Fluorescence Inspection of Jet Turbine Blades
Dr John Day and Scott Greenwell at the Interface Analysis Centre, University of Bristol, have been using a VS60 from our VS range of cameras to image the Aluminium Oxide (Alumina) used as a protective coating for turbine blades by Rolls-Royce PLC*. The Alumina contains small traces of Chromium impurity absorbed from the superalloy used to manufacture the turbine blade. Chromium doped Alumina exhibits the same fluorescence response as Ruby with 2 extremely sharp and intense red emission lines at around 693nm. By imaging the blades under green light with an Atik camera and a tuneable filter set to 693nm pass band they can image the Alumina directly and then, by tuning to a nearby wavelength, image any other contaminants that may also fluoresce in that region. The difference in the two images provides a rapid way of determining the integrity of the protective coating.
* “Development of an imaging system for the detection of alumina on turbine blades” Greenwell, S; Kell, J; Day, J. Meas. Sci. Technol. 25 (2014) 035902 (6pp).
- a) shows a reflected light image of a turbine blade annotated by a marker pen.
- b) shows a fluorescence image with bandpass filter set to 693nm , showing Alumina and contribution from other fluorescent contaminants
- c) shows fluorescence image with filter set to 670nm bandpass, rejecting Alumina contribution at 693nm
- d) Image c is subtracted from image b to show alumina coverage on the turbine blade surface.
Atik were proud to be invited to co-author a white paper demonstrating how time-gated luminescence images can be obtained by analog summation of a series of sequential images that were obtained with a modified cooled interline CCD camera (314L+), and a fluorescence microscope modified to use a UV LED for illumination. An abstract of the white paper is available here. A second paper, How to Build a Time Gated Luminescence Microscope is also available here.
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