Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
i7~3
~ACKGROUND OF THE INVENTION
The present invention relates to a method for measuring the amount
of substance associated with a material in the presence of a contaminant,
and more particularly to a method for measuring the amount of water associated
with a paper material in the presence of carbon.
Methods for detecting moisture in paper material are well known
in the prior art, see e.g. United States Patent No. 3,614,450. Typically,
an infrared source emits two bands of electromagnetic radiation. A first
band (usually 1.8 microns - so called reference channel) is insensitive to
absorption by the moisture. A second band (usually 1.94 mQcrons - so called
measure channel) is sensitive to absorption by the moisture. The two bands
of radiation are directed at the paper material. Detectors are positioned
to receive the bands of radiation after they have been reflected from the
paper or transmitted through the paper. The detectors convert the radiation
received into electrical signalsO The ratio of the signal of the reference
channel to the measure channel is indicative of the moisture content of the
paper material. A fundamental assumption of this method is that neither the
reference channel nor the measure channel is sensitive to absorption by other
compounds in the paper material.
As ecological demands increase, the use of recycled paper also
increases. This has ocurred most frequently in the news print industry.
Used newspaper is recycled with new pu]p to produce fresh news print. The
use of recycled news print in the manufacturing process introduces contaminant,
namely carbon from the printing ink, into the process. The presence of
car~on effects the measurement of moisture of the paper material in that the
bands ~both reference channel and measure channel) of electromagnetic
radiation are absorbed by the carbon. Thus, the ratio of the signals of the
reference channel to the measure channel would not be determinitive of the
-1_ ~
. .'' '' ''', : ' .
.
, .
-
. ~ :
moisture content of the paper material.
Heretofore, one way to correct for the presence of carbon is todetermine a ~iori the influence of carbon on the ratio of the signals for
a particular moisture level. For example a 7% level of moisture for a
par~icular paper material, a ratio of the signals without carbon was
determined to be 2.2 and as carbon was introduced the ratio of the signals
- detected, for the same level of moisture, became 2.00
For a different level of moisture, the ratio of the signals would
also vary as the amount of carbon present in the paper materialO In this
manner, a family of curves was pre-determined and usually stored in a com-
puter. The amount of carbon present in the paper material was determined
from the change in the signal strength of the reference channel. Since the
reference channel was insensitive to the presence of water, the change in
signal strength of the reference channel could be attributed to the presence
of carbon. With knowledge of the ratio of the signals and the amount
of deviation of the signal strength in the reference channel, indicating
the amount of carbon present, the moisture level of the paper material could
thus be calculated from the family of pre-determined curves. The drawback
of this method, of course, is that a large amount of data had to be pre-
determined and stored in a medium which is easily and quickly accessible.
Moreover, the method that was developed was based upon empirical results
and not upon theoretical basisO As a result, it was limited in its
accuracy and in its range of application.
SUMMARY OF THE INVENTION
A method of measuring the amount of substance associated with a
material in the presence of a contaminant, wherein the contaminant has an
electromagnetic radiation absorption characteristic different from the
electromagnetic radiation absorption characteristic of the substance,
.: - . : : : . ... :.: :
. .
- '' ~ . ' ' ' .' ' ':
: - :
"' . - ' ''
S7~
comprises emitting a first band of electromagnetic radiation. The first band
is directed at the material and is characterized in that it lies outside an
absorption band of the substance but within an absorption band of the con-
taminant. The first band is detected, after it has impinged on the material,
by a detector which produces a first electrical signal in response to the
radiation detected. A second band of electromagnetic radiation is also
emitted and is aligned to impinge the material. The second band is character-
ized in that it lies within an absorption band of the substance and also lies
within an absorption band of the contaminant. The second band is detected,
after it has impinged the material, by a receiver which generates a second
electrical signal, in response to the radiation detected. The second
electrical signal is subtracted from the first electrical signal.
According to the invention there is provided a method of measuring
the amount of substance associated with a material in the presence of a con-
taminant, said contaminant having an electromagnetic radiation absorption
characteristic different from the electromagneti& radiation absorption
characteristic of said substance, wherein said method comprising the steps
of: emitting a first band of electromagnetic radiation, wherein said first
band lies outside an absorption band of said substance, and lies within an
; 20 absorption band of said contaminant; directing said first band to lmpinge
said material; detecting said first band after reflecting from said material;
generating a first electrical signal, in response to said first band detect-
ed; emanating a second band of electromagnetic radiation, wherein said
second band lies within an absorption band of said substance, and also lies
wlthin an absorption band of said contaminant; aligning said second band to
impinge said material; receiving said second band after reflecting from said
material; producing a second electrical signal, in response to said second
band received; and calculating the amount of substance in accordance with the
;:
--3--
, ~t
- ~, ' ~ '
5~9
formula:
amount of substance = A+B(M + M)-C(N ~ N)
where A, B, C are calibration constants; M = intensity of second band
received without material divided by intensity of second band received with
material; N = intensity of first band detected without material divided by
intensity of first band detected with material.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic side view of an apparatus using the method
of the present invention.
Figure 2 is a schematic side view of another apparatus using the
method of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention relates to a method of measuring the amount
of substance associated with a material, in the presence of a contaminant.
The contaminant has an electromagnetic radiation absorption characteristic
different from that of the substance. In the method of the present invention,
a first band of electromagnetic radiation is emitted from a source. The
first band has the characteristic of being within an absorption band of the
contaminant, but outside an absorption band of the substance. The Eirst band
is directed to impin~e the material. A detector is positioned to receive
the first band after impinging the material. A first electrical signal in
response to the first radiation detected is generated by the detector. A
second band of electromagnetic radiation is produced and is also aligned to
impinge the material. The second band has the characteristic of being within
an absorption band of the substance and within an absorption band of the con-
taminant. The second band is detected by a receiver after the second band
has impinged the material. The receiver generates a second electrical signal
in response to the second band of radiation detected. The second electrical
~4~
. : . .
.. . , .' . ~
.
: - - ~ - - : ; -
'
7g
signal is subtracted from the first electrical signal.
A particular application of the method of the present invention is
in the measurement of moisture of paper material in the presence of carbon.
This can be best understood by referring to Figure 1, which is a schematic
4a
~1~257~
side view of an apparatus 10 using the method of the present invention. h
paper material 12, substantially in a sheet form, moves in a direction shown
by arrow 14. The paper material 12 can be the manufactured product of a
Fourdrinier machine (not shown). As is well known in paper making technology,
the control of the amount of moisture or water in the paper is critical in
controlling quality and economic return. In the paper matcrial 12 of Figure
1, however, the paper material 12 also contains carbon particles 16
(greatly exaggerated). A first source 18 emits a first band of electro-
magnetic radiation, directed towards the paper material 12 in a direction
along the dotted line 20. The first band, after impinging the paper material
12 reflects from it and travels in the direction along the dotted line 22 and
is received by a fir9t receiver 24. The first receiver 24 converts the first
band received into a first electrical signal 26. The first band is chosen
such that it lies within an electromagnetic absorption band of carbon but
lies outside of an electromagnetic absorption band of water. Typically,
this is at about 1.8 microns. A second source 28 emits a second band of
~ electromagnetic radiation, directed towards the paper material 12 in a
; direction along the dotted line 30. The second band, after impinging the
paper material 12, reflects from it and travels in the direction along the
dotted line 32 and is received by a second receiver 34. The second receiver
34 convert9 the 9econd band received into a second electrical signal
36. The second band is chosen such that it lies within an electromagnetic
absorption band of water and is also within an electromagnetic absorption
band of carbon. Typically, this is about 1.94 microns. The second electrical
signal 36 is subtracted from a first electrical signal 26 by a computer 380
The result is determinitive of the amount of moisture in the paper material
12.
In general, the first source 18 and the second source 28 can be any
- 5 _
, .
..
, - , , :, :,
,,~ - - :: - , : . . .
5~9
source emitting the desired electromagnetic radiation. They can even be the
same source, e.g. an infrared lamp. The dotted lines 20 and 30 can coincide
and thus the first band and second band would impinge the same area on~
the paper material 12. In fact, for accuracy, this is preferred. In the
event the dotted lines 20 and 30 coincide such that the first band and the
second band impinge the same area on the paper material 12, then the dotted
lines 22 and 32 would also coincide. In that event, the first receiver
24 and the second receiver 34 are positioned to receive both bands with a
beam splitter such as that disclosed in United States Patent No. 3,641,349.
The first receiver 24 and the second receiver 34 can be any suitable
detector, such as photodiode. The apparatus 10 of FYgure 1 uses the method
of the present invention in which the measurement of the amount of moisture
of the paper material 12 is accomplished by reflecting bands of electro-
magnetic radiation from the paper material 12. In this application, known
as reflectance measurement, the calculation of the amount of moisture
associated with the paper material 12 in the presence of carbon, by subtracting
the second signal 36 from the first signal 26, can be further simpli ~ed to:
' amount of moisture = A + B (M + -) - C (N + 1)
M N
where A~ B~ C are constantsof the apparatus 10 obtained
from initial calibration,
M is the intensity of second band (1094 micron) received
without the paper material 12 (eOg. replace the
paper material 12 by a reflector) divided by the
intensity of the 9econd band received with the
paper material 12 ( i.e. the intensity of second
band received during the measurement process), and
N is the intensity of the first band (1.8 micron)
received without the paper material 12(eOg.
_ 6 -
: ~ -
-: ~ , ,. . - . ' , ~ '
1~ ii79
replace the paper material by a reflector)
divided by the intensity of the first band
received with the paper material 12 (i.e. the
intensity of first band received during the
measurement process).
The measurement of the intensity of the first band and the second band are
made usually during standardization, i.eO when the apparatus 10 moves off-
sheet from the paper material 12. These measurements are made to correct
for errors caused by dirt build-up, source aging etc.
Referring to Figure 2, there is shown a schematic side view of
another apparatus 40 using the method of the present invention. A paper
material 42, substantially in a sheet form, moves in a direction shown by
arrow 44. The paper material 42 contains carbon particles 46 (greatly
exaggerated). A first source 48 emits a first band of electromagnetic
radiation, directed towards the paper material 42 in a direction along the
dotted line 50. me first band, after impinging the paper material 42,
transmits through it, and travels in the direction along the dotted line
52 and is received by a first receiver 54. The first receiver 54 converts
the first band received into a first electrical signal 56. The first band
is chosen such that it lies within an electromagnetic absorption band of
carbon but lies outside of an electromagnetic absorption band of water.
Typically, this is at about 1.8 microns. A second source 58 emits a second
band of electromagnetic radiation, directed towards the paper material 42
in a direction along the dotted line 60. The second band~ after impinging the
paper material 42, transmits through it and travels in the direction along -
the dotted line 62 and is received by a second receiver 64. m e second
receiver 64 converts the second band received into a second electrical
signal 66c The second band is chosen such that it lies within an electro-
.: .. - , . . ... .. : - : .
79
magnetic absorption band of water and is also within an electromagnetic
absorption band of carbon. Typically, this is at about 1094 microns. The
second electrical signal 66 is subtracted from a first electrical signal
56 by a computer 68. The result is determinitive of the amount of moisture
in the paper material 42.
The apparatus 40 of Figure 2 is similar to that disclosed and
shown in United States Patent No. 3,793,524. The apparatus 40 comprises a
first diffusing plate 41 to one side of the paper material 42, while a
second diffusing plate 43 is to the other side of the paper material 42. In
addition the sources 48, 58 and the receivers 54, 64 are off-set from one
another, iOe. no amount of radiation is received directly by the receivers
54 and 64 from the sources 48 and 58. The advantages of the diffusing
plates 41 and 43, and the off-set geometry are discussed fully in United
States Patent ~o. 3,793,524. In general, the first source 48 and the second
source 58 can be any source emitting the desired electromagnetic radiation.
They can even by the same source, e.gO an infrared lampO The dotted lines
50 and 60 can coincide and thus the first band and second band would impinge
the same area on the paper material 420 In fact, for accuracy, this is
preferred. In the event the dotted lines 50 and 60 coincide such that the
first band and the second band impinge the same area on the paper material
42, then the dotted lines 52 and 62 would also coincideO In that event,
the first receiver 54 and the second receiver 64 are positioned to receive
both bands with a beam splitter, such as that disclosed in United States
Patent No. 3,641~349. The first receiver 54 and the second receiver 64 can
be any 9uitable detector such as photodiode. The apparatus 40 of Figure 2
uses the method of the present invention in which the measurement of the
amount of moisture of the paper material 42 is accomplished by transmitting
bands of electromagnetic radiation through the paper ~aterial 42. In this
-- 8 --
i79
application, known as transmittance measurement, the calculation of the
amount of moisture associated with the paper material 42 in the presence
of carbon, by subtracting the second signal 66 from the first signal 56,
can be further simplified to:
amount of moisture = A + B ~M - C ~N
where A, B, C are constants of the apparatus 40
obtained from initial calibration;
M is the intensity of the second band (1.94 micron)
received without the paper material 42 (e.gO
remove the paper material 42 and measure the
intensity of the second band) divided by the
intensity of the second band received with the
paper material 42 (i.e. the intensity of the
second band received during the measurement
process); and
N is the intensity of the first band (1.8 micron)
received without the paper material 42`(e.gA
remove the paper material 42 and measure the
intensity of the second band) divided by the
intensity of the first band received with the
paper material 42 (i.e. the intensity of the first
band received during the measurement process).
me measurements of the intensity of the first band and the second band
are made usually during standardization, iOe. when the apparatus 40 moves
off_sheet from the paper material 420 These measurements are made to
correct for errors caused by dirt build-up, source aging etc.
It should be appreciated that the method of the present invention
is not limited in its application to the determination of the amount of
.. . . . . . .
.. - ............... . . . , - .
.... .
.
5;~
moisture associated with paper material in the presence of carbon, either
through reflectance measurement or transmittance measurementO The method
of the present invention can be used to determine the amount of any substance
associated with a material in the presence of a contaminant. For example, the
method of the present invention can also be used to determine the amount of
plastic in a plastic film in the presence of carbon, or to determine the
amount of water in a paper material in the presence of other colored dyes.
The theoretical basis for the method of the present invention is as
follows: The amount of monochromatic light reflected or transmitted from a
diffusing sheet depends on the absorption coefficient K and the scattering
coefficient S. It shall be assumed that, in accordance with Beer's Iaw,
the absorption depends on the concentration of substance in the sheet,
the concentration of contaminant, and the concentration of some unknown
(albeit small amount). In addition, it is assumed that the absorption
coefficients are additive so that the total absorption coefficient K is the
sum:
K = K (substance ) + K (contaminant) + K (other) + KS + KC + Ko
From the theory of Kubelka and Munk (Kubelka, Paul,
"New Contributions to the Optics of Intensely
Light-Scattering Materials~ Part I'l, Journ.
Opt. Soc, Am., 38, 1945.), the total absorption
coefficient can also be related to reflectance
R and scattering coefficient S. Thus:
M MS + KMC + KMo 2 _ (M +~~r) ~ S
N NS + KNC + KN0 = 2 (N + -N) ~ SN
where M and N are the ratio of measure and reference bands respectively
as previously discussed.
- 10 -
.. . . . ..
. . : : - . : : -
. " . ~, . - ,- : ~ .
: . :' -', ~ ' : .. '
79
If it is assumed that the contaminant absorbs equally at the reference
channel and at the measure channel, i.e. KMC = KNC then the difference of
the two equations yields:
(KMS ~ KNS) + (KMo ~ KN0) = 2M (M + M) ~ 2 (N + N) ~ (SM S~)
since (KMs- KNs) is proportional to the amount of
substance, and the terms (KMo - KN0)~ 2 ~ 2 and
(SM ~ SN) are constants, the equation becomes:
amount of substance = A + B (M + M) ~ C (N + 1)
where A, B and C are constants determined by calibration.
In the case of light transmitted through the sheet, the effect of
the light scattered from the sheet and then reflected from the diffusing
plates to impinge the sheet, must be considered~ mus, the theory of Kubelka
and Munk must be rewritten to include multiple passes and to take into
account the off-set geometry. m e analysis, thereafter, however, is the
same. The coefficient of absorption K can be determined for the measured
channel and the reference channel. me difference is taken and the resultant
is proportional to the amount of substance.
It should be appreciated that the method of the present invention
does not require a large amount of a priori data. Moreover, it i9 accurate
and has a wi~e range of applicability to correct for the presence of any
contaminant.
-- 11 --
. .
, , ' : , ' ,: ' ' '
': ' . ' ' . . ' , ' : : -,
. ' - ~ -
