SOLID MATERIALS FLOW RATE MEASUREMENT

DEBITMETRIE D'UN ECOULEMENT DE POUDRES OU OU DE GRANULATS

English Abstract

ABSTRACT OF THE DISCLOSURE
A flow gauge for measuring the mass flow rate of freely
flowing material, falling through a path, said flow
gauge comprising a pair of sensors spaced longitudinally
along the chute, the sensors being connected to a computing
means for receiving the output of each sensor, where said
output is a measure of the density of the flow at the
location the sensor, the computing means utilising the
output of the sensors to provide a measure of the mass
flow rate, said sensors comprising a radiation source and
a radiation detector in opposed relation to the source and
on the other side of the flowing material from the detector,
for detecting the radiation passing through the flowing
material.

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A method of measuring the mass flow rate of a
freely flowing material flowing under the force of gravity
through a path of predetermined crossectional area
comprising the steps of measuring the mass density of flow
at a first sensing location, measuring the mass density of
flow at a second sensing location spaced a predetermined
vertical distance below said first sensing location and
computing the mass flow rate of the material from the
measurements thus obtained.
2. A method as set forth in claim 1 wherein the
measurement of density as each point is made by a radiation
source and a radiation detector in opposed relation to the
source and on the other side of the flowing material from
the detector for detecting the radiation passing through the
flowing material.
3, A method as claimed in claim 1 including the step
of determining a transmission factor by taking a ratio of
the measure of the output of the detection obtained during
no flow and a measure obtained during flow to obtain a
density measure of the material flow at each sensing
location,
4. A method as claimed in claim 2 wherein the density
measure is derived from the equation <IMG>
where "d" represents the area density of the flow, "T"
represents the transmission factor, and "a" represents the

the crossectional area of the path.
5. A method as claimed in claim 3 wherein the density
measure is utilized to derive a measure of the velocity at
the upper sensing location and where the measure of the mass
flow rate is determined by the following equation R = V x d
x W where "R" represents the mass flow rate, "V" represents
the velocity of the flow rate at the upper sensing location,
"d" represents the area density of the flow, and "W"
represents the width of the flowing material.
6. A method as claimed in claim 5 wherein the
velocity measure of the material flow at the highest sensing
location encountered by the material flow is derived from
the equation
<IMG>
where "g" represents the constant gravitational acceleration
applied to the flow, "s" represents the distance between the
sensing locations, and "d1" and "d2" represent respectively
the measure of density obtained at the upper and lower
sensing locations.
7. A method for measuring the mass flow rate of
particulate material falling freely through a chute
comprising the steps of measuring the density of flow at
each of two locations spaced longitudinally along the chute
by means of a radiation source and a radiation detector

mounted to the chute in opposed relation on either side of
the flow of particulate material, measuring the density
during a "no flow" and "a flow" state in the chute and for
deriving a measure of density at the location of the sensor,
said measure of density being determined by
<IMG>
(where "d" represents the area density of flow, "N" and "No"
represents the measurement under "flow" and "no flow" states
and "a" represents the crossectional area of the path) and
using the measure of density at each location to determine
the velocity of the flow at one or the other location by
<IMG>
(where "g" represents the gravational acceleration constant
"s" represents the spacing between the location, and "d1"
and "d2" represent respectively the measure of density
obtained at the upper and lower locations respectively) and
the velocity is utilised to determine the mass flow rate by
R = V x d x W (where"d" represents the area density at the
location at which the velocity has been calculated, and "W'
represents the width of the flowing material).
8. A method as claimed in claim 1 wherein the
measurement indication of material flow is submitted to a
series of tests to verify the reliability.
11

9. A method as claimed in claim 8 wherein said
verification tests comprise ensuring the measure falls
within predetermined upper and lower limits to verify that
there is in fact material flow and the radiation source is
operative.
10. A method as claimed in claim 8 wherein said
verification tests comprise testing the measure for any
consistent variation over a period of time to verify the
reliability of the measure obtained during no material flow.
11. A method as claimed in claim 10 including the step
of periodically interrupting the material flow to obtain a
fresh measurement during no material flow, in the event of
the previous measurements for no material flow being
determined as unreliable.
12. A method as claimed in claim 1 or claim 7 wherein
the the output sensoring locations is subjected to a
mathematical equivalent to a conventional electronic filter
to account for the existence of noise in the output, but
where the mathematical equivalent is adjusted according to
the rate of flow of the material.
13. A method as claimed in claim 1 or claim 7 wherein
said radiation source is a radioactive isotope.
14. A method as claimed in claim 1 or claim 7 wherein
said radiation is a radioactive isotope and further
including the step of collimating the emissions from the
source to a direction substantially towards the detector,
12

and using a shutter to control the emission of radiation
from the source through the collimator.
15. A method as claimed in claim 1 further including
the step of directing a pressurized fluid across to inhibit
the collection of material on the detection face.
16. A method as claimed in claim 1 wherein the
measurement indications of material flow are submitted to a
series of tests to verify the reliability.
17. A method as claimed in claim 8 wherein said
verification tests comprise ensuring the measure falls
within predetermined upper and lower limits to verify that
there is in fact material flow and the radiation source is
operative.
18. A method as claimed in claim 8 wherein said
verification tests comprise testing the measure for any
consistent variation over a period of time to verify the
reliability of the measure obtained during no material flow.
19. A method as claimed in claim 10 including the step
of periodically interrupting the material flow to obtain a
fresh measurement during no material flow, in the event of
the previous measurements for no material flow being
determined as unreliable.
20. A method as claimed in claim 19 wherein the
velocity measure of the material flow at the highest sensing
location encountered by the material flow is derived from
13

the equation:
<IMG>
where "g" represents the constant gravitational acceleration
applied to the flow," s" represents the distance between the
sensing locations, and "d1" and "d2" represent respectively
the measure of density obtained at the highest and lowest
sensing location.
21. A method for measuring the mass flow rate of
particulate material falling freely through a chute
comprising the steps of measuring the density of flow at
each of two locations spaced longitudinally along the chute
by means of a radiation source and a radiation detector
mounted to the chute in opposed relation on either side of
the flow of particulate material, measuring the density
during a no flow and a flow state in the chute and for
deriving a measure of density at the location of the sensor,
said measure of density being determined by
<IMG>
(where "d" represents the area density of flow, "N" and "No"
represents the measurement under flow and no flow states and
"a" represents the crossectional area of the path) and using
the measure of density at each location to determine the
velocity of the flow at one or the other location by:
<IMG>
(where "g" represents the gravitational accelaration
constant, "s"
11

represents the spacing between the location, and "d1" and
"d2" represents respectively the measure of density obtained
at the highest and lowest locations) and the velocity is
utilized to determine the mass flow rate by R = V x d x W
("d" represents the area density at the location at which
the velocity has been calculated, and "W" represents the
width of the flowing material).
22. A method as claimed in claim 13 further including
the step of collimating the emissions from the source to a
direction substantially towards the detector, and using a
shutter to control the emission of radiation from the source
through the collimator.
23. A method as claimed in claim 7 further including
the step of directing a pressurized fluid across to inhibit
the collection of material on the detection face.
24. A flow gauge for measuring the mass flow rate of
freely flowing material, falling through a path, of
predetermined cross section said flow gauge comprising a
pair of sensors spaced longitudinally along the path, the
sensors being connected to a programmable computing means
for receiving the output of each sensor, where said output
is a measure of the area density of the flow at the location
of the sensor, the computing means operating on the output
of the sensors to provide a measure of the mass flow rate,
said sensors comprising a radiation source and a radiation
detector in opposed relation to the source and on the other
side of the flowing material from the detector, for
detecting the radiation passing through the flowing
material.

25. A flow gauge as claimed in claim 24 wherein means
are associated with the gauge to indicate a flow of material
through the path, and said programmable computing means
determines a ratio of the measure of the output of the
sensor obtained during no flow and a measure obtained during
flow to obtain a density measure of the material flow at the
location of each sensor, said ratio being termed the
transmission factor.
26. A flow gauge as claimed in claim 25 wherein the
density measure is derived from the equation <IMG>
where "d" represents the area density of the flow, "T"
represents the transmission factor, and "a" represents the
crossectional are of the path.
27. A flow gauge as claimed in claim 25 wherein the
density measure at both sensors is operated on and by the
computing means to derive a measure of the velocity at the
location of the sensors and where the measure of the mass
flow rate is determined by the following equation
R = V x d x W where "R" represents the mass flow rate, "V"
represents the velocity of the flow rate at one sensor, "d"
represents the area density of the flow at said one sensor,
and "W" represents the width of the flowing material at said
one sensor.
28. A flow gauge as claimed in claim 26 wherein the
density measure at both sensors is operated on and by the
computing means to derive a measure of the velocity at the
location of the sensors and where the measure of the mass
16

flow rate is determined by the following equation
R = V x d x W where "R" represents the mass flow rate, "V"
represents the velocity of the flow rate at one sensor, "d"
represents the area density of the flow at said one sensor,
and "W" represents the width of the flowing material at said
one sensor.
29. A flow gauge as claimed in claim 25, 26 or 27
wherein the velocity measure of the material flow at the
first sensor encountered by the material flow is derived
from the equation
<IMG>
where "g" represents the constant gravitational acceleration
applied to the flow, "s" represents the spacing between the
sensors, and "d1" and "d2" represent respectively the
measure of density obtained from the output of the upper
sensor and the lower sensor.
30. A flow gauge as claimed in claim 28 wherein the
velocity measure of the material flow at the first sensor
encountered by the material flow is derived from the
equation
<IMG>
where "g" represents the constant gravitational acceleration
17

applied to the flow, "s" represents the spacing between the
sensors, and "d1" and "d2" represent respectively the
measure of density obtained at the upper and lower sensors.
31. A flow gauge for measuring the mass flow rate of
particulate material falling freely through a path of
predetermined cross section, said flow gauge comprising a
pair of sensors spaced longitudinally along the path and
being connected to a programmable computing means said
sensors comprising a radiation source and a radiation
detector mounted in the path in opposed relation on either
side of the flow of particulate material, said sensors
providing an output during a no flow and a flow state in the
path and the programmable computing means determines from
the output of each sensor under "flow" and "no flow"
conditions a measure of density at the location of the
sensor, said measure of density being determined by
<IMG>
(where "d" represents the area density of flow, "N" and "No"
represent the sensor output under "flow" and "no flow"
states and "a" represents the crossectional area of the
path) and wherein the measure of density at each sensor
location is utilized to determine the velocity of the flow
at one or the other sensor by
<IMG>
(where "g" represents the gravitational acceleration
constant, "s"
18

represents the spacing between the sensors, and "d1" and
"d2" represent respectively the measure of density obtained
at the upper and lower sensors) and the velocity is operated
on to determine the mass flow rate by R = V x d x W (where
"d" represents the area density at the sensor location at
which the velocity has been calculated, and "W" represents
the width of the flowing material).
32. A flow gauge as claimed in claim 31 wherein means
are associated with the gauge to indicate a flow of material
through the path, of predetermined cross section and said
programmable computing means determines a ratio of the
measure of the output of the sensors obtained during "no
flow" and a measure obtained during flow to obtain a density
measure of the material flow at the location of each sensor,
said ratio being termed the transmission factor.
33. A flow gauge as claimed in claim 24, 25 or 26
wherein the output of the sensors, obtained when the means
to indicate material flow indicates such flow, is tested to
verify the reliability of the output.
34. A flow gauge as claimed in claim 24, 25 or 26
wherein the output of the sensors, obtained when the mean
to indicate material flow indicates such flow, is tested to
verify the reliability of the output wherein said tests on
the output comprise ensuring the measure falls within
predetermined upper and lower limits to verify that there is
in fact material flow or non-flow or the radiation source is
operative.
19

35. A flow gauge as claimed in claim 24, 25 or 26
wherein the output of the sensors, obtained when the means
to indicate material flow indicates such flow, is tested to
verify the reliability of the output, said tests on the
output comprise testing the measure for any consistent
variation over a period of time to verify the reliability of
the measure obtained during no material flow.
36. A flow gauge as claimed in claim 24, 25 or 26
wherein the output of the sensors, obtained when the means
to indicate material flow, indicates such flow, is tested to
verify the reliability of the output, said tests on the
output comprise testing the measure for any consistent
variation over a period of time to verify the reliability of
the measure obtained during no material flow said
programmable computing means can interrupt the material flow
to obtain a fresh output of the sensors during no material
flow, in the event of the previous output for no material
flow being determined as unreliable.
37. A flow gauge as claimed in claim 24, 25 or 26
wherein said radiation source is a radioactive isotope.
38. A flow gauge as claimed in claim 24, 25 or 26
wherein said radiation source is a radioactive isotope
provided with a collimator to limit the emissions from the
source to that directed substantially towards the detector,
and a shutter to control the emission of radiation from the
source through the collimator.
39. A flow gauge as claimed in claim 24, 25 or 26

wherein the opposed faces of the source and the detector has
associated therewith an outlet of pressurized fluid directed
onto the respective faces to inhibit the collection of
material on the detection face.
40. A flow gauge as claimed in claim 31 or 32 wherein
the opposed faces of the source and the detector have
associated therewith an outlet of pressurized fluid directed
onto the respective faces to inhibit the collection of
material on the detection face.
41. The flow gauge as claimed in claim 24, 25 or 26
wherein the path is substantially vertical.
42. The flow gauge as claimed in claim 31 or 32
wherein the path is substantially vertical.
21

Description

1~3~97~
This invention relates to the measurernent of ~low
rate of materials.
In the processing, or handling or loading of
particulate materials such as ores and grains, it is usually
necessary at some stage to measure the flow rate of
material. Existing metllods o carrying out this function
involves the use of some type of gauge or weighing clevice
placed over or otherwise used in conjuction with moving
belts on which the material is being conveyed. There are
several factors which limit the accuracy of these clevices
and they cannot be used where there is no conveyor belt or
where the working area is very confined.
It is an object of this invention to measure the
flow rate of particulate material flowing under the
influence of gravity from a chute feeder or like outlet.
The term particulate materlal may refer to
material composed of homogenous material of substantially
uniform particle size andjor dellsity or it may reEer to
heterogeneous material of differing particle size and/or
density, or any combination of such parameters. In addition
the material may be fluidised or in a slurry form.
In one form the invention resides in a flow gauge
for measuring the mass flow rate of freely flowing material,
falling through a path, said flow gauge comprising a pair of
sensors spaced longitudinally along the chute, the sensors
bein~ connected to a computing means for receiving the
output o~ each sensor, where said OUtp-lt is a measure of the
density of the flow at the location of the sensor, the
computin~ means utilising the output o~ the sensors to
provide a meas~lre o~ the mass flow rate, said sensors
comprising a radiation source and a radiation detector in
opposed relation to the source and on the other side of the
- 2 - ~ }

3l~Z3~7~
~lown~3 matcriclJ. Erom the detector, ~or de~tccting the
radiation passing throucJh the ~lowing material.
In another Eorm, the invention resides in a flow
gauge for measuring the mass Elow rate of particulate
material falling freely through a chute, said flow gauqe
comprising a pair of sensors spaced longitudinally along the
chute and being connected to a computing means, said sensors
comprising a radlatlon source and a radiation detector
mounted to the chute in opposed relation on either side of
the flow of particulate material, said sensing means
providing an output during a no flow and a flow state in the
chute and the computing means determines from the output of
each sensor under flow and no flow conditions a measure of
density at the location oE the sensor, said measure of
density being determined by
N
log No
d = --____
("d" represents the area density of flow, "N" and "No"
represents the sensor output under flow and no flow states
and "a" represents the area of the cross sectional area of
falling material) and wherein the measure of density at each
sensor location is utilised to determine the velocity of the
flow at one or the other sensor by
V = 1 2gs
I dl -1
\ ~12
("g" represents the gravitational accelleration constant,
"s" represents the spacing between the sensors, and "dl" and
"d2" represent the measure of density obtained from the two
sensors respecitvely) and the velocity is utilised to
determine the mass flow rate by
R = V x d x W
-- 3 --

`-``` ~3LZ3~
( d re~)re;ents the area density at the sensor location at
which the velocity has been calcuLated and W represents the
width o~ the Elowing mat:erial).
The invention will be more fully understood int he
light of the following description of one speciEic
embodiment. The description is macle with reEerence to the
accompanying drawings of which:
Figure 1 is a sectional elevation of a flow path
of ore showing the source and detectors of the embodiment;
and
~igure 2 is a sectional plan of the flow path of
Figure 1 along line A A.
The embodiment as shown in the drawings comprises
two grammaradiation sources 11 or csl37 which are fixed to
the side wall of the chute 13. Suitable radiation shielding
is provided around the source 11 other than the opening
which is directed in line with the diametric axis of the
chute and is provided with a shutter (not shown) to
selectively permit the excape of the radiation. Suitable
collimation means 15 is associated with the aperture such as
to reduce any scatter radiation from the source such that
any radiation emitted therefrom is substantially in line
with the diametric axis of the chute. The detectors 17 are
disposed on the diametrically opposed side of the chute 13
from the source 11 such as to receive the peak radiation
from the opposed source 11 and each detector is set to
detect the characteristic energy radiation of the csl37
source (i.e. 0.662MeV~. The emission face of each
collimator 15 is associated with an air outlet 19 which is
in communication with a source of compressed air. The
outlet is located such as to prevent material flowing past
the emission face of the collimator from coming in contact

L123~7;~
with the face arld adhering thereto. Similar compressed air
outlets 21 arc associat(d with each detector to maintain the
collection face of each detector substan~ially clear of
deposits.
In locating the sources and detectors to the chute
it is necessary that the spacing between the upper and lower
set be precise. It is also necessary that the orientation
of each source and its associated detector be precise in
order that the detector be located to receive the maximum
intensity of the radiation beam.
The gamma radiation beam passing through the
curtain of ore passing through the chute is attenuated by
the ore. The ratio between the transmission of the gamma
radiation through the çhute with and without the ore flowing
gives a transmission factor
T - N
No
("N" and "No" represent the count at the detector when ore
is flowing and when ore is not flowing respectively for
identical count periods). The area density of the ore
curtain flowing through the chute can be calculated from the
transmission factor by:
d = log T
t"a" is the mass absorbtion coeEficient of the ore)
Knowing the area density of the ore curtain and
the width of the curtain the velocity of the ore flow must
be termined in order to calculate the actual ore flow
through the chute.
In order to determine the velocity the two sets of
nuclear sources and detectors described above are used to
determine the area density of the ore curtain at their
respective locations through the transmission factor T. On
~ _ 5 .

39~7~
its passccJe through the chute the ore is acceleratec1 anc1
thus the velocity o the ore bctween the nuclear source an~
cletector set is increased and while the mass flow past each
source cletector set is the same tl1e ore densities measured
are different. Thus from the basic law of linear motion
V22 = Vl2 ~ 2~Js
( g is the gravitational acceleration) it may be
established that the vel.ocity at the upper source and
detector set can be calculatecl from
V = 1~
I dl -1
I d2
( s is the vertical spacing between the upper and the lower
source and detector set).
The mass flow rate can then be calculated as
R = dl Vl W
( W is the curtain width)
As well as providing the instaltaneous flow rate
the gauge also can incorporate a counter which can
accumulate the total tonnage which passes the source
2~ detector sets during a given period.
In practice there will be a slight variation in
the value of No because of diurnal and seasonal temperature
variations which will cause the detector to dri~t slightly.
There will also be a slight reduction in the value of No due
to gradual deeay of the radioaeti.ve souree. These
variations are allowed for by taking measurements of No at
every shut down of the ore supply through the chute so that
any trends which are present in the drifting of the zero
count rate can be detected and the trencl can be projected
into the next run to ensure that the most accurate value
possible is used ~or No. Provision may be made to cause a
temporary shutdown during a run in the event of the current
c$,~,

a~Y~
value of No being sensecl to be unreliable in order to
facilitate the determination o~ a reliable value of No.
The nuclear source and detector sets are
associated with a programmed computor which receives the
count from the detectors and carries out the required
ca~culation. The qauge incorporates a flow sensor to detect
a -Elow of ore through the cute together with sensors to
determine whether the shutters oE the sources are closed or
open.
The programme of the computor of the gauge is such
that during a period of there being no flow of ore the
sensors provide a periodical No count which is used to
update and maintain a current value of the zero transmission
factor of the chute when no ore is Elowing through the
chute. In the event of the ore flowing through the chute a
start up signal from a suitable sensor initiates the
program~e into its calculation mode. The count N which is
obtained with the ore Elowing through the chute is initially
submitted to a series of tests to determine whether or not
2n the value received for N is realistic or not.
The tests on N basically comprise comparing the
value obtained with the value of No to cl~termine whether the
value of N is larger or smaller than predetermined limits in
which the anticipated value of N can be expected to fall. A
count in excess of the upper limit would be an inclication
that the ore is in fact not flowing and that the initial
start up signa1 was a false alarm. In such an event the
programme would return to the No counting mode and await a
fresh start up signal as well as providing a visual signal
at the flow gauge read out of the false alarm. In the event
of the value for N fal1ing below an anticipated value such
would be an indication that in fact the shutters of the
- 7 -

~L~23~2
sources are closecl. In such an everlt the pro~ramrne may
initiate the necessary action to open the shutters and/or
inclicate at the gauge readout that a Eault exists at the
shutters.
A further test may be applied to the incoming
value of ~ to cletermine any driEt in the value of N which
may indicate some dri~ting of the deteetor due to
temperature variations or like effects. If such drifting is
detected as being possible, the programme initiates a shut
down of the ore flo~ in order that the value of No may be
recheeked and once a value has been established may
reinitiate the ore flow. Alternatively the programme may
only indicate that the value of No has possibly become
unreliable without eausing a shutdown oc the ore flow.
It has also been found desirable to subjeet the
value of N and No to a filter in order to overeome the error
resulting from the periodic fluctuation o~ the value of N
and No due to the utilisation of a radioàctive source. The
filters are of an automatically programmable form which
comprises mathematical equivalents of conventional
electronic filters but having the specific advantages that
their parameters adjust to follow the rate of flow of ore,
thereby maximising the accuracy of flow measurement and the
accuraey of total tonnage measurement.
It should be appreeiatecl that while the embodiment
has been clescribed in re~lation to one partieular souree of
gamma radiation the invention neecl not be restrictecl to that
souree or indeed to the use of gamma radiation. The
radiation of the sensors may comprise, any suitable form of
electromagnetie radiation, radioactive souree radiation sueh
as alpha or beta radiation or X~radiation, or ultrasonic
radiation.
8 --