Crystal Instruments 2021 Webinars

March 29, 2021
Modal Testing with Shaker Excitation – What are some of the issues to consider?  

Dr. Peter Avitabile, PE

This one hour discussion focuses on aspects of conducting a modal test with shaker excitation. Where to locate the shakers, what kind of attachment is needed, what kind of excitation to use and common pitfalls and misunderstandings are presented. Live measurements are also included to show the excitation, response and measurements that are typically acquired in this measurement process.

April 20, 2021
Modal Parameter Estimation Requires Consistent FRFs – What are some of the common pitfalls?

Dr. Peter Avitabile, PE

This one hour discussion focuses on why there is a need to acquire good consistently related FRF measurements. Inconsistent measurements can be the result of poor structure set up or effects of attachment of shakers to the structure. Also, taking measurements over a long duration can suffer from environmental changes or time effects on the physical test set up. Roving hammer vs roving accelerometers can also cause issues. Many of these different effects are discussed to lend insight into the difficulty seen in reducing poorly measured or inconsistent FRF measurements. Live measurements are shown to illustrate some of the typical issues encountered so they can be avoided.

May 11, 2021
Major Mistakes Taking FRF measurements – How to avoid these common problems.

Dr. Peter Avitabile, PE

This one hour discussion focuses on common measurement problems encountered in experimental modal testing. Many times the difference between a roving hammer and roving accelerometer test is not clearly understood and this is discussed and explained. In addition, understanding coherence and associated measurements are addressed; the problematic double impact is also discussed. Issues related to reference points, avoiding node points and mass loading effects are also discussed. Some remarks on coordinates and point/direction are also included. Live measurements are

June 1, 2021
Vibration Shaker Qualification Testing – Basic overview of the pieces.

Dr. Peter Avitabile, PE

This one hour discussion focuses on why we do vibration testing – what’s the point. Examples of some of the types of tests commonly deployed are illustrated to show a range of applications. Some of the basic concepts of the shaker system are described and discussed. The elements of a shaker system (shaker, controller and fixture) are briefly discussed to understand their purpose, effect, importance and things to realize about your shaker system. Basic types of shakers and brief sizing discussions are mentioned. Some typical types of vibration tests commonly deployed are presented.

June 15, 2021
Vibration Shaker Qualification Testing – What’s the big deal about the fixture.

Dr. Peter Avitabile, PE

The Device Under Test (DUT) is subjected to some vibration loading in an honest attempt to replicate some in-service or field environment. But there needs to be some way to attach the DUT to the shaker with a “connection mechanism” that does not distort the excitation signal and faithfully attempts to replicate the service environment. This “fixture” can make or break a vibration test. What needs to be considered? Is there any interaction between the fixture and the DUT? Some discussion of the fixture and its all important role is discussed.

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