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Modal analysis and Steinberg Decoupling

Question asked by Mark Wylie on Jul 9, 2014
Latest reply on Jul 12, 2014 by Jared Conway

Hi guys,

I am performing modal analysis of an electronics enclosure and using Steinberg’s Octave rule to decouple the chassis and the PCBs. According to Steinberg’s book “Vibration analysis for electronic equipment”, the chassis fundamental and the PCBs fundamental frequencies  ONLY should be separated by an octave (i.e. Mode 1  = 200 Hz chassis, PCBs should be Mode 1 400 Hz or Mode 1=  100 Hz). This rule does not mention matching the frequencies which coincide on the same axis.

 

My question is:

 

Steinberg only states that the fundamental frequency be compared and mentions nothing of coincidental axes (i.e. I may have a chassis fundamental frequency in Z direction and a PCB board  mounted perpendicularly in the chassis who’s fundamental frequency is in the X direction).

 

In my opinion I should be comparing the chassis Mode (Hz) in the X axis with the “critical” axis of the PCB, the X-axis in this case. This may be, for example, Mode 3 of the chassis, which has dominant mass participation in the X axis with the PCB fundamental (X axis also).

 

Any input?

 

Many thanks,

 

Mark

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