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National Instruments works with test companies that use fiber optics to test airframes.

No shortcuts for verifying, validating aerospace system designs

Product designs are increasingly being tested multiple times as they move forward, not just when versions are completed. Verifying the integrity of designs and ensuring that everything meets the original requirements is an important step in the design of products that meet safety requirements. As systems become more complex, it’s becoming more difficult to find all potential problems.

“You need very stringent modified condition/decision coverage analysis to make sure all branches are tested during the verification process,” said Jim McElroy, Vice President of Marketing at LDRA. “It’s important to verify code on the host. Our tests let them use simulation until the target hardware is ready. Then they run the same tests on the target hardware.”

Many of the software tests are run before target hardware is developed. When pieces of hardware are completed, they are often integrated into hardware-in-the-loop (HIL) systems to ensure that code runs the same on simulated hardware and real hardware.

“The simulation of plant models with HIL systems is allowing for faster regression testing of controllers for both normal and abnormal operating conditions,” said Mahendra Muli, New Business Development Director at dSPACE. “With capabilities for simulating bus communications over various standard communication bus interfaces, such as ARINC 429, 1394B, Ethernet etc., the entire system can be simulated without the need for real components. This is helping reduce costs in development as more and more testing on the test bench is helping catch errors early on.”

Though HIL is used widely throughout the aerospace industry, there’s some discussion about reducing reliance on these tests. Sometimes, simulated tests can cover more possible faults that can cause problems.

“We’re still in an environment where HIL comes into play,” said Bill Chown, Product Marketing Manager, System Design Management at Mentor Graphics. “Conceptually, we see interest in reducing the use of HIL. If you build an instance of hardware, you have one instance. Meeting safety standard requirements requires looking at all the corner cases.”

While there’s some potential for reducing HIL for electronic tests, there’s no chance that physical prototypes are going away. These prototypes confirm that everything works in a real-world system. These prototype tests go well beyond software, systems, and electronic cabinets. Safety tests must also cover the enclosure for electronics—the airframe.

“In basic airframe testing, the strain gauge is still the king,” said David Potter, Principal Market Development Manager at National Instruments. “Fiber-optic sensing is a new sensor technology that’s getting a lot of interest. It’s well suited for measuring strain in composites, which flex more than metals. Fiber-optic sensors have a better range and better fatigue life, they don’t fail as quickly.”

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