From bits and bytes to airframe cracks

At Autotest 2014 held in St. Louis, more than 70 companies exhibited products and services related to MIL/Aero ATE. The Giga-tronics AXIe-based EW and radar multivendor demo received lots of attention as did recent Keysight Technologies PXIe introductions and the extensive capabilities of the RADX LibertyGT 1211B synthetic test instrument. Look for an in-depth discussion of the products at Autotest in our December issue.

During the four-day event, I attended several of the technical presentations and panel sessions. The first presentation, Testing Ultra-Precise, Strategic-Grade Instrumentation Using a Flexible and Modular Common Test Station Architecture by Draper Lab’s Matthew Van Laethem, discussed how Draper worked with Bloomy Controls to develop a universal test system. 

The specifications address the test requirements of representative inertial sensors as expressed in a capability matrix. FPGAs are used extensively in the test hardware to eliminate the inaccuracies associated with analog circuitry as well as to provide greater flexibility. On the software side, a Java scripted object notation approach was adopted because it supports readability, minimal formatting, flexibility, and the choice of APIs for many languages. 

All inputs and outputs of the PXI-based test equipment are routed to a mass interconnect that provides connectivity via interface test adapters developed for different sensors.  

The panel session Nondestructive Testing for Aerospace Applications…Needs, Solutions, and Future featured seven papers followed by a lively Q&A session. Dr. Glenn Light kicked things off with a discussion of magnetostrictive sensors the Southwest Research Institute has developed and applied to measure structural degradation such as cracking in airframes. The thin sensor produces a guided acoustic wave in the surface to which it has been bonded. Similar to a reflectometer, the sensor detects waves reflected from discontinuities. Knowing the speed of sound in the material under test allows the damage to be pinpointed.

GE’s Bradley Gilliland presented two elements of the company’s ongoing InspectionWorks initiative. This product is intended to improve data consistency through more precise and well-defined test processes. With an emphasis on inspection history, it supports data mining and, in a future release, analytics. Test procedures are accompanied by videos for guidance.

Both Ron Goodman and Dr. Donald Palmer represented Boeing and discussed various aspects of composites. Today, very large and complex composite subassemblies are inspected by ultrasonic scanning on part-specific test jigs. The goal is to move inspection farther forward in the build process to ensure quality rather than simply perform pass/fail testing on completed parts.

Dr. Eric Lindgren from the Air Force/USAF Research Laboratory explained that because fault propagation in composites is only poorly understood, the emphasis must be on inspection to mitigate the risk of component failure. This point linked neatly with Dr. William Prosser’s comments based on experience at NASA’s Langley Research Center. He discussed the inspection of spacecraft in flight such as is now done via a boom-mounted camera. And, he also commented on the Orion program.

One of the reasons that Orion is not being made from composites is the lack of comprehensive fault modeling. Because the material’s behavior isn’t thoroughly understood and predictable, the theoretical weight savings isn’t attainable: Structures must be over-designed to ensure safety.

Finally, Dr. Reza Zoughi from Missouri University of Science and Technology presented work done on high-resolution microwave imaging using synthetic aperture techniques. Microwaves are attractive for inspection purposes because, unlike X-rays, they are nonionizing.

I also attended a signal analyzer presentation by Keysight Technologies’ John Stratton. The different architectures used in spectrum/signal analyzers each have their own advantages and disadvantages, which Stratton described in detail. Included was a discussion of a relatively new digital image rejection technique that can offer large speed improvements when working with well-behaved signals.

The panel session 2014 Outlook of Modular Instrumentation in the T&M Industry was the latest update to this yearly event. Presenters included representatives of companies producing VXI, PXI/PXIe, and AXIe modules. 

The modular market is growing by about 17% per year compared to overall instruments at about 4% according to Frost & Sullivan. In his introductory comments, Modular Methods’ Larry Desjardin set an up-beat tone, explaining that the addition of new modules increases the acceleration of the transition to modular standards.  

The release of the new AXIe-0 specification is a major step toward facilitating further adoption of the format. With a large board area and high power capability, AXIe appears to be the logical successor to VXI when PXI’s real estate and power are insufficient. 

However, the remaining VXI suppliers have little impetus to adopt AXIe given the large installed base of VXI in MIL/Aero ATE systems. With eCASS deployment planned to continue for many years and given budget constraints leading to  further weapons platform service life extensions, why change from VXI?

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