CA1199813A - Optical method and apparatus for measuring the consistency of pulp slurry - Google Patents
Optical method and apparatus for measuring the consistency of pulp slurryInfo
- Publication number
- CA1199813A CA1199813A CA000417058A CA417058A CA1199813A CA 1199813 A CA1199813 A CA 1199813A CA 000417058 A CA000417058 A CA 000417058A CA 417058 A CA417058 A CA 417058A CA 1199813 A CA1199813 A CA 1199813A
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- CA
- Canada
- Prior art keywords
- electromagnetic radiation
- wavelength
- water
- radiation
- reflected
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000034 method Methods 0.000 title claims abstract description 26
- 239000013055 pulp slurry Substances 0.000 title claims abstract description 25
- 230000003287 optical effect Effects 0.000 title abstract description 6
- 230000005670 electromagnetic radiation Effects 0.000 claims abstract description 59
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 48
- 238000010521 absorption reaction Methods 0.000 claims abstract description 30
- 230000003595 spectral effect Effects 0.000 claims abstract description 4
- 238000001914 filtration Methods 0.000 claims description 30
- 239000002002 slurry Substances 0.000 claims description 26
- 230000008569 process Effects 0.000 claims description 19
- 230000005855 radiation Effects 0.000 claims description 10
- 229920001131 Pulp (paper) Polymers 0.000 claims description 8
- 230000001419 dependent effect Effects 0.000 claims description 4
- 230000009102 absorption Effects 0.000 description 19
- 239000000306 component Substances 0.000 description 15
- 238000005259 measurement Methods 0.000 description 14
- 229920002522 Wood fibre Polymers 0.000 description 6
- 239000000203 mixture Substances 0.000 description 6
- 238000012360 testing method Methods 0.000 description 4
- 238000002834 transmittance Methods 0.000 description 4
- 239000002023 wood Substances 0.000 description 4
- 239000000835 fiber Substances 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 238000005660 chlorination reaction Methods 0.000 description 2
- 229940000425 combination drug Drugs 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 238000003908 quality control method Methods 0.000 description 2
- 238000000985 reflectance spectrum Methods 0.000 description 2
- 230000035945 sensitivity Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 230000008901 benefit Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000004061 bleaching Methods 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000012994 industrial processing Methods 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000031700 light absorption Effects 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000004537 pulping Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/47—Scattering, i.e. diffuse reflection
- G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/34—Paper
- G01N33/343—Paper pulp
Landscapes
- Chemical & Material Sciences (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Immunology (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Physics & Mathematics (AREA)
- Pathology (AREA)
- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Medicinal Chemistry (AREA)
- Investigating Or Analysing Materials By Optical Means (AREA)
- Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)
- Spectrometry And Color Measurement (AREA)
- Testing Of Optical Devices Or Fibers (AREA)
Abstract
Abstract A novel method and apparatus for measuring pulp slurry consistency by optical means is disclosed. The method involves utilizing the electromagnetic radiation absorption characteristics of water at wavelengths in the spectral range 200 to 5000 nm.
Description
~9~
This invention is directed to a novel method and apparatus for measuring the consistency of various types of pulp and water mixture (pulp slurries). The invention is based on optical phenomena of pulp/water mixtures and the use of this phenomena in the measurement of the consistency of such mixtures.
In the pulp and paper industry individual wood fibres are separated from bulk wood during the paper making process either by mechanical or chemical means, or combina-tions of the two. Water is mixed with the wood fibres to form a wood pulp slurry which is typically more than 80%
water. In order to achieve good quality control of the pulping processes, and to consistently manufacture an end product (paper) of specified standards, it is essential to know the ratio of wood fibres to total mass (this ratio is known in the trade as "consistency") at each point in the process. For example, it is important for quality control purposes to be able to measure the consistency of pulp slurry as it flows through a pipe onto a storage~tower or chamber, where the pulp moves very slowly or is at times completely motionless. It is equally important to be able to determine the slurry consistency of chemical pulp : (bleached or unbleached), thermo-mechanical pulp, ground-wood pulp, mixtures of different pulps, or the slurry con-sistency during the bleaching process.
Most sensors presently used in industry for measuring the consistency of water/pulp mixtures (pulp 30. slurries) are mechanical in operation. Such mechanical sensors, by one means or another, measure the.force which the moving pulp slurry produces on a mechanical arm, plate or the like. These mechanical sensors have well-known limitations, such as distortion due to velocity of the slurry, they are affected by different wood species, and freeness (drainage). Furthermore, such.mechanical sensors ~ -- 1 --9~3~3 cannot be readily installed in a tower or chamber through which pulp slurry is moving slowly or in which pulp slurry is contained. Mechan-~- la -ical sensors are also limi.ted to specific pulp consistencies ~lnd do not accurately measure pulp slurry consistencies below about 1% or above about 5%.
There is on the marke-t a chlorination sensor that provides insensitivity to consistencey variations. (The sen-sor is disclosed and claimed in U.S. Paten-t No. 3,934,602, John J. Howarth, November 30, 1976). This sensor is directed basically to controlling chlorination and does this by the measurement of transmi-ttance in the visible and near infra-red portion of the electromagne-tic (light) spectrum. This patent also discloses the measuring of consistency by de-tect-ing the transmi-ttance of pulp slurry at different distances from the radiation source. A second device uses a combina-tion of reflectance and -transmittance measurements for -the same purpose. Niether of these techniques uses specific filtering of radiation as a key means -to determine consistency.
An objec-t of this inven-tion is to provide an opti-cal device and method which are capable of accurately measur-ing the consis-tency of pulp slurry of different qualities (regardless of type of wood fibre) and to perform the measure-ment under various process conditions of various geometry such as in pipes, towers or chambers, independen-t of velo-city and over the ~ull temperature range of 0....100C.
Accordingly, the present invention provides a pro-cess of measuring the consistency of pulp slurry consisting mainly of wood pulp and water which comprises: (a) beaming electromagnetic radiation at the slurry, the wavelength of the radiation being about 200 nm to abou-t 5000 nm; (b) receiving reflec-ted electromagnetic radiation from the slurry;
(c) separating the reflected electromagne-tic radiation into components; and (d) measuring the relative intensities of -the componen-ts at wavelengths having different absorption charac-teristics in water.
The principle of measurement is based on the unique characteristics of light (electromagne-tic radiation) in the range of about 200 nm to about 5000 nm, the beaming of such light at a pulp slurry and -the de-tection and measurement of the ]ight that is reflec-ted from pulp fibre in the slurry.
The measurement of consistency depends directly upon the fact that water within the pulp slurry at-tenuates ligh-t to dif-ferent degress a-t differen-t wavelengths wi-thin the range mentioned.
Reflectance of pulp is measured by using "wa-ter-sensitive" and "non-water-sensitive" wavelengths and by mathematically comparing these signals. Thus the result is that the method of measurement is sensitive to changes of amount of water in the slurry, but highly insensitive to various other factors tha-t would normally disturb or inter-fere with the measurement. This in itself is mainly based on the fact that these "in-terfering" factors affect bo-th measured wavelengths in the same way. Common measuremen-t dis-turbing factors can be, for example, brightness, wood species or chemicals dissolved or present in the wa-ter portion of -the slurry.
The wavelength of the electromagnetic radiation may be in the range of about 200 nm to about 5000 nm. Narrower ranges may be within the range of about 400 nm to about 1600 nm, or the range of about 700 nm to abou-t 1250 nm.
The reflected electromagnetic radiation may be separated into two components.
The first component of reflected elec-tromagnetic radiation may be passed through a band-pass filter having a nominal centre-wavelength of abou-t 960 nm. The second com-ponent of reflected electromagnetic radiation may be passedthrough a band-pass filter having a nominal centre-wavelength of about 800 nm.
Alternatively, the first component of reflected electromagnetic radiation may be passed through a band-pass filter having a nominal centre-wavelength of about 1200 nm and the second component of reflec-ted electromagnetic radia-tion may be passed through a band-pass filter having a centre wavelength of about 1060 nm.
Alternatively, -the first component of reflected electromagnetic radiation may be measured at a wavelength corresponding to a maximum in-water absorption in the spectral range about 200 nm to about 5000 nm and the second component of reflected electromagnetic radia-tion may be measured at a wavelength corresponding to a water absorpti.on value much less -than that of the first component.
The invention further provides an apparatus for measuring pulp slurry consistency comprising: (a) means for beaming electromagnetic radia-tion containing wavelengths having differen-t absorption characteristics in water a-t a pulp slurry consisting mainly of wood pulp fibres and water;
(b) means for receiving electromagnetic radiation reflected from the slurry; (c) means for separating the reflected elec-tromagnetic radia-tion into components; (d) first filtering means for filtering one of the -two components of the reflec-ted elèctromagne-tic radiation; (e) second filtering means for filtering another component of reflected electromagnetic radiation; (f) said first and second filtering means passing wavelengths having different absorption characteristics in water; (g) Eirst photodetector means for detecting the reflec-ted electromagnetic radiation filtered through -the first fil-tering means and producing a first electronic signal depen-.
dent on the intensity of the filtered radia-tion, (h) second photodetector means for detecting the reflec-ted electromag-netic radiation filtered through the second filtering means iL~3~
and producing a second electronic signal dependent on the in-tensity of the flltered radiation; (i) means for amplifying -the first and second electronic signals; and (j) means for comparing the two signals to determine the pulp consistency therefrom.
The first filtering means (d) may be selec-ted so that it mainly transmits electromagnetic radi.a-tion of a wave-length tha-t corresponds to one of the maximum absorption ranges of water, and the second filtering means (e) may be selected so that it mainly -transmits electromagnetic radia-tion of a wavelength at which water absorption is substantially less than a-t the wavelength of the firs-t filtering means.
The centre-wavelength of the first filtering means (d) may be about 960 nm and -the centre-wavelength of the second filtering means (e) may be at a waveleng-th at which water absorption is considerably less than that of the first filtering means.
The second filtering means (e) may pass electro-magnetic radiation of a wavelength a-t which the water absorp-tion is more than five times less than the water absorption of the electromagnetic radiation transmitted by the first filtering means (d).
The elec-tromagnetic radiation beaming means (a) may emit electromagnetic radiation falling wi-thin the range of abou-t 200 to 5000 nm.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 demonstrates the attenuati.on of electro-magnetic radiation in water as a function of wavelength;
g~
Figure 2 represents a cross-sec-tional side view of an optical consistency sensor;
Figure 3 represents an electronic block diagram of the components comprising the optical consistency sensor;
Figure 4 represents a graphical depiction of eleven tests performed to demonstrate -the consistency sensor signal versus pulp slurry consis-tency for semi.-bleached kraft-pulp and Figure 5 represents a graphical example of six tests performed -to demonstrate minimizing the effect of brigh-tness change on the consistency sensor signal.
The reflectance of elec-tromagnetic radiation from a slurry (which is a two phased mixture of liquid-solids) is generally directly affected by the amount of liquid present because the slurry is usually mainly water. This applies to pulp slurries, and accordingl.y the reflectance of electro-magnetic radiation from -the pulp-water slurry is affected mainly by the amount of water presen-t. In -the spectral electro-5a magnetic range about 200 to about 5000 nrn, the absorption ofradia-tion in water displays peaks and valleys at various wavelengths.
Because the pulp slurry is mainly water, with a minority of dissolved and suspended components, light beamed at the slurry will most of the time travel through the liquid component of the slurry with little interference.
However, some of the light is reFlected. The slurry reflects light from fibres close to the surface and also to a large extent -from individual fibres that are located deeper under the surface. The transmittance of water or the slurry liquid therefore becomes a key in determining the degree that a slurrry as a whole will reflect electromag-netic radiation of a specific wavelength.
The reflectance of wood fibres is dependent on the wavelength of incidental radiation as well. At wavelengths of over about 800 nm, wood fibre electromagnetic radiation reflectances becomes relatively insensitive to change in wavelength. In contrast, water displays distinct varia-tions in absorption at wavelengths over about 800 nm.
Figure 1, which depicts electromagnetic absorption values relative to wavelength shows that water displays an absorption maximum (peak) at about 960 nm. It displays an absorption mlnimum (valley) at a wavelength of abou-t 1060 nm. Again, at about 1200 nm, water absorption reaches a maximurn (peak). The same cyclical trend continues at electromaynetic radiation wavelengths over 12G0 nm with minimums and maximums alternating. This means that other wavelengths can also be used for purposes of the invention.
These absorption peaks and valleys can be utilized to measure the amount of water in the pulp slurry (and hence "consis~ency") by beaming light of a relatively broad band-width, e.g. about 200 nm to about 5000 nm, selecting and . ~
.~''3~3 using filters which transmit the reflected elec-tromagnetic radiation only at preselected wavelengths. By selecting the filters used so that one filter is adapted to the wavelength o-f light absorption maximum and ratioing the signal from this to the signal from another filter adapted to a ligh-t absorption minimum wavelength, it is possible to ob-tain a measurable result which is not particularly - 6a -~, dependent upon or affec~ed by properties of the slurry that normally affect the reflectance spectrum in the wavelength range selected.
Instead the result i~ sensitive to consistency changes. This is demonstrated by the graphical representations depicted in Figures 4 S and 5 which show ~he test measurement results of different pulps, when the two filte~s were respectively of 960 nm and 800 nm wave-length with a band width of 5 nm.
Referring to Figures 2 and 3, which illustrate the construction of the sensor, electromagnetic radiation (light~ from a tungsten filament incandescent lamp (5)~ which generates light in the spectrical range about 200 nm to about 5000 nm~ is carried through a fibre optic light cable (2), and transmitted through a window (14) into a pulp slurry existent on the other side of the window~ Some of this light is transmitted through the slurry and some is reflected back in the direction of and through window (14).
second light cable (2a) is located parallel to cable (2) and collects and transmits light reflected from the pulp slurry through window (14) to lens (13) and ultimately to two photodetectors (11) and (lla). A beam splitter (7) and two separate filters (~) and (8a) divide the reflected light passed through lens (13) so that each photodetector (11) and (lla) receives only approximately one half of the reflected light.
The photodetectors (11) and (lla) are activated by the light and produce signals which are amplified and processed using an electronic divider to give the ratio of the two reflectances at distinct wave-lengths. The ratio signal is converted to a 4...20 mA current signal ~hat is suitable for industrial processing, control and evaluation, for example, by a computer.
.. . .
Cables 2 and 2a are housed in a sensor shaft (1). The ends of the ~wo cables are held in place by a light csble support (3). The optic and electronic equipment are housed in a sensor box ~10). A flange (4) attaches the sensor shaft (1) to the sensor box (10). The optics are mounted on and supported by optics mounting block t6). The two 8~3 filters (8) and (8a) are held in place by a pair of filter holders (9). The electronics circuit board (12) is also housed in box (lO).
The ef fects of stray light are eliminated by the use of light-tight gaskets (15) at various key joints.
S
The two filters (8~ are selected so that they each have a fairly narrow bandwidth, for example, a transmission bandwidth of 5 nm. The centre-wavelength (the wavelength that corresponds to ~lm trans~
mission), of one of the filters is selected to equal an absorption peak of water, e.g. a wavelength of 960 nm or 1200 n~.
The other filter (8a) is then selected to have a centre-wavelength as close to the first filter wavelength as possible but at the same time, a wavelength at which water absorp~ion is considerably less, prefer-abIy more than five to ten times less, eg. a wavelength of 800 nm or1060 Dm.
Thus, when reflectance` from the pulp slurry is measured, the signal from the first filter (8) is much more affected by the amount of water present per unit volume in the slurry than the signal from the second filter (8a). Both signals, on the other hand, are almost equally affected by other pulp slurry ph~nc ~ that affect reflectance. This, in turn, means that the ratio (or output of the sensor) is highly sens;tive to co~s;stency variation and highly insensitive to factors other than consistency variation.
Figure 5 illustrates graphically six tests performed to demonstrate how bri~htness disturbance is ~in;~i7ed by the sensor. The sensitivity to consis~ency is found to be considerably greater than sensitivity to changes in brightness. Here the two samples represent the prac~ical extremes of the brightness scale. In actual process conditions, changes as large as this would not be experienced.
: ~
Another aspect to be considered in ~ilter selection is tllat at times one disturbing factor may be stronger than all others. For example~
brightness may be ~airly constant, but changes in wood species may be frequent and unpredictable. In such cases, the second wavelength is ~9~3 selected to gi~e - Im insensitivity to the said disturbing factor by measuring samples of the pulp in question and by selecting the second filter so that it has possibly a slightly different wavelength from the normal second filter selection.
A number of variations of the basic structure can be made to achieve results which are equal to or slightly inferior to the results obtained with the sensor as previously described. The4e are as follows:
1. The fibre optic cable can be eliminated by placing the light source, the beam-splitter, filters and detector immediately next to the window at the tip of the sensor.
This invention is directed to a novel method and apparatus for measuring the consistency of various types of pulp and water mixture (pulp slurries). The invention is based on optical phenomena of pulp/water mixtures and the use of this phenomena in the measurement of the consistency of such mixtures.
In the pulp and paper industry individual wood fibres are separated from bulk wood during the paper making process either by mechanical or chemical means, or combina-tions of the two. Water is mixed with the wood fibres to form a wood pulp slurry which is typically more than 80%
water. In order to achieve good quality control of the pulping processes, and to consistently manufacture an end product (paper) of specified standards, it is essential to know the ratio of wood fibres to total mass (this ratio is known in the trade as "consistency") at each point in the process. For example, it is important for quality control purposes to be able to measure the consistency of pulp slurry as it flows through a pipe onto a storage~tower or chamber, where the pulp moves very slowly or is at times completely motionless. It is equally important to be able to determine the slurry consistency of chemical pulp : (bleached or unbleached), thermo-mechanical pulp, ground-wood pulp, mixtures of different pulps, or the slurry con-sistency during the bleaching process.
Most sensors presently used in industry for measuring the consistency of water/pulp mixtures (pulp 30. slurries) are mechanical in operation. Such mechanical sensors, by one means or another, measure the.force which the moving pulp slurry produces on a mechanical arm, plate or the like. These mechanical sensors have well-known limitations, such as distortion due to velocity of the slurry, they are affected by different wood species, and freeness (drainage). Furthermore, such.mechanical sensors ~ -- 1 --9~3~3 cannot be readily installed in a tower or chamber through which pulp slurry is moving slowly or in which pulp slurry is contained. Mechan-~- la -ical sensors are also limi.ted to specific pulp consistencies ~lnd do not accurately measure pulp slurry consistencies below about 1% or above about 5%.
There is on the marke-t a chlorination sensor that provides insensitivity to consistencey variations. (The sen-sor is disclosed and claimed in U.S. Paten-t No. 3,934,602, John J. Howarth, November 30, 1976). This sensor is directed basically to controlling chlorination and does this by the measurement of transmi-ttance in the visible and near infra-red portion of the electromagne-tic (light) spectrum. This patent also discloses the measuring of consistency by de-tect-ing the transmi-ttance of pulp slurry at different distances from the radiation source. A second device uses a combina-tion of reflectance and -transmittance measurements for -the same purpose. Niether of these techniques uses specific filtering of radiation as a key means -to determine consistency.
An objec-t of this inven-tion is to provide an opti-cal device and method which are capable of accurately measur-ing the consis-tency of pulp slurry of different qualities (regardless of type of wood fibre) and to perform the measure-ment under various process conditions of various geometry such as in pipes, towers or chambers, independen-t of velo-city and over the ~ull temperature range of 0....100C.
Accordingly, the present invention provides a pro-cess of measuring the consistency of pulp slurry consisting mainly of wood pulp and water which comprises: (a) beaming electromagnetic radiation at the slurry, the wavelength of the radiation being about 200 nm to abou-t 5000 nm; (b) receiving reflec-ted electromagnetic radiation from the slurry;
(c) separating the reflected electromagne-tic radiation into components; and (d) measuring the relative intensities of -the componen-ts at wavelengths having different absorption charac-teristics in water.
The principle of measurement is based on the unique characteristics of light (electromagne-tic radiation) in the range of about 200 nm to about 5000 nm, the beaming of such light at a pulp slurry and -the de-tection and measurement of the ]ight that is reflec-ted from pulp fibre in the slurry.
The measurement of consistency depends directly upon the fact that water within the pulp slurry at-tenuates ligh-t to dif-ferent degress a-t differen-t wavelengths wi-thin the range mentioned.
Reflectance of pulp is measured by using "wa-ter-sensitive" and "non-water-sensitive" wavelengths and by mathematically comparing these signals. Thus the result is that the method of measurement is sensitive to changes of amount of water in the slurry, but highly insensitive to various other factors tha-t would normally disturb or inter-fere with the measurement. This in itself is mainly based on the fact that these "in-terfering" factors affect bo-th measured wavelengths in the same way. Common measuremen-t dis-turbing factors can be, for example, brightness, wood species or chemicals dissolved or present in the wa-ter portion of -the slurry.
The wavelength of the electromagnetic radiation may be in the range of about 200 nm to about 5000 nm. Narrower ranges may be within the range of about 400 nm to about 1600 nm, or the range of about 700 nm to abou-t 1250 nm.
The reflected electromagnetic radiation may be separated into two components.
The first component of reflected elec-tromagnetic radiation may be passed through a band-pass filter having a nominal centre-wavelength of abou-t 960 nm. The second com-ponent of reflected electromagnetic radiation may be passedthrough a band-pass filter having a nominal centre-wavelength of about 800 nm.
Alternatively, the first component of reflected electromagnetic radiation may be passed through a band-pass filter having a nominal centre-wavelength of about 1200 nm and the second component of reflec-ted electromagnetic radia-tion may be passed through a band-pass filter having a centre wavelength of about 1060 nm.
Alternatively, -the first component of reflected electromagnetic radiation may be measured at a wavelength corresponding to a maximum in-water absorption in the spectral range about 200 nm to about 5000 nm and the second component of reflected electromagnetic radia-tion may be measured at a wavelength corresponding to a water absorpti.on value much less -than that of the first component.
The invention further provides an apparatus for measuring pulp slurry consistency comprising: (a) means for beaming electromagnetic radia-tion containing wavelengths having differen-t absorption characteristics in water a-t a pulp slurry consisting mainly of wood pulp fibres and water;
(b) means for receiving electromagnetic radiation reflected from the slurry; (c) means for separating the reflected elec-tromagnetic radia-tion into components; (d) first filtering means for filtering one of the -two components of the reflec-ted elèctromagne-tic radiation; (e) second filtering means for filtering another component of reflected electromagnetic radiation; (f) said first and second filtering means passing wavelengths having different absorption characteristics in water; (g) Eirst photodetector means for detecting the reflec-ted electromagnetic radiation filtered through -the first fil-tering means and producing a first electronic signal depen-.
dent on the intensity of the filtered radia-tion, (h) second photodetector means for detecting the reflec-ted electromag-netic radiation filtered through the second filtering means iL~3~
and producing a second electronic signal dependent on the in-tensity of the flltered radiation; (i) means for amplifying -the first and second electronic signals; and (j) means for comparing the two signals to determine the pulp consistency therefrom.
The first filtering means (d) may be selec-ted so that it mainly transmits electromagnetic radi.a-tion of a wave-length tha-t corresponds to one of the maximum absorption ranges of water, and the second filtering means (e) may be selected so that it mainly -transmits electromagnetic radia-tion of a wavelength at which water absorption is substantially less than a-t the wavelength of the firs-t filtering means.
The centre-wavelength of the first filtering means (d) may be about 960 nm and -the centre-wavelength of the second filtering means (e) may be at a waveleng-th at which water absorption is considerably less than that of the first filtering means.
The second filtering means (e) may pass electro-magnetic radiation of a wavelength a-t which the water absorp-tion is more than five times less than the water absorption of the electromagnetic radiation transmitted by the first filtering means (d).
The elec-tromagnetic radiation beaming means (a) may emit electromagnetic radiation falling wi-thin the range of abou-t 200 to 5000 nm.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:-Figure 1 demonstrates the attenuati.on of electro-magnetic radiation in water as a function of wavelength;
g~
Figure 2 represents a cross-sec-tional side view of an optical consistency sensor;
Figure 3 represents an electronic block diagram of the components comprising the optical consistency sensor;
Figure 4 represents a graphical depiction of eleven tests performed to demonstrate -the consistency sensor signal versus pulp slurry consis-tency for semi.-bleached kraft-pulp and Figure 5 represents a graphical example of six tests performed -to demonstrate minimizing the effect of brigh-tness change on the consistency sensor signal.
The reflectance of elec-tromagnetic radiation from a slurry (which is a two phased mixture of liquid-solids) is generally directly affected by the amount of liquid present because the slurry is usually mainly water. This applies to pulp slurries, and accordingl.y the reflectance of electro-magnetic radiation from -the pulp-water slurry is affected mainly by the amount of water presen-t. In -the spectral electro-5a magnetic range about 200 to about 5000 nrn, the absorption ofradia-tion in water displays peaks and valleys at various wavelengths.
Because the pulp slurry is mainly water, with a minority of dissolved and suspended components, light beamed at the slurry will most of the time travel through the liquid component of the slurry with little interference.
However, some of the light is reFlected. The slurry reflects light from fibres close to the surface and also to a large extent -from individual fibres that are located deeper under the surface. The transmittance of water or the slurry liquid therefore becomes a key in determining the degree that a slurrry as a whole will reflect electromag-netic radiation of a specific wavelength.
The reflectance of wood fibres is dependent on the wavelength of incidental radiation as well. At wavelengths of over about 800 nm, wood fibre electromagnetic radiation reflectances becomes relatively insensitive to change in wavelength. In contrast, water displays distinct varia-tions in absorption at wavelengths over about 800 nm.
Figure 1, which depicts electromagnetic absorption values relative to wavelength shows that water displays an absorption maximum (peak) at about 960 nm. It displays an absorption mlnimum (valley) at a wavelength of abou-t 1060 nm. Again, at about 1200 nm, water absorption reaches a maximurn (peak). The same cyclical trend continues at electromaynetic radiation wavelengths over 12G0 nm with minimums and maximums alternating. This means that other wavelengths can also be used for purposes of the invention.
These absorption peaks and valleys can be utilized to measure the amount of water in the pulp slurry (and hence "consis~ency") by beaming light of a relatively broad band-width, e.g. about 200 nm to about 5000 nm, selecting and . ~
.~''3~3 using filters which transmit the reflected elec-tromagnetic radiation only at preselected wavelengths. By selecting the filters used so that one filter is adapted to the wavelength o-f light absorption maximum and ratioing the signal from this to the signal from another filter adapted to a ligh-t absorption minimum wavelength, it is possible to ob-tain a measurable result which is not particularly - 6a -~, dependent upon or affec~ed by properties of the slurry that normally affect the reflectance spectrum in the wavelength range selected.
Instead the result i~ sensitive to consistency changes. This is demonstrated by the graphical representations depicted in Figures 4 S and 5 which show ~he test measurement results of different pulps, when the two filte~s were respectively of 960 nm and 800 nm wave-length with a band width of 5 nm.
Referring to Figures 2 and 3, which illustrate the construction of the sensor, electromagnetic radiation (light~ from a tungsten filament incandescent lamp (5)~ which generates light in the spectrical range about 200 nm to about 5000 nm~ is carried through a fibre optic light cable (2), and transmitted through a window (14) into a pulp slurry existent on the other side of the window~ Some of this light is transmitted through the slurry and some is reflected back in the direction of and through window (14).
second light cable (2a) is located parallel to cable (2) and collects and transmits light reflected from the pulp slurry through window (14) to lens (13) and ultimately to two photodetectors (11) and (lla). A beam splitter (7) and two separate filters (~) and (8a) divide the reflected light passed through lens (13) so that each photodetector (11) and (lla) receives only approximately one half of the reflected light.
The photodetectors (11) and (lla) are activated by the light and produce signals which are amplified and processed using an electronic divider to give the ratio of the two reflectances at distinct wave-lengths. The ratio signal is converted to a 4...20 mA current signal ~hat is suitable for industrial processing, control and evaluation, for example, by a computer.
.. . .
Cables 2 and 2a are housed in a sensor shaft (1). The ends of the ~wo cables are held in place by a light csble support (3). The optic and electronic equipment are housed in a sensor box ~10). A flange (4) attaches the sensor shaft (1) to the sensor box (10). The optics are mounted on and supported by optics mounting block t6). The two 8~3 filters (8) and (8a) are held in place by a pair of filter holders (9). The electronics circuit board (12) is also housed in box (lO).
The ef fects of stray light are eliminated by the use of light-tight gaskets (15) at various key joints.
S
The two filters (8~ are selected so that they each have a fairly narrow bandwidth, for example, a transmission bandwidth of 5 nm. The centre-wavelength (the wavelength that corresponds to ~lm trans~
mission), of one of the filters is selected to equal an absorption peak of water, e.g. a wavelength of 960 nm or 1200 n~.
The other filter (8a) is then selected to have a centre-wavelength as close to the first filter wavelength as possible but at the same time, a wavelength at which water absorp~ion is considerably less, prefer-abIy more than five to ten times less, eg. a wavelength of 800 nm or1060 Dm.
Thus, when reflectance` from the pulp slurry is measured, the signal from the first filter (8) is much more affected by the amount of water present per unit volume in the slurry than the signal from the second filter (8a). Both signals, on the other hand, are almost equally affected by other pulp slurry ph~nc ~ that affect reflectance. This, in turn, means that the ratio (or output of the sensor) is highly sens;tive to co~s;stency variation and highly insensitive to factors other than consistency variation.
Figure 5 illustrates graphically six tests performed to demonstrate how bri~htness disturbance is ~in;~i7ed by the sensor. The sensitivity to consis~ency is found to be considerably greater than sensitivity to changes in brightness. Here the two samples represent the prac~ical extremes of the brightness scale. In actual process conditions, changes as large as this would not be experienced.
: ~
Another aspect to be considered in ~ilter selection is tllat at times one disturbing factor may be stronger than all others. For example~
brightness may be ~airly constant, but changes in wood species may be frequent and unpredictable. In such cases, the second wavelength is ~9~3 selected to gi~e - Im insensitivity to the said disturbing factor by measuring samples of the pulp in question and by selecting the second filter so that it has possibly a slightly different wavelength from the normal second filter selection.
A number of variations of the basic structure can be made to achieve results which are equal to or slightly inferior to the results obtained with the sensor as previously described. The4e are as follows:
1. The fibre optic cable can be eliminated by placing the light source, the beam-splitter, filters and detector immediately next to the window at the tip of the sensor.
2. The light source can be made using light emitting diodes (LEDs~.
These make the sensor of simpler construction and design but make it less adaptable to different specific process conditions, for example, very narrow band filters Gf a specific wavelength must be used in order to compensate for disturbances. As LED-technology advances~
this should become a more attractive alternative because of simpli-city and costs.
These make the sensor of simpler construction and design but make it less adaptable to different specific process conditions, for example, very narrow band filters Gf a specific wavelength must be used in order to compensate for disturbances. As LED-technology advances~
this should become a more attractive alternative because of simpli-city and costs.
3. Multiple filters can be used, or measurement of the total spectrum in question can be made to give the same result but with more freedom for wavelength selection and different compensations.
4. In place of a two-signal ratio, calculations as follows can be used to produce a usable result under certain conditiolls:
(a) the difference of the two signals;
(b) one signal divided by the sum of two;
(c) one signal alone (this variation becomes more useful with higher consistencies than about 4...5% and with a high brightness pulp);
and (d) one signal plus constant divided by second signal plus constant.
(a) the difference of the two signals;
(b) one signal divided by the sum of two;
(c) one signal alone (this variation becomes more useful with higher consistencies than about 4...5% and with a high brightness pulp);
and (d) one signal plus constant divided by second signal plus constant.
5. The filters may be mounted on a filter wheel;
.LO
.LO
6. One or more electromagnetic detectors may be used depending on the number of filters used and whether or not a filter wheel is used;
7. Various processing elements may be subst~tuted in place of the divider. For example, a microprocessor could readily be used.
It is not intended that the above list is complete, the list is e.~ ~ir~ plr~
e~ t~vr only.
A result similar to the one discussed above can be obtained by using n c~
wavelengths that all coincide with absorption ~ - of water and then summing the individual signals. In such a case, however, the benefit for being able to compensate for other disturbing phenomena of the reflectance spectrum is to large e~tent lost.
Some of the advan$ages of-~y ;nvention over existing sensors now used include:
(a) maintenance requirements are small;
(b) a measurement range of 0.05 to 15% in consistency is possible using the same basic sensor;
(c) installation of the sensor can be done through a ball valve for easy inspection later;
(d) measurement is highly independent of flow rate (in comparison to mechanical devices);
(e) the sensor can be installed virtually anywhere in the process where there is minimal flow and enough space for reflectance of light from the slurry; and (f) geometry of piping and physical containers do not affect the measurement.
It will be readily apparent to those skilled in the art that various modifications to the embodiment described and shown in the drawing can be made without departing from the spirit and scope of the invention as defined in the following claims.
It is not intended that the above list is complete, the list is e.~ ~ir~ plr~
e~ t~vr only.
A result similar to the one discussed above can be obtained by using n c~
wavelengths that all coincide with absorption ~ - of water and then summing the individual signals. In such a case, however, the benefit for being able to compensate for other disturbing phenomena of the reflectance spectrum is to large e~tent lost.
Some of the advan$ages of-~y ;nvention over existing sensors now used include:
(a) maintenance requirements are small;
(b) a measurement range of 0.05 to 15% in consistency is possible using the same basic sensor;
(c) installation of the sensor can be done through a ball valve for easy inspection later;
(d) measurement is highly independent of flow rate (in comparison to mechanical devices);
(e) the sensor can be installed virtually anywhere in the process where there is minimal flow and enough space for reflectance of light from the slurry; and (f) geometry of piping and physical containers do not affect the measurement.
It will be readily apparent to those skilled in the art that various modifications to the embodiment described and shown in the drawing can be made without departing from the spirit and scope of the invention as defined in the following claims.
Claims (20)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process of measuring the consistency of pulp slurry consisting mainly of wood pulp and water which compri-ses: (a) beaming electromagnetic radiation at the slurry, the wavelength of the radiation being about 200 nm to about 5000 nm; (b) receiving reflected electromagnetic radiation from the slurry; (c) separating the reflected electromagnetic radiation into components; and (d) measuring the relative intensities of said components at wavelengths having different absorption characteristics in water.
2. A process as defined in claim 1, wherein the reflected electromagnetic radiation is separated into two components.
3. A process as defined in claim 1, wherein the wavelength of the electromagnetic radiation is within the range of about 400 nm to about 1600 nm.
4. A process as defined in claim 3, wherein the wavelength of the electromagnetic radiation is within the range of about 700 nm to about 1250 nm.
5. A process as defined in claim 2, wherein the first component of reflected electromagnetic radiation is passed through a band-pass filter having a nominal centre-wavelength of about 960 nm.
6. A process as defined in claim 5, wherein the second component of reflected electromagnetic radiation is passed through a band-pass filter having a nominal centre-wavelength of about 800 nm.
7. A process as defined in claim 2, wherein the first component of reflected electromagnetic radiation is passed through a band-pass filter having a nominal centre-wavelength of about 1200 nm.
8. A process as defined in claim 5, wherein the second component of reflected electromagnetic radiation is passed through a band-pass filter having a centre-wavelength of about 1060 nm.
9. A process as defined in claim 2, wherein the first component of reflected electromagnetic radiation is measured at a wavelength corresponding to a maximum in-water absorption in the spectral range about 200 nm to about 5000 nm.
10. A process as defined in claim 9, wherein the second component of reflected electromagnetic radiation is measured at a wavelength corresponding to a water absorption value much less than that of the first component.
11. An apparatus for measuring pulp slurry consistency compris-ing: (a) means for beaming electromagnetic radiation containing wavelengths having different absorption characteristics in water at a pulp slurry consisting mainly of wood pulp fibres and water;
(b) means for receiving electromagnetic radiation reflected from the slurry; (c) means for separating the reflected electromagnetic radiation into components; (d) first filter-ing means for filtering one of the two components of the reflected electromagnetic radiation; (e) second filtering means for filtering another component of the reflected electromagnetic radiation; (f) said first and second filter-ing means passing wavelengths having different absorption characteristics in water; (g) first photodector means for detecting the reflected electromagnetic radiation filtered through the first filtering means and producing a first electronic electronic signal dependent on the intensity of the filtered radiation; (i) means for amplifying the first.
and second electronic signals; and (j) means for comparing the two signals to determine the pulp consistency therefrom.
(b) means for receiving electromagnetic radiation reflected from the slurry; (c) means for separating the reflected electromagnetic radiation into components; (d) first filter-ing means for filtering one of the two components of the reflected electromagnetic radiation; (e) second filtering means for filtering another component of the reflected electromagnetic radiation; (f) said first and second filter-ing means passing wavelengths having different absorption characteristics in water; (g) first photodector means for detecting the reflected electromagnetic radiation filtered through the first filtering means and producing a first electronic electronic signal dependent on the intensity of the filtered radiation; (i) means for amplifying the first.
and second electronic signals; and (j) means for comparing the two signals to determine the pulp consistency therefrom.
12. An apparatus as defined in claim 11, wherein said means for comparing the two signals divides one into the other to give a ratio of the two reflectances.
13. An apparatus as defined in claim 11, wherein the first filtering means (d) is selected so that it mainly transmits electromagnetic radiation of a wavelength that corresponds to one of the maximum absorption ranges of water.
14. An apparatus as defined in claim 13, wherein the second filtering means (e) is selected so that is mainly transmits electromagnetic radiation of a wavelength at which water absorption is substantially less than at the wavelength of the first filtering means.
15. An apparatus as defined in claim 11, wherein the centre-wavelength of the first filtering means (d) is about 960 nm.
16. An apparatus as defined in claim 15, wherein the centre-wavelength of the second filtering means (e) is at a wavelength at which water absorption is considerably less than that of the first filtering means.
17. An apparatus as defined in claim 16, wherein the second filtering means (e) passes electromagnetic radia-tion of a wavelength at which the water absorption is more than five times less than the water absorption of the electromagnetic radiation transmitted by the first filtering means (d).
18. An apparatus as defined in claim 11, wherein the electromagnetic radiation beaming means (a) emits electro-magnetic radiation falling within the range about 200 to about 5000 nm.
19. An apparatus as defined in claim 11, wherein the electromagnetic radiation beaming means (a) emits electro-magnetic radiation falling within the range of about 400 nm to about 1600 nm.
20. An apparatus as defined in claim 11, wherein the electromagnetic radiation beaming means (a) emits electro-magnetic radiation falling within the range of about 700 nm to about 1250 nm.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US32796081A | 1981-12-07 | 1981-12-07 | |
| US327,960 | 1981-12-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1199813A true CA1199813A (en) | 1986-01-28 |
Family
ID=23278858
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417058A Expired CA1199813A (en) | 1981-12-07 | 1982-12-06 | Optical method and apparatus for measuring the consistency of pulp slurry |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS58108436A (en) |
| CA (1) | CA1199813A (en) |
| DE (1) | DE3244892A1 (en) |
| FI (1) | FI824185L (en) |
| FR (1) | FR2517827B1 (en) |
| NO (1) | NO824088L (en) |
| SE (1) | SE8206940L (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5416577A (en) * | 1993-07-02 | 1995-05-16 | Honeywell Inc. | Color sensor for optically measuring consisting and brightness of materials |
| US5420682A (en) * | 1993-07-02 | 1995-05-30 | Honeywell Inc. | Method and apparatus for compensating spectral data with a color sensor |
| WO2012007542A1 (en) | 2010-07-16 | 2012-01-19 | Matthew Rice | Optical measurement method and apparatus |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IT1196832B (en) * | 1986-12-10 | 1988-11-25 | Cselt Centro Studi Lab Telecom | PROCEDURE FOR MEASURING THE VISCOSITY OF A BODY |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3161768A (en) * | 1961-01-27 | 1964-12-15 | Nat Res Dev | Method and apparatus for the analysis of emulsions and suspensions |
| US3405268A (en) * | 1965-03-12 | 1968-10-08 | Brun Sensor Systems Inc | Radiant energy absorption gage for measuring the weight of a base material and the content of a material sorbed by the base material |
| DE1598467B1 (en) * | 1967-07-26 | 1972-03-16 | Frieseke & Hoepfner Gmbh | DEVICE FOR CONTACTLESS MEASUREMENT OF HUMIDITY OR THE CONCENTRATION OF OTHER SUBSTANCES IN MOVING BALANCES |
| US3614450A (en) * | 1969-02-17 | 1971-10-19 | Measurex Corp | Apparatus for measuring the amount of a substance that is associated with a base material |
| DE1917628C3 (en) * | 1969-04-05 | 1975-04-30 | Frieseke & Hoepfner Gmbh, 8520 Erlangen | Method and device for contactless measurement of moisture or the concentration of other substances in moving material tracks |
| US3675019A (en) * | 1971-03-19 | 1972-07-04 | Measurex Corp | Apparatus for measuring the amount of a substance that is associated with a base material |
| DE2264433A1 (en) * | 1972-11-11 | 1974-05-16 | Siemens Ag | DEVICE FOR COLORIMETRIC EXAMINATION OF SUBSTANCES FOR SIGNIFICANT COMPONENTS |
| US3827808A (en) * | 1973-05-09 | 1974-08-06 | Industrial Nucleonics Corp | Method and apparatus for measuring the opacity of sheet material in which the transmittance signal is compensated for the reflectivity of the material |
| US4288160A (en) * | 1973-12-28 | 1981-09-08 | Nekoosa Papers Inc. | Optical property measurement system and method |
| US3994602A (en) * | 1974-01-14 | 1976-11-30 | Measurex Corporation | Optical reflectance gauge and method therefor |
| DE2910673C2 (en) * | 1979-03-19 | 1985-08-08 | Paul Lippke Gmbh & Co Kg, 5450 Neuwied | Method for contactless measurement of the absolute content of a substance (secondary substance) in a mixture (main substance and secondary substance) of several substances in the form of a thin film, in particular for measuring the absolute content of water in paper |
-
1982
- 1982-12-03 FI FI824185A patent/FI824185L/en not_active Application Discontinuation
- 1982-12-04 DE DE19823244892 patent/DE3244892A1/en not_active Withdrawn
- 1982-12-06 SE SE8206940A patent/SE8206940L/en not_active Application Discontinuation
- 1982-12-06 NO NO824088A patent/NO824088L/en unknown
- 1982-12-06 CA CA000417058A patent/CA1199813A/en not_active Expired
- 1982-12-07 JP JP57213459A patent/JPS58108436A/en active Pending
- 1982-12-07 FR FR8220496A patent/FR2517827B1/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5416577A (en) * | 1993-07-02 | 1995-05-16 | Honeywell Inc. | Color sensor for optically measuring consisting and brightness of materials |
| US5420682A (en) * | 1993-07-02 | 1995-05-30 | Honeywell Inc. | Method and apparatus for compensating spectral data with a color sensor |
| WO2012007542A1 (en) | 2010-07-16 | 2012-01-19 | Matthew Rice | Optical measurement method and apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| NO824088L (en) | 1983-06-08 |
| FR2517827B1 (en) | 1987-07-03 |
| FR2517827A1 (en) | 1983-06-10 |
| DE3244892A1 (en) | 1983-07-28 |
| JPS58108436A (en) | 1983-06-28 |
| SE8206940L (en) | 1983-06-08 |
| FI824185A0 (en) | 1982-12-03 |
| FI824185L (en) | 1983-06-08 |
| SE8206940D0 (en) | 1982-12-06 |
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