Blade tip clearance measurement available with the Mentor Visual iQ+ VideoProbe 

In this article:

• Explains how the Mentor Visual iQ+ VideoProbe automates blade tip clearance measurement by identifying blades and liners, mapping blade edges, and calculating minimum, maximum, and average clearances.
• Highlights practical use cases, including gas turbine and compressor efficiency checks that require repeatable, data‑driven blade clearance measurements.
• Summarizes best practices to improve measurement accuracy, covering 3DPM vs. 3D Stereo selection, probe positioning, lighting, and reference plane validation.

What is the blade tip clearance measurement available with the Mentor Visual iQ+ VideoProbe?

Automatically identifies the blade and liner, maps the edge of the blade, and determines the minimum, maximum, and average clearance within the mapped blade edge region.

Example Applications:

• Compressor and turbine efficiency checks

3D Surface Mask:

When enabled in Settings, the 3D Surface Mask shows liner points near the reference plane in green and points offset from the reference plane by either the Min or Max result distance in light blue.

Best Practices to Improve Measurement Accuracy:

Technology Choice

• Both 3DPM and 3D Stereo can be used.
• The 105° FOV of 3DPM tips allows a wider blade tip to be viewed and measured from a given distance than 3D Stereo.
• 3D Stereo may provide better results than 3DPM in compressors having shiny blades and liners.
• With 3DPM, a non-perpendicular view of the blade can improve data quality by directing mirror reflections from the blade and liner away from the camera.
• The 3DPM XL4TM61105SF green tip may be unable to generate 3D data on the liner when inserted

Setup

• Position the probe tip as close as possible to the blade while keeping the blade tip region of interest in the view.
• Position the probe tip with the optics close to the liner to give a clear view of the blade tip and gap.
• Adjust the view to avoid seeing other edges in the image near the blade tip as they may affect the system’s ability to accurately map the blade edge.
• If possible, adjust the tip orientation to create a visible dark shadow on the liner side of the blade edge, which helps with blade edge mapping. Rotating the tip such that the viewing optics are between the illumination exit point and the liner can create this shadowing.
• With shiny compressor blades, use Dark Boost and/or Brightness to optimize visibility of the blade tip with minimal glare near the edge.

Checking the Reference Plane

• The 3D Surface Mask should show green over most of the liner in the vicinity of the blade tip.
• The blue rectangle should line up with the liner in the point cloud view.
• Check the 3D liner data in the point cloud view. If large anomalies are present, adjust the tip position for a view less perpendicular to the blade. Otherwise, manually adjust the 3 liner cursor positions to maximize green mask coverage and improve blue rectangle alignment.

Checking the Blade Edge Mapping

• Verify that the blade edge line closely follows the blade edge in the 2D image.
• Activate the Min and Max cursors and verify in the zoom window that they are accurately positioned on the blade edge.
• Check the point cloud for data quality on the blade near the tip. If significant anomalies exist, adjust the setup and capture a new image.
• Verify that the blade curvature is followed by the blade edge line in the point cloud view.
• Exclude areas near the ends of the mapped edge that are affected by 3D noise, missing corners, etc., from the analysis by moving either bounding cursor away from the edges.
• The algorithm applies fitting and filtering to reduce the impact of small gaps or noise in the blade 3D data. This may result in the blade edge line being slightly offset from the blade edge data in the point cloud view where the gaps or noise exist.