Note: Descriptions are shown in the official language in which they were submitted.
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CA 02618209 2008-12-03
-1-
OPTICAL PROBES AND METHODS FOR SPECTRAL ANALYSIS
The present application is a divisional application of Canadian Patent
Application Serial No. 2,402,230, filed March 9, 2001, and which is the
Canadian National
Phase application of International Publication No. WO 0169213, filed March 9,
2001.
Background of the Invention
Most analytical techniques used in industry require taking samples to the
laboratory
to be analyzed by time consuming procedures. For use in the field, e.g., on-
site analysis,
spectral analyzers have been gaining favor because of the potential speed of
analysis and
the fact that they often represent a non-destructive means of analyzing
samples. Based on
surface, but often the constituent components beneath a sample surface.
Typically, in spectroscopic applications an optimal range of wavelengths is
selected
to irradiate a sample, where reflected or transmitted light is measured to
determine the
characteristics of the sample. Some samples, for example, are best analyzed
using a near
infrared spectrum of light while others are optimally analyzed using a range
such as
visible or mid infrared spectrum.
Many spectral analyzers utilize a narrow spot size to intensely irradiate a
sample to
be analyzed. Illuminating a sample with a highly intense incident light
typically results in
an easier collection of larger amounts of reflected light, thus improving
system
performance. Unfortunately, a narrow spot size can sometimes provide
inaccurate
measurements because a small spot may not be representative of the intended
sample,
particularly where the sample is heterogenous in nature, such as, for example,
grains, seeds,
powders or and other particulate or suspended analytes. A narrow spot may
unduly heat the
sample, affecting the nature of the spectra.
To illustrate, it has been long recognized that the value of agricultural
products such
as cereal grains and the like are affected by the quality of their inherent
constituent
components. In particular, cereal grains with desirable protein, oil, starch,
fiber, and
moisture content and desirable levels of carbohydrates and other constituents
can command
a premium price. Favorable markets for these grains and their processed
commodities have
therefore created the need for knowing content and also various other physical
characteristics such as hardness and "test weight" (bulk density).
Accordingly, when a
truck with a trailer load of grain arrives at a grain elevator, the elevator
operator needs to
obtain a good statistical sample of the grain in the truckload, and then
measure the
CA 02618209 2008-02-08
2
properties of the samples. From this sampling, the overall properties of the
grain (such as
protein, oil and moisture content) are estimated for the truckload. Fast
measurement and
immediate answers are desired so that the grain may be judged as acceptable or
not, and if
acceptable, directed to the proper storage location based on the measured
characteristics.
Current methods utilize a physical sampling probe, which is driven vertically
down into the
grain and mechanically or pneumatically withdraws samples from various depths.
The
withdrawn samples are then analyzed, e.g., by infrared techniques. However,
the cost of
labor and time for serially withdrawing individual samples and then processing
the samples
can limit the number of samples withdrawn from a given truckload of grain and
therefore
potentially hamper the ability to obtain good sampling statistics.
Another problem with on-site spectroscopic detection techniques can arise in
situations where the analyte to be detected, e.g., fluids or particulates, is
being transported
across the field of vision of the spectral analyzer, such as in a chute or on
a conveyor belt.
For instance, an open fluid or particle "stream" having a varying cross-
sectional dimension
can present difficulties where it is necessary that some portion of the
spectral probe be
positioned at a fixed distance from the surface of the stream. To illustrate,
the truckload of
grain referred to above may transported from the truck to locations within the
elevator
facilities on conveyor belts, in some cases at speeds as fast as 10
feet/second. The
unevenness of the stream of grain on the belt can be problematic to
positioning a
spectroscopy probe at a constant fixed distance from a surface of the grain
stream. On the
other hand, inserting the probe into the stream to maintain a constant
distance between the
probe head and the grain being analyzed may cause unacceptable turbulence in
the flow of
particles or fluid.
Moreover, in certain instances the fluid or particle stream may be fast enough
that
difficulties are encountered in obtaining enough measurements for good
statistical
sampling, particularly where the particle or fluid stream is heterogeneous in
composition.
Returning again to the example of the grain elevator, many of the transpoi-t
processes which
may be amenable to spectroscopic detection from the standpoint of
accessibility to the
grain, e.g., for placement of infrared probes and the like, may in fact be
less than ideal due
to the speed with which the grain would be transported by the field of vision
of the probe.
Grain being unloaded from a truck, for example, may be unloaded though
delivery chutes at
CA 02618209 2008-02-08
3
a rate of tens of bushels per second. In view of the potential heterogeneity
in the grain being
monitored, and the speed with which the grain is moving, providing good
statistical
sampling of the quality of the grain by spectroscopic techniques using a probe
positioned
along the flow path can be impaired by the lack of time to get an adequate
number of
sample spectra.
Summary of the Invention
The present invention relates to spectral analysis systems and methods for
determining physical and chemical properties of a sample by measuring the
optical
characteristics of its transmitted and/or reflected light. In general, the
systems and methods
of the present invention are useful for examining the spectroscopic
characteristics of
materials, such as particles or liquids, though the systems may be used to
characterize other
materials such as suspensions of particles and even gases. In certain
embodiments, it is
especially advantageous to use the subject system in connection with non-
uniform material,
e.g. consisting of components of different compositions, because the system of
the present
invention does not require the samples to be homogeneous in order to achieve
reliable
results.
However, in addition to characterizing heterogeneous materials, the subject
systems
can also be used to ascertain whether or when a mixture or a stream of
material is
sufficiently homogeneous or fulfils certain specifications with regard to
content and/or
particle size.
One aspect of the present invention relates to an insertion probe system for
spectral
analysis of flowable materials, or other materials, including static
materials, into which a
probe can be inserted, for which internal spectroscopic sampling is desired.
In such
embodiments, the invention provides a spectral analysis system including a
probe which
can be inserted into, e.g., bins, bales, vats, blenders, silos, mixers, drums,
flow streams, and
the like, of granular, powder or liquid matter and suspensions.
In general, the probe may include a probe head having: (i) a light source
arranged to
irradiate a sample volume of the material proximate the probe head, which
source may be a
lamp or other radiation source disposed in the probe head or it may be the
radiant end of an
optical fiber or other waveguide delivering light from a source distal to the
probe head; and
CA 02618209 2008-02-08
4
(ii) an optical pick-up, arranged to receive light energy reflected or
otherwise emitted from
a sample in the irradiated sample volume. The light source provides a suitably
broad
bandwidth of light for irradiating the sample, and in certain preferred
embodiments,
simultaneously irradiates at multiple wavelengths. The light pick-up receives
light reflected
or emitted from a sample being irradiated, and is in optical communication
with one or
more detectors which measure the intensity of the light reflected or emitted
by the sample
in a wavelength-dependent manner. Where the detector is located distal to the
probe head,
the pick-up may be an aperture in the probe head connected with an optical
fiber or other
waveguide which communicates light reflected or emitted by the sample to the
detector.
Where the detector is proximal to the irradiated sample, as it may be if
disposed in the
probe head, the pick-up may simply be an aperture for permitting light being
reflected by
the sample to enter the probe head. The system can also include one or more
signal
processing circuits, such as in the form of a computation subsystem, for
processing signals
from the detector.
A salient feature to certain preferred embodiments of the subject insertion
probe
relates to the sample volume irradiated by the probe. As described in further
detail below,
the irradiated sample volume can be shaped to be circumferential, or at least
substantially
circumferential, to the light source, and preferably to the long (insertion)
axis of the probe.
For instance, the probe may irradiate a toroidal sample volume wrapping
circumferentially
around the light source. Moreover, the sample volume is preferably disposed
180 to 360
circumferentially around the light source, and more preferably 270 to 360 ,
and even more
preferably 360 around the light source. In cei-tain embodiments, the
irradiation pattern
provides for an irradiation surface area of about 10 times R2, and more
preferably at least
about 25 times R2, at least about 50 times R2, at least about 75 times R2 or
even at least
about 100 times R2, where R is the radius of the probe. By providing a larger
sample
volume, the advantages to such configurations of the system include the
ability to collect
data more likely to be statistically representative of a heterogeneous mixture
and to get
better signal-to-noise in the spectral analysis. Moreover, a larger sample
volume permits a
more efficient use of the light and helps to provide improved signal-to-noise.
Another aspect of the present invention relates to a variable surface probe
system
for spectroscopic analysis of a moving sample of a flowable material. In
particular, the
CA 02618209 2008-02-08
invention provides a spectral analysis system including a probe which can be
variably
positioned in contact with the moving surface of the material, or a fixed
distance below the
surface, without substantially disrupting the flow of the material. In such
embodiments, the
invention provides a spectral analysis system including a probe which can be
inserted or
5 placed on top of, e.g., moving material on a conveyor belt, grain belt, and
the like.
In general, the probe may include a probe head having: (i) a light source
arranged to irradiate the flowable material proximate the probe head, which
source may be a lamp or
other radiation source disposed in the probe head or it may be the radiant end
of an optical
fiber or other waveguide delivering light from a source distal to the probe
head; (ii) an
optical pick-up, arranged to receive light energy reflected or otherwise
emitted from a
sample in the irradiated sample volume; (iii) a planing element which permits
the probe
head to skim the surface of the flowing material when in contact; and,
optionally, (iv) a
constant force generator which applies a force to the probe head to maintain a
constant
amount of contact between the probe and the sample. The planing element of the
probe
may be, merely to illustrate, convex or concave such that when contacted with
the surface
of the moving material, e.g., at a shallow angle of attack, the planing
element allows the
probe to traverse the flowing material without creating significant turbulence
in the
material. The light source provides a suitably broad bandwidth of light for
irradiating the
sample, and in certain preferred embodiments, simultaneously with multiple
radiation
wavelengths. The light pick-up receives light reflected or emitted from a
sample being
irradiated, and is in optical communication with one or more detectors which
measure the
intensity of the reflected light, e.g., in a wavelength-dependent manner.
Where the detector
is located distal to the probe head, the pick-up may be an aperture in the
probe head
connected with an optical fiber or other waveguide which communicates light
reflected or
emitted by the sample to the detector. Where the detector is proximal to the
irradiated
sample, as it may be if disposed in the probe head, the pick-up may simply be
an aperture
for permitting light being reflected by the sample to enter the probe head.
The system can
also include one or more signal processing circuits, such as in the form of a
computation
subsystem, for processing signals outputted from the detector.
Still another aspect of the present invention relates to a multihead probe
system for
spectroscopic analysis of a moving sample of a flowable material. In such
embodiments,
CA 02618209 2008-02-08
6
the invention provides a spectral analysis system including a probe which can
be inserted
into a fast moving flow, e.g., a truck discharging its load at a grain
elevator. It may be used
in any granular solid or liquid or gas that moves through or along a passage,
either enclosed
or open. This could include manure, soil, sludge, mining materials, raw and
fine chemicals,
pharmaceuticals, food stuffs, waste materials, hazardous waste, petroleum and
its products,
commercial gaseous products, stack gases, etc.
In particular, the invention provides a spectral analysis system including a
plurality
of probe heads, e.g., which are simultaneously (relative to each other) able
to irradiate and
collect spectral information on the moving sample. In general, each of the
plurality of
probes may include a probe head having: (i) a light source arranged to
irradiate the flowable
material proximate the probe head, which source may be a lamp or other
radiation source
disposed in the probe head or it may be the radiant end of an optical fiber or
other
waveguide delivering light from a source distal to the probe head; and (ii) an
optical pick-
up, arranged to receive light energy reflected or otherwise emitted from a
sample in the
irradiated sample volume. Each light source provides a suitably broad
bandwidth of light
for irradiating the sample, and in certain preferred embodiments, the light
sources may
simultaneously irradiate the sample with multiple radiation wavelengths, e.g.,
each light
source may provide light at a distinct wavelength. The light pick-up receives
light reflected
or emitted from a sample being irradiated, and is in optical communication
with one or
more detectors which measure the intensity of the reflected light, e.g., in a
wavelength-
dependent manner. Where the detectors are located distal to the probe head,
the pick-up
may be an aperture in the probe head connected with an optical fiber or other
waveguide
which communicates light reflected or emitted by the sample to the detector.
Where the
detector is proximal to the irradiated sample, as it may be if disposed in the
probe head, the
pick-up may simply be an aperture for permitting light being reflected by the
sample to
enter the probe head. The system can also include one or more signal
processing circuits,
such as in the form of a computation subsystem, for processing signals
outputted from the
detector.
Still another aspect of the invention relates to a probe system for
spectroscopic
analysis of a sample material that minimizes the effects of surface reflection
on the spectral
analysis of the sample thereby improving the spectral analysis. In such
embodiments, the
CA 02618209 2008-02-08
7
invention provides a probe system for spectral analysis in industrial, drug
manufacturing,
chemical and petrochemical settings and the like. In one particular
embodiment, the probe
is used in situations with sample materials having a large component of
surface reflections
relative to light paths passing through particles or a bulk of sample material
in a diffuse,
scattering path.
In particular, the invention provides a probe head for use with a spectrometer
to
analyze a material, the probe head having: (i) a light source arranged to
irradiate a sample
volume of the material proximate the probe head, which source may be a lamp or
other
radiation source disposed in the probe head; (ii) an optical pick-up, arranged
to receive light
energy reflected or otherwise emitted from the sample in the irradiated sample
volume and
transmit the emitted light to the spectrometer for analysis; (iii) an optical
blocking element
positioned within the optical path between the light source and the optical
pick-up to force
the optical path into the sample volume; and (iv) a reference shutter for
selectively blocking
light emitted from the irradiated sample volume from reaching the optical pick-
up to
facilitate calibration. The optical blocking element minimizes direct surface
reflections
from the sample or from components of the probe head, such as, for example, a
sample
window positioned in contact with or proximate the material, relative to light
passing
through and reflecting from the material within the sample volume to thereby
improve the
accuracy of the analysis of the material. The light source provides a suitably
broad
bandwidth of light for irradiating the sample, and in certain preferred
embodiments,
simultaneously with multiple radiation wavelengths. The light pick-up receives
light
reflected or emitted from a sample being irradiated, and is in optical
communication with
one or more detectors which measure the intensity of the reflected light,
e.g., in a
wavelength-dependent manner. Where the detector is located distal to the probe
head, the
pick-up may be an aperture in the probe head connected with an optical fiber
or other
waveguide which communicates light reflected or emitted by the sample to the
detector.
Where the detector is proximal to the irradiated sample, as it may be if
disposed in the
probe head, the pick-up may simply be an aperture for permitting light being
reflected by
the sample to enter the probe head. The system can also include one or more
signal
processing circuits, such as in the form of a computation subsystem, for
processing signals
outputted from the detector.
CA 02618209 2008-02-08
8
In one embodiment of the subject method, the composition of the inspected
material
can be quantified by detecting molecular vibrational modes characteristic of
one or more
constituents of the material, as for example proteins, lipids, fatty acids,
etc. This aspect of
the method comprises irradiating the sample with electromagnetic radiation,
e.g., infrared
radiation, e.g., preferably near infrared radiation, in a wavelength range
which is converted
by the sample into molecular vibrations, e.g., in the wavelength range of
infrared radiation,
and measuring at least one of an absorption or transmission of the
electromagnetic radiation
by the sample. Infrared radiation refers broadly to that part of the
electromagnetic spectrum
between the visible and microwave regions. This encompasses the wavelengths
from about
700 nm to about 50,000 nm. Near infrared radiation includes wavelengths in the
range of
about 700-2500 nm. For instance, it has been discovered that protein levels in
grains can be
determined by measuring near infrared absorption at particular wavelengths. As
used
herein, the term "near infrared" or "near IR" is intended to encompass light
in a spectrum
ranging from about 700 to about 2500 nm, more preferably from about 1300 to
about 2400,
and, in some instances, most preferably from about 1400 to about 2200 nm.
In certain preferred embodiments, the subject systems and methods measure a
spectral response to short wavelength, near infrared (NIR) radiant energy in
the range 700-
2500 nm, and even more preferably from 600 to about I 100 nanometers (nm). The
system
may also be set up to irradiate the sample in the visible spectrum, including
wavelengths as
low as about 400 nanometers (nm). The spectral response at shorter wavelengths
helps in
the modeling of proteins and other constituents in conjunction with the
response at higher
wavelengths, and be useful in those embodiments where grains or other protein-
containing
materials are being characterized.
Although the infrared spectrum is characteristic of the entire molecule,
certain
groups of atoms give rise to bands at or near the same frequency regardless of
the structure
of the rest of the molecule. It is the persistence of these characteristic
bands that permits the
practitioner to obtain useful structural information by simple inspection and
reference to
generalized charts of characteristic group frequencies. To illustrate, the
conjugated diketone
is a structure that is likely to be persistent irrespective of the length of a
fatty acid.
Furthermore, other chemical structures of proteins, fatty acids and other
natural constituents
have been determined that and are suitable for detection by infrared means.
CA 02618209 2008-02-08
9
Infrared radiation of frequencies less than about 100cm 1(wavelengths longer
than
10,000 nm) can be absorbed and converted by a constituent of the sample into
energy of
molecular rotation. This absorption is quantized; thus a molecular rotation
spectrum can
consist of discrete lines. Infrared radiation in the range from about 10,000-
100 crn 1(1000
nm- 10,000 nm) can be absorbed and converted by the sample into energy of
molecular
vibration. This absorption is also quantized, but vibrational spectra appear
as bands r-ather
than as lines because a single vibrational energy change can be accompanied by
a number
of rotational energy changes. The frequency or wavelength of absorption
depends on the
relative masses of the atoms, the force constants of the bonds and the
geometry of the atoms
in the fatty acid.
Band positions in infrared spectra are presented either as wavenumbers or
wavelengths and are understood to be equivalent. The wavenumber unit (cm"',
reciprocal
centimeters) is used most often since it is proportional to the energy of the
vibration and
since most modern instruments are linear in the cm' scale. Wavelength, X, is
referred to
herein in ter-ms of micrometers ( m, 10-6 meters) or nanometers (nm, 10-9
meters).
Wavenumbers are reciprocally related to wavelength, e.g., 1/k.
Band intensities can be classically expressed either as transmittance (T) or
absorbance (A), though for the purpose of this application both of will be
understood as
within the meaning of the term "absorbance" or "absorption". As used in the
art,
transmittance is the ratio of the radiant power transmitted by a sample to the
radiant power
incident on the sample, and absorbance is the logarithm, to the base 10, of
the reciprocal of
the transmittance (A=loglo(1/T)). The term absorbance or absorption further
include
scattered light, such as measured in Raman spectroscopy.
Moreover, other forms of vibrational spectroscopy, such as Raman spectroscopy,
can be used as part of the subject methods. The Raman vibrational spectrum of
these
molecules can consist of a series of sharp lines which constitute a unique
fingerprint of the
specific molecular structure. Raman spectroscopy presents a means of obtaining
vibrational
spectra, especially over optical fibers, with visible or near infrared light,
and provides a
viable alternative to infrared spectrophotometry for use in the subject
methods. These
wavelength regions are efficiently transferred without significant absorption
losses over
conventional optical fiber materials. In Raman spectroscopy, monochromatic
light is
CA 02618209 2008-02-08
directed onto a sample and the spectrum of the scattered light is determined.
However, due
to a very weak signal, the excitation light must be quite intense, though
laser light sources
are readily available. In addition, optical filtering is necessary to separate
the weak
scattered signal from the intense Rayleigh line.
5 In yet another embodiment of the subject method, the constituents of a
sample are
determined in the sample by detecting molecular electronic modes
characteristic of such
constituents. This aspect of the method includes irradiating the sample with
electromagnetic
radiation, e.g., ultraviolet-visible radiation, e.g., ultraviolet radiation,
in a wavelength range
converted by the sample into electronic vibrations/electron orbital
transitions, e.g., in the
10 wavelength range of 200-400 nm, e.g., at a wavelength of 275 nm and
measuring the
absorption of the electromagnetic radiation by the sample. In the ultraviolet
and visible
region of the spectrum, molecular absorption is dependent on the electronic
structure of the
molecule. Absorption of energy is quantized, resulting in the elevation of
electrons from the
ground state to higher energy orbitals in an excited state. For many
electronic structures, the
absorption does not occur in the readily available portion of the ultraviolet
region.
There is, however, an advantage to the selectivity of ultraviolet absorption:
characteristic groups can be recognized in molecules of widely varying
complexities. As a
large portion of a relatively complex molecule can be transparent in the
ultraviolet region, a
spectrum can be obtained similar to that of a much simpler molecule.
Wavelengths in the ultraviolet region of the spectrum are usually expressed in
nanometers or angstroms (A). The near ultraviolet (quartz) region includes
wavelengths of
200-380 nm. The atmosphere is transparent in this region and quartz optics may
be used to
scan from 200 to 380 nm. Atmospheric absorption starts near 200 nm and extends
into the
shorter-wavelength region (10-200 nm), which is accessible through vacuum
ultraviolet
spectrometry.
The total energy of a molecule is the sum of its electronic energy, its
vibrational
energy, and its rotational energy. Energy absorbed in the ultraviolet region
produces
changes in the electronic energy of the molecule. These transitions consist of
the excitation
of an electron from an occupied orbital (usually a non-binding p or binding 7i-
orbital) to the
next higher energy orbital (an antibonding, 7r* or 6*, orbital). The
antibonding orbital is
designated by an asterisk.
CA 02618209 2008-02-08
11
Since ultraviolet energy is quantized, the absoiption spectrum arising from a
single
electronic transition should consist of a single, discrete line. A discrete
line is not obtained
since electronic absorption is superimposed on rotational and vibrational
sublevels. The
spectra of simple molecules in the gaseous state consist of narrow absorption
peaks, each
representing a transition from a particular combination of vibrational and
rotational levels
in the electronic ground state to a corresponding combination in the excited
state. At
ordinary temperatures, most of the molecules in the electronic ground state
will be in the
zero vibrational level; consequently, there are many electronic transitions
from that level. In
molecules containing more atoms, the multiplicity of vibrational sublevels and
the
closeness of their spacing cause the discrete bands to coalesce, and broad
absorption bands
or "band envelopes" ai-e obtained.
The principal characteristics of an absorption band are its position and
intensity. The
position of absorption corresponds to the wavelength of radiation whose energy
is equal to
that required for an electronic transition. The intensity of absorption is
largely dependent on
two factors: the probability of interaction between the radiation energy and
the electronic
system and the difference between the ground and the excited state. The
probability of
transition is proportional to the square of the transition moment. The
transition moment, or
dipole moment of transition, is proportional to the change in the electronic
charge
distribution occurring during excitation. Intense absorption occurs when a
transition is
accompanied by a large change in the transition moment. Absorption with E
,,,a.X values >104
is high-intensity absorption; low-intensity absorption corresponds to s,,,dX
values <103.
Accordingly, the subject method relies on optically detecting individual
chemical
groups of a constituent of a sample which have been determined to be reliable
as indicators
for quantitatively determining the level of the constituent in the sample.
In one embodiment, the method comprises utilizing one of the subject systems
for
illuminating (e.g., irradiating) the sample at a plurality of discrete
wavelengths, e.g. selected
from the infrared, visible or ultraviolet spectrum. In certain embodiments,
the wavelengths
the sample is irradiated with include at least one sample wavelength and one
reference
wavelength. The sample wavelength is defined as being a wavelength for
detecting a
chemical feature whose existence is dependent on the presence of a constituent
in the
sample. The reference wavelength, on the other hand, is selected as a
frequency which is
CA 02618209 2008-02-08
12
not absorbed by the sample in a manner dependent on the presence of the
constituent.
Measurements of the intensity of transmitted, absorbed, or reflected light at
such
wavelengths are taken, and an analysis of transmittance, absorbance, or
reflectance ratios
for various wavelengths is performed.
In preferred embodiments, the reference wavelength is closely spaced and can
be
chosen so as to provide a "baseline" for determining the intensity of the peak
of interest,
such as the band intensity of a peak arising due to the constituent. Changes
in the ratios can
be correlated from the sample wavelength, which obviously will vary with the
state amount
of the constituent in the sample, and the second (reference) wavelength, which
is
sufficiently removed from the sample wavelength so that measurements of light
absorption
at this second wavelength is relatively insensitive to the concentration of
the constituent,
and yet which is sufficiently close to the first wavelength to minimize
interference from
scattering effects and the like. Typically, the window bracketing these
closely spaced
wavelengths will be less than about 300 nm and preferably less than about 60
nm wide and,
in some instances, more preferably less than about 30 nm wide. The reference
wavelength
can be chosen so as to detect a chemical feature which remains relatively
unchanged (e.g.
does not change in significant manner) as the normal makeup of the sample
changes, or can
be selected as a wavelength which does not correspond to any sharp absorption
bands but
which provides baseline correction to compensate for convoluted or "rolling"
baselines.
As will be understood, there are a wide variety of materials for which the
systems
and methods of the present invention can be used for characterization. Without
intending to
be limiting, exemplary materials include:
vegetable foods, such a wheat, corn, rye, oats, barley, soybeans, amaranth,
triticale,
and other grains, rice, coffee and cocoa, which may be in the form of whole
grains or beans,
or a ground or comminuted product (analysis for protein, starch, carbohydrate
and/or
water), seeds, e.g. peas and beans, such as soybeans (analysis for protein,
fats and/or water),
products mainly consisting of or extracted from vegetable raw materials, such
as snacks,
dough, vegetable mixtures, margarine, edible oils, fibre products, chocolate,
sugar, syrup,
lozenges and dried coffee extract (powder/granulate),
animal foodstuffs, such as dairy produce, e.g. milk, yogurt and other soured
milk
products, ice cream, cheese (analysis for protein, carbohydrate, lactose, fat
and/or water),
CA 02618209 2008-02-08
- 13-
meat products, e.g. meat of pork, beef, mutton, poultry and fish in the form
of minced oi-
emulgated products (analysis for protein, fat, water and/or salts) and eggs,
which foodstuffs
may be present in a completely or partly frozen condition,
fermentation broths, such as alcoholic beverages, e.g. wine or beer,
fodder, e.g. pellets or dry/wet fodder mixtures of vegetable products, fats
and
protein-containing raw materials, including pet food,
manure and compost, including composting garbage, grass clippings,
pharmaceutical products, such as tablets, mixtures, powders, creams and
ointments,
biological samples including, for example, biological fluids such as blood,
wine,
spinal fluid, saliva, etc, and tissue samples, and
technical substances, e.g. wet and dry mixtures of cement and mortar,
plastics, e.g.
in granular form, mineral materials, such as solvents and petro-chemical
products, e. g. oils,
hydrocarbons and asphalt, solutions of organic or inorganic substances, e. g.
sugar solutions,
glue and epoxies, and
liquids with light scattering properties in suspension, slurries, fluidized
materials
including both solid and liquid and similar entities.
The components comprising the systems of the present invention are preferably
integrated into a single unit, e.g., to create either a portable spectral
analyzer or one which is
readily disposed along a path of a moving material.
In one aspect, the present invention resides in a probe head for use with a
spectrometer to analyze a material, the probe head comprising: a shaft
extending along a
longitudinal axis; a sample window positioned so as to be in contact with or
proximate the
material; a light source arranged within the shaft; a reflector arranged
within the shaft a
longitudinal distance from the light source to reflect at least a portion of
the light from the
light source in a direction generally perpendicular to the longitudinal axis
of the shaft and
through the sample window to irradiate a sample volume of the material
proximate the
probe head; and an optical pick-up arranged within the shaft to receive light
emitted from
the irradiated sample volume and transmit the received light to the
spectrometer,
characterized by: an optical blocking element optically separating the sample
window into
first and second windows and being positioned in the optical path between the
light source
and the optical pick-up such that light from the light source is reflected
through the first
window to the sample material and the optical pick-up receives light from the
sample
CA 02618209 2008-02-08
- 13a-
material entering through the second window, whereby direct surface
reflections from the
sample window or the sample material are blocked from reaching the optical
pick-up.
In one aspect, the present invention resides in a probe head assembly for use
with a
spectrometer to analyze a material, the probe head assembly comprising: a
probe head
having a housing, a sample window arranged in the housing, a light source
arranged to
irradiate a sample volume of the material proximate to the sample window, an
optical pick-
up arranged to receive light emitted from the irradiated sample volume through
the sample
window and transmit the emitted light to the spectrometer for analysis, an
optical blocking
element biased into contact with the sample window and when in contact with
the sample
window, the optical blocking element is positioned in an optical path between
the light
source and the optical pick-up to force the optical path into the sample
volume and to
effectively minimize direct surface reflection from the sample window or the
sample
volume by blocking such direct surface reflection from reaching the optical
fiber, whereby
an allowed optical path, which includes the optical path, originates from the
light source,
undergoes diffusive transport in the sample volume, and is collected and
transported within
an aperture of the optical pick up, and a reference shutter adapted to
selectively block light
emitted from the irradiated sample volume from reaching the optical pick-up to
facilitate
calibration of the spectrometer.
In another aspect, the present invention resides in a method of
spectroscopically
analyzing a material comprising: irradiating a sample volume of the material
with light from
a light source through a sample window, transmitting light emitted from the
irradiated
sample volume through the sample window to an optical pickup that is optically
connected
to a spectrometer, positioning an optical blocking element in an optical path
between the
light source and the optical pickup, thereby forcing the optical path between
the light source
and the optical pick-up into the sample volume and inhibiting reflections from
the sample
window within the optical path from reaching the optical pickup, and to
facilitate calibration
of the spectrometer, selectively blocking light emitted from the irradiated
sample volume
from reaching the optical pick-up.
Brief Description Of The Drawings
The foregoing and other objects, features and advantages of the invention will
be
apparent from the following more particular description of preferred
embodiments of the
CA 02618209 2008-02-08
- 13b -
invention, as illustrated in the accompanying drawings in which like reference
characters
refer to the same parts throughout the different views. The drawings are not
necessarily to
scale, emphasis instead being placed upon illustrating the principles of the
invention.
Fig. I is a schematic representation, in cross-section, of an optical probe
for
insertion into a flowable sample material, according to the present invention;
Fig. 2 is a schematic representation, in cross section, of an optical probe
including an
elliptical reflector, according to the present invention;
CA 02618209 2008-02-08
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Fig. 3 is a schematic representation, in cross-section, of an optical probe
head
including an elliptical reflector and a cylindrical shutter, according to
invention;
Fig. 4 is a schematic representation of the probe head of Fig. 3, illustrating
the probe
head inserted within a flowable sample material;
Figs. 5a and 5b are schematic illustrations of a method of determining the
shape of
the elliptical surface of the elliptical reflector of the probe head of Fig.
2;
Fig. 6a is a schematic illustration of an optical probe having a planing
element for
contacting a stream of flowable material, according to the present invention;
Figs. 6b and 6c are cross sectional views of embodiments of the planing
element of
the optical probe of Fig. 6a;
Fig. 7a is a schematic drawing of a multiple probe head apparatus for
analyzing a
stream of flowable material, according to the present invention;
Fig. 7b is a cross-sectional view of the multiple probe head apparatus of Fig.
7a;
Fig. 8 is a schematic illustration of a spectral analyzer, according to the
present
invention;
Fig. 9 is a flow chart depicting a process for measuring absorptivity of a
sample
according to the principles of the present invention;
Figs. l0a and l Ob are schematic illustrations of an alternative embodiment of
an
optical probe head of the present invention;
Figs. 11 a and l lb are perspective views of one embodiment of the optical
blocking
element of the probe head of Figs. l0a and l Ob;
Fig. 12a and 12b are perspective view of one embodiment of the reference
shutter of
the probe head of Figs. l0a and l Ob; and
Fig. 13 is a perspective view of an optical probe head implementing the
optical
blocking element and the reference shutter of Figs. l0a-b and 11 a-b,
respectively,
illusti-ating the probe head of the optical window with the sample window
removed.
Detailed Description Of The Invention
1. Overview
One aspect of the invention provides a probe for insertion into a flowable
material.
An exemplary use of the subject probe is in the analysis of grain. To
illustrate, it has been
CA 02618209 2008-02-08
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long recognized that the value of agricultural products such as cereal grains
and the like are
affected by the quality of their inherent constituent components. In
particular, cereal grains
with desirable protein, oil, starch, fiber, and moisture content and desirable
levels of
carbohydrates and other constituents can command a premium price. When a truck
with a
trailer load of grain arrives at a grain elevator, the elevator operator needs
to obtain a good
statistical sample of the grain in the truckload, and then measure the
properties of the
samples. The present invention provides a probe assembly which eliminates the
need for
physical sampling of the grain. Rather, the grain is examined
spectroscopically while it is
still in the truck or other container. One feature of the probe pertains to
the shape of the
output light, e.g., the sample volume. As described in further detail below,
the irt-adiated
sample volume can be shaped to be circumferential, or at least substantially
circumferential,
to the light source, and preferably to the long (insertion) axis of the probe.
By providing a
larger sample volume, the advantages to such configurations of the system
include the
ability to collect data more likely to be statistically representative of a
heterogeneous
mixture and to get better signal-to-noise in the spectral analysis.
Another aspect of the invention relates to a probe system optimized for a
variable
surface for spectroscopic analysis of a moving sample of a flowable material.
The present
invention provides a probe assembly which eliminates the need for physical
sampling of the
grain. Rather, the grain is examined spectroscopically while it is on a
conveyor belt or
similar apparatus.
Another aspect of the invention relates to multiple probe assemblies for
obtaining
spectral information from flowing materials. As set out in the background, the
methods
used to unload and transport materials such as grain at elevator facilities
can have very high
throughput. Where multiple measurements may be required to obtain good
sampling
statistics, the present invention contemplates the use of multiple probe
assemblies to permit
simultaneous acquisition of spectral data from several points in the material,
whether those
points be in the same stream (e.g., the same chute from a truck) or in
different streams (e.g.,
from different chutes from a truck). The use of the subject multiple probe
systems can be
particularly important for analyzing heterogeneous materials which may have
undergone
separation, e.g., such as the dynamical separation process which can occur in
the storage
container during the movement of material.
CA 02618209 2008-02-08
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Another aspect of the invention relates to a probe optimized for measurement
of
material which has a large component of surface reflections relative to light
paths passing
through the particles of bulk of the material in a diffuse, scattering path.
Measurements
may be required in mixing vats and the like, for example, a measurement in a
vat of a
pharmaceutical mixture of an active substance and an inactive substance or
filler, both of
which may have a large component of surface reflections. The present invention
contemplates the use of a probe for measuring the spectra of a such a mixture
using
preexisting window in the vat or other container. The use of the subject probe
can be
particularly important for analyzing the amount of dispersion of an active
ingredient within
a inert or inactive ingredient, or quantifying the heterogeneity of such a
mixture.
All aspects of the current invention include a probe which has the capability
of
simultaneously forcing the optical path via an optical block, together with a
reference
shutter or similar aspect which offers easy quality control and updates the
systems'
instrument calibration.
II. Definitions
For convenience, the meaning of certain terms and phrases employed in the
specification and appended claims are provided below.
The term "light" as used herein refers to radiant electromagnetic energy which
may
be in the visible or non-visible wavelength (s) range, which is detectable by
spectroscopic
techniques. The term includes radiant energy at visible, infrared and
ultraviolet
frequencies.
As used herein, the terms "spectrophotometric" and "spectroscopic" are used
interchangeable and refer to the spectral properties of a sample, such as the
degree to
which the sample transmits or reflects electromagnetic radiation at certain
frequencies. The
systems and methods of the present invention can employ, for example, W-VIS
spectroscopy, IR spectroscopy or Raman spectroscopy to determine the
spectroscopic
characteristics of a sample.
The expression "near-infrared spectroscopy" is used to designate methods of
measurements based upon the interaction between matter and electromagnetic
radiation in
the wavelength range fi-om 700 to 2500 nm. The reason for using this
expression is that it
CA 02618209 2008-02-08
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refers to the part of the infrared wavelength range lying closest to the
visual range of the
spectrum (400 to 700 nm). In the literature, the expression "near-near-
infrared range" is
used for electromagnetic radiation with wavelengths from 700 to 1200 nm.
Near-infrared spectroscopy can be used in the subject systems for determining
components of various materials, e.g. proteins, nucleic acids, fatty acids and
water to name
but a few. Each type of chemical bond such as O-H, C-H, C=O, C-N, N-H, absorbs
light at
wavelengths characteristic for the molecule part concerned. The cause of the
absorption is
that two different atoms being bonded to each other function in the manner of
an electric
dipole taking energy from the electric and magnetic fields in the radiation,
making the group
of atoms concerned vibrate. Thus, a C=0 bond in a triglyceride will absorb
light at a
wavelength, that is different from that absorbed by a C=0 bond in a protein
molecule. By
measuring how much the light is changed by passing through a sample at
multiple
wavelengths, it is possible to determine the percentage of a component of the
sample.
III. Exemplary Embodiments
Referring to the insertion probe embodiment of the present invention, there is
provided a probe head 100, as shown in Fig. 1, for spectroscopic measurement
of properties
of matter, for instance grain. The probe head 100 includes a shaft 102 having
a distal end
104 spaced apart along the longitudinal axis of the shaft from a proximal end
106. The
probe head 100 is designed to be inserted into a material to create a flow of
material past
and around the probe head during spectroscopic analysis to facilitate rapid
and accurate
analysis of the material. To this end, the shaft 102 and the distal end 104 of
the probe head
100 preferably are adapted to penetrate and travel in a mass of flowable
material, such as,
grain, by optimizing the shape of the shaft 102 and the distal end 104 to
minimize
turbulence within the material when the probe head is inserted into the
material. For
example, the shaft 102 can be cylindrical in shape, having a circular cross-
section, and the
distal end 104 can have a conical shape that tapers to a point to form an
insertion point for
the probe head 100, as illustrated in Fig. 1. One skilled in the art will
recognize, however,
that the shaft 102 can be constructed with alternative cross-sectional shapes,
such as, for
example, elliptical, oval, or rectilinear, without departing from the scope of
the present
invention. In addition, one skilled in the art will appreciate that the shaft
102 can have a
CA 02618209 2008-02-08
-18-
non-uniform cross-section, although a uniform cross-section is preferred, as
illustrated in
Fig. 1, to minimize turbulence in the sample material. Likewise, the distal
end 104 of the
shaft 102 is not limited to the conical shape illustrated in Fig. 1. The
distal end 104 can be
constructed having alternative shapes selected to minimize turbulence or wear
as the probe
head is inserted into the sample material.
The shaft 102 may be made of metals such as stainless steel, steel or
aluminum; or
made from moldable and durable plastic; or other materials. The materials may
be chosen
for ease of cleaning and maintenance. The shaft 102, including the distal end
104, can also
be constructed of material which optimizes the appropriate measurements of the
sample
material. To further optimize the flow of material as the probe head 100 is
inserted, the
probe head shaft 102 and ends 104 and 106 are preferably constructed from
materials, or
coated with a material, to minimize friction between the probe surface and
sample matei-ial.
The probe head 100 may also include an upper window 160 and a lower window
130 positioned circumferentially about the cylindrical shaft 102. Each of the
windows can
be formed of a suitable material, such as sapphire or glass, which is
transmissive at the
wavelengths of interest, and which does not see a significant absorption shift
due to
temperature changes. Sapphire also resists scratching and, therefore, debris
brushing against
its surface will not damage the window.
In one embodiment, a light source 140 may be placed within the cylindrical
shaft
102 between the distal end 104 and the lower window 130. The source may be,
for
example, a hot filament of a white light bulb, or any other material capable
of generating
light. In other embodiments, the light source can be a number of (power) laser
diodes, each
emitting light of a respective wavelength. Typically, multiple (e.g., 4-20)
diodes can be
placed on the same chip. Each laser diode emits light over a small range of
wavelengths
within the range from 800-1050 nm. In certain instances, e.g., where the laser
has a small
irradiation area, it may be desirable to include a lambertian diffuser through
which the laser
light passes, in order to provide the wide angle irradiation contemplated for
the subject
probe.
The probe head 100 may also include an optical pick-up, 190, arranged to
receive
light emitted from the sample in the irradiated sample volume 150 and transmit
the received
light to, for example, a spectrometer, for analysis. The optical pick up 190
can be an
CA 02618209 2008-02-08
- 19-
aperture, a waveguide, an optical fiber or any other optical element suitable
for transmitting
light for analysis.
Adjacent to the light source 140 is ai-eflector 118, which may be secured
within the
cylindrical shaft 102 against an optical blocking element 170, discussed
below, separating
the upper window 160 from the lower window 130. The reflector 118 includes a
first
reflective surface 120 that reflects and shapes the light output from the
light source 140
through the lower window 130, so that when the probe head 100 is inserted into
matter of
which the properties are to be measured, the output from the light source 140
may be
caused to diffuse from the shaft 102 into the matter surrounding the probe
head 100.
The pattern of light diffusion from the shaft 102, in one embodiment, is
illustrated in
Fig. 1 as a cross section of a torus 150. Such a pattern may be generated when
light from
the light source 140 diffuses from the lower window 130 into the surrounding
matter and
some of the diffused light is reflected back through the upper window 160 on
the shaft 102.
It should be noted that the light entering the shaft 102 through the upper
window 160 may
be optically separated and optically blocked from the lower window 130 by the
optical
blocking element 170. Light entering through the upper window 160 may be
reflected and
concentrated by a second reflective surface 180 of reflector 118 to the
optical pick-up 190,
in this exemplary embodiment, a light collecting optical fiber 190 positioned
within the
cylindrical shaft 102. The optical fiber 190 may be a single fiber or a
plurality of fibers
with or without special shaping to the tip or inclusion of lens (es) at the
tip and may be
connected to an NIR spectrometer and analysis system 106, so that the
collected light may
be transported thereto for analysis.
The reflective surfaces 120 and 180 of the reflector 118 may be made of any
reflective material and may be oriented at any angle suitable for guiding
light from the light
source into the sample material (reflective surface 120) and for guiding light
reflected from
the material (reflective surface 180). As discussed in detail below, the angle
of the
reflective surfaces 120 and 180 can be selected to optimize the size and shape
of the sample
volume and, thereby, maximize the accuracy of the spectral analysis. In the
exemplary
embodiment illustrated in Fig. 1, the reflector 118 is diamond-shaped in cross-
section and is 30 composed of two cone-shaped halves 122 and 124, each having
an outer surface that forms
one of the reflective surface 180,120, respectively. The upper cone-shaped
half 122 is
CA 02618209 2008-02-08
-20-
inverted and contacts the lower cone shaped-half 124 such that the bases of
the cone-shaped
halves meet along a center line 126 of the reflector 118. Thus, a plane
oriented
perpendicular to the axis of the shaft 102 and passing through the center line
126 of the
reflector 118 is a generally circular in shape. The reflector 118 can have a
unitary
construction, as illustrated in Fig. 1, or can be constructed from multiple
components
connected to form a single reflector or separated such that the reflective
surfaces 120 and
180 are provided on two or more independent reflectors. One skilled in the art
will
appreciate that the size and shape of the reflector 118 can be varied to
provide the optimal
size, shape, and orientation of the reflective surfaces 120,180.
In a preferred embodiment, the optical fiber 190 and the light source 140 are
arranged on a common axis that is parallel to the longitudinal axis of the
shaft 102. One
skilled in the art will appreciate that the optical fiber 190 and the light
source 140 can be
positioned along an axis that is oriented at an angle from the longitudinal
axis or the shaft
102. In addition, the distance between the light source 140 and the optical
fiber 190, as
well as the reflector 118, can be varied and is preferably selected to
optimize the size and
shape of the sample volume being analyzed.
As discussed above, the upper window 160 and the lower window 130 may be
separated by an optical blocking element, such as light-blocking ring 170 in
the exemplary
embodiment illustrated in Fig. 1. The light-blocking ring 170 is preferably
made of an
opaque material and is provided to discriminate against surface reflection
from the material
being probed and from the upper window 160 and the lower window 130 by forcing
the
path length of the light into the sample material being analyzed. The
thickness, t, shown in
Fig. 1 of the light-blocking ring 170 can be varied according to the optical
characteristics of
the material being probed and is preferably selected to maximize the accuracy
of the
spectral analysis by blocking and, thus, inhibiting surface reflections from
reaching the
optical pick-up 190. One skilled in the art will appreciate that the light
blocking element
170 is optional, as in certain embodiments the influence of direct surface
reflections on the
accuracy of the spectral analysis may not be a concern.
RefeiTing now to Fig. 2, in order to provide a pattern of light diffusion and
reflection to permit optimal collection and measurement, the reflective
surface 120 and the
reflective surface 180 may be configured so that its optical surface may
correspond to a
CA 02618209 2008-02-08
-21-
revolution of a section of an ellipse 210. It is well known from optical
geometry that light
rays from one focal point of an ellipse will reflect to the other focal point
of an ellipse.
Therefore one of the optimal shapes of the reflector surfaces 120 and 180 is a
shape which
coiTesponds to an ellipse. The equation of an ellipse which governs this
relationship is
x s z
- + y =1
a b
where a is the distance from one focal point to a point on the ellipse
surface, and h is the
distance from the other focal point to the same point on the ellipse surface,
as best
illustrated in Figs. 5a-5b. This equation also describes the optimal surface
for the reflective
surfaces 120 and 180. For a given material, the optimal focal points in the
material may
change, and thus change the parameters a and b in the equation above.
The ellipse 210, in one embodiment, preferably has one of its foci 220 at the
light
source 140 and another 230 at a diffusion length into the sample at a level of
symmetry,
e.g., substantially equivalent to the height of the block 170. An analogous
ellipse 212, has a
foci 191 at the tip of the fiber and a second foci 230 at a diffusion length
into the sample, as
best illustrated in Figs. 5a-5b. Thus, the geometry or shape of the reflective
surfaces 120
and 180 preferably corresponds to the surface of ellipse 210 and ellipse 212,
respectively.
In certain embodiments, the reflective surfaces 120 and 180 may be
approximated by one or
more straight lines or one or two sections of a circle, for ease of
manufacture.
Alternatively, the reflective surfaces 120 and 180 may approximate polar
symmetry
by being a section of a square, hexagon, octagon or other polygon, so long as
such
configuration provides a pattern of light diffiision and reflection to permit
optimal
collection and measurement.
Referring to Fig. 3, the probe head 100 may be provided with a passage 310
through
the reflector 180 so that light directly from the source 140 may be collected
by the optical
fiber 190 for calibration. The passage 310 may be an open tube, and may
include reflecting
walls, or may be an optical fiber or a plurality of fibers. In one embodiment,
the passage
310 is provided with a first shutter 330 which may close the passage 310,
except during
calibration, so that during measurement of the material 315, light directly
from the source
140 may be prevented from reaching the optical fiber 190. During calibration,
the first
shutter 330 can be moved into an open position, as shown in Fig. 3, while a
cylindrical
CA 02618209 2008-02-08
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second shutter 320 may be slid into a first position over the lower optical
window 130 to
prevent any diffused light reflected from the materia1315 being measured from
reaching
the collecting optical fiber 190. In this manner only direct light from the
source 140 can
reach the collecting optical fiber 190 for calibration. The second shutter 320
may be slid 5 into a second position, shown in Fig. 3, wherein the lower
optical window 130 may be
exposed to permit light from the source 140 to diffuse into the materia1315
being measured
and reflected toward the collecting optical fiber 190 via reflective surface
180.
Alternatively, the second shutter 320 may be moved into a position over the
upper optical
window 160 to prevent any light from the matter 315 from reaching the optical
fiber 190.
In an another embodiment, the second shutter 320 may be slid into a position
over both
windows 130 and 160 for a "dark" calibration measurement, as discussed in more
detail
below.
The probe head 100, in accordance with an embodiment of the present invention,
can generate a light output which can significantly increase the volume of
material sampled.
The volume of material that may be sampled may, to a certain extent, be
dependent on the
strength of the output from the light source 140 in the radial direction, and
the scale length
of diffuse scattering and absorption in the matter being measured for the
wavelengths in
use. The volume sampled, however, need not be limited circumferentially, as
the probe can
be configured to permit light output from the light source 140 to diffuse from
the probe
head 100 approximately 360 about the shaft 102, as illustrated in Fig. 1.
Thus, as the
probe head enters or is withdrawn from a volume of matter being measured, the
volume of
material which may be measured is substantially a cylindrical donut shape
volume 410, as
illustrated in Fig. 4.
In certain embodiments, the probe head 100 and windows 130 and 160 can be
adjusted or blocked to direct the output from source 140 in a range of angles
from 0 to
360 circumferentially about the shaft 102. For example, portions of the both
windows 160
and 130 can be opaque to manipulate the angles of measurement about the shaft.
Alternatively, portions or all of the reflective surfaces 120 or 180 can be
blocked, for
example, with an opaque material or coating or formed fi=om a non reflecting
material, to
direct the output from source 140 at selected angles circumferentially about
the light source
140.
CA 02618209 2008-02-08
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In certain embodiments, the upper window 160 can include a diffuser in the
path of
the light received from the irradiated sample to ensure that only spectral
information is
measured without imaging of the sample.
Figs. 6a and 6b illustrate an exemplary embodiment according to the present
invention that is capable of being variably positioned in contact with the
moving surface of
a flowing materia1350. The illustrated probe 300 includes a probe head 301
having a light
source 304 arranged to irradiate a sample volume 310 of the flowable material
350, such as
grain, as the grain passes an irradiation window proximate the probe head 301.
The light
source 304 may be a lamp or other radiation source disposed in the probe head
301, or it
may be the radiant end of an optical fiber or other waveguide delivering light
from a source
distal to the probe head 301. The probe head 301 may also include an optical
pick-up 306,
arranged to receive light emitted from the sample in the irradiated sample
volume 310 and
transmit the received light to, for example, a spectrometer, for analysis. The
probe head 301
can be configured as illustrated in Fig. 8, discussed in detail below.
Alternatively, the probe
head 301 can be configured in a manner analogous to the probes described in
commonly
owned U.S. Patent No. 6,100,526, or in other manners known in the art.
As the illustrated probe 300 is designed to be in contact with the surface of
the
flowing materia1350. The probe preferably includes a planing element 315, that
preferably
is planar in shape and has a contact surface 302. The contact surface 302 is
shaped in a
convex downward fashion, as illustrated in Fig. 6a, such that when the planing
element
contacts the surface of the moving material 350, the planing element 315, and,
thus, the
probe 300, skims the surface of the flowing material 350 without creating
significant
turbulence in the material. Preferably, the planing element 315 is oriented at
an angle of
attack 316 that is relatively shallow, for example, less than 15 , to further
minimize
turbulence in the sample material. One skilled in the art will appreciate that
the shape and
curvature of the contact surface 302 of the planing element 315 can be
optimized for the
material being probed and is not necessarily limited to the convex shape
described herein.
For example, the planing element 315 can optionally have a curved lip 312
along its
periphery to further minimize turbulence in the material, as illustrated in
Fig. 6c.
CA 02618209 2008-02-08
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The planing element 315 can be made from such materials as stainless steel,
steel or
aluminum; or made from moldable and durable plastic; or from other materials.
The
material of the planing element 315 is preferably optimized to the material
being analyzed.
For example, the planing element 315 can be made from a strong, abrasive
resistant metal,
ceramic, or other material to facilitate measurement of an abrasive material
such as grain.
Alternatively, the planing element can be made from a low-friction material or
coated with
a friction reducing material.
The illustrated probe 300 is supported by a shaft 318 and may also include a
constant force generator 320 for applying a constant static force to the
planing element 315
of the probe head 301 to maintain the planing element 315 in contact with the
surface of the
sample 350. The constant force generator 320 can be a spring, weight or
pneumatic system
such as a piston device for tensioning the probe head 301 against the sample
350. The
exemplified probe 300 may also be provided with bearings 325 to help guide the
motion of
the shaft 318 supporting the probe head 301.
Fig. 7a illustrates yet another aspect of the present invention, showing an
embodiment of a multihead probe system for spectroscopic analysis of a moving
sample of
a flowable material. In particular, the invention provides a probe assembly
400 including a
plurality of probe heads 401, e.g., which are simultaneously (relative to each
other) able to
irradiate and collect spectral information on a moving sample 410. The probe
heads 401, in
the illustrated embodiment, are disposed in a common housing 420 which is
preferably
shaped so as to minimize turbulence in the moving sample 410. Preferably, the
housing
420 is streamlined in shape, with the shape providing a large force normal to
the free stream
of the material and as little drag as possible. In one embodiment, illustrated
in Fig. 7b, for
example, the housing 420 may be shaped like an airfoil, having a rounded
leading edge 412
that prevents flow separation.
In general, each of the plurality of probe heads 401 may include a light
source 404
arranged to irradiate the moving sample 410. The light source 404 may be a
lamp or other
radiation source disposed in the probe head 401 or it may be the radiant end
of an optical
fiber or other waveguide (not shown) delivering light from a source distal to
each of the
probe head 401.
CA 02618209 2008-02-08
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The probe heads 401 will also each include an optical pick-up 406, arranged to
receive light energy reflected or otherwise emitted from a sample in the
irradiated sample
volume. The optical pick-up 406 receives light reflected or emitted from a
moving sample
410 being irradiated, and is in optical communication with one or more
detectors of the
spectrometer which measure the intensity of the reflected light, e.g., in a
wavelength-
dependent manner. The detectors can be located distal to the probe head 401 in
a
spectrometer 450, as illustrated in Fig 7a, and the optical pick-ups 404 may
each be an
aperture in the probe head 401 connected with an optical fiber 430 or other
waveguide
which communicates light reflected or emitted by the moving sample 410 to the
detector.
Alternatively, the detector may be proximal to the irradiated sample, e.g.
with the probe
head 401, and the pick-up may simply be an aperture for permitting light being
reflected by
the sample to enter the probe head. Such a probe head is illustrated in Fig. 8
and described
in more detail below.
In certain embodiments, the probe heads 401 can be arranged along the
longitudinal
axis of the shaft, such as shown in Fig. 7a. In other embodiments, the probe
heads 401
may be arranged in a two dimensional matrix. There may be from as few as 2
probe heads
401 to, in certain embodiments, hundreds of probe heads 401 in the array. The
probe heads
401 can be placed below the center line of the housing 420, as illustrated in
Figs. 7a and 7b,
or can be located in other positions within the housing. Preferably, the probe
heads 401 are
located along common axes that are preferably oriented parallel to the
longitudinal axis.
The probe heads 401 may be evenly spaced along each axis, as illustrated, or
may
alternatively be placed at independent, discreet distances from one another
depending on
the shape of the housing 420 and the material being analyzed.
Each probe head 401 may include a single light source and a single optical
pick-up,
as illustrated in Figs. 7a and 7b. This would facilitate, for example, probe
heads 401 placed
so as to sample the flowing material from two different locations.
Alternatively, the
housing 420 may include more probe heads than light sources, so that one light
source
provides light for more than one probe head 401. This would facilitate, for
example,
multiple measurements made simultaneously increasing the temporal utilization
of a
spectrometer. A skilled artisan recognizes that these simultaneous
measurements are
averaged in a rigorous way which maximizes resolution.
CA 02618209 2008-02-08
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Likewise, the multiprobe head systems can include fewer spectrometers or
detectors
than probe heads 401, wherein the signals from multiple pick-ups are combined
before
being communicated to the detector. Alternatively, the spectrometers can be
set for series
or parallel multiplexing of the optical signals in the pick-ups.
Fig. 8 shows a probe head 90 for analyzing the constituent or color components
of a
sample 14. The applications of the spectral analyzer device are rather
unlimited as it can be
used in any situation that requires or benefits from a large illumination spot
size and wide
angle viewing detector. The probe head 90 is particularly suited for use in
the embodiments
described above in connection with Figs. 6a-c and 7a-b.
The probe head 90 uses a suitable continuous or pulsed irradiating light
source 10.
Radiation from the light source 10 shines forward through a first window 12 to
the surface
of a sample 14. The light source 10 simultaneously produces light of multiple
wavelengths
in a region of interest. Depending on the application, the present invention
supports
wavelength analysis in a range of LJV, visible, and infrared nanometers. The
actual range
of light used in a particular application depends on the wavelength response
of the detector
which is matched with a light source capable of emitting such wavelengths.
The desired range of wavelengths to be analyzed dictates the type of detector
used
in the present invention, which typically is wavelength limited. For example,
a fairly
inexpensive silicon photodiode array is capable of detecting light intensities
of wavelengths
between 400 and 1100 nanometers. Other detectors optionally used in the
invention are
lead sulfide and lead selenide detectors, which support a response between
1000 to 3000
nanometers and 3000 to 5000 nanometers respectively. Optionally, other
detectors used in
the invention for near-infrared radiation include silicon, germanium, InGaAs,
and PMTs
(Photo-Multiplier Tubes).
The light source 10 is positioned to shine upon the sample 14 to be analyzed.
Preferably, the light source 10 is a quartz halogen or tungsten filament bulb
and is widely
available.
The light source 10 and related components are preferably positioned within a
suitable housing 11. In such an instance, a first window 12 is disposed
between the light
source 10 and the sample 14 to be analyzed. This prevents debris from entering
the cavity
and obstructing the illuminating light source 10. The first window 12 is
formed of a
CA 02618209 2008-02-08
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suitable material, such as sapphire or glass, which is transmissive at the
wavelengths of
interest, and which does not see a significant absorption shift due to
temperature changes.
Sapphire also resists scratching and, therefore, debris brushing against its
surface will not
damage the window.
The housing 11, including the enclosed light source 10, first window 12, and
other
related components to be described, is thus positioned to monitor the sample
14 to be
analyzed. This is accomplished by positioning the housing 11 such that light
radiating from
the light source 10, shines through the first window 12 onto the sample 14.
The housing 11 can be positioned such that the first window 12, as well a
second
window 13, contact an observation window 15, which may be a part of a
preexisting
window in a sample containment apparatus, e.g. an observation window in a vat,
bin, or the
like.
A parabolic mirror or reflector 17 is disposed within the light source cavity
to direct
light from the light source 10 to the sample 14 being analyzed. In the
preferred
embodiment, the light emanating from light source 10 is either collimated or
focused to
enhance the intensity of the light reflected off the sample. However, lens 20
optionally
provides a means of additionally focusing or de-focusing the light into a more
or less
intense beam. In other words, the irradiated light shining on the sample 14 is
optionally
focused to enhance the source.
In an alternate embodiment, more than one light source 10 can be used, such as
an
array of e.g., semiconductor lasers or light emitting diodes. Typically, the
array would be
focused on the same point.
It is preferred that the light source 10 be placed such that it directly
illuminates the
sample 14 to be analyzed through the first window 12 with no fiber optic or
other device
other than the first window 12 itself being disposed between the light source
10 and the
sample 14.
In the preferred embodiment, the illumination spot size from the light source
10
onto the sample 14 is approximately 1 to 3 inches in diameter, creating a spot
of light
between 0.5 and 10 square inches. Effectively, the incident light 48 shines
through the first
window 12 onto the sample 14 to produce reflected light 49 directed towards
the second
window 13 and an analysis chamber where light intensities are analyzed.
CA 02618209 2008-02-08
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A wide illumination spot size and corresponding viewing aperture is preferred
because it results in more accurate measurements of the sample 14 to be
analyzed. This is
due to the fact that small inhomogeneities relative to the larger spot size
within a sample
region are typically negligible with respect to the whole. In other words, the
wider spot size
produces a better averaging effect because a potential inhomogeneity in a
sample is not at
the focus of the illumination spot.
Without a wide viewing aperture, colorimeter and constituent measurements
based
on small spot sizes can produce inaccurate results if the operator of such a
device
erroneously takes a sample measurement of an inhomogeneity in the sample not
representative of the whole. For example, a small black spot on a dark blue
background
barely detectable by the naked eye could fool an operator that the color of
the sample is
black rather than blue. The above-described probe embodiments help to reduce
erroneous
colorimeter measurements by advantageously including a wider illumination spot
size and
viewing detector to support the aforementioned color averaging effect.
Spectral analyzers available in the market often incorporate costly optical
hardware
for receiving the light reflected off a sample 49 and directing it to an
optical detector
located at a distance. To view even a small spot with these systems requires a
high
intensity light source. This method of using optical hardware to redirect the
reflected
sample light 49 limits the spot size to a narrow diameter because the
reflected light must be
focused into a small fiber optic cable.
The exemplary embodiment described, on the other hand, advantageously
positions
a detector 52 with a wide viewing aperture located in a second chamber 65
immediately
adjacent the first chamber 68 to receive the reflected sample light 49. This
eliminates the
need for costly fiber optic hardware because received light no longer needs to
be directed to
a detector at a remote location. Rather, reflected sample light 49 naturally
strikes a detector
52 located immediately in the second chamber 65. To match the performance of
the pi-esent
probes, a fiber system would require a very large fiber bundle for redirecting
reflected
sample light to a remote detector.
An optical blocking element 70 also serves to separate the first and second
windows
12 and 13 and to force the optical path of the light source 10 and the
detector 52 into the
sample 14. In this manner the incident light 48 and the sample light 49
intersect within the
CA 02618209 2008-02-08
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sample 14 and thereby discriminate against (prevent) direct surface reflection
by inhibiting
light directly reflected from the first window 12 and from the surface of the
sample at the
window 12 from reaching the detector 52.
Eliminating the fiber optic pickup and associated fiber optic cables has
advantages
in addition to enabling the use of a wider illumination spot size. Typically,
fiber optic
cables have a limited transmission bandwidth. Hence, when they are used to
steer reflected
light to a detector located far away, the spectral range of directed light is
limited to the
transmission bandwidth of the cable. Moreover, the use of fiber optic cables
are further
prohibitive because the fiber optic cables supporting the wavelengths of mid
infrared are
particularly expensive and have large throughput losses associated with them.
In some
cases, just a few meters of this type of cable can be more than a thousand
dollars. The
exemplary probe head 90 illustrated in Fig. 8 is not as bandwidth limited nor
burdened with
unnecessary additional cost because it does not incorporate any fiber optic
cables to
transmit light.
The use of a fiber optic cable to transmit the reflected sample light 49 is
additionally
undesirable because the integrity of the optical signal within a fiber optic
cable is
susceptible to heat distortion and mechanical vibrations. This is especially
true when the
fiber optic cable supports the transmission of light in the infrared region.
Both the heat
distortion and mechanical vibrations, particularly prevalent in a portable
device, negatively
impact the integrity of the mode structure of the optical signal used to
detect constituents in
a sample. By placing the detector 52 in a second chamber 65 immediately
adjacent the
light source 10 without incorporating an optical fiber in the reflected sample
light path 49,
the probe head 90 advantageously avoids the aforementioned problems.
The probe described above replaces the small fiber, which typically has an
aperture
area of less than 1 square millimeter, with a large viewing aperture of
typically 0.5 to 10
square inches. This allows for viewing large fields of view with low light
intensities. With
additional optics, the aperture size can be adjusted to create a variable
field of view and
allows a large sample to be imaged from a distance.
As mentioned, light emitted by the light source 10 passes through the first
window
12 into the sample 14 to be analyzed. Incident light 48 from light source 10
then reflects
CA 02618209 2008-02-08
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off the sample 14, where the reflected sample light 49 is angularly directed
back through
second window 13.
In the preferred embodiment, the angle of the light source 10 and detector
unit 52 in
the second chamber 65 are optimized so that most of the reflected sample light
49 is
directed to the second chamber 65 for spectral analysis of the sample 14. For
example, the
light source 10 may be optimally angled at approximately 60 relative to the
first window
12 while the detector unit 52 in the second chamber 65 may be angled at
approximately 60
relative to the second window, as shown in illustrative Fig. 8.
The first and second windows 12, 13 are preferably parallel and in the same
plane as
shown. However, other embodiments optionally include windows that are
positioned at an
angle with respect to each other, while the first and second chamber 65,68 are
still
positioned adjacent to each other.
The second chamber 65, as mentioned, includes optical devices for detecting
the
reflected sample light 49. Specifically, the reflected sample light 49 passes
through the
second window 13 into the second chamber 65 where it is spectrally analyzed.
Diffuser 59
acts to scatter the reflected sample light 49, spatially distributing the
intensity of the light
throughout the second chamber 65 for more accurate simultaneous spectral
readings and to
prevent imaging of the sample. For example, reflected sample light 49 of
various
wavelengths is more evenly distributed throughout the second chamber 65.
Otherwise, high
intensity light regions caused by reflected sample light 49 results in less
accurate
constituent measurements due to imaging effects.
Hermetically sealed chamber 46 is positioned in the second chamber 65 to
receive
reflected sample light 49. An optically transmissive third window 60 allows
diffused light
emanating from the diffuser to shine onto wavelength separator 50 and array
detector 52
(e.g., CCD), both of which are positioned within the hermetically sealed
chamber 46. This
airtight chamber protects sensitive optical components from corrosive and
measurement-inhibiting elements such as humidity and dust. Without the
hermetically
sealed chamber 46, a buildup of dust and other debris on the detection unit 52
and
wavelength separator 50 will negatively effect constituent measurements. It
should be noted
that all, none or part of the second chamber 65 is optionally designed to be
hermetically sealed.
CA 02618209 2008-02-08
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The wavelength separator 50 within hermetically sealed chamber 46 in a
preferred
embodiment provides spatial separation of the various wavelengths of diffusely
reflected
light energy of interest. Suitable wavelength separators 50 include linearly
variable filters
(LVF), gratings, prisms, interferometers or similar devices. The wavelength
separator 50 is
preferably implemented as a linearly variable filter (LVF) having a resolution
(Avk, where
k is the wavelength) of approximately one to four percent.
The now spatially separated wavelengths in turn are fed to the detector 52.
The
detector 52 is positioned such that it simultaneously measures the response at
a broad range
of wavelengths. In the preferred embodiment, the detector 52 is an array of
charge coupled
devices (CCDs), which individually measure the light intensity at each of the
respective
wavelengths. In other words, each cell of the CCD array is tuned to measure
the intensity
of an individual bandpass of light.
Other suitable detectors 52, however, are constructed from fast scan
photodiodes,
charge injection devices (CIDs), or any other arrays of detectors suitable for
the task of
simultaneously detecting the wavelengths of interest.
In a preferred embodiment, the detector 52 is a silicon CCD array, such as a
Fairchild CCD 133A available from Loral-Fairchild. This CCD array 52 is a
1,024-
element array processing wavelengths in the range from about 570 to about 1120
nm. As
mentioned, other detectors supporting different bandwidths are optionally
used.
In addition, the detector 52 such as a CCD array is typically temperature
sensitive so
that stabilization is usually preferred. Cooling is achieved using a
thermoelectric cooler.
The preferred embodiment of the present probe also includes a reflector 22
disposed in the
first chamber to reflect reference photons 23 to the wavelength separator 50
and
detector 52 positioned in the second chamber 65 depending on the position of
the light
blocking shutter, discussed below. The reflector 22 is preferably fixed such
that repeated
measurements are based upon the same reference light intensity.
A light blocking shutter 19 is provided to selectively allow the appropriate
light to
flow into the second chamber 65. Shutter 19 controls the passage of either
sample light 49
into the second chamber 65, or the passage of reference light 23 reflected off
reference light
reflector 22 into the second chamber 65. The second shutter 19 can also be
used to block
CA 02618209 2008-02-08
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all incoming light for measuring a "dark" reference signal. Shutter 19 can
also be
implemented as a dual shutter mechanism, as will be understood by one of skill
in the art.
Control electronics and shutter motor 18 located adjacent to the second
chamber 65,
provide a mechanism for controlling light into second chamber 65. Shutter
position
commands are received via electronic signals transmitted by controller 35
residing in the
electronics block 30.
Light blocking shutter 19 is appropriately positioned for each of three
measurements. A first measurement involves blocking both the reflected sample
light 49
and reference photons 23. This reference measurement of the "dark" second
chamber 65
serves as a means of calibrating the detector unit or array 52. A second
measurement
involves blocking the reflected sample light 49 and measuring the reference
photons 23.
This measurement serves to calibrate the system to the light source 10.
Finally, a third
measurement involves blocking the reference rays 23 and measuring the
reflected sample
photons 49. Details of the measurements and related computations are further
described in
Fig. 9.
The electronic signals 27 are bundled together in a wire harness 28 connecting
the
pt-obe head housing 11 and electronics block 30. In a practical deployment of
the probe
head 90, it is preferred that the electronics block 30 be as close. as
possible to housing 11.
However, in some applications it may be necessary to separate the probe head
90 and
electronics block 30.
The electronics block 30 includes an analog to digital converter 33, a
constituent
computation function 34, a controller 35, and a display interface 36. In the
preferred
embodiment, the computation function 34, controller 35 and display interface
36 are
implemented as software in a computer, microcontroller, microprocessor and/or
digital
signal processor. Electronic signals 27 in wii-e harness 28 provide
connectivity between the
electronics in the probe head housing 11 and the electronics block 30.
As mentioned, one application of the systems of the present invention involves
mounting the electronics block 30 in a shielded environment, such as a cab,
while the probe
head 90 is mounted in a position to detect the sample 14 to be analyzed.
Therefore, based
on this separation, the electronics are designed to ensure that signal
integrity does not suffer
because of the length of the wire harness 28. For example, the electronic
signals 27 within
CA 02618209 2008-02-08
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wire harness 28 are properly shielded to prevent excess coupling noise, which
may
deleteriously effect A/D readings of the CCD array detector 52. The controller
35
coordinating the A/D sampling process, as mentioned, controls the shutter
mechanisms
positioned in the second chamber 65 for the various spectral measurements.
The individual electrical signals provided by the CCD for each wavelength are
then
fed from the output of the detector 52 to analog to digital converter 33 where
the electrical
signals are converted to digital signals for processing.
A computation block 34, preferably implemented in a microcomputer or digital
signal processor as described above, then carries out calculations on the
basis of the
received wavelength intensities to obtain either the color characteristics or
percentage
concentrations of constituents of the sample 14. The results of the sample
analysis are then
communicated to an operator in any desired way such as by a meter or
presenting them to a
display. The display is optionally integral to a laptop computer or display,
such as an LCD,
on or near the electronics block 30 or probe head 90. The computation block
may be part
of the electronics block 30 or may be physically separated from it.
In the preferred embodiment, the electronics block 30 and probe head 90 are
integrated to produce a handheld portable spectral analyzer. This embodiment
is
particularly beneficial in colorimeter applications that require analyzing the
sample in a
fixed location such as a home where, for example, wallpaper or paint is fixed
to a wall.
Based on its portability, the analyzer is easily maneuvered to test samples in
awkwardly
tight spaces. Additionally, because of its small size, it is less likely to be
damaged or
dropped during transit or use.
The analyzer may also support calculating constituent concentrations in
samples
such as grain. Techniques for calculating percentage concentrations of grain
based upon
samples of light and particular wavelengths are the multi-variate techniques
detailed in the
book by Sharaf, M. A., Illman, D. L., and Kowalski, B. R., entitled
"Chemometrics" (New
York: J. Wiley Sons, 1986).
Preferred wavelengths of interest depend upon the constituents being measured.
For
example, when measuring protein concentration, the algorithms makes use of
absoiptance
attributable to the vibration-rotational overtone bands of the sub-structure
of protein. At
longer wavelengths absorption coefficients are large, the path length is
short, and thus one
CA 02618209 2008-02-08
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would not sample the interior of the grain particles. At shorter wavelengths
the absorption
coefficients are small and the signal is thus weak.
The probe head 90 provides for irradiation of the sample followed by spatial
separation and detection of multiple wavelengths in parallel, making for rapid
analysis of
this sample. Moreover, since the optical portions of the unit are
substantially insensitive to
vibrations, the probe head 90 may be deployed in environments where real time
analysis of
samples is performed in harsh environments.
Furthermore, the use of the CCD array as detector unit 52 provides advantages
over
prior art techniques that use discrete or scanned diode arrays. In particular,
the CCD bins
are all filled with charge at the same time. in parallel with one another.
They are then
emptied and the results read out by the controller 35 are processed while the
CCD array
begins filling again. Based on sampling over a time period, each pixel or bin
detects
reflected light intensities off the sample over the same time interval. This
is particularly
important if the sample happens to be moving across the viewing region of the
device. In
contrast, diode arrays must be read sequentially so that for example, any
given element is
producing a signal from the sample that is distinct from those seen by
previous pixels.
The signal to noise ratio of the probe head 90 measurements may be improved by
averaging over the course of many measurements.
The preferred absorption measurement includes the following process
illustrated in Fig. 9:
1. Block both the sample reflection light and reference light from the
wavelength detector unit (step 201)
2. Perform a reading on the wavelength detector unit, storing
measurement data in D for dark spectrum (step 202).
3. Block the sample reflection light and allow reference light to shine
on wavelength detector unit (step 203).
4. Perform a reading on the wavelength detector unit, storing
measurement data in R for reference light spectrum (step 204).
5. Block the reference light and allow sample reflection light to shine
on wavelength detector unit (step 205)
6. Perform a reading on the wavelength detector unit, storing
measurement data in S for sample spectrum (step 206).
CA 02618209 2008-02-08
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7. Calculate the absorptance spectrum A, where the light absorption as
derived from these diffuse reflectance measurements is given by:
A = LoGio (R-D)/(S-D).
Further data processing therefore may provide a second derivative of
absorptance
spectrum A to remove constant and linear offsets so that only quadratic and
higher order
features in the absorptivity spectrum are utilized in the determination of
protein content. In
addition, since the absorptivity variations from the presence of protein are
quite small,
multiple realizations, averaging, and second derivative analysis are typically
used to
produce the desired absorptivity number at a particular wavelength.
An alternative embodiment of a probe head for use with a spectrometer to
analyze
material is illustrated in Figs. LOa and lOb. The probe head 501 is
particularly useful for
analyzing materials having diffuse reflecting properties such as powders,
slurries, etc. The
probe head 501 includes a light source 540 for irradiating a sample volume of
the material
510 proximate the probe head 501 through a window 530 formed in the probe head
501.
The light source 540 may be a lamp or other radiation source disposed in the
probe head
501, or it may be the radiant end of an optical fiber or other waveguide
delivering light
from a source distal to the probe head 501. Alternatively, more than one light
source 540
may be used, such as an array of e.g. semiconductor lasers or light emitting
diodes.
Preferably, the array would be focused on the same point. The window 530 may
be formed
of a suitable material, such as sapphire or glass, which is transmissive at
the wavelengths of
interest, and which does not allow for a significant absorption shift due to
temperature
changes.
The probe head 501 may also include an optical pick-up, such as, for example
an
optical fiber 590, arranged to receive light emitted from the sample in the
irradiated sample
volume and transmit the received light to, for example, a spectrometer, for
analysis. The
optical fiber 590 may be a single fiber or a multiple fiber bundle capable of
both incoherent
and coherent waves. The optical fiber 590 may be made from quartz, glass,
plastic or other
transmitting materials. Preferably, the optical fiber 590 has a numerical
aperture of 0.2 to
0.5. Optionally, the optical fiber 590 can be hollow, with adequately
reflecting walls.
CA 02618209 2008-02-08
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Alternatively, the optical fiber 590 may be replaced in situ by a detection
system, such as,
for example, in the manner of the probe head described above in connection
with Fig. 8.
The probe head 501 may be constructed out of metals such as stainless steel,
steel or
aluminum ; or made from moldable and durable plastic; or other materials. The
materials
may be translucent, transparent, or opaque and may be chosen for ease of
cleaning and
maintenance. The probe head 501 can also be constructed of material which
optimizes the
appropriate measurements of the sample material. The exterior surface 503 of
the probe
head 501 may be geometrically shaped to optimize the probe measurements.
The exemplary probe head 501 may also include an optical blocking element 550
positioned in the optical path between the light source 540 and the light
collecting optical
fiber 590. The optical blocking element 550 forces the path of light into the
materia1510
thereby reducing error due to surface reflection and increasing the signal to
noise ratio of
the spectral analysis. The optical blocking element 550 is opaque and
preferably is in
contact with or effectively splits/bifurcates the window 530. The optical
blocking element
550 may be constructed out of metals such as stainless steel, steel or
aluminum; or made
from moldable and durable plastic; or other opaque materials. In one preferred
embodiment, the optical block element 550 is biased into contact with the
window 530 by
spring loading, via a spring 555 or by other biasing mechanisms.
A typical, theoretical light path 545 is shown in Fig. 10a to illustrate an
optical path
of light into and reflected from the material 510 during data collection. The
optical block
element 550 effectively minimizes the direct surface reflection from the
window 530 or the
material 510 by blocking such direct surface reflection from reaching the
optical fiber 590.
In this manner, the allowed optical paths, including theoretical optical path
545, originates
from light source 540, undergoes diffusive transport in the material 510, and
is collected
and transported within the numerical aperture of the optical fiber 590.
The probe head 501 may include a reference shutter 520 for calibrating or re-
normalizing the spectrometer, in particular the signal processing algorithm of
the
spectrometer, to account for any signal changes relative to previous
calibrations of the
spectrometer. The reference shutter 520 includes a reflective surface 522
having a
reasonably uniform value of reflectance over the wavelength of interest. To be
effective for
calibration, the reflectance value of the reflective surface preferably
remains unchanged
CA 02618209 2008-02-08
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with regards to time, temperature, usage, etc. The reflective surface 520 may
be made out
or, or coated by, stable reflective materials such as gold, white ceramics,
Spectralon ,
stable white paint, and other such materials.
The reference shutter 520 is movable between an open, measurement position,
illustrated in Fig. 10a, and a closed, calibration position, illustrated in
Fig. 10b. In the open,
measurement position, the reference shutter 520 is positioned out of the
optical path
between the light source 540 and the optical fiber 590 to facilitate spectral
analysis of the
material 510. In the closed, calibration position, the reference shutter 520
is positioned in
the optical path between the light source 540 and the optical fiber 590 to
effectively block
light from the sample materia1510 from reaching the optical fiber 590. As
shown in Fig.
10b by illustrative, theoretical optical path 555, light from the light source
540 reflects off
the reflective surface 522 to the optical fiber 590. The reference shutter 520
may be moved
between the closed and open positions by a rotary solenoid, or by other
electromagnetic,
electromechanical, or mechanical mechanisms.
During calibration of the system, it is preferable that the optical blocking
element
550 be moved away fi-om the window 520 to allow the reference shutter 520 to
move into
the closed position, as illustrated in Fig. l Ob. Preferably, the optical
blocking element 550 is
moved a distance from the window 520, e.g., gap G in Fig. lOb, such that
sufficient light
from the light source 540 can reflect from the reflective surface 522 of the
shutter 520 and
reach the optical fiber 590 at an angle within the numerical aperture of the
optical fiber 590.
The optical blocking element 550 can be moved towards and away from the window
530 by
a rotaty solenoid, or by other electromagnetic, electromechanical, or
mechanical
mechanisms. Alternatively, the movement of the optical blocking element 550
can be
mechanically coupled to the movement of the shutter 520, as discussed below,
such that
separate movement mechanisms, e.g. solenoids, for the optical blocking element
550 and
the shutter 520 are not necessary.
Figs. 11-13 illustrate an exemplary, preferred embodiment of the probe head
501.
Figs. 11a and 11b, illustrate a prefeiTed embodiment of the optical blocking
element 550.
The exemplary optical blocking element 550 includes a blocking surface 554 for
contacting
the window 530 and a cylindrical housing 556 for attachment to the optical
fiber 590. The
cylindrical housing 556 includes an opening 558 for allowing light to enter
the cylindrical
CA 02618209 2008-02-08
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housing and reach the optical fiber 590. Spring 555, as shown in Fig. 13, can
be seated
about the exterior of the housing 556 to bias the blocking surface 554 into
contact with the
window 530. The blocking surface 554 is sized and shaped to effectively block
light
directly reflected from the window 520 and the surface of the sample
materia1510. In
particular, the width A of the blocking element, illustrated in Fig. 1 lb, is
preferably
optimized for the material 510 being probed and for the position of the light
source 540 and
the optical fiber 590 within the probe head 501, to minimize and, preferably
completely
block, light directly reflected from the window 530 and the surface of the
material from
reaching the optical fiber 590.
The optical blocking element 550 may include an arm 564 extending
perpendicularly from the longitudinal axis of the housing 556, and thus, the
optical fiber
590, and is provided to contact a camming surface of the shutter 520 to
facilitate linear
movement of the optical blocking element 550 when the reference shutter 520 is
moved
into the closed position, as discussed in more detail below. A second arm 562
may be
included to be contained within a slot within the probe head 501 to prevent
axial rotation of
the optical blocking element 550.
An exemplary embodiment of the shutter 520 is illustrated in Figs. 12a and
12b.
The exemplary shutter 520 is configured for rotational movement about a
rotation axis 572.
The shutter 520 includes a cylindrical hub 574 that can be coupled to a rotary
solenoid and
an arm 576 that extends from the hub 574 in a direction perpendicular from the
hub 574.
The arm 576 is generally planar in shape and includes the reference surface
522 formed at
the end distal from the hub 574. The reference surface 522 of the shutter 520
can thus be
rotated about the rotation axis 572 between the open and closed position.
A camming arm 578 is provided proximate the reference surface 522 and extends
generally perpendicular to the longitudinal axis of the arm 576. The camming
arm 578
includes a camming surface 582 for engaging the arm 564 of the optical
blocking element
550 in a camming relationship. As the shutter 520 rotates the reference
surface 522 from the
open position, illustrated in Fig. 10A, to the closed position, illustrated in
Fig. l Ob, the
camming surface 582 engages the arm 564 of the optical blocking element 550 to
move the
blocking surface 554 out of contact with the window 530. Thus, the camming
surface 582
CA 02618209 2008-02-08
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translates the rotational motion of the shutter 520 into axial motion along an
axis generally
perpendicular to the window 530.
EQUIVALENTS
While this invention has been particularly shown and described with references
to
preferred embodiments thereof, it will be understood by those skilled in the
art that various
changes in form and details may be made therein without departing from the
spirit and
scope of the invention as defined by the appended claims. Those skilled in the
art will
recognize or be able to ascertain using no more than routine experimentation,
many
equivalents to the specific embodiments of the invention described
specifically herein. Such
equivalents are intended to be encompassed in the scope of the claims.
