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What is "subsynchronous"?

What is "subsynchronous"?

What is "subsynchronous"?

(OP)
I have a portabel vibration analyzer, CMVA60 (MAKER:SKF).
When I print the vibration spectrum, the output is consist of spectrum and displacement value of overall/ synchronous / subsynchronous / nonchronous.

what's the overall/ synchronous / subsynchronous / nonsynchronous?

Please help me!

RE: What is "subsynchronous"?

sub syncronous vibration is < running speed

syncronous is at 1x, 2x, 3x etc times running speed

non-sync is not syncronous. I believe non-sync might also exclude sub-sync (?).

overall combines all of the components.

RE: What is "subsynchronous"?

As Pete stated, synchronous components are integral multiples, or harmonics, of a fundamental frequency. They may also exist as multiples of an integral fraction of the fundamental frequency, in which case they are called sub harmonics.

Examples of non-synchronous would be rolling element bearing fault frequencies, or oil whirl in a journal bearing.

RE: What is "subsynchronous"?

(OP)
Thanks!
I understood "sub hamonics" is x/2, x/3....x/9.
(x=running speed).
Isn't "sub syncronous" equal to "sub harmonics"?

RE: What is "subsynchronous"?

sub-harmonics is a subset of subsycnrounous.

There can be other subsyncrounous vib which is not a subharmonic. Example is oil whirl which occurs at some irrational fraction 0.46358... times running speed.

(The 5 decimal places wasn't intending to convey the precision of my number, only that it was irrational).

RE: What is "subsynchronous"?

1.)overall is the sum of all peaks coming from 0-Fmax e.g. 0-60,000cpm or simply the overall vibration.
2.)synchronous is also called as the 1xrpm, 2xrpm....10xrpm; or hamonics values of 1xrpm.
3.)subsynchronous all peaks located before the 1xrpm.
4.)nonsynchronous or sub-harmonics are peaks that are non-integer of 1xrpm e.g. 1/3rpm;2/3xrpm....etc or simply peaks between synchronous(1xrpm and 2xrpm.....9xrpm and 10xrpm).

RE: What is "subsynchronous"?

4.)nonsynchronous or sub-harmonics are peaks that are non-integer of 1xrpm e.g. 1/3rpm;2/3xrpm....etc or simply peaks between synchronous(1xrpm and 2xrpm.....9xrpm and 10xrpm).

No, that is wrong.

The test for whether they are synchronous is - do they maintain a consistent phase relationship to the rotational frequency? If they do then they are synchronous.

I must confess electricpete's example is disturbing, if the oil whirl speed is at a constant but irrational ratio of the rotational speed then I can't decide if it is synchronous or not!

 

Cheers

Greg Locock

RE: What is "subsynchronous"?

Oil whirl is non-syncronous. Your phase test would prove it.

RE: What is "subsynchronous"?

Yes, but on a waterfall plot of amplitude vs frequency vs speed it would show up as a nice diagonal line, just like a synchronous signal.


But I agree, whirl is non synchronous.

I suppose my doubt was raised by thinking about using a triggered sampling method in the time domain. All non synchronous data averages to zero, as does subsynchronous data, and non-integer harmonics. Therefore how can subsynchronous and non-integer harmonics truly be considered synchronous? The answer is, in my opinion, that there is no such thing as sub-synchronous, it just means you've taken the wrong signal to use as the fundamental. We should use 1/2 order as our speed base for 4 stroke engines, for example.


Cheers

Greg Locock

RE: What is "subsynchronous"?

(OP)
Thanks!
I wonder if "non-synchronous" value is including "sub-synchronous" or not.

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