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Sure, you can do a transfer function of slid (did you mean skid?) compared to pump housing. Coherence is a measure of causality between input and output. Let's say you measure the COH = ~1 between the ?skid? and pump.  In this case, the relationship between the two are the same but not sure what useful information that gives me or whether it helps me figure out the problem.

As Gary stated, it is used primarily in impact/modal testing to provide confidence in the cause/effect (e.g. impact to response) relationship.

For the case you mentioned (large difference between skid and pump), might imply looseness in bolting.

I might be wrong in my reasoning, others can elaborate.

Regards

Jim P

 

 

RM
Last edited by Registered Member

http://www.calpoly.edu/~cbirds...ng%20%20Analysis.pdf

Top of page 11

Think of it this way, you are comparing two signals and you want to know if the frequency on sensor A is the same as sensor B. IF the frequency is the same coming into both sensors then there should be a coherence value of .95-1.0.....IF the frequency is not the same then coherence could be from .6 to 0.....

An indication of a natural frequency in an FRF plot would be a peak present at a given frequency, and at that frequency there is a 180 degree phase shift and a coherence close to 1.0

Dave

RM

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