Error compensation in a spectrometer

• US 8,638,443 B2
• Filed: 05/24/2011
• Issued: 01/28/2014
• Est. Priority Date: 05/24/2011
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Haran, Frank M., Savard, Stphane
• Primary Examiner(s): Chowdhury, Tarifur
• Assistant Examiner(s): NIXON, OMAR H
• Application Number:
  US13/114,920
• Publication Number:
  US 20120300206A1
• Time in Patent Office: 980 Days
• Field of Search: 356/452
• US Class Current: 356/452
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation
• CPC Class Codes: G01N 21/3586 by Terahertz time domain spectroscopy [THz-TDS]

Abstract

A method for compensating for errors in a spectrometer is provided that includes measuring at least a portion of a path length for a signal traveling through the spectrometer during a measurement scan of a material. A detector signal corresponding to the measurement scan is generated. Compensation for errors in the detector signal is provided based on the measurement of the path length.

Claims

1. A method comprising:

obtaining a measurement of at least a portion of a path length for a signal traveling through a spectrometer during a measurement scan of a material;

obtaining a detector signal corresponding to the measurement scan; and

compensating for one or more errors in the detector signal based on the measurement, wherein the compensating comprises correcting the detector signal based on the measurement;

wherein obtaining the measurement comprises obtaining a measurement of at least one optic distance in one or more heads of the spectrometer; and

wherein compensating for the one or more errors in the detector signal comprises;

determining a change in the at least one optic distance; and

correcting the detector signal based on the change in the at least one optic distance.

2. The method of claim 1, wherein obtaining the measurement comprises obtaining a measurement of a Z-distance between a first head of the spectrometer and a second head of the spectrometer.

3. The method of claim 2, wherein compensating for the one or more errors in the detector signal comprises:

determining a variation in the Z-distance during the measurement scan;

determining a change in a mean value of the Z-distance for the measurement scan; and

correcting the detector signal based on the variation in the Z-distance and based on the change in the mean value of the Z-distance.

4. The method of claim 2, wherein correcting the detector signal further comprises:

correcting the detector signal based on a difference between an expected delay in the detector signal and an actual delay in the detector signal, the difference due to a variation in the Z-distance and a change in a mean value of the Z-distance.

5. A method comprising:

obtaining a measurement of at least a portion of a path length for a signal traveling through a spectrometer during a measurement scan of a material;

obtaining a detector signal corresponding to the measurement scan; and

compensating for one or more errors in the detector signal based on the measurement, wherein the compensating comprises correcting the detector signal based on the measurement;

wherein obtaining the measurement comprises obtaining measurements of optic distances in one or more heads of the spectrometer, the measurements including;

a measurement of a first optic distance between an emitter and a beam splitter;

a measurement of a second optic distance between the emitter and a mirror;

a measurement of a third optic distance between a detector and the beam splitter; and

a measurement of a fourth optic distance between the detector and an edge of a first of the one or more heads.

6. The method of claim 5, wherein correcting the detector signal comprises:

determining a change in the optic distances; and

correcting the detector signal based on the change in the optic distances.

7. The method of claim 5, wherein correcting the detector signal further comprises:

correcting the detector signal based on a difference between an expected delay in the detector signal and an actual delay in the detector signal, the difference due to a variation in a Z-distance during the measurement scan and a change in a mean value of the Z-distance for the measurement scan.

8. A system comprising:

a spectrometer comprising;

an emitter configured to generate an emitter signal;

a plurality of optical components configured to guide the emitter signal through the spectrometer;

a detector configured to generate a detector signal based on the emitter signal; and

a path length evaluator configured to generate a measurement of at least a portion of a path length for the emitter signal; and

an analyzer configured to correct the detector signal based on the measurement;

wherein the path length evaluator comprises at least one laser encoder configured to measure at least one optic distance between a first object and a second object in a first head of the spectrometer.

9. The system of claim 8, wherein the path length evaluator further comprises a Z-sensor configured to measure a Z-distance between the first head of the spectrometer and a second head of the spectrometer.

10. The system of claim 9, wherein the Z-sensor comprises an eddy-current sensor.

11. The system of claim 8, wherein the path length evaluator is configured to generate:

a measurement of a first optic distance between an emitter and a beam splitter;

a measurement of a second optic distance between the emitter and a mirror;

a measurement of a third optic distance between a detector and the beam splitter; and

a measurement of a fourth optic distance between the detector and an edge of the head.

12. The system of claim 9, wherein the analyzer is configured to correct the detector signal by determining a difference between an expected delay in the detector signal and an actual delay in the detector signal, the difference due to a variation in the Z-distance and a change in a mean value of the Z-distance.

13. A spectrometer comprising:

an emitter configured to generate an emitter signal;

a plurality of optical components configured to guide the emitter signal through the spectrometer;

a detector configured to generate a detector signal based on the emitter signal; and

a path length evaluator configured to measure at least a portion of a path length for the emitter signal;

wherein the path length evaluator comprises at least one laser encoder configured to measure at least one optic distance between a first object and a second object in a head of the spectrometer.

14. The spectrometer of claim 13, wherein the at least one laser encoder comprises at least one interferometric encoder.

15. The spectrometer of claim 13, further comprising a reflector coupled to the second object;

wherein the at least one laser encoder is configured to measure the at least one optic distance by directing a laser signal to the second object; and

wherein the reflector is configured to reflect the laser signal back to the at least one laser encoder.

16. The spectrometer of claim 13, wherein the at least one laser encoder comprises:

a first laser encoder configured to measure a first optic distance between the emitter and a first one of the optical components; and

a second laser encoder configured to measure a second optic distance between the detector and a second one of the optical components.

17. The spectrometer of claim 15, wherein the reflector comprises one of:

a mirror or a retroreflector.

18. The spectrometer of claim 16, wherein:

the first laser encoder is coupled to the emitter; and

the second laser encoder is coupled to the detector.

19. An apparatus comprising:

at least one distance converter configured to receive a measured distance corresponding to a measurement scan in a spectrometer and to convert the measured distance into a distance correction, wherein the measured distance comprises a measurement of at least a portion of a path length for a signal used by the spectrometer during the measurement scan; and

a detector data corrector configured to receive the distance correction, to receive a detector signal corresponding to the measurement scan, and to apply the distance correction to the detector signal;

wherein the at least one distance converter comprises a Z-distance converter configured to determine a variation in a Z-distance during the measurement scan and to determine a change in a mean value of the Z-distance for the measurement scan;

wherein the Z-distance converter is configured to convert the measured distance into the distance correction by determining a difference between an expected delay in the detector signal and an actual delay in the detector signal due to the variation in the Z-distance and the change in the mean value of the Z-distance; and

wherein the distance correction comprises the difference between the expected delay and the actual delay.

20. The apparatus of claim 19, wherein:

the at least one distance converter further comprises an optic distance converter configured to receive at least one optic distance measurement corresponding to the measurement scan and to convert the measured optic distance into an optic distance correction; and

the detector data corrector is configured to receive the optic distance correction and to apply the optic distance correction to the detector signal.

21. The apparatus of claim 20, wherein a head of the spectrometer comprises an emitter, a detector, a beam splitter and a mirror, and wherein the at least one optic distance measurement comprises:

a first optic distance measurement corresponding to a distance between the emitter and the beam splitter;

a second optic distance measurement corresponding to a distance between the emitter and the mirror;

a third optic distance measurement corresponding to a distance between the detector and the beam splitter; and

a fourth optic distance measurement corresponding to a distance between the detector and an edge of the first head.