Spectroscopic instrument calibration
First Claim
1. In an indirect method for determining a property-p for a sample-u, using spectral data-k measured by an instrument-k, capable of determining such spectral data-k for said sample-u, in combination with a calibration equation-k, having:
- at least one constant-k;
a dependent variable-k; and
at least one independent variable-k;
wherein each value for said dependent variable-k is determined specifically by specific values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, functionally determined from said spectral data-k;
wherein the improvement comprises;
(1) defining said calibration equation-k by recourse to a calibration equation-i for instrument-i, wherein said calibration equation-i has;
at least one constant-i;
at least one independent variable-i; and
a dependent variable-i;
wherein each value for said dependent variable-i is determined specifically by specific values for each said at least one independent variable-i, and wherein each said at least one independent variable-i has a value-i equal to a spectral feature-i, functionally determined from spectral data-i, and wherein calibration equation-i and -k determine, respectively, values for each said dependent variable-k and-i, that are functionally related to one another by a function-f that transforms dependent variable-i into dependent variable-k, said method for defining said calibration equation-k by recourse to said calibration equation-i comprising;
(a) obtaining respectively with instrument-i and instrument-k spectral data-i and spectral data-k, respectively, for each member of a sample-c, comprising at least one member c, thereby functionally determining value-k and value-i, respectively, equal to said at least one spectral feature-k and said at least one spectral feature-i, respectively, for each member of sample-c used in step (b);
(b) determining, in accordance with calibration equation-i, a value for said dependent variable-i for each member of sample-c and in place of each said value of said dependent variable-k in calibration equation-k inserting a value which is functionally related by function-f to said value for said at least one dependent variable-i and selecting an appropriate value for each said at least one constant-k in said calibration equation-k to define a calibration equation-k;
wherein said calibration equation-k in conjunction with said at least one spectral feature-k and the inverse of function-f functionally define each predicted value corresponding to each dependent variable-k for each member c, of sample-c, wherein a sum of each absolute difference between each said predicted value and said dependent variable-i for each member c, of sample-c is minimized at least so that said calibration equation-k predicts a value for property-p of each unknown sample that has a value for property-p within a range of interest with a standard error of prediction not substantially greater than a standard error value selected from the group consisting of a standard error of estimate and a standard error of prediction wherein at least one of said standard errors is necessarily present in a direct method used to determine values for property-p to obtain directly or indirectly calibration equation-i; and
(2) obtaining spectral data-k for said sample-u by means of instrument-k, and determining a value-u for each spectral feature-u, and defining in conjunction with said calibration equation-k a value for dependent variable-u which when transformed by inverse function-f yields a value for property-p of sample-u.
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Accused Products
Abstract
A calibrated spectrometer can indirectly determine a physical or chemical property of a sample based upon spectral responses measured by the spectrometer with respect to the particular sample. This invention is directed to a method for calibrating or recalibrating a first spectrometer in light of a second spectrometer, or itself, respectively. The calibration employs a unique selection and manipulation of spectral data obtained from both the first and the second instrument. The recalibration employs a unique selection and manipulation of spectral data from the same first instrument, that is obtained both before and after the need for recalibration arises. Instead of modifying the respective responses of the first and second instrument, or the first instrument before and after the need for calibration arises, this invention modifies the calibration equation of the second, or recalibrated instrument, to yield consistent results to those obtained by the first instrument, or the first instrument before it goes out of calibration. A calibration equation is an equation which transforms spectral data of a particular sample at a variety of wavelengths to a calculated value for a chemical or physical property. Generally, the form of such calibration equations is that of a linear combination of absorbances or mathematical transforms of absorbances measured by the first and second instrument for each sample. The accuracy of the calibrated or recalibrated instrument is maintained and in some instances improved.
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Citations
79 Claims
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1. In an indirect method for determining a property-p for a sample-u, using spectral data-k measured by an instrument-k, capable of determining such spectral data-k for said sample-u, in combination with a calibration equation-k, having:
- at least one constant-k;
a dependent variable-k; and
at least one independent variable-k;
wherein each value for said dependent variable-k is determined specifically by specific values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, functionally determined from said spectral data-k;
wherein the improvement comprises;(1) defining said calibration equation-k by recourse to a calibration equation-i for instrument-i, wherein said calibration equation-i has;
at least one constant-i;
at least one independent variable-i; and
a dependent variable-i;
wherein each value for said dependent variable-i is determined specifically by specific values for each said at least one independent variable-i, and wherein each said at least one independent variable-i has a value-i equal to a spectral feature-i, functionally determined from spectral data-i, and wherein calibration equation-i and -k determine, respectively, values for each said dependent variable-k and-i, that are functionally related to one another by a function-f that transforms dependent variable-i into dependent variable-k, said method for defining said calibration equation-k by recourse to said calibration equation-i comprising;(a) obtaining respectively with instrument-i and instrument-k spectral data-i and spectral data-k, respectively, for each member of a sample-c, comprising at least one member c, thereby functionally determining value-k and value-i, respectively, equal to said at least one spectral feature-k and said at least one spectral feature-i, respectively, for each member of sample-c used in step (b); (b) determining, in accordance with calibration equation-i, a value for said dependent variable-i for each member of sample-c and in place of each said value of said dependent variable-k in calibration equation-k inserting a value which is functionally related by function-f to said value for said at least one dependent variable-i and selecting an appropriate value for each said at least one constant-k in said calibration equation-k to define a calibration equation-k;
wherein said calibration equation-k in conjunction with said at least one spectral feature-k and the inverse of function-f functionally define each predicted value corresponding to each dependent variable-k for each member c, of sample-c, wherein a sum of each absolute difference between each said predicted value and said dependent variable-i for each member c, of sample-c is minimized at least so that said calibration equation-k predicts a value for property-p of each unknown sample that has a value for property-p within a range of interest with a standard error of prediction not substantially greater than a standard error value selected from the group consisting of a standard error of estimate and a standard error of prediction wherein at least one of said standard errors is necessarily present in a direct method used to determine values for property-p to obtain directly or indirectly calibration equation-i; and(2) obtaining spectral data-k for said sample-u by means of instrument-k, and determining a value-u for each spectral feature-u, and defining in conjunction with said calibration equation-k a value for dependent variable-u which when transformed by inverse function-f yields a value for property-p of sample-u. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
- at least one constant-k;
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13. In an indirect method for determining a property-p for a sample-u, using spectral data-k measured by an instrument-k, capable of determining such spectral data-k for said sample-u, in combination with a calibration equation-k, having at least one constant-k, a dependent variable-k, and at least one independent variable-k;
- wherein each value for said dependent variable-k is determined specifically by particular values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, functionally determined by said spectral data-k, wherein the improvement comprises;
(1) Defining said calibration equation-k by recourse to a calibration equation-i for instrument-i, wherein said calibration equation-i has at least one constant-i;
at least one independent variable-i; and
a dependent variable-i;
wherein each value for said dependent variable-i is determined specifically by specific values for each said at least one independent variable-i, and wherein each said at least one independent variable-i has a value-i equal to a spectral feature-i, functionally determined from spectral data-i, and wherein calibration equation-i and -k determine, respectively, values for each said dependent variable-k and-i, that are functionally related to one another by a function-f that transforms dependent variable-i into dependent variable-k;
for property-p;
said method for defining said calibration equation-k by recourse to said calibration equation-i comprising;(a) obtaining a calibration equation for said instrument-i and assuming a calibration equation-k for said instrument-k has the following form;
Ysk =Ak +Σ
j {Bjk Xjsk } and calibration equation-i has the same or different form;
where;Ysi is a dependent variable-i in calibration equation-i, and Ysk is functionally related to Ysi by a function-f; Ak and Ai are each intercept constants-i and -k in calibration equations-i and -k, respectively; Xjsi and Xjsk are each one of said at least one independent variable-i and -k in calibration equations-i and -k, respectively, having a value equal to at least one said spectral feature-i and -k, respectively, of a member s, at wavelength-j; and Bji and Bjk are slope constants-i and -k, respectively, corresponding to coefficients for each of said at least one of independent variable-i and -k at wavelength-j, respectively; (b) obtaining with instrument-i and -k, spectral data-i and -k, respectively, for each member of a sample-c comprising at least one member c, thereby uniquely determining value-k and -i, respectively, equal to said at least one spectral feature-k and-i, respectively, for each member of sample-c used in step (c); (c) determining said intercept constant-k and said at least one slope constant-k corresponding respectively to Ak and Bjk which substantially minimizes the following expression;
Σ
c (Yci -Ak -Σ
j Bjk Xjck)2 ;
whereby a calibration equation-k for instrument-k is obtained by reference to said calibration equation for instrument-i; and(2) obtaining spectral data-u for said sample-u by means of instrument-k, and determining functionally a value-u for each spectral feature-u therein;
wherein each said value-u is used in combination with said calibration equation-k to determine a value for dependent variable-k, Yuk, for sample-u which is functionally related by the inverse of function-f to said property-p of said sample-u. - View Dependent Claims (14, 15, 16, 17, 18)
- wherein each value for said dependent variable-k is determined specifically by particular values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, functionally determined by said spectral data-k, wherein the improvement comprises;
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19. In an indirect method for determining a property-p for a sample-u, using spectral data-k measured by an instrument-k, capable of determining such spectral data-k for said sample-u, in combination with a calibration equation-k, having at least one constant-k, a dependent variable-k, and at least one independent variable-k;
- wherein each value for said dependent variable-k is determined specifically by specific values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, functionally determined by said spectral data-k;
wherein the improvement comprises;(1) defining said calibration equation-k by recourse to a calibration equation-i for instrument-i, wherein said calibration equation-i has;
at least one constant-i comprising an intercept constant-i and at least one slope constant-i;
at least one independent variable-i; and
a dependent variable-i;
wherein each value for said dependent variable-i is determined specifically by specific values for each said at least one independent variable-i, and wherein each said at least one independent variable-i has a value-i equal to a spectral feature-i, functionally determined from spectral data-i, and wherein calibration equation-i and -k determine, respectively, values for each said dependent variable-k and -i, that are functionally related to one another by a function-f that transforms dependent variable-i into dependent variable-k;
said method for defining said calibration equation-k by recourse to said calibration equation-i comprising;(a) obtaining a calibration equation for said instrument-i for property-p, and assuming a calibration equation-k for said instrument-k;
wherein each have the following form;
space="preserve" listing-type="equation">Y.sub.s.sup.i =A.sup.i +Σ
.sub.j {B.sub.j.sup.i X.sub.js.sup.i }
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">Y.sub.s.sup.k =A.sup.k +Σ
.sub.j {B.sub.j.sup.k X.sub.js.sup.k }where; Ysi is the dependent variable-i for member s in calibration equation-i and Ysk is functionally related to Ysi by a function-f; Ak and Ai are each intercept constants-i and -k in calibration equations-i and -k, respectively; Xjsi and Xjsk are each one of said at least one independent variable-i and -k in calibration equations-i and -k, respectively, each having a value equal to at least one said spectral feature-i and -k, respectively, of each member s, of sample-s at wavelength-j; and Bji and Bjk are slope constants-i and -k, respectively, corresponding to coefficients for each of said at least one of independent variables-i and -k at wavelength-j, respectively; (b) obtaining with instrument-i and -k, spectral data-i and -k, respectively, for each member of a sample-c comprising at least one member c, and functionally determining value-k and -i, respectively, equal to said at least one spectral feature-k and -i, respectively, for each member of sample-c used in step (c); (c) determining values of Bjk and Ak so that the following two equations are simultaneously substantially satisfied;
Bjk =Bji Σ
c Xjci Xjck /Σ
c (Xjck)2 and Ak =Σ
c (Yci -Σ
j Bjk Xjck)/n;
where n=number of members to sample-c;
whereby a calibration equation-k for instrument-k is obtained by reference to said calibration equation for instrument-i; and(2) obtaining spectral data-u by means of instrument-k for said sample-u, and functionally determining a value-u for each spectral features-u therein;
wherein each said value-u is used in combination with said calibration equation-k to determine a value for dependent variable-k, Yuk, for sample-u which is functionally related by the inverse of function-f to said property-p of said sample-u. - View Dependent Claims (20, 21)
- wherein each value for said dependent variable-k is determined specifically by specific values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, functionally determined by said spectral data-k;
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22. In an indirect method for determining a property-p for a sample-u, using spectral data-k measured by an instrument-k, capable of determining such spectral data-k for said sample-u in combination with a calibration equation-k, having at least one constant-k, a dependent variable-k, and at least one independent variable-k;
- wherein each value for said dependent variable-k is determined specifically by specific values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, uniquely determined by reference to said spectral data-k;
wherein the improvement comprises;(1) defining said calibration equation-k by recourse to a calibration equation-i for instrument-i, wherein said calibration equation-i has;
at least one constant-i;
at least one independent variable-i; and
a dependent variable-i;
wherein each value for said dependent variable-i is determined specifically by specific values for each said at least one independent variable-i, and wherein each said at least one independent variable-i has a value-i equal to a spectral feature-i, functionally determined from spectral data-i, and wherein calibration equation-i and -k determine, respectively, values for each said dependent variable-k and -i, that are functionally related to one another by a function-f that transforms dependent variable-i into dependent variable-k;
said method for defining said calibration equation-k by recourse to said calibration equation-i comprising;(a) obtaining a calibration equation for said instrument-i for property-p, and assuming a calibration equation-k for said instrument-k wherein each have the following form;
space="preserve" listing-type="equation">Y.sub.s.sup.i =A.sup.i +Σ
.sub.j {B.sub.j.sup.i X.sub.js.sup.i }
space="preserve" listing-type="equation">and
space="preserve" listing-type="equation">Y.sub.s.sup.k =A.sup.k +Σ
.sub.j {B.sub.j.sup.k X.sub.js.sup.k }where; Ysi is the dependent variable-i in calibration equation-i, and Ysk is functionally related to Ysi by a function-f; Ak and Ai are each intercepts constants-i and -k in calibration equations-i and -k, respectively; Xjsi and Xjsk are each one of said at least one independent variable-i and -k in calibration equations-i and -k, respectively, each having a value equal to at least one said spectral feature-i and -k, respectively; and Bji and Bjk are slope constants-i and -k, respectively, corresponding to coefficients for each of said at least one of independent variables-i and -k corresponding to spectral features-i and -k at least one wavelength-j, respectively; (b) obtaining with instrument-i and -k, spectral data-i and -k, respectively, for each member of a sample-s comprising at least one member c, used in step (c), thereby uniquely determining value-k and -i, respectively, equal to said at least one spectral feature-k and -i, respectively, for each member of sample-c having a total of n members; (c) determining said intercept constant-k and said at least one slope constant-k corresponding, respectively, to values of Bjk and Ak so that the following are substantially satisfied;
Bjk =Bji Σ
c Xjci /Σ
c (Xjck) and Ak =Σ
c (Yci -Σ
j Bjk Xjck)/n;
whereby a calibration equation-k for instrument-k is obtained by reference to said calibration equation for instrument-i;(2) obtaining spectral data-u for said sample-u by means of instrument-k, and determining functionally a value-u for each spectral feature-u therein;
wherein each said value-u is used in combination with said calibration equation-k to determine a value for dependent variable-k, Yuk, for sample-u which is functionally related by the inverse of function-f to said property-p of said sample-u. - View Dependent Claims (23, 24)
- wherein each value for said dependent variable-k is determined specifically by specific values for each said at least one independent variable-k, and wherein each said at least one independent variable-k has a value-k equal to a spectral feature-k, uniquely determined by reference to said spectral data-k;
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25. In a method for recalibrating an instrument-k in light of its former calibrated condition as instrument-i or for calibrating instrument-k, previously uncalibrated, in light of a calibrated instrument-i wherein a calibrated instrument is one having a particular calibration equation, here calibration equation-k, based upon which equation spectraldata of a sample can be used to predict a physical or chemical property of said sample, the improvement which comprises:
- determining said calibration equation-k by means of a calibration equation-i, each said calibration equation-k and -i, respectively, having;
at least one constant-k and -i;
a dependent variable-k and -i; and
at least one independent variable-k and -i;
wherein each value, respectively, for said dependent variable-k and -i is determined specifically by particular values for each said at least one independent variable-k and -i and wherein each said at least one independent variable-k and -i has respectively a value-k and -i equal to a spectral feature-k and -i, functionally determined, respectively, by spectral data-k and -i, determined respectively, by an instrument-k and -i capable of determining, respectively, said spectral data-k and -i for a sample, s;
said method comprising;(a) obtaining respectively with instrument-i and instrument-k spectral data-i and spectral data-k, respectively, for each member of a sample-c, comprising at least one member c, thereby functionally determining value-k and value-i, respectively, equal to said at least one spectral feature-k and said at least one spectral feature-i, respectively, for each member of sample-c used in step (b); (b) determining in accordance with calibration equation-i, a value for said dependent variable-i for each member of sample-c and in place of each said value of said dependent variable-k in calibration equation-k inserting a value which is related by a function-f to each said value for said dependent variable-i and selecting an appropriate value for each said at least one constant-k in said calibration equation-k to produce a calibration equation-k;
wherein said calibration equation-k in conjunction with said at least one spectral feature-k and the inverse of function-f functionally define each predicted value corresponding to each dependent variable-k for each member c, of sample-c, wherein a sum of absolute differences between each said predicted value and said dependent variable-i for each member c, of sample-c is minimized at least so that said calibration equation-k predicts a value for property-p of each unknown sample that has a value for property-p within a range of interest with a standard error of prediction not substantially greater than a standard error value selected from the group consisting of a standard error of estimate and a standard error of prediction wherein at least one of said standard errors is necessarily present in a direct method used to determine values for property-p to obtain directly or indirectly calibration equation-i. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49)
- determining said calibration equation-k by means of a calibration equation-i, each said calibration equation-k and -i, respectively, having;
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33. In the method of 32, the further improvement of applying a slope and bias correction, said applying a slope and bias correction comprising the steps of:
- determining values for m and b, which substantially satisfy the following expressions;
space="preserve" listing-type="equation">m={(Σ
.sub.c Y.sub.c.sup.a Σ
Y.sub.c.sup.k)/IΣ
.sub.c (Y.sub.c.sup.a Y.sub.c.sup.k)}/{{Σ
.sub.c Y.sub.c.sup.k Σ
.sub.c Y.sub.c.sup.k }
space="preserve" listing-type="equation"> /I-Σ
.sub.c Y.sub.c.sup.k Y.sub.c.sup.k }
space="preserve" listing-type="equation">b={Σ
.sub.c Y.sub.c.sup.a -mΣ
.sub.c Y.sub.c.sup.k }/Iwhere; Yca is selected from the group of values consisting of a directly determined value for property-p of a particular member c, of sample-p, a predicted value for property-p of a particular member c, of sample-p by means of a calibration equation for property-p in range of interest, and a combination thereof; I is the number of members of sample-p; substitute said values for m and b into the following expression resulting in a further improved calibration equation for the dependent variable-k for instrument-k, which is as follows;
space="preserve" listing-type="equation">Y.sub.c.sup.k ={mA.sup.k +b}+Σ
.sub.j {mB.sub.j.sup.k X.sub.jc.sup.k };whereby an improved calibration equation over that originally determined without the slope and bias correction is achieved.
- determining values for m and b, which substantially satisfy the following expressions;
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50. In an indirect method for determining a property-p for a sample-u by measuring and using spectral data-(ku) measured by an instrument-k capable of measuring such spectral data-(ku) for said sample-u in conjunction with a calibration equation-k,
wherein said calibration equation-k defines a dependent-variable-(ku), in terms of at least one constant-k and at least one independent-variable-(kju), wherein said at least one independent-variable-(kju) has a value equal to at least one spectral-feature-(kju) determined from said spectral data-(ku) for said sample-u by a first functions that involves wavelength-j, and wherein said dependent-variable-(ku) has a value substantially equal to said property-p for said sample-u when values for each said at least one constant-k and each said at least one independent-variable-(kju) are substituted appropriately into said calibration equation-k; - wherein the improvement comprises;
determining a value for each said at least one constant-k by recourse to a calibration equation-i, wherein said calibration equation-i defines dependent-variable-(ic) as a function of an independent-variable-(ijc) which independent-variable-(ijc) is equal to a spectral feature-(ijc) functionally determined from spectral data-(ic) corresponding both to member c of a calibration sample-c having a total of n members and to each wavelength-j, and said dependent-variable-(ic) has a value substantially equal to said property-p of said member c, of said sample-c;
said determining a value for each said at least one constant-k comprises the steps of;(1) using respectively spectral data-(ic) and spectral data-(kc) for each member c, of said calibration sample-c measured respectively by instrument-i and instrument-k, to determine each said at least one independent-variable-(kjc) corresponding to each member c, and to determine from said calibration equation-i a value for said dependent-variable-(ic) corresponding to each member c; (2) maintaining consistent a set of equations that results from substituting in place of the value for dependent-variable-(kc) that value for dependent-variable-(ic), while selecting a value for each said at least one constant-k so that a sum of absolute differences in value between each new-dependent-variable-(kc) and dependent-variable-(ic) corresponding to each said member c, is substantially minimized;
wherein said new-dependent-variable-(kc) is determined by calibration equation-k after substituting each selected value for each said at least one constant-k along with each said at least one independent-variable-(kjc) in said calibration equation-k. - View Dependent Claims (51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62)
- wherein the improvement comprises;
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63. In a method for recalibrating an instrument-k in light of its former calibrated condition as instrument-i or for calibrating instrument-k, previously uncalibrated, in light of a calibrated instrument-i wherein a calibrated instrument is one having a particular calibration equation, here calibration equation-k, based upon which equation spectral data of a sample can be used to predict a physical or chemical property of said sample, the improvement which comprises:
- determining said calibration equation-k for instrument-k by means of said calibration equation-i for instrument-i, wherein said calibration equation-k defines a dependent-variable-(ku), in terms of at least one constant-k and at least one independent-variable-(kju), wherein said at least one independent-variable-(kju) has a value equal to at least one spectral feature-(kju) determined from said spectral data-(ku) measured by said instrument-k for said sample-u by a first function that involves wavelength-j, and wherein said dependent-variable-(ku) has a value substantially equal to a property-p for said sample-u when values for each said at least one constant-k and each said at least one independent-variable-(kju) are substituted appropriately into said calibration equation-k;
wherein said calibration equation-i defines dependent-variable-(iu) as a function of an independent-variable-(iju) which independent-variable-(iju) is equal to a spectral feature-(iju) determined from spectral data-(iu) measured by said instrument-i for said sample-u corresponding to each wavelength-j, and has a value substantially equal to said property-p of said sample-u;
said method for determining said calibration equation-k by means of said calibration equation-i comprising;(1) using respectively spectral data-(ic) and spectral data-(kc) for each member c, of a group of samples having n members that are each measured respectively by said instrument-i and instrument-k, to determine each said at least one independent-variable-(ijc) and independent-variable-(kjc), respectively, involving each wavelength-j corresponding to each member c, and to determine from calibration equation-i a value for said dependent-variable-(ic) corresponding to each member c; (2) maintaining consistent a set of equations that results from substituting in place of the value for dependent-variable-(kc) that value for dependent-variable-(ic), while selecting a value for each said at least one constant-k so that a sum of absolute differences between each new-dependent-variable-(kc) and dependent-variable-(ic) corresponding to each said member c, is minimized;
wherein said each new-dependent-variable-(kc) is determined by calibration equation-k after substituting each selected value for each said at least one constant-k along with each said at least one independent-variable-(kjc) in said calibration equation-k. - View Dependent Claims (64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75)
- determining said calibration equation-k for instrument-k by means of said calibration equation-i for instrument-i, wherein said calibration equation-k defines a dependent-variable-(ku), in terms of at least one constant-k and at least one independent-variable-(kju), wherein said at least one independent-variable-(kju) has a value equal to at least one spectral feature-(kju) determined from said spectral data-(ku) measured by said instrument-k for said sample-u by a first function that involves wavelength-j, and wherein said dependent-variable-(ku) has a value substantially equal to a property-p for said sample-u when values for each said at least one constant-k and each said at least one independent-variable-(kju) are substituted appropriately into said calibration equation-k;
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76. A method for calibrating or recalibrating a first instrument, instrument-k, by reference to a second instrument, instrument-i, comprising in any order:
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(a) obtaining spectral data by means of instrument-k and instrument-i, corresponding respectively to data-k and data-i for each member of a calibration set; (b) determining by means of a calibration equation, calibration equation-i, of said instrument-i, a value, value-i, for a dependent variable, dependent variable-i, corresponding to each member of said calibration set; (c) substituting a value, value-f, related by function-f to said value-i for said dependent variable-i, for each member of the calibration set in place of that value for said dependent variable-k in a calibration equation-k which contains constants-k and a dependent variable, dependent variable-k; (d) selecting values for said constants-k in calibration equation-k so that the sum of absolute differences between; (1) each dependent variable-k calculated based on said calibration-k with said selected constants-k and data-k for each member of said calibration set; and (2) corresponding values for identical members of said calibration set determined by function-f and corresponding value-i for dependent variable-i of each said member; is substantially minimized; whereby said constants-k can be inversely transformed by an inverse to function-f to define calibration equation-k.
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77. A method for determining constants in a calibration equation, calibration equation-1, for a first instrument by recourse to a second instrument having a calibration equation, calibration equation-2, comprising in any order:
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(a) determining from calibration equation-2 a value for each dependent variable-2 corresponding to each member of a calibration set based on spectral data-2 for each member of said calibration set measured by means of instrument-2; and (b) determining constants-1 in said calibration equation-1 so that the sum of absolute differences between; (1) said value for each said dependent variable-2 for each member of said calibration set; and (2) that corresponding value of dependent variable-1 calculated for each said member based upon calibration equation-1; is substantially minimized. - View Dependent Claims (78, 79)
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Specification