RECONSTRUCTION OF FREQUENCY REGISTRATION FOR QUANTITATIVE SPECTROSCOPY

• US 20170059477A1
• Filed: 08/03/2016
• Published: 03/02/2017
• Est. Priority Date: 08/03/2015
• Status: Active Grant

• Current Assignee: Endress+Hauser Optical Analysis Incorporated
• Original Assignee: Spectrasensors, Inc. (Endress+Hauser AG)
• Inventors: Ludlum, Kevin, Feitisch, Alfred, Liu, Xiang, Schrempel, Mathias
• Granted Patent: US 11,953,427 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01J 2003/423 Spectral arrangements using lasers, e.g. tunable
• CPC Class Codes: G01J 3/0297 Constructional arrangements for removing other types of optical noise or for performing calibration
• CPC Class Codes: G01J 3/28 Investigating the spectrum using colour filters G01J3/51
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01J 3/457 Correlation spectrometry, e.g. of the intensity G01J3/453 takes precedence
• CPC Class Codes: G01N 2021/3595 using FTIR
• CPC Class Codes: G01N 2021/399 Diode laser
• CPC Class Codes: G01N 21/211 Ellipsometry optical thickness measurement G01B11/06
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/35 using infrared light G01N21/39 takes precedence
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/359 using near infrared light
• CPC Class Codes: G01N 21/39 using tunable lasers

Abstract

Frequency registration deviations occurring during a scan of a frequency or wavelength range by a spectroscopic analysis system can be corrected using passive and/or active approaches. A passive approach can include determining and applying mathematical conversions to a recorded field spectrum. An active approach can include modifying one or more operating parameters of the spectroscopic analysis system to reduce frequency registration deviation.

Claims

1. A method comprising:

characterizing a frequency registration deviation of a spectroscopic analysis system, the characterizing comprising recording a field calibration spectrum indicative of one or more changes of a light source of the spectroscopic analysis system relative to a calibrated state of the spectroscopic analysis system;

deriving a conversion function comprising at least one mathematical operation for reducing the frequency registration deviation relative to the calibrated state of the spectroscopic analysis system;

converting a field spectrum recorded with the spectroscopic analysis system for a field sample comprising a sample fluid, the converting comprising applying the conversion function to the field spectrum to produce converted field spectral data comprising spectral data registered to corrected frequency response of the spectroscopic analysis system; and

calculating one or more of a pressure of the field sample, a temperature of the field sample, and a concentration for one or more analytes in the field sample using the converted field spectral data.

2. A method as in claim 1, wherein the at least one mathematical operation of the conversion function converts the field spectrum to be linear with regard to frequency.

3. A method as in claim 1, wherein the at least one mathematical operation of the conversion function reduces the frequency registration deviation of the spectroscopic analysis system relative to a calibration state frequency registration deviation of a spectroscopic analysis system.

4. A method as in claim 1, wherein the recording of the field calibration spectrum comprises use of a wavelength/frequency calibrator;

and wherein the deriving of the conversion function comprises fitting a mathematical expression to model a relative frequency difference between spectral features occurring in the field calibration spectrum and known spectral markers provided by the wavelength/frequency calibrator.

5. A method as in claim 4, wherein the wavelength/frequency calibrator comprises at least one of an optical wavemeter, an optical interferometer, an etalon, an optical resonator, a frequency comb, and a reference and or the sample cell containing a calibration fluid whose absorption spectra provide multiple individually resolvable frequency markers.

6. A method as in claim 4, wherein the wavelength/frequency calibrator comprises an optical interferometer and further comprises at least one of a phase-locked-loop and a frequency synthesizer for interpolating interference fringes and increasing a frequency resolution of the interferometer.

7. A method as in claim 1, further comprising recording the field spectrum at least approximately concurrently with the field calibration spectrum.

8. A method as in claim 7, wherein the recording of the field spectrum at least approximately concurrently with the field calibration spectrum comprises simultaneously recording the field spectrum and the field calibration spectrum.

9. A method as in claim 8, wherein the spectroscopic analysis system comprises a beam splitter, the beam splitter directing a first portion of a beam emitted by the light source such that the first portion passes through the sample fluid and on to a first detector for characterizing intensity changes resulting from interaction of the first portion with the sample fluid, which are recorded in the field spectrum, the beam splitter further directing a second portion of the beam such that the second portion passes through the wavelength/frequency calibrator and on to a second detector for characterizing intensity changes resulting from interaction of the second portion with the wavelength/frequency calibrator.

10. A method as in claim 8, wherein the spectroscopic analysis system is configured to direct at least a first portion of a beam emitted by the light source such that the first portion passes through the sample fluid and on to a first detector for characterizing intensity changes resulting from interaction of the first portion with the sample fluid, which are recorded in the field spectrum, and wherein the spectroscopic analysis system comprises the wavelength/frequency calibrator positioned to receive light emitted from at least one second reflector of a light source and/or a back facet of the light source and/or by high reflector leakage from the light source, the spectroscopic analysis system further comprising a second detector for characterizing intensity changes resulting from interaction of the light with the wavelength/frequency calibrator.

11. A method as in claim 7, wherein the recording of the field spectrum at least approximately concurrently with the field calibration spectrum comprises alternately recording the field spectrum and the field calibration spectrum and/or recording the field calibration spectrum at preset intervals and/or when triggered by a preset frequency registration deviation.

13. A method as in claim 11, wherein the spectroscopic analysis system comprises a reflector and/or a beam splitter configured to be inserted into a path of a beam emitted by the light source, the reflector directing at least part of the beam when inserted into the path such that the at least part of the beam passes through the wavelength/frequency calibrator and on to a detector for characterizing intensity changes resulting from interaction of the at least part of the beam with the wavelength/frequency calibrator, and wherein when the reflector is not inserted, the at least part of the beam is directed through the sample fluid and on to the detector or another detector for characterizing intensity changes resulting from interaction of the first portion with the sample fluid, which are recorded in the field spectrum.

14. A method as in claim 11, wherein the wavelength/frequency calibrator is moveable such that the wavelength/frequency calibrator can be positioned along at least part of a beam of light emitted by the light source such that the at least part of the beam passes through the wavelength/frequency calibrator and on to a detector for characterizing intensity changes resulting from interaction of the at least part of the beam with the wavelength/frequency calibrator, and such that the wavelength/frequency calibrator can be positioned away from the at least part of the beam such that the at least part of the beam is directed through the sample fluid and on to the detector for characterizing intensity changes resulting from interaction of the first portion with the sample fluid, which are recorded in the field spectrum.

16. A method as in claim 1, wherein the at least one mathematical operation comprise one or more of adding, subtracting, multiplying, dividing, and integrating.

17. A method as in claim 1, wherein the conversion function comprises at least one additional different mathematical operation applied to a first part of the spectral data set but not to a second part of the spectral data set and/or at least one of a vector and a matrix comprising values that mathematically operate on the spectral data set.

19. A method as in claim 1, further comprising:

determining an adjustment to at least one operating parameter of the spectroscopic analysis system necessary to reduce the characterized frequency registration deviation of the spectroscopic analysis system;

applying the determined adjustment to the spectroscopic analysis system; and

recalculating one or more of the pressure of another field sample, the temperature of the other field sample, and the concentration for one or more analytes in the other field sample using a subsequent field spectrum recorded by the spectroscopic analysis system with the determined adjustment applied.

20. A method as in claim 19, wherein the adjustment to at the least one operating parameter comprises a first adjustment of at least one operating parameter applied to a first part of a scan range of the light source and at least one second adjustment of at least one operating parameter applied to at least one second part of the scan range.

21. A method as in claim 19, wherein the at least one operating parameter comprises one or more of a center operating value of a current provided to the light source, a temperature provided to the light source, a scan amplitude applied to the light source, a scan frequency applied to the light source, a scan profile applied to the light source, a modulation profile applied to the light source, a modulation amplitude applied to the light source, a modulation phase delay applied to the light source, a nominal current value applied to the light source, a current ramp rate applied to the light source, a laser modulation current applied to the light source, a modulation frequency applied to the light source, a phase shift applied to at least one section of the light source, an effective index of refraction change applied to at least one section of the light source, a detection circuit gain setting, a grating angle or position, a filter rotation angle, a temperature of a thermal-optical filter, lock-in amplifier detection phase, and a detection gain.

23. A method as in claim 1, wherein the calculating comprises calculating one or more of the pressure of the field sample, the temperature of the field sample, and the concentration for the one or more analytes in the field sample.

12. (canceled)

15. (canceled)

18. (canceled)

22. (canceled)

24-49. -49. (canceled)

50. A computer readable medium storing instructions, that when executed by one or more programmable processors, cause the one or more programmable processors to perform operations comprising:

characterizing a frequency registration deviation of a spectroscopic analysis system, the characterizing comprising recording a field calibration spectrum indicative of one or more changes of a light source of the spectroscopic analysis system relative to a calibrated state of the spectroscopic analysis system;

deriving a conversion function comprising at least one mathematical operation for reducing the frequency registration deviation relative to the calibrated state of the spectroscopic analysis system;

converting a field spectrum recorded with the spectroscopic analysis system for a field sample comprising a sample fluid, the converting comprising applying the conversion function to the field spectrum to produce converted field spectral data comprising spectral data registered to corrected frequency response of the spectroscopic analysis system; and

calculating one or more of a pressure of the field sample, a temperature of the field sample, and a concentration for one or more analytes in the field sample using the converted field spectral data.

51. A system comprising computer circuitry configured to perform operations comprising:

characterizing a frequency registration deviation of a spectroscopic analysis system, the characterizing comprising recording a field calibration spectrum indicative of one or more changes of a light source of the spectroscopic analysis system relative to a calibrated state of the spectroscopic analysis system;

deriving a conversion function comprising at least one mathematical operation for reducing the frequency registration deviation relative to the calibrated state of the spectroscopic analysis system;

converting a field spectrum recorded with the spectroscopic analysis system for a field sample comprising a sample fluid, the converting comprising applying the conversion function to the field spectrum to produce converted field spectral data comprising spectral data registered to corrected frequency response of the spectroscopic analysis system; and

calculating one or more of a pressure of the field sample, a temperature of the field sample, and a concentration for one or more analytes in the field sample using the converted field spectral data.

52. A system as in claim 51, further comprising one or more of a light source;

a detector;

a sample cell;

optical components for reflecting, splitting, or otherwise directing light;

temperature control components; and

computer or other electronic circuitry for controlling the components and/or collecting and analyzing data.