Optics: measuring and testing – For light transmission or absorption
Reexamination Certificate
2001-03-09
2004-06-22
Lee, Michael G. (Department: 2876)
Optics: measuring and testing
For light transmission or absorption
Reexamination Certificate
active
06753966
ABSTRACT:
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 spectroscopy technology, it is possible not only to determine the characteristics of a sample 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 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 transport 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 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 (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 comm
Foley & Hoag LLP
Franklin Jamara A.
Lee Michael G.
Textron Systems Corporation
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