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Signal Averaging Dangers

March 29, 2018

The problem:

With high level, short duration random tests, many controllers simply multiply a low level response and display that data as what is happening at high level. This shows a very smooth line on the graph but that graph is invalid; it is based on the false assumption that the behaviors of a product at a high level will exactly mimic product behaviors at a low level.  The display does not show what is really happening at the high level.

Engineers want to know if there are any out of tolerance conditions or resonances at high level.  Are they over or under testing their product?  Should they abort the test?  This is critically important when extremely high value products are at stake.  The simplistic multiply responses method often gives engineers a false sense of security and does not give them the ability to make an informed decision.

The solution:

With VR’s patented iDOF™ technology, the PSD plot will accurately display the actual vibrations at any level, quickly converge to a smooth plot, and manifest significantly lower variance (i.e., less raggedness). Using an advanced, statistically proven technique, iDOF quickly cuts through PSD estimation errors appearing at the start of a test or after a change in test level.  The resulting trace exposes control error (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 will clearly and quickly highlight resonances that a test engineer wants and needs to see during the random test start-up and level changes. It gives the test engineer the ability to see what is truly happening.