As it is known, 2xLF sidebands frequently show up around RBPF in AC motors.

In this case of a 4 pole motor it appears that sidebands are spaced around RBPF at 1xLF or possibly at 2xRPM. It is hard to differentiate due to insufficent resolution. But neither one makes any sense, or I am not aware of of it.

What appears to be 1xLF orders are also present in the PeakVue.

Hi res spectrum ( resolution 2 CPM) does not show 1xFL.
All that was not in there before. Prior to this only 2xLF were present as we all are used to. Weird.....

See attached.

Thanks,
Dave

Sys_fan1_1xLF.doc (176 KB, 59 downloads)

You could check whether it is twice RPM or one times LF by switching off the motor.

How many fan blades?

I have seen one times LF sidebands around RBPF many times, with low amplitudes. Motors are running fine till date.

Can you feel the vibration for real? I've had my analyzer behaving strangely near some VFDs. Screen starts flickering, data shows negative values & so on. Just thinking out loud.

Regards,

Aditya

Adytia,

Can not shut down the fan to distiquish between 2xRPM and 1xLF. It is likely 1xLF.

I am not worrying about imminent failure of this motor, just curious about the phenomenon itself since for non-VFD driven motors 2xLF sidebands around RBPF in normal spectrum and 2xLF in enveloped spectrum, as oppose to 1xLF, are normally present if any.

I have not noticed any strange analyzer behaviour near the motor.

David

Since it appears to be electrical (sidebands around RBPF) have you considered performing MCSA?