SELF CALIBRATION METHODS FOR OPTICAL ANALYSIS SYSTEM

• US 20090316150A1
• Filed: 03/10/2006
• Published: 12/24/2009
• Est. Priority Date: 11/28/2005
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Freese, Robert P., Myrick, Michael L., Perkins, David L.
• Granted Patent: US 8,345,234 B2
• Time in Patent Office: Days
• US Class Current: 356/326
• CPC Class Codes: G01J 2003/1217 Indexed discrete filters or choppers
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0232 using shutters
• CPC Class Codes: G01J 3/08 Beam switching arrangements
• CPC Class Codes: G01J 3/42 Absorption spectrometry; Double beam spectrometry; Flicker spectrometry; Reflection spectrometry beam switching arrangements G01J3/08
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence

Abstract

Disclosed is a system and methodologies for providing self-calibration in an optical analysis system. Illumination light is directed toward a material to be sampled while provisions are made to modify the characteristics of at least a portion of the illumination light falling on a reference detector. The modified characteristics may include light presence and/or spectral characteristics. Light presence may be modified by rotating or moving mirror assemblies to cause light to fall on either a sample detector or a reference detector while spectral characteristics may be modified by placing materials having known spectral characteristics in the path of the illumination light.

Claims

1. A method for calibrating an optical analysis system, comprising the steps of:

providing an illumination source;

providing a sample detector;

providing a mirror between the illumination source and the sample detector;

modulating a light from the illumination source;

providing a reference detector; and

modifying at least one characteristic of the light arriving at the sample detector and reference detector from the illumination source,

whereby a baseline may be established for measurements taken by the optical analysis system.

2. The method of claim 1, wherein the light is modulated by a photoelastic modulator.

3. The method of claim 1, wherein the light is modulated by a chopper wheel.

4. A method for calibrating an optical analysis system, comprising the steps of:

providing an illumination source;

providing a sample detector;

providing a mirror between the illumination source and the sample detector;

providing a chopper wheel having a predetermined number of windows between the illumination source and the mirror;

providing a reference detector; and

modifying at least one characteristics of light arriving at the sample detector and reference detector from the illumination source,

whereby a baseline may be established for measurements taken by the optical analysis system.

5. The method of claim 4, where the step of modifying comprises periodically turning the mirror so that light from the illumination source is alternately directed to the sample detector and the reference detector.

6. The method of claim 4, further comprising the steps of:

providing a second mirror; and

coupling the second mirror to the first named mirror;

wherein the step of modifying comprises displacing the coupled first named mirror and second mirror so that light from the illumination source is alternately directed to the sample detector and the reference detector.

7. The method of claim 4, further comprising the step of placing at least one known spectral characteristic material in at least one of the predetermined windows of the chopper wheel.

8. The method of claim 4, further comprising the step of placing at least two known spectral characteristic materials in at least two separate predetermined windows of the chopper wheel.

9. The method of claim 4, wherein the step of modifying comprises placing a light turning element in the chopper wheel.

10. The method of claim 9, wherein the light turning element has a known spectral characteristic.

11. The method of claim 9, further comprising the step of placing at least one known spectral characteristic material in at least one of the predetermined windows of the chopper wheel.

12. The method of claim 9, further comprising the step of placing at least two known spectral characteristic materials in at least two separate predetermined windows of the chopper wheel.

13. A self-calibrating optical analysis system, comprising:

an illumination source;

a sample detector;

a mirror between the Illumination source and the sample detector;

a chopper wheel having a predetermined number of windows positioned between the illumination source and the mirror;

a reference detector; and

means for modifying at least one characteristic of light arriving at the sample detector and reference detector from the illumination source,

whereby a baseline may be established for measurements taken by the optical analysis system.

14. The system of claim 13, where the means for modifying comprises means for turning the mirror so that light from the illumination source is alternately directed to the sample detector and the reference detector.

15. The system of claim 13, wherein the means for modifying comprises a second mirror coupled to the first named mirror and wherein displacement of the coupled first named mirror and second mirror alternately directs light between the sample detector and the reference detector.

16. The system of claim 13, further comprising at least one known spectral characteristic material placed in at least one of the predetermined windows of the chopper wheel.

17. The system of claim 13, further comprising at least two known spectral characteristic materials placed in at least two separate predetermined windows of the chopper wheel.

18. The system of claim 13, wherein the means for modifying comprises at least one light turning element positioned in at least one window of the chopper wheel.

19. The system of claim 18, wherein the light turning element has a known spectral characteristic.

20. The system of claim 18, further comprising at least one known spectral characteristic material placed in at least one of the predetermined windows of the chopper wheel.

21. The system of claim 18, further comprising at least two known spectral characteristic materials placed in at least two separate predetermined windows of the chopper wheel.

22. The system of claim 13, wherein the means for modifying comprises:

a second mirror; and

at least one light turning element positioned in at least one window of the chopper wheel,

whereby light from the illumination source may be directed by the at least one light turning element to said reference detector by way of said second mirror.

23. The system of claim 22, further comprising a housing wherein said illumination source, said chopper wheel and said second mirror are separated from said first mirror, said sample detector and said reference detector.