Sidebands with CSI Peakvue

[steve383]

I have noticed sidebanding around turning speed and it's harmonics with peakvue. On 1800 rpm equipment the sidebanding is around 3Hz. On 3600 rpm equipment the sidebanding is around 5 Hz. I see this on motors, pumps, fans etc. It is not cage or slip pole. Any suggestions would be appreciated? I believe it is caused from bearing looseness but can not pin point the cause of the low frequency sidebands. Any ideas?

 

[vanstoja]

These sound like pole pass frequency sidebands which equal number of poles times slip frequency. See thread237-96648 and thread237-82207 for a connection to broken rotor bars or other squirrel cage rotor circuit defects.

 

[GregLocock]

Normal looseness would tend to come through as 3x rotational, not a 3 Hz sideband

Cheers

Greg Locock

 

[electricpete]

That's a strange one. 1x + harmonics in peakvue would normally suggest impacting/looseness as you mentioned. Sidebands around 1x and it's harmonics in the peakvue spectrum would suggest that the 1x impacting/looseness is modulated at that lower frequency around 5% of 1x. One interesting thing if you have the capability is to look at the peakvue time waveform to see if you can see this type of pattern.

Since you see it on many pieces of equipment makes it even more puzzling. The more reproduceable it is among machines might steer toward something to do with the setup filters?


=====================================
Eng-tips forums: The best place on the web for engineering discussions.