ERROR COMPENSATION IN A SPECTROMETER

• US 20120300206A1
• Filed: 05/24/2011
• Published: 11/29/2012
• Est. Priority Date: 05/24/2011
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Haran, Frank M., Savard, Stéphane
• Granted Patent: US 8,638,443 B2
• Time in Patent Office: Days
• US Class Current: 356/326
• 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:

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

generating a detector signal corresponding to the measurement scan; and

compensating for errors in the detector signal based on the measurement of the path length.

2. The method of claim 1, wherein measuring at least a portion of the path length comprises measuring 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 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 3, wherein measuring at least a portion of the path length further comprises measuring at least one optic distance in the first head.

5. The method of claim 4, wherein compensating for errors in the detector signal further 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.

6. The method of claim 5, wherein measuring at least one optic distance comprises:

measuring a first optic distance between an emitter and a beam splitter;

measuring a second optic distance between the emitter and a mirror;

measuring a third optic distance between a detector and the beam splitter; and

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

7. 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.

8. The spectrometer of claim 7, wherein the path length evaluator comprises a Z-sensor configured to measure a Z-distance between a first head of the spectrometer and a second head of the spectrometer.

9. The spectrometer of claim 8, wherein the Z-sensor comprises an eddy-current sensor.

10. The spectrometer of claim 8, wherein the path length evaluator further comprises a laser encoder configured to measure at least one optic distance between a first object and a second object in the first head.

11. The spectrometer of claim 10, wherein the laser encoder comprises an interferometric encoder.

12. The spectrometer of claim 10, further comprising a reflector coupled to the second object, wherein the 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 laser encoder.

13. The spectrometer of claim 12, wherein the reflector comprises one of a mirror and a retroreflector.

14. The spectrometer of claim 8, wherein the path length evaluator further 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.

15. The spectrometer of claim 14, wherein the first laser encoder is coupled to the emitter and the second laser encoder is coupled to the detector.

16. An apparatus comprising:

a Z-distance converter configured to receive a Z-distance measurement corresponding to a measurement scan in a spectrometer and to convert the measured Z-distance into a Z-distance correction, wherein the Z-distance comprises a distance between a first head of the spectrometer and a second head of the spectrometer; and

a detector data corrector coupled to the Z-distance converter, wherein the detector data corrector is configured to receive the Z-distance correction, to receive a detector signal corresponding to the measurement scan, and to apply the Z-distance correction to the detector signal.

17. The apparatus of claim 16, wherein the Z-distance converter is configured to convert the measured Z-distance into the Z-distance correction by determining a variation in the Z-distance during the measurement scan and determining a change in a mean value of the Z-distance for the measurement scan.

18. The apparatus of claim 17, wherein the Z-distance converter is further configured to convert the measured Z-distance into the Z-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, and wherein the Z-distance correction comprises the difference between the expected delay and the actual delay.

19. The apparatus of claim 16, further comprising:

an optic distance converter coupled to the detector data corrector, wherein the optic distance converter is 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

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

20. The apparatus of claim 19, wherein the first 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.