Signal Averaging Dangers

March 29, 2018

The Problem

For high level, short duration random tests, many controllers simply 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 behaviors of a product at a high level will exactly mimic product behaviors 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 critically important 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

With VR’s patented 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). 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 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 clearly and quickly highlights resonances that a test engineer needs to see during the random test start-up and level changes. It gives the test engineer the ability to determine the true occurrance at any level.