NEAR INFRARED MEASUREMENT APPARATUS FOR ORGANIC MATERIALS

Abstract: An instrument (10) for near infrared interactance quantitative analysis measurements to improve accuracy and repeatability of the measured results. These objectives are achieved by placing a narrow bandpass optical filter (23) between near infrared emitting diode radiation sources (16, 16', 17, 17', 18 and 18') and a radiation transmission tube (12). The filter (23) allows for more distinct isolation of the desired wavelengths in the measurement to achieve improved accuracy and repeatability. The filters (23) also eliminate the time consuming task of sorting through several diodes in search of a particular diode (16, 16', 17, 17', 18 and 18') whose output wavelength band is centered at the desired wavelength.

Description: "NEAR INFRARED MEASUREMENT APPARATUS FOR ORGANIC MATERIALS" Field of the Invention This invention relates to improvements in instru- ments for performing near infrared quantitative analysis of organic constituents that are present in materials. BACKGROUND OF THE INVENTION Near infrared quantitative analysis instruments for measuring constituents such as fat or oil present in a sample material are known and commercially available. One type of near infrared quantitative analysis instru¬ ment analyzes near infrared energy reflected off of a surface of the sample to provide quantitative data on organic constituents present in the material. This type of instrument requires that the sample surface be very consistent, thereby necessitating that the material be ground into a fine powder with consistent particle size. For some types of samples, such as sunflower seeds, this is practically impossible. Another type of near infrared quantitative instru¬ ment analyzes the energy transmitted through a finite thickness of sample (e.g., 2 cm) to provide quantitative data on the amounts of organic constituents present in the sample. An example of an instrument of this type is described in commonly owned U.S. Patent No. 4,286,327 granted August 25, 1981 to Robert D. Rosenthal and Scott Rosenthal, entitled "Apparatus for Near Infrared Quantitative Analysis." This type of transmission measurement approach avoids the requirement that samples be ground into a uniform particle size powder as in the previous described reflectance measurement system. However, the transmission approach requires that access to the sample be available on two opposite surfaces, one surface where near infrared energy enters the sample, and an opposite surface where energy exits the sample. In certain applications, such as measurement of a person's body fat and the like, neither the reflectance measurement need for grinding the sample into a uniform powder, nor the transmission need for a two-sided measurement, can be accomplished. In these situations, still another type of near infrared quantitative instru¬ ment has proven useful. Such instrument utilizes near infrared radiation and an optical interactance principle wherein a source of light is directed into the sample material in a circular pattern by an illumination tube, and a detector is positioned in the center of the illum¬ ination tube. The near infrared radiation goes into the sample material, and via interactance, a portion of the energy is reemitted from the material in the center of the illumination tube, where it is detected by the detector and utilized for a reading. A commercially available instrument that utilizes this technique is manufactured and sold under commonly owned U.S. Patent No. 4,633,087, granted December 30, 1986 to Glenn K. Rosenthal, Jeffrey D. Stevens and Robert D. Rosenthal, entitled "Near Infrared Apparatus for Measurement of Organic Constituents of Materials." For applying the principle of infrared radiation interactance, such device utilizes multiple, selected wavelength, infrared emitting diodes (IREDs) that provide the source of optical radia¬ tion through a translucent tube. Such device employs pairs of matched IREDs, and manufacturing the device has heretofore required that the IREDs be sorted for the particular wavelengths that are used to make the measure- ments. Due to manufacturing tolerances, the exact center wavelengths of a particular production batch of IREDs generally vary, requiring each production batch to be sorted to provide matched pairs of IREDs, and to identify those IREDs that have the particular center wavelengths which are most suitable for making measurements. When there are IRED production runs where there happen to be little variation in center wavelengths, a large number of IREDs must be tested in order to select out those few that provide the wavelengths required. Such time-consuming testing procedures and waste of unsuitable IREDs adds considerably to the production costs of the instrument. Accordingly, there remains a need in the art for improvements in near infrared radiation interactance instruments that avoid unnecessary sorting and waste of IREDs in the manufacture of the instruments. SUMMARY OF THE INVENTION The present invention avoids time-consuming and wasteful sorting of IREDs during the manufacture of previously described near infrared radiation interactance instruments by interposing narrow bandpass optical filters between the IREDs and the illumination tube to provide narrow band near infrared radiation of predeter¬ mined wavelength for taking measurements. The narrow bandpass optical filters provide specific wavelength selection independent of the center wavelength of the near infrared emitting diodes. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially schematic perspective view of a near infrared quantitative analysis instrument to which the invention is applicable. FIG. 2 is a detailed sectional partially schematic view showing a narrow bandpass optical filter in accord¬ ance with the invention positioned to filter near infrared radiation passing from an IRED to a light- transmitting tube. FIGS. 3A and 3B graphically illustrate relative energy transmittance to a sample by an instrument as shown in FIG. 1 in the absence and presence respectively of narrow bandpass optical filters in accordance with the invention. FIGS. 4A and 4B graphically illustrate "Figure of Merit" values for instruments as shown in FIG. 1 in the absence and presence respectively of narrow bandpass optical filters in accordance with the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is applicable to a near infra¬ red interactance analysis-'instrument as described in the above-mentioned commonly owned U.S. Patent No. 4,633,087. With reference to Fig. 1, such an instrument 10 is of hollow cylindrical form and, includes a hollow tubular member 12 having a wall of solid translucent material selected so that it transmits and does not substantially or inconsistently absorb near infrared energy in the bandwidth of interest, namely, from about 800 to about 1100 nanometers. Examples of suitable materials out of which tubular member 12 may be constructed include, but are not limited to, translucent nylon, translucent polytetrafluoroethylene and the like. Means for providing at least one point source of near infrared radiation of a predetermined wavelength is positioned at an upper end portion 13 of tubular member 12. The near infrared point source means at the upper end portion 13 of tube 12 are positioned so that near infrared radiation of a predetermined wavelength or wavelengths emitting from the point source means will be transmitted by the tubular member 12 from the upper end portion 13 to a flat bottom surface 14 of tube 12. The near infrared point source means preferably comprises a plurality of pairs of two infrared emitting diodes (IREDs). The IREDs are preferably positioned symmetri¬ cally about the upper end part 13 of tube 12, with the two IREDs which comprise a pair of IREDs being of about the same wavelength and being peripherally positioned approximately 180 * apart around the upper end of tube 12. Three pairs of such IREDs, 16, 16', 17, 17', 18 and 18*, are shown in a preferred embodiment illustrated in Fig. 1. In other exemplary embodiments, two or four pairs of IREDs are utilized as the point source means. Light transmitting tube 12 is of a suitable length to provide sufficient internal light, scattering to smooth out the pulsed light sources so that light from the IREDs is transmitted through tube 12 and emerges uniformly at the bottom surface of the tube. For example, a suitable length for a 1 inch diameter extruded translucent nylon tube, having a wall thickness of 1/8 inch, is about 1-3/4 inch. Preferably, the tube 12 is no longer than is necessary to uniformly smooth out the pulsed light sources, in order to minimize the loss of near infrared radiation. The ideal tube length can be easily deter¬ mined by utilizing a commercially available infrared viewer (nightscope) . A tube may be sized by observing near infrared radiation passing through the tube and trimming the tube until the light emerges uniformly. A silicon detector is then passed around the end of the tube to check for uniform output. For light shielding purposes, the cylindrical walls of tubular light transmitting member 12 are shielded on the outside by an outer tubular opaque shield 20 and on the inside by inner tubular opaque shield 22. The upper end portion 13 of tubular member 12 is also shielded from ambient light by a top cover, not shown. An optical detector 28, capable of detecting near infrared radiation, is positioned inside of and at the bottom end portion of the tubular member 12. Inner tubular shield 22 is positioned between detector 28 and transmitting tube 12, thereby providing an opaque mask which prevents near infrared radiation from tube 12 from impinging directly on detector 28. Optical detector 28 generates an electrical signal when the detector detects near infrared radiation. The optical detector 28 is connected to the input of an electrical signal amplifier 30 by suitable electrical conducting means 33. Amplifier 30 may be an inexpensive signal amplifier, and amplifies signals generated by detector 28 in response to radiation detected by the detector. The detector 28 preferably is positioned within tube 22. The output of amplifier 30 feeds the amplified signal generated by detector 28 to a readout box 32 through conductive lines 34. The readout box 32 may have a display 36 for directly reading the percentage of fat in a sample material S. An electrically conductive window 29, which is transparent to near infrared energy, is grounded directly to the apparatus electronics. Window 29 is located in front of the optical detector 28. This conductive window provides shielding from electro-magnetic interferences that are commonly encountered in industrial and consumer premises. The presently described instrument is of the type that utilizes the principle of interactance, which principle is known in the art and differs from reflect¬ ance and transmittance. In interactance, light from a source is shielded by an opaque member from a detector and interactance of the light with the test subject is then detected by the detector. The instrument takes multiple readings of each IRED and utilizes data processing means to lower the noise. Multiple readings of each IRED is accomplished by feeding the output of amplifier 33 to an integrating analog-to- digital converter 40 having a twelve bit output, which is connected to a digital processor 41 connected to readout box 32. In operation, window 29 is positioned against a surface of test subject S. Light emerging from tube 12 interacts with test subject S and is detected by detector 28. Detector 28 then generates an electrical signal which is processed as described above. An instrument as described up to this point is as disclosed in the previously mentioned and commonly owned U.S. Patent No. 4,633,087. Such instrument utilizes near infrared emitting diodes (IREDs) 16, 16', 17, 17', 18 and 18' which are spaced 60 * apart with IREDs of similar wavelengths being spaced 180 * apart about the upper end portion 13 of light-transmitting tube 12. As noted above, because of variation in the exact center wave¬ length of each production batch of IREDs, manufacturing such an instrument previously required laborious sorting of the IREDs for particular wavelengths due to variation of the exact center wavelengths of the IREDs in each production batch, resulting in considerable waste and expense. The present invention eliminates the need for such sorting and waste by providing narrow bandpass optical filters (as shown schematically in Fig. 2) in the light scattering tube 12 directly in front of each of the near infrared emitting diodes, such as IRED 18. A filter 23 is positioned between each IRED and tube 12 for filtering near infrared radiation exiting each IRED and thereby allowing a narrow band of near infrared radiation of predetermined wavelength to pass through the filter into tube 12. Utilization of narrow bandpass optical filters provides for specific wavelength selection independent of the center wavelengths of the particular near infrared emitting diodes being used. Each member of a particular pair of diodes has a filter that allows substantially the same predetermined wavelength of near infrared radiation to pass through. When utilizing the invention with an instrument as shown in Fig. 1, the optical filters associated with first and second pairs of near infrared emitting diodes 16, 16' and 17, 17' allow near infrared radiation having a wavelength of about 930 and about 950 nanometers respectively to pass through to the tube 12. The optical filters associated with the remaining pair of near infrared emitting diodes 18, 18' allow near infrared radiation having a wavelength between about 880 and 890 nanometers to pass through to tube 12. An additional benefit of using narrow bandpass filters in accordance with the present invention is that the filters allow more distinct isolation of the measure- ment bands, thereby providing improved accuracy and measurement repeatability. This is illustrated in a comparison of Fig. 3A showing the bandwidth spread of sorted IREDs without filters as in prior U.S. Patent No. 4,633,087, and Fig. 3B utilizing unsorted IREDs with narrow bandpass filters in accordance with the present invention. Utilization of narrow bandpass filters in accordance with the present invention significantly improves the accuracy of near infrared interactance instruments as compared to using sorted IREDs without filters, as in prior U.S. Patent No. 4,633,087. Fig. 4A graphically shows the "Figure of Merit" values for a number of instruments manufactured in accordance with prior U.S. Patent No. 4,633,087 utilizing sorted IREDs without narrow bandpass optical filters. The term "Figure of Merit" is a measure of the calibration accuracy of the instrument. "Figure of Merit" is defined as the range of data (i.e., the highest percent sample minus the lowest percent sample) divided by two times the standard error of calibration. A "Figure of Merit" of 3.0 or higher has statistical merit and can be used in commercial instru¬ ments. A "Figure of Merit" above 5 is considered a major improvement compared to a figure of merit of 3. Fig. 4B shows the "Figure of Merit" values of near infrared interactance instruments manufactured in accordance with the present invention with narrow bandpass optical filters between the IREDs and the light scattering tube. A comparison of Figs. 4A and 4B graphically demonstrates the significant improvement of accuracy that utilization of narrow bandpass optical filters " provides to near infrared interactance instruments.

Claims: CLAIMS; What is claimed is: 1. A near infrared quantitative instrument for measuring a fat/oil-containing sample material, compris¬ ing: (a) means for providing at least one point source of near infrared radiation; (b) a narrow bandpass optical filter means for filtering near infrared radiation and allowing a narrow band of near infrared radiation of a particular wave¬ length to pass through; (c) a tube having a wall portion, the wall portion comprising a material which is capable of transmitting near infrared radiation, the material having a composition which does not substantially or inconsis¬ tently absorb near infrared radiation, the tube having first and second ends, the point source means and the filter means being positioned at the first end of said tube with the filter means between the point source means and the tube for transmitting near infrared radiation through the filter means and then through the wall portion of said tube, the tube being of a sufficient . length that near infrared radiation from the point source means positioned at the first end of the tube will emerge substantially uniform at the second end of the tube; the second end of the tube for positioning against the said sample material; the second end of the tube peripherally defining a generally central area; (d) a near infrared radiation detector positioned for detecting near infrared radiation entering the generally central area peripherally defined by the second end of the tube, the detector being capable of providing an electrical signal upon detection of near infrared radiation; (e) means for preventing near infrared radiation from the wall of the tube from impinging directly on said detector; (f) means for shielding the outside of the tube from ambient light; (g) means connected to the detector for amplifying an electrical signal provided by said detector; and (h) means for data processing and readout, the data processing and readout means being connected to the amplifier means and being capable of processing the amplified signal and providing a readout indicative of the percent fat in the sample material. 2. The measuring instrument of claim 1 further including an electro-magnetic interference shield comprising a grounded electrically conductive window which is substantially transparent to near infrared energy, the window being positioned at the second end of the tube and shielding the detector from electro-magnetic interference. 3. The measuring instrument of claim 2 wherein the detector is positioned inside the tube near the second end thereof and adjacent the window. 4. The instrument of claim 1 wherein the point source means comprises a plurality of pairs of near infrared emitting diodes, the diodes being peripherally positioned generally symmetrically around the tube with filter means positioned between each of the diodes and the tube, wherein the diodes of each pair of diodes are peripherally positioned about 180° apart around the tube, and wherein the filter means associated with each diode of each pair of diodes allows substantially the same predetermined wavelength of near infrared radiation to pass through. 5. The instrument of claim 4 wherein optical filter means associated with a first pair of near infrared emitting diodes allows near infrared radiation having a wavelength of about 930 nanometers to pass through to said tube, optical filter means associated with a second pair of near infrared emitting diodes allows near infrared radiation having a wavelength of about 950 nanometers to pass through to said tube, and optical filter means associated with another pair of- near infrared emitting diodes allows near infrared radiation having a wavelength between about 880 and 890 nanometers to pass through to said tube. 6. The instrument of claim 5 wherein the data processing means compares a plurality of simultaneous readings to see if successive readings are within a predetermined tolerance. 7. The instrument of claim 1 wherein the material of the cylinder wall is polytetrafluoroethylene or nylon.

Inventors: ROSENTHAL ROBERT D, ROSENTHAL, ROBERT, D.
Applicants: FUTREX INC, FUTREX, INC.
Application year: 1988
Main classification: G01J3
IPC codes: G01J3, G01N21