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PROBLEM TYPICAL
SOURCE SPECTRUM REMARKS
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GEARS (CONTINUED)
I. LOOSE BEARING FIT
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(-4 O
a- â
K Q GMF
2 2GMF
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Excessive Clearance of bearings supporting
the gears can not only excite many running speed hamnonica. but will orlon
cause high amplitude
response al GMF, 2GMF and/or 3GMF Tnese high GMF
amplitudes are
actually a response to. and not the cause o1,
loosenesswatt: in the bearings
supporting the gearing Such excessive clearance
can be Caused limner
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~~
GMF
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by extensive bearing wear or by
improper beanng fit onto the toumai during
installation, Left uncorrected, n can cause excessive gear wear
ano damage to other components
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AC INDUCTION MOTORS
A. STATOR ECCENTRICITY SHORTED LAMINATIONS OR LOOSE
IRONtx
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3200 UNE RADIAL
2%
A Ai.
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2FL
Stator problems generate
high vibration al 2X tine
frequency (2F,). Stator
FFT eccenlhei ry produces uneven stationary arc gap
between rotor and stator
which produces very directional vib ahon Differential Air
Gap should not
exceed 5% for induction motors and 109: for synchronous motors,
Sot
Fl . UNE FREO loot and warped bases
can produce an eccentric Stator. Loose eon is
due
to stator SuPpen weakness or looseness. Shorted
stator laminations Can
cause uneven, N which
Oalized heating can distort the stator itself.
This
produces thermaey.ind-ced vibration which
can significantly grow with
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12K CPM operating time reusing
stator distortion and static air gap problems.
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B. ECCENTRIC ROTOR
(Variable Air Gap)
F, w Electrical L rte Freq. N, s Synch, Speed =
120F,
F, = Slip Freq_ = N,- RPM
F. = Pote Pass Freq. - F, X P
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Eccentric Rotors produce a rotating vanable
arr gap between the rotor and
3200 UNE FFT stator which induces pulsating
vibration (normally between 2F, and closest
- runn am nispectrum ng speed
hnoc). Olten requires 'zoom' to separate 2F.
RADIAL and running speed harmonic. Eccentric rotors
generate 2F., surrounded by
2FL Fp SIDEBANDS
Pole Pass frequency Sidebands (F,j, aS well as F, sidebands
around
t X 2X AROUND 2FL rur'+ning speed. F, appears
itself al tow frequency (Pole Pass Freq cy uen -
LL Slip Frequency x *Poles) Common velues of F, range
from about 20 to
120 CPM (0.3 -20 Hz), Soft loot or misakgnment
Olten induces
a variable
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P w *Poles
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12% CPM air gap due to distortion (actually a
mechanical problem_ rot electrical).
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C. ROTOR PROBLEMS
Stalag ~~
Rotor Bars Ns
·
·~
·
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R.oIAL 3200 UNE FFT Broken or Cracked roter bars or
Snorting rings: bad loints between rotor
r,slocawosw.ouNoO.ta seers NAKNONtC,5 bars and shorting
rings: or shelled rotor !ampnations will produce hrgn IX
1x zx Sa +% running speed
vbrahon with pole pass frequency sideoands (F,) In
F
· SX ex addition,
these problems will Often generate F, sidebands
around trie
second, third, (birth and filth
running speed harmonics Loose Or Open
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2 Pole Motor
Air-Gap
Conductors
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Rota
,--
·'
·1500
· l: ~:
·
`~
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UNE FFT rotor bars are indicated by 2X
line heq (2F,) srdebands surrounding Rotor
em....oronsxwssraeo ..mix are Bar Pass
Frequency (RBPF) andlor its harmonics (RBPF . Number
of
a, sswea,Os rabl.oriber *,mete
wile.* Bars X RPM) Often wilt cause high levels al 2X
RBPF, wan only a smelt
,x RBPF 2X RBPF amplitude at IX
RBPF Electrically induced arcing between loose rotor
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Magnetic Field ._s
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!! Ix 1 .I. bas and end
rings will chan show high lests et 2)c RBPF (with
2f,
1 J.1 11111
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SioebandS), but Imre or no increase in amplitudes a! I
X RBPF
3eox CPM
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(Loose Connector)
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D. PHASING PROBLEMRADIALPhasing
prabtems due to [pose or broken connectors can cause
excessive vibration a; 2X Line Freq (2F,)
whrth Wilt have erdebands around it spaced
2F, al f/S Line Free (1(3 F,: Levels
el 2F can exceed 10 in/sec d tee
I l,1 F,
SQEBANDE
1% r A.t., ARddNQ uncorrected This is part ci-larly a
prCbtem it !ne detective connector is Only
i A ` sporadically making contact. Loose or
broken connectors must be repai
·ed
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to prevent catins:rophlc fartufe
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AC SYNCHRONOUS
MOTORS
(Loose Stator Coils)
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1600 LINE Fri Loose Stator Cols in synchronous motors
will generate fairly high vibration
al Coil Pass Freq. (CPF) which equals the
number 01 stator toits X RPM
COIL PASS FREO fa Stator
Colts w lereISS X eCoils/Pole). The Coil Pass Frequency
will be
surrounded by IX RPM sidebands Synchronous motor
problems may
1x - lx ReM also be indicated by high
amplitude peaks al approx. 60.000 To 90,000
2% SIOEBANDS CPM, accompanied by 2F, aidebands. Take
at least one spectrum up to
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90.000 CPM on each motor bearing housing
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DC MOTORS AND CONTROLS
A. NORMAL SPECTRUM
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SCR FRE0=6F, (Full-Wave Reddiedi
Many DC Motor and Control Problems can be detected by
vibration
i 2
·3F, (HarNweve
Rectit,ed; analysis- Fultwave rectited, motors (6 SCR's( generate a
Signal at 6X
,' Une Frequency (6F1-360 Hz-21,600
CPM): white hall-wave rectified DC
" SCR FRED motors (3 SCR's( generate 3X
Line Freq (3FL-t60 Hz= 10,600 CPM). The
SCR
firing Frequency is normally present in a OC Motor Soeclrum, but at
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low amplitude. Note the absence 01 Other peaks at multiples of
F,
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B. BROKEN ARMATURE WINDINGS, GROUNDING PROBLEMS OR
FAULTY SYSTEM TUNING
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Z
=`âSCR a i`
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When OC Motor spectra are dominated by high levels a! SCR or
2X SCR. mis normally indicates either Broken Motor Winnings or Faulty
Tuning of
FRED the Electrical Contrai System. Proper tuning atone can
lower vibration at
SCR and 2X SCR sigrtibcanily if control
problems predominate. High ampleudas
at these Irequennes would normally be above
approximately
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10 insect peak at t X SCR and about 04 in/sec at 2 X
SCR Finng Freq
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C. FAULTY FIRING CARD OR BLOWN FUSE
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cents
rcIr3XSCR
offA~o
2r3X SCR
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When one Icing card laits to lire,
then 112 OI power is lost. and can
cause
SCR repeated momentary speed Changes in the motor.
This Can lead to high
amplitudes a! trSX and 2/3X
SCR Frequency fl /3X SCR Freq, = 1X F, for half-wave hie-Wied,
but 2X FL for a tue.wave rectified SCR)
Cau67t: Card/SCR configuration Should be
known before troubleshooting
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motor (*SCRs, *Finng Cards, etc.).
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D. FAULTY SCR, SHORTED CONTROL CARD, LOOSE CONNECTIONS
AND/OR BLOWN FUSE
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1
=` â
N :
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Fautry SCR's. Shorted Contrai Cards and%or
Loose Connections can
5CR generate noticeable amplitude peaks at
many combinations of line
FRED frequency (FJ and SCR firing frequency. Nomlauy,
1 bbd SCR can cause
high levels et FL and/or
511, in 6 SCR motors. The point to be made is
that neither
F,. 2FL, 4F1, nor SF atlould be present in DC
Motor spectra.
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E. FAULTY COMPARITOR CARD
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SrcEaANDsuELrEOuti
>{ TO sPEEo WAATiON5
C 3200 UNE SPECTRUM
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Faulty Comparator Cards cause probtenu with
RPM fluctuation or
'hunting'. This causes a constant conapsinq and
regenerating of Ins
magnetic herd. These sidebands often approximate the
RPM fluctuation
SCR FREI]. and require e high resoluppn FFT to
even detect them Such sidebands
COuld also be due to generation end
regeneration et the magnetic field.
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F. ELECTRICAL CURRENT
PASSAGE TH R U DC
MOTOR BEARINGS
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aereacNce FA£OUENUrs
7 Nit usLerCoueLCPro
_ c IF Ft11m~~`esen'
N spç LINE
SPf GTRl1/1
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ENetni~l rig tyby
N-in~~ Flub a norm detected e series of
dilterence
frequencies with the spacing most often at the outer race
dereaf frequency (BPFO). aven II sum suing is present on both the outer
and inns, races They most often show up in a range centered et
about 100,000 to t 50,000
CPM A 180K CPM Spectrum with 1600 Ines is
recommended lui
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teOK GPM defection with measurements on both the OB and
lB OC motor bearings
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