Motor+Fan, BPF(+ - 1*RPM)
Motor+Fan, BPF(+ - 1*RPM)
(OP)
I am a pretty begineer in the area of motor and fan system. It has 3 blades and 60Hz BLDC motor. The operating speed is 800RPM. There are the higher tonal noises at each BPF and sidebands(320+-13Hz(=operating speed)) of 8th harmonics of the BPF. Is there anyone who can explain about the causes of the sideband tonal noises and why sideband tonal noises only appear near 8th harmonics ?
Thanks for your help in advance.
skan
Thanks for your help in advance.
skan





RE: Motor+Fan, BPF(+ - 1*RPM)
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Motor+Fan, BPF(+ - 1*RPM)
RE: Motor+Fan, BPF(+ - 1*RPM)
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Motor+Fan, BPF(+ - 1*RPM)
If this is the case, you should be able to put it on a log scale and look at the lower order harmonics and see sidebands on those as well.
It is not clear what the cause of your sidebands is.
Also I am curious how you determined this is 8th harmonic of blade pass frequency rather than 24th harmonic of running speed. Additionally if this machine operates at syncronous speed (I don't know anything about BLDC motors), then perhaps the frequency may be related to a harmonic of the line frequency.
You will find a lot of fantastic assistance on rotating equipment vibration questions at maintenanceforums.com
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RE: Motor+Fan, BPF(+ - 1*RPM)
RE: Motor+Fan, BPF(+ - 1*RPM)
I=mB+/-nV where B and V are blade and vane numbers and m and n are integers, ie, harmonic numbers. Then I=0,1,2...,etc rank the highest to lowest amplification factors. For example a 6-vane diffuser downstream of a 3-blade impeller would yield I=0 for the 2nd blade harmonic interacting with the 1st vane harmonic and for the 8th blade harmonic interacting with the 4th vane harmonic.