Electro-Optic Tunnel Gauges

electro.jpg (23674 bytes)Problem: Measuring the inside diameter of tubes and holes has often been expensive and inaccurate and in many instances impossible. Manufacturers have measured outside diameter of pipe and hose during extrusion or seam welding for years thereby eliminating scrap caused by bad outside diameters. These manufacturers always wanted to measure inside diameter during tube production, but no one offered an instrument to do so. Also, the traditional method of measuring inner diameters off-line, e.g. plug gauges, is expensive and requires frequent and costly recalibration.

Solution: Air Force Research Laboratory Sensors Directorate (AFRL/SN) under a Cooperative Research and Development Agreement (CRADA) with Gauge & Measurement Technologies, Ltd. (GMT) of Dayton, Ohio, developed a laser based device called Tunnel GaugeTM for measuring interior dimensions of tubular or hollow structures. The Tunnel Gauge accommodates a broad range of tubular structures from several feet in diameter to less than 1" in diameter with accuracy to .002".

GMT in conjunction with Kirkendall Metrology Inc. (KMI), is actively pursuing potential customers and have received numerous inquiries about the Tunnel Gauges from manufacturers of extruded hose and tubing, naval cannon barrels, aircraft engine bellows, automobile brake calipers, cold-rolled metal tubing and others. An order for the first Tunnel Gauge was placed by a hydraulic cylinder manufacturer.


  • Society benefits by getting more accurate tubing with less scrap and rework and hence lower cost.
  • GMT/KMI benefit by the addition of Tunnel Gauge to its line of non-contact measurement system offerings.
  • Ohio produces more tubing and extrusions than any other state in the U.S. Having Tunnel Gauge nearby should benefit the competitiveness and market share of this major Ohio industry.
  • The Air Force benefits by the development of these new designs for use in measuring gun barrel rifling.
  • The Air Force also receives royalties on the license of Tunnel Gauge to GMT.

Current Status:

  • Several prototypes have been built, the first order has been received.
  • The patent application has been allowed. The patent is to be issued before the end of the year by the U.S. Patent and Trademark Office.
  • A limited direct mail campaign has brought forth strong interest from a high percentage of firms.
  • An off-line Tunnel Gauge, accurate to .002" is available for sale at a cost substantially less than a comparable set of plug gauges.
  • Several customers have volunteered to be Beta test sites.
  • Tunnel Gauge won a "Thomas Edison Emerging Technology" Award for 1997.
If you have any questions about this Cooperative Research and Development Agreement or are interested in getting more information about technology transfer and CRADA projects, please contact Jim Singer at Wright Technology Network (937) 253-0217 or CRADA@wtn.org

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