Signal Averaging Dangers

Back to: Random Testing

For high-level, short-duration random tests, many vibration controllers multiply a low-level response and display the data as the true high-level occurrence. The line on the graph is smooth, but the graph as a whole is invalid.

The assumption that the product’s behavior at a high level will mimic its behavior at a low level is false. Therefore, the graph is not a true representation of the high-level responses.

Engineers want to uncover out-of-tolerance conditions or high-level resonances. They may ask, Am I over or under-testing? Should I abort the test? This information is critical when the test product is high-value. The simple method of multiplying responses can give an engineer a false sense of security and does not give them the ability to make an informed decision.

The Solution: iDOF

With VR’s iDOF® technology, the PSD plot accurately displays the true vibration at any level, quickly converges to a smooth plot, and manifests a significantly lower variance (i.e., less raggedness). The paper, Meeting the Challenge of Short-duration Random Vibration Testing, introduces the methods of PSD averaging during the level changes of a short-duration random test.

If you prefer a video format, consider reviewing the following resource:

Webinar (50:35)

Using an advanced and statistically proven technique, iDOF quickly cuts through PSD estimation errors at the start of a test or after a change in test level. The resulting trace exposes control errors (such as resonances) even when the number of available degrees of freedom is low.

Test engineers can expect to quickly see a smooth line except when real-life resonances and vibration patterns dictate that a deviation should appear.

iDOF clearly and quickly highlights the resonances an engineer needs to see during the random test start-up and level changes. It allows the engineer to determine the true occurrence at any level.

For a more in-depth understanding of the software, the iDOF whitepaper, An Exploration of Power Spectral Density (PSD) Estimation, addresses the methods of handling level changes during random vibration testing.