Rotating machinery analysis - order tracking 3

[SomptingGuy]

People,

How do you do your order analysis? Do you use synchronous sampling (or resampling) using a tach signal? Or do you simply acquire narrow band spectra and then extract the orders by summation across a number of bins?

It's been a while since I last did this sort of thing in the lab and times/practices do change.

- Steve

 

[AlbertFM]

I use synchronous sampling. I enter the info of the tach with a NI acquisition card where I also connect the accelerometers.

 

[electricpete]

We don't use synchonous sampling. (In fact I hadn't heard of that..not sure I understand why it would be needed).

We simply get high enough frequency resolution (long enough sample duration) to give us confidence in our frequency estimate of the relevant peaks. Additionally, there are techniques to resolve frequencies to a precision much better than the bin width in most cases as discussed here
thread384-208992

We use E-monitor software which makes these tasks relatively easy.

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[electricpete]

I just realized maybe you guys are talking about transient analysis (coastdown) ?

If so, then .... never mind
(disregard my comments)

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[ivymike]

sometimes people do vib measurement during acceleration too...

 

[GregLocock]

If you've got fast slew rates it can give you a better signal (or it can be worse), and it has the advantage that the phase of the signals relative to the clock is easier to understand, I think. Balancing machines are often synchronous, probably for this reason. Also your data files tend to be smaller.

For driveline work I could be persuaded either way, but for engine noise I would stick with frequency based analysis. A lot of engine noise work is based on subjective assessments, you can't listen to a synchronous signal (well you can but it would be very odd).


Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SomptingGuy]

I should have been clearer, sorry. This is (quasi-steady) transient analysis of engine (intake/exhaust to be precise) noise. Typically a slow run up or down.

From the replies so far, it sounds like there is no clear consensus.

- Steve