Optical instrument calibration system

• US 4,866,644 A
• Filed: 08/29/1986
• Issued: 09/12/1989
• Est. Priority Date: 08/29/1986
• Status: Expired due to Term

• Current Assignee: John S. Shenk, Mark O. Westerhaus
• Original Assignee: John S. Shenk, Mark O. Westerhaus
• Inventors: Shenk, John S., Westerhaus, Mark O.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): Dixon, Joseph L.
• Application Number:
  US06/901,875
• Time in Patent Office: 1,110 Days
• Field of Search: 364/509, 364/556, 364/496, 364/497, 364/525, 364/571, 364/512, 364/578, 364/553, 364/581, 73/23.1, 73/1 R, 250/222.1, 250/571, 358/107, 356/124, 356/127, 356/26
• US Class Current: 356/319
• CPC Class Codes: G01J 2003/068 tuned to preselected wavelengths
• CPC Class Codes: G01J 2003/1243 Pivoting IF or other position variation
• CPC Class Codes: G01J 2003/2866 Markers; Calibrating of scan
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01N 2021/3129 Determining multicomponents by multiwavelength light
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 2201/12753 and storage

Abstract

In a calibration system for optical instruments of the type which make measurements at incrementally spaced wavelengths throughout a spectrum, a plurality of standard samples are measured by a master instrument and a field instrument. The measurement data obtained from each instrument are then statistically correlated to determine a calibration file which is stored with the field instrument. The calibration file includes identification on the field instrument of index locations at which the field instrument will respond to the same wavelength as corresponding index points on the master and includes correction coefficients for each of the index locations. The calibration file is stored in a computer connected to the field instrument and the computer is provided with a program to correct the measurements made by the field instrument in accordance with the stored calibration file.

Claims

1. An optical measuring system comprising a master optical instrument comprising means to make optical measurements on test samples at different wavelengths throughout a spectrum, a field optical instrument comprising means to make optical measurements on test samples throughout said spectrum, a computer connected to said field instrument to receive measurement values made by field instrument, said computer comprising means to carry out arithmetic operations on the measurement values received from said field instrument in response to a given test sample to convert said values to a set of calibrated values which are substantially identical to the measurement values that would be obtained from said given test sample by said master instrument, said optical instruments being indexed to make optical measurements in response to different wavelengths at index points incrementally spaced throughout the spectrum, said computer including means to define index locations on said field instrument corresponding to the index points on said master instrument on a one to one basis, said field instrument producing an output for each of said index locations in response to the same wavelength that the master instrument responds to at the corresponding index point, said computer including means storing a plurality of correction coefficients corresponding on a one to one basis to said index locations, said computer further including means to correct the photometric value determined for each of said index locations in accordance with the correction coefficients stored in said computer for the corresponding index location.

2. An optical measuring system as recited in claim 1, wherein said correction coefficients for each of said index locations have predetermined values determined by comparing the measurement values made by said field instrument with the measurement values made by said master instrument on a plurality of samples.

3. An optical measuring system comprising a master optical instrument comprising means to make optical measurements on test samples at different wavelengths throughout a spectrum, a field optical instrument comprising means to make optical measurements on test samples throughout said spectrum, a computer connected to said field instrument to receive measurement values made by field instrument, said computer comprising means to carry out arithmetic operations on the measurement values received from said field instrument in response to a given test sample to convert said values to a set of calibrated values which are substantially identical to the measurement values that would be obtained from said given test sample by said master instrument, said optical instruments being indexed to make said index points incrementally spaced throughout said spectrum, the index points of said field instrument being at different wavelengths than said index points of said master instrument, wherein said computer includes means to define index locations throughout said spectrum in said field instrument corresponding on a one to one basis with said index points in said master instrument, said index locations each being a point on an index scale of said field instrument at which said field instrument will respond to the same wavelength that said master instrument responds to at the corresponding index point on said master instrument.

4. An optical measuring system as recited in claim 3, wherein said computer includes means to derive wave shifted photometric output values for each of said index locations representing the measurement response of said field instrument at said index locations from the measurement values obtained by said field instrument at the index points of said field instrument.

5. An optical measuring system as recited in claim 4, wherein said index locations are determined by comparing the measurement values obtained by said master instrument from a plurality of standard samples with the measurement values obtained by said field instrument from said plurality of said standard samples.

6. A method of calibrating a field optical instrument to correspond to a master optical instrument, wherein said optical instruments are of the type that operate to make optical measurements on test samples at different wavelengths throughout a spectrum, comprising the steps of measuring a plurality of samples with said master instrument to obtain a first file of data comprising measurements on each of said samples at different wavelengths throughout said spectrum, measuring said plurality of samples with said field instrument to obtain a second file of data comprising measurements of each of said samples throughout said spectrum, comparing said first file of data with said second file of data to determine a calibration file of values which when applied to measurement values obtained by said field instrument from an unknown sample will result in corrected values which are substantially identical to the measurement values that would be obtained from said unknown sample by said master instrument, the values in said calibration file each being dependent upon the measurements made by said master instrument upon said plurality of samples and being dependent upon the measurements made by said field instrument upon said plurality of samples, storing said calibration file in a computer and programming said computer to correct the measurements made by said field instrument in accordance with said calibration file.

7. A method as recited in claim 6, wherein said calibration file is determined by statistically correlating said second file of data with said first file of data.

8. A method of calibrating as recited in claim 6, wherein said calibration file includes an identification of a plurality of index locations distributed throughout said spectrum on an index scale of said field instrument, each corresponding on a one to one basis with index points distributed throughout said spectrum on an index scale of said master instrument, said index locations each corresponding to the point on the index scale of said field instrument at which said field instrument will respond to the same wavelength that said master instrument responds to at the corresponding index point.

9. A method of calibration as recited in claim 8, wherein each of said index locations are determined by calculating a point of maximum statistical correlation between the data in said second file and the data in said first file measured at each of said index points of said master instrument.

10. A method of calibration as recited in claim 8, wherein said calibration file includes correction coefficients corresponding on a one to one basis to said index locations and wherein said step of programming said computer includes programming said computer to determine from the measurements made on said unknown sample, a photometric value corresponding to each of said index locations and correcting said photometric values in accordance with the corresponding correction coefficients.

11. An optical measuring system comprising a master optical instrument comprising means to make optical measurements on test samples at different wavelengths throughout a spectrum, a field optical instrument comprising means to make optical measurements on test samples throughout said spectrum, a computer connected to said field instrument to receive measurement values made by field instrument, said computer comprising means to carry out arithmetic operations on the measurement values received from said field instrument in respoinse to a given test sample to convert said values to a set of calibrated values which are substantially identical to the measurement values that would be obtained from said given test sample by said master instrument, said computer including a file of calibration data including values determined by comparing the response of said master instrument to a plurality of samples with the response of said field instrument to said plurality of samples, the values in said calibration file each being independent upon the measurements made by said master instrument upon said plurality of samples and being dependent upon the measurements made by said field instrument upon said plurality of samples, said means to carry out arithmetic operations employing said file of calibration data in said arithmetic operations.