Near infrared spectrophotometers (NIRS) are used in a wide variety of industries to analyze the composition of various materials. These NIRS are particularly useful in determining the composition of materials, if there are contaminants in certain materials and can provide the results of analysis within a matter of minutes. In contrast, chemical tests often take days to provide the results of analysis, by which time it may be too late to stop contaminated or otherwise inappropriate material from being used where it shouldn't be. NIRS are also more reliable and faster to calibrate than standard research spectrophotometers.
However, these machines also have a number of problems associated with them.
One problem is that most NIRS have to be individually calibrated. This is because the analysis of the data relies on determining the difference between a reference spectra and the spectra received back from the sample. This is a complex relationship and thus, anything that can affect the light path of the machine can affect its calibration. Unfortunately it takes a long time to calibrate a NIRS and the cost of doing so is approximately as expensive as the machine. However, once calibrated, the machine can work inexpensively and quickly.
A further problem can arise in that a separate calibration is required for every physical test. Thus, if the NIRS is expected to test a number of different materials, a considerable time can be spent in calibrating the machine to give meaningful results.
Because of this, at present there are a large number of organizations having a number of NIRS machines all operating independently and with separate calibrations.
Another problem is that if a machine breaks down, a considerable amount of time is required to install another machine. Usually the replacement machine has to be recalibrated while the previous machine is being repaired.
Another problem is that the on-board processing of NIRS machines is not fast enough to provide real-time results. This is a problem in that often NIRS machines are used in production lines, for example, on-line sampling of oil, wheat and so forth. A delay of some minutes before detecting whether there is say a contaminant, or a certain quality of the material, can radically slow down the production line, or result in the contaminated material not being removed from the rest of the material.
Although it may be possible to incorporate more powerful onboard processing into the NIRS, it is expensive to do so and the cost also mounts up when multiplied by a number of machines.
Yet another problem with NIRS machines is that their compactness enables them to be readily stolen and used elsewhere.
There have been several types of spectrophotometer systems designed in order to try and overcome of the problems previously mentioned, one of which was disclosed in U.S. Pat. No. 5,953,118, of O'Rourke et al, which issued Sep. 14, 1999.
The patent disclosed “According to its major aspects and broadly stated, the present invention is a high-resolution, high-sensitivity multiplexed spectrophotometry apparatus that includes an optical multiplexer with a plurality of fiber terminals, a spectrophotometer operatively connected to the multiplexer, a programmable on-board computer with chemometric software, and, in a preferred embodiment of the invention, at least one light source.”
“A major feature of the present invention is the spectrophotometer, which includes precision holographic optics, a charge coupled device (CCD) detector, electronics, and an integral cooling system. These components are fitted into a compact, streamlined housing that serves as both the spectrophotometer housing and the detector housing. The spectrophotometer is mounted to the multiplexer so that any selected optical terminal can readily be brought into precise, reproducible alignment with the spectrophotometer input.”
“. . . with a repeatability of no more than approximately 5 microns (that is, reproducible positioning to within 5 microns or less), attainable switching times no greater than approximately 1 second/channel, and high total optical throughput.”
These sections within the specification clearly show that each spectrometer has its own onboard programmable computer and is totally reliant upon the performance of the optical multiplexer.
Due to the long switching times of approximately one second per channel, this invention cannot be used for real time measurements and the fact that there has to be a physical realignment within the multiplexer for each individual input means that the accuracy and repeatability of measurements must be questioned.
This is not only due to the probability of inaccurate repositioning but also to the fact that mechanical movement of the optical system can introduce debris into the optical path thereby making any further readings inaccurate.
A further problem is that each spectrometer of U.S. Pat. No. 5,953,118 would need to be calibrated individually and it does not have a central store of calibration figures or results.
U.S. Pat. No. 5,701,175, of Kositzak et al, which issued Dec. 23, 1997, discloses a moveable spectrophotometer wherein a programmed computer can be used for identifying the position of the spectrophotometer at a given time, as can be seen from its abstract.
“A spectrophotometer mouse is provided for making color spectrum measurements of desired areas on a surface over which the mouse is moveable. The spectrophotometer mouse includes a housing shaped to conform to the hand of an operator, and a spectrophotometer in the housing having an input (such as a light receiving aperture) for measuring the color spectrum of the target area on the surface. The mouse has a position sensing encoder which is coupled to a programmed computer for identifying the position of the mouse on the surface. This programmed computer may be internal or external of the housing. The computer is used for locating the target area on the surface with reference to a pointer on the mouse, and then detecting when an operator has moved the mouse such that the input of the spectrophotometer is substantially coincident with the located target area. The computer automatically actuates the spectrophotometer so that the spectrum of light from the target area is received at the input of the spectrophotometer and is measured. In addition to providing color spectrum measurements of target areas on the surface, the position sensing features of the mouse can also be operated as a typical computer-type mouse for command input to a graphical user interface. Thus, the operator can use the spectrophotometer mouse to measuring the color spectrum of target areas on the surface, or as a typical computer-type mouse.”
This patent only deals with a single spectrophotometer and not with a series of spectrophotometer with a centralized processing unit.
It is clear from its specification that this spectrophotometer mouse is intended to be used in a stand-alone system and not as part of a group or an array, but if a number of these mice were used together then they would still have to be calibrated individually. Therefore they would still suffer from some of the major problems described earlier.
U.S. Pat. No. 5,691,817, to Cargill et al, which issued Nov. 25, 1997, discloses an apparatus and method for calibration of a spectrophotometer.
However, the disclosure still exhibits major calibration problems as the specification clearly shows (as can be seen in the enclosed excerpt below) that the calibration must be performed on each individual spectrophotometer which is not only costly and time consuming, but is also difficult.
“A spectrophotometer apparatus (200) is adapted to provide spectral reflectance measurements of object samples. The apparatus (200) comprises a source light (254) and a reflection optics assembly (264, 268). Signals representative of reflected light are analyzed and data provided to an operator representative of the spectral response characteristics of the object sample (252). The apparatus (200) further comprises a side sensor (276) having a fixed spectral responses characteristic for compensating the reflectance measurements in accordance with the light intensity emanating from the lamp. For purposes of calibration, a series of time-sequenced measurements are made of a reference sample. Utilizing these measurements, the apparatus (200) provides computations of compensation coefficients for each spectral segment. The compensation coefficients are utilized, with the side sensor measurements, to provide normalization of the reflectance measurements for each segment and for each measurement within the timed sequence. For each segment, a scale factor is then determined. The sale factors, compensation coefficients and side sensor measurements are employed to compensate actual reflectance measurements, with further compensation provided by a determination of temperature coefficients.”
It will be appreciated from the above excerpt that this patent discloses a device that is only meant to be used in a stand alone situation.
U.S. Pat. No. 5,400,138, of Peterson et al, which issued Mar. 21, 1995, discloses a portable spectrophotometer which has a data memory in which a sequence of generalized commands is stored in order that the spectrophotometer is able to perform the correct sequence of commands when used in a remote location necessitating it being disconnected from the host computer.
“A color measuring system includes a portable spectrophotometer connectable to a general-purpose computer. The portable unit includes a microprocessor with a read-only program memory storing machine executable instructions to implement data processing for color measurement purposes and input/output functions including key reading and data transfer functions and display functions. A random-access data memory is used to temporarily store process data for later transfer to the general-purpose computer. An editor program and a compiler program in the general-purpose computer may be used to generate a program for the microprocessor using high-level, generalized commands. After such a program has been written and compiled in the general-purpose computer, it is transferred to a command buffer area in the random-access data memory of the microprocessor. The microprocessor, in its program memory, includes a command interpreter including a predefined sequence of machine executable instructions for each generalized command. When executed, the command interpreter reads a generalized command from the data memory and, if necessary, updates relevant data pointers and executes the predefined sequence of machine executable functions in the program memory corresponding to the generalized command being processed. A user, using the general-purpose computer, may specify any desired sequence of measurement operations by specifying functions to be performed by the microprocessor, including the display of prompts to the operator of the portable spectrophotometer to instruct the operator to perform various specified operations.”
U.S. Pat. No. 5,400,138 not only will be unable to perform real-time measurements, but each of these spectrophotometer would need to be calibrated individually and are designed to be used remotely from the host computer and not as part of a spectrophotometry array.
The device of U.S. Pat. No. 5,400,138 is very limited in its ability and applicability in that it has to be pre-programmed with a set of command instructions and is then disconnected from the host computer which greatly limits the applications in which this device would be suitable.
U.S. Pat. No. 5,251,006, to Honigs et al, which issued Oct. 5, 1999, discloses an automatic calibration system for use on a spectrophotometer; however, this device has severe limitations in that a calibration assembly must be fitted to each spectrophotometer that needs to be calibrated.
As can be seen in the following excerpt from the specification, the core of the invention is the integration of permanent reference standards within each spectrophotometer. These reference standards are used to calibrate the spectrophotometers.
“The automatic calibration apparatus according to the invention is designed to be employed in a conventional spectrophotometer such as those disclosed in the Landa U.S. Pat. No. 4,264,205 or McGee U.S. Pat. No. 4,969,739. Central to the invention, is the integration of permanent reference standards in the spectrophotometer from which the spectrophotometers are calibrated.”
U.S. Pat. No. 5,251,006 uses a somewhat costly way of calibrating a number of spectrophotometers inasmuch as each spectrophotometer would need its own set of reference standards permanently within its structure.
This system has little advantage over those previously available as each spectrophotometer still has to be calibrated individually.
U.S. Pat. No. 4,798,464, of Boostrom, which issued Jan. 17, 1989, discloses a scanning array spectrophotometer which uses different light sources with overlapping spectral characteristics in order to improve the usable bandwidth of the spectrophotometer.
This patent does not disclose any method of calibration of the spectrophotometer other than to determine which range of wavelength can provide data that is free from objectionable errors that would originate from the source of each scan.
Because this is only a problem in a spectrophotometer which scans a wide range of wavelengths, for instance from 200 to 850 nanometers, it would therefore be irrelevant to any spectrophotometer that will only scan from about 390 to above 900 nanometers as this can be achieved from a single tungsten halide lamp.
U.S. Pat. No. 4,635,735, of Crownover, which issued Jan. 13, 1987, discloses a method and apparatus for the continuous analysis of drilling mud which is outlined in the following:
“An oil well drilling rig (10) recirculates drilling mud which is analyzed continuously by pumping it through a gas separation unit (72) where the gases in the mud become separated and mixed with the carrier gas and are conveyed to gas analyzing devices (196) where the concentration of the different hydrocarbon components of the gases in the mud are continuously measured and the signals representative of these measurements are processed together with mud flow rate, and the carrier gas flow rate or the sample gas flow rate signals in a signal processor (64) to provide a continuous log of gas component concentration during drilling.”
This system does disclose a real-time measurement system in which the results are logged in order to ascertain the material that is being measured.
The patent, however, does not disclose a method of calibration for the sensing equipment or if calibration is indeed performed, it also appears that only a single sensing unit is connected to the computer.
U.S. Pat. No. 3,847,486, of Nov. 12, 1974, discloses an automated spectrophotometer apparatus and a computer system for simultaneous measurement of a plurality of kinetic reactions.
This invention relates to a system that is used for a single spectrophotometer to measure a number of samples in order to determine a difference between the samples being measured. The excerpts from within the specification detail the invention as disclosed.
“A spectrophotometer apparatus for the automatic positioning of multiple samples and sample blanks for measuring, for example, double differential absorbance, that is, sample absorbance with respect to both blank absorbance and time. The apparatus contains appropriate electronic hardware, for example suitable electronic computer and printout devices to generate a final digital printout of multiple analytical reaction rate results.”
“The present invention relates to an improved method and apparatus for determining multiple analytical reaction rate results, particularly for clinical enzyme reactions. More particularly, the present invention is directed to a method and apparatus for the proper positioning of a plurality of samples and sample blanks for simultaneously making a plurality of rate measurements on each sample using a particular arrangement of electronic computer hardware to produce a digital printout of the reaction rate results.”
“An object of the present invention is to provide an improved method and apparatus for making automated kinetic measurements for clinical enzyme reactions.”
“Another object of the present invention is to determine the linearity of the reaction by making a plurality of measurements on each sample.”
“Still another object of the present invention is to provide an improved spectrophotometer apparatus for the automatic positioning of multiple samples and sample blanks for measuring for example, double differential absorbance, that is, sample absorbance with respect to both blank absorbance and time.”
“A further object of the present invention is to provide an improved method and apparatus for measuring different types of reaction rates during the same analytical run.”
“A still further object of the present invention is to provide an improved method and apparatus for automatically substrating a blank measurement during an analytical run which is essential for clinical enzyme analysis if rapid and error-free results are to be realized.”
“Still another object of the present invention is to provide an improved method and apparatus for making multiple, discrete measurements on a plurality of samples and sample blanks to affect simultaneous reaction rate analysis on all of the samples.”
“Another object of the present invention is to combine with the above spectrophotometer apparatus, appropriate electronic hardware, including electronic computer and printout devices to generate a final digital printout of these simultaneous multiple kinetic measurements for clinical enzyme reactions.”
This clearly reveals that this patent has limited application in that it discloses a single spectrophotometer which is used to measure a number of samples.
Even if a number of these systems were ganged together to form an array, each of the spectrophotometers would need to be calibrated individually.
The prior art disclosures above all attempt to overcome some of the problems associated with the use of spectrometers, but they all still suffer from severe problems in that they need to be individually calibrated and that the majority of them would not be appropriate for applications where real-time results are needed.
Even those that are capable of providing some form of real-time analysis suffer from the inherent calibration problems.
None of the disclosures is capable of forming part of an integrated system with a central hub connected to a number of spectrometer assemblies and in which results and calibration values can be stored.
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