What is "subsynchronous"?

[lmh4534]

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!

 

[electricpete]

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.

 

[dgallagher]

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.

 

[lmh4534]

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

 

[electricpete]

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).

 

[1x]

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).

 

[GregLocock]

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

 

[electricpete]

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

 

[GregLocock]

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

 

[lmh4534]

Thanks!
I wonder if &quot;non-synchronous&quot; value is including &quot;sub-synchronous&quot; or not.

 

[electricpete]

Try asking Dr. Bob at SKF Condition Monitoring forum:

http://forums.skfcm.com/postlist.php?Cat=&Board=reliability