the first conduit as it passes
the second hollow conduit to form a signal from backscattered electromagnetic
energy, receiving the backscattered energy signal from the particulate
matter and converting the received backscattered energy signal to
mass flow rate in pounds-per-hour.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features of the present invention will be more
filily 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 diagrammatic representation of a typical flow meter
application for the non-contact mass flow meter of the present invention
in a gravity flow application;
FIG. 2A is a side view of a typical flow tube and attached sensor
tube;
FIG. 2B is a top view of the rectangular flow tube with the sensor
tube attached;
FIG. 2C is a top view of a circular flow tube with a sensor tube
attached;
FIG. 3 is a cross-sectional view of a typical sightglass that could
be used with the present invention;
FIG. 4 illustrates the equipment necessary to calibrate the solids
flow meter of the present invention;
FIG. 5 is a graph of mass rate through the meter in pounds-per-hour
versus sensor output in milliamps illustrating the original non-linear
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, re-mill stream;
FIG. 10 is a diagrammatic representation of a typical pneumatic
conveying non-contact 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; and
FIG. 11C is a top view of a circular flow tube utilizing two sensors.
FIG. 12 is a flow chart illustrating th method of detecting the
particulates according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
FIG. 1 shows a typical flow meter application for the non-contact
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 masses 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 low-energy microwave
beam emitted from the sensor 32 shown in FIG. 1 and FIGS. 2A, 2B,
and 2C cover the entire cross-sectional 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 Doppler-shifted 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 non-contact 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 low-energy microwave beam 34
through a sightglass 36 and across the entire cross-sectional 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 cross-sectional 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 cross-sectional area of
the flow tube. In such case, a back-reflected Doppler-shifted 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 non-contact 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. Note in
FIG. 2C that the sightglass 36 may be positioned at any place along
beam 34 such as at 36', so long as it passes the entire beam 34.
The sightglass 36 is mounted between brackets 38 and 40 that are
held together by bolts and nuts 42 and 44. Sightglass 36 is well
known in the art and may be of a type entitled Series NW available
in different diameters and different types of mountings.
FIG. 4 illustrates a calibration circuit 48 containing equipment
set up to calibrate the solids flow meter 52 illustrated in phantom
lines. This flow meter may be of the type disclosed in U.S. Pat.
5550537 except that the flow tube and the sensor tube have the
same diameter so that substantially all of the particulate matter
can be illuminated by the radar or high frequency beam. As can be
seen in 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 IMP23-107 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 K-Tron 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. 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 was used to keep a constant mass rate to
the meter 52. The product, as an example, was regular table rolled
oats No. 5 ConAgra, Inc., with a bulk density of 25.38-28.84 pounds
per cubic foot.
The solids feed equipment 50 was adjusted until a known 745.9 pounds/hour
of rolled oats was being fed to the flow meter 52 at constant mass
rate. The sensor 32 was 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 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 feed in flow path
52 was stopped. With no material flowing to the flow meter 52 the
+/-keys on the keypad 54 were 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 3-seconds.
Next, the feed through conduit 51 is set at 745.9 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 (millilamps) 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 Rate (milliamps) (lbs/hr) (mA) (lbs/hr) ______________________________________
3.90 0. 3.90 0.0 Eq(2) 6.30 6.00 Eq(2) 9.34 8.00 Eq(1) 11.32 10.00
161.9 Eq(1) 14.51 12.00 242.8 Eq(1) 15.08 14.00 341.9 Eq(1) 16.94
16.00 460.0 Eq(1) 19.08 18.00 597.6 Eq(1) 19.21 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 Y=aX.sup.b can be determined by simple regression
analysis, which is a well-known 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) Y=aX.sup.b with the values of the constants
a and b as described above, a close fit between the predicted data
pairs and the experimental data pairs was found as shown in Table
I between 8 miluliamps 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)
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 non-linear 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 non-linear.
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 present flow meter, the sensor tube must have a diameter
at least equal to the flow tube. This will allow beam to contact
the entire cross-sectional 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 cross-sectional 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 Y.sub.1 =aX.sup.b where X is the independent
variable (sensor output in mA), Y 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 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, X is the
independent variable, Y.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
Y.sub.3 =ae.sup.bX, where a and b are constants, Y.sub.3 is the
mass rate, and X 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 Y.sub.4 =e.sup.a+bX
could also be utilized, where a and b are constants, Y.sub.4 is
the mass rate, and X 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 Y=a+bX could also be used where X, Y, a, and b have
the definitions set forth above.
First, for example, in calibrating the meter 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 4-20 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 (Y.sub.1 Y.sub.2 Y.sub.3
or Y.sub.4) best fit the data. One equation may fit the date over
the entire 4-20 milliamp range accurately or two or more equations
may be needed to accurately fit the data over the entire range.
Thus, again, as an example, using three equations, the mass rate
Y and the sensor output X could be represented over the entire sensor
output range of 4-20 milliamps by the following algorithm which
uses three equations:
______________________________________ Y = a.sub.01 + a.sub.11
X + a.sub.21 X.sup.2 + a.sub.31 X.sup.3 + a.sub.41 X.sup.4 (for
the sensor output range X from 4 to .ltoreq.5.6 milliamps) Y = a.sub.12
X.sub.2.sup.b12 (for the sensor output range X.sub.2 from >5.6
to .ltoreq.18.1 milliamps) Y = a.sub.13 e.sup.b13 X3 (for the
sensor output range X.sub.3 from >18.1 to .ltoreq.20 ______________________________________
milliamps).
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.18.1 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.
FIG. 10 is a variation of the present flow meter 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
out-flow 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.
After understanding the above, it is logical that one could use
two or more sensors side-by-side and adjust the distance between
the sensors and the distance from the sensors to the flow tube and
therefore cover the entire cross-sectional area of the flow tube.
Thus, two or more sensors could be used with this concept. Such
a concept with two sensors is illustrated in FIGS. 11A, 11B, and
11C. In 11A, a side view of the flow tube is shown with the beams
88 90 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 84 86 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 Doppler-shifted energy.
Since the moving particles create a Doppler-shifted 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 "X" in equations (1) and (2) (algorithms
1 and 2). Then the two equations Y.sub.1 and Y.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.
Thus, there has been disclosed a novel Doppler-radar flow meter
wherein the sensor tube is at least the same diameter as the flow
tube so that the sensor beam can cover the entire cross-sectional
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 Doppler-shifted energy. In addition, from the generation
of actual flow rates versus sensor output signal (in milliamps or
volts or in a converted digital readout) one or more equations can
be used to determine a best fit so that the smart indicator can
determine an accurate flow rate through the meter. The constants
in the equations are determined by regression analysis in a well-known
manner. Further, two or more sensors can be used if desired to obtain
even further accuracy.
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. |