Portable laser plasma spectroscopy apparatus and method for in situ identification of deposits

• US 20030218745A1
• Filed: 05/22/2002
• Published: 11/27/2003
• Est. Priority Date: 05/22/2002
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Benicewicz, Pamela, Wu, Pingfan, Rozier, Elena, Travaly, Andrew Joseph
• Granted Patent: US 6,762,836 B2
• Time in Patent Office: Days
• US Class Current: 356/318
• CPC Class Codes: G01N 21/718 Laser microanalysis, i.e. with formation of sample plasma

Abstract

A portable Laser Plasma Spectroscopy (LPS) system and process is provided for performing in situ, near-real time, remote elemental analysis and identification of deposits or other foreign material found on surfaces of machine parts, such as turbine compressor blades or the like, wherein identification of the elemental constituents of a particular deposit is obtained without incurring significant ablative damage to the machine part substrate material underlying the deposit.

Claims

1. A method for performing Laser Plasma Spectroscopy (LPS) on a foreign substance or deposit found on a surface of a machine part or object, comprising the steps of:

a) collecting light emitted from a plasma generated by focusing a predetermined amount of laser output light energy onto a surface of a machine part or object;

b) directing at least a portion of light collected in step (a) to an optical filter that only passes one predetermined narrow wavelength band containing elemental atomic emission wavelengths that are characteristic of one or more elemental components of a characteristic material comprising said machine part or object;

c) detecting an amount of light passed by said filter; and

d) preventing further laser output light energy from impinging on the machine part or object when light in step (c) is detected;

wherein an identification of one or more elemental constituents of the foreign substance or deposit found on a surface of a machine part or object is obtained through LPS without incurring further ablation to the characteristic material of the machine part or object that lies beneath the foreign substance or deposit.

2. The method of claim 1 wherein a plasma is generated from one or more pulses of laser output light energy.

3. The method of claim 2 wherein each pulse of laser output light energy is focused to an intensity of 1 GW/cm² or greater.

4. The method of claim 1 wherein preventing step (d) comprises activating a shutter to block said laser output energy.

5. The method of claim 4 wherein the shutter comprises a mechanical shutter.

6. The method of claim 1 wherein said portion of light in step (b) is directed to the optical filter by using one branch portion of a bifurcated fiber optic cable.

7. The method of claim 1 wherein said portion of light in step (b) is directed to the optical filter by a beam splitter.

8. The method of claim 1 wherein 10% of light collected in step (a) is directed to the optical filter.

9. The method of claim 1 further comprising the step of directing a portion of light collected in step (a) to a spectrometer device.

10. The method of claim 2 wherein further pulses of laser output light energy are prevented from impinging on the machine part or object after a single laser output light energy pulse produces light detected in step (c).

30. The method of claim 1 wherein the machine part or object is a turbine compressor blade.

31. The method of claim 1 wherein the machine part or object is a component in power generating equipment.

11. A method for performing in situ Laser Plasma Spectroscopy (LPS) on a foreign substance or deposit found on a surface of a machine part or object, comprising the steps of:

a) transporting a portable LPS apparatus to the situs of the machine part or object;

b) using an optical fiber to deliver laser output light energy from a laser device forming a part of the LPS apparatus to a foreign substance or deposit on a surface of a machine part or object, wherein the foreign substance or deposit is vaporized creating a luminous plasma;

c) using an optical fiber to collect light radiation from the plasma created in step (b);

d) delivering light radiation collected in step (c) to a spectrometer forming a part of the LPS apparatus, the spectrometer including a semiconductor array detector device for detecting spectral components of light resolved by the spectrometer;

e) collecting data output from the detector device using a portable computing device connected to a detector controller device;

f) using the portable computing device to analyze data collected in step (e) to determine an emission spectra profile for the plasma light radiation collected in step (c); and

g) using the portable computing device to perform a comparison of data collected in step (e) with predetermined atomic emission spectra data maintained in a database.

12. A method as defined by claim 11 wherein the portable computing device includes a display and further comprising the step of:

using the portable computer device to display an emission spectra profile of plasma light radiation collected in step (c).

13. The method of claim 12 wherein the emission spectrum displayed by the portable computer device comprises an intensity vs. wavelength graph of collected plasma light radiation.

14. A method as defined by claim 11 further comprising the step of:

using the portable computer device to compute a match, within predetermined limits of error, between intensity peak features in an emission spectrum of plasma light radiation collected in step (c) and intensity peak features from predetermined atomic emission spectra data obtained from said database.

15. A method as defined by claim 14 wherein the portable computing device includes a display and further comprising the step of:

using the portable computer device to display an emission spectrum of plasma light radiation collected in step (c), wherein a displayed emission spectrum includes intensity peak features labeled with indicia indicative of elemental constituents identified from the step (g) comparison of the plasma emission spectral profile with predetermined atomic emission spectral data.

16. A method as defined by claim 14 wherein the portable computing device includes a display and further comprising the step of:

using the portable computer device to display an emission spectra profile of plasma light radiation collected in step (c), wherein a displayed emission spectrum includes intensity peak features labeled with indicia indicative of the name of the matching element and/or a computed value indicative of the degree of error in the computed match.

17. The method of claim 11 wherein the database of predetermined atomic emission spectral data is maintained within the portable computing device.

18. The method of claim 11 wherein said database of predetermined atomic emission spectral data is maintained at a remote location and accessed at the situs of the machine part or object by the portable computing device via wired or wireless communication link.

19. The method of claim 11 wherein steps (f) and, (g) are performed by the computing device in real time.

20. The method of claim 11 wherein the optical fiber used in step (c) is the same optical fiber used in step (b).

32. The method of claim 11 wherein the machine part or object is a turbine compressor blade.

33. The method of claim 11 wherein the machine part or object is a component in power generating equipment.

21. A method for performing in situ Laser Plasma Spectroscopy (LPS) on a foreign substance or deposit found on a surface of a machine part or object, comprising the steps of:

a) using a portable LPS apparatus to obtain an intensity vs. wavelength emission spectral data profile of said foreign substance or deposit at a situs of the machine or object, said portable LPS apparatus including a portable computing device;

b) using the portable computing device at the situs of the machine or object to perform a comparison of intensity vs. wavelength emission spectra data profile obtained in step (a) with predetermined atomic emission spectra data maintained in a database accessible by the portable computing device; and

c) using the portable computer device at the situs of the machine or object to compute a match, within predetermined limits of error, between intensity peak features in an emission spectra data profile of plasma light radiation obtained in step (a) and intensity peak features from predetermined atomic emission spectra data obtained from said database.

22. The method of claim 21 further comprising the step of using the portable computer device to display an emission spectra data profile of plasma light radiation obtained in step (a), wherein a displayed emission spectra profile includes intensity peak features labeled with indicia indicative of the name of the matching element and/or a computed value indicative of the degree of error in the computed match.

34. The method of claim 21 wherein the machine part or object is a turbine compressor blade.

35. The method of claim 21 wherein the machine part or object is a component in power generating equipment.

23. A portable LPS apparatus for providing in situ elemental analysis of a foreign substance or deposit located on a surface of a machine part or object, comprising:

a laser device;

a spectrometer device;

a semiconductor array detector device coupled to the spectrometer device for detecting a spectrum of light resolved by the spectrometer device;

a low-level light detecting device;

an optical fiber probe for delivering the laser device output light energy to a location on a surface of a machine part or object that is remote from the LPS apparatus;

means for collecting light radiation emitted from a plasma created during LPS;

a timing source for controlling on/off gating of the array detector and the low-level light detecting device at a substantially identical time and duration during an LPS plasma evolution event;

means for providing a portion of collected plasma light radiation to the low-level light detecting device;

a bandpass filter arrangement for limiting the portion of collected plasma light radiation provided to the lowlevel light detecting device to one predetermined narrow wavelength band encompassing an elemental atomic emission wavelength or wavelengths that are characteristic of one or more elemental components of a characteristic material comprising the machine part or object; and

a shutter device for preventing laser output light energy from reaching a surface of said machine part or object in response to light of a specific range of wavelengths detected by the low-level light detecting device;

wherein identification of the elemental constituents of the foreign substance or deposit is obtained without incurring substantial ablation of a machine part or object substrate material underlying the foreign substance or deposit.

24. The apparatus of claim 23 further comprising a laser light impenetrable housing which encloses one or more optical components.

25. The apparatus of claim 23 wherein the optical fiber probe is contained within a flexible protective sheath.

26. The apparatus as defined by claim 24 wherein the protective sheath incorporates a lens positioned at an output end of the fiber and a sheath that extends beyond the lens at least an amount equal to a focal length of the lens.

27. The apparatus of claim 23 further comprising a portable computing device for performing an analysis on data collected by the array detector to determine an emission spectra profile of collected plasma light radiation.

28. The system according to claim 27 wherein the analysis is performed by the portable computing device substantially in real time.

29. The system according to claim 27 wherein the emission spectra profile of collected plasma light radiation is displayed by the computing device as a graph of intensity vs. wavelength.

36. The apparatus of claim 23 wherein the machine part or object is a turbine compressor blade.

37. The apparatus of claim 23 wherein the machine part or object is a component in power generating equipment.