CEMB N330, Руководство пользователя

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D - 6 A rapid guide to interpreting a spectrum
3. FORMULAE FOR CALCULATING TYPICAL BEARING DEFECT FREQUENCIES
The most common case:
a - fixed external ring (rotating internal ring)






 






 
cos
PD
BD S
= FTF 1
2
Housing frequency






 






  
cos
PD
BD
N
S
= BPFO 1
2
Defect on outer track






 






 
cos
PD
BD
+ N
S
= BPFI 1
2
Defect on inner track














 






 







2
1
2
cos
PD
BD
BD
PD S
= BSP
Defect on roller/ball
b - rotating external ring (fixed internal ring)






 






 
cos
PD
BD S
= FTF 1
2
Housing frequency






 






  
cos
PD
BD
N
S
= BPFO 1
2
Defect on outer track






 






 
cos
PD
BD
+ N
S
= BPFI 1
2
Defect on inner track














 






 







2
1
2
cos
PD
BD
BD
PD S
= BSP
Defect on roller/ball
The frequencies of bearings can be calculated if we know:
S
= number of shaft rpm
PD = primitive diameter BD = ball/roller diameter
N = number of balls/rollers
Θ = angle of contact
Approximate calculation formulae (± 20%)
FTF = 0.4 x S (a) or 0.6 x S (b)
BPFO = 0.4 x N x S (a) or (b)
BPFI = 0.6 x N x S (a) or (b)
BSP = 0.23 x N x S (N < 10) (a) or (b)
= 0.18 x N x S (N ≥ 10) (a) or (b)