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EM MAIIL TIP T PS A Learn ning Publicaation from Full Spectrrum Diagno ostics

Vol. 87 Septem mber 2012




Volume 87 Septem mber 2012 P Available A e New White Papers

2 Trainin ng Sche edules 2012

The currrent Email Tips T library includes a White W Paper on o the Vibration Analysis s Periodic Table and a close-up view of the t Table its self.

CORE E TRAINING SERIES: ASN NT: Intro (IV VA) – VAI – VAII – VAIIII ISO O: Cat I, Cat C II, Cat III,, Cat IV CONC CENTRATED D TRAINING G TRACK: • TWF – Spectrum – Phase – Be earings SPECIALTY & AD DVANCED TRAINING T • ODS/M Modal – Preccision Balanccing • On-site e Mentoring

Printting This s Email Tip 1. Sele ect the “Prin nt” Icon ect “Print Pu ublication” 2. Sele ect “Save Fiile” and “OK” 3. Sele T will Down nload as a PDF P Email Tip and be Ready for Printing. P Eas sy as 1, 2,, 3.

s Featurres: This Month’s Variablle Speed Op peration of Centrifugal Pumps and Vib bration Cha aracteristics s Displac cement Res sponse with h Speed A New Vendor Application Re eview ement Beariing Pocket Guide A New Rolling Ele w Review

Ano other Loo ok at the e Cover: The chart c on the e cover wass constructe ed from a conbin nation of generic centrifuga al pump perform mance curvves super-im mposed with h empirical radial load cuvves courtesy of “Th he Pump book”. The e load curve es show va ariations in Handb pump specific speeds, imp peller/casing g diameter ratios and impelle er/casing wid dth ratios fo or standard d colors exxtend from volute systems. The added he pump approaches ca avitation at green to red as th ons and reccirculation at a low-flow high-flow conditio conditiions.

Pump p Vibratio on & VFD’s The Variable V F Frequency Drive ha as made significcant in-road ds into ind dustry overr the last severa al years. Sp peed contro ol of induction motor drives has been a key comp ponent in in ncreased efficien ncy and ve ersatility in the manu ufacturing world. There are however, several op perational acks to co ontrolling these mottors with drawba VFD’s.. Among g the most m com mmonly discussed d problem ms are rolling element bearing damage from Electro-Ero E osion or “Fluting” as stray currentt seeks a path to ground g thro ough the bearing g racew ways, and a Res sonance Ampliffication frrom residu ual unbalan nce now applied over a much broader frequencyy range. topics, These although very importantt have been discussed d at length in n numerous publicatio ons.

Some e of the lessser discusssed issue es include elevatted vibratio on amplitud des from centrifugal c forcess in the rottor as the speed is increased. This response is known n as the “speedsquarred” affectt. If speed is dou ubled, the unbala ance amplitude is incrreased by a power of 2 (orr squared). The additional “forces” measu ured as vib bration on the bearing housings are re eacted as increased load in the e bearing itself. This can become a problem off sufficient bearin ng life, bein ng that the e L10 Life is a cubic functio on of applied load in n the beariing. This means that if the bearing load is dou ubled, the ng expectted Life can be reduced bearin significantly

Figurre 3.0 Unbalance is Proporrtional to Spe eed Squared Figure 1.0 1 REB Flutin ng in a VFD Controlled C Mo otor

2 Natural Frrequency Amp plification from m VFD’s Figure 2.0

s Electrrically, the 2x Line Frrequency signatures that provide p the vibration analyst clu ues to the motorr health are unchanged d, except fo or the fact that 2x Line Freq quency is now not a fiixed value at 12 Now the analyst must 20 Hz. m first determ mine the e operating (syncchronous) freque ency from m the mo otor contro ol center (reado out) prior to calculatting the pe eaks that should d appear in n the measu urement spectrum as faults develop (Slip, Pole Passing, Rotor R Bar Passin ng, etc.). This is nott a difficult task, but can be slightly confusing. c Again, note that the m a non-V VFD motor faults are not diifferent from

but the signatures will vary with the control frequency. Some lesser-discussed issues on the driven side of the machine are also introduced with variable frequency drives and the associated variable speed control. When the motor drives a centrifugal pump, a compressor, a fan or a blower several performance problems may result. In a pump operated at “low-flow” conditions recirculation can occur. In pumps operated at very high-flow conditions, cavitation may result. Both problems are erosion inducing problems. The pump is designed with parameter known as the “Best Efficiency Point” (BEP). The VFD operating speed has an influence on how much variation exists away from the desired BEP.

Figure 4.0 Centrifugal Pump Design Curve Alarms

In VFD driven fans, similar performance issues exist. Variations in speed can influence stable operation resulting in problems such as Stall, Rotating Stall, and fan Surge. Some extended problems related to the earlier mentioned Resonance Amplification include the Critical Speed class of problems. Resonance typically implies excitation of a static or nonrotating natural frequency structure. A Critical Speed is defined as an excitation of a rotor (rotating) natural frequency. Operating at a Critical Speed is especially problematic, in that, sensitive clearances in bearings and seals can be eliminated by the rotor deflections. A typical result is rotor-stator rub, rotor instabilities and possibly bent shafts and rotors. Some other specialized problems known as “Roll Chatter” or “Roll Barring” can occur in paper machine press rolls, textile calendar systems, and sheet metal forming applications when operating speeds are increased into resonant ranges of the equipment. When residual unbalance forces are increased with elevated speed operation, driving forces of sufficient energy are created to excite structural natural frequencies. In these cases roll damage can be the result.

Figure 5.0 Fan & Blower Design Curves

Figure 6.0 Roll Barring / Roll Chatter Issues

Displacement Limits The Table (below) is constructed as a severity guideline for Fluid Film Journal type bearings. The displacement severity profiles are not a function of machine type as normally presented in vibration trending with a velocity parameter. Rather the critical displacement levels are closely associated with bearing internal clearances. An operating displacement level in excess of 50% of the bearing diametrical clearance indicates a fast approaching instability threshold. The displacement amplitude parameter varies with speed, thus in the table below greater permissible amplitudes are found at lower speeds. The allowable amplitudes are reduced as speed is increased. An equivalent (seismic) velocity (inches per second) level is presented in the table left hand column for a severity reference. The more commonly circulated Rathbone Chart for Displacement is found to the right. This chart shows the variations of amplitude with frequency, again note the trend of greater allowable amplitudes as frequency (rotor speed) is reduced.

Produ uct Revie ews:

Literrature Rev views:

Comm mtest Instruments Ltd.

Reliab bility Solutiions

www.Co m


Full Spe ectrum Diagno ostics was re equested to be a part of a Beta Test group for a new addition a to the suite of diagnosstic application ns in the 4-channel Comm mtest vb8 Analyze er unit. The current vb8 8 firmware ap pplications include:

Full Sp pectrum Diag gnostics form mally announ nces a new pocketb book publica ation from Re eliability Solu utions. The 120 page 3.5 x 6.0 inch spiral bound guide title ed:

ƒ ƒ ƒ ƒ ƒ ƒ ƒ

Rotor Balanccing Orbit Plotting g Bump Testin ng Coast-down / Run-up Cross-chann nel Phase Long Time Waveform W Time Synchrronous Averag ging

The late est addition to o the existing set of applications is a full blow wn Experimen ntal Modal Analysis A platfform. The intuitive firmware app plication required minimal instruction or tutoring to get up to speed. Th he graphic dissplays are full-featu ured and inclu ude all FRF parameters p (M Magnitude, Phase, Real, Imagin nary, and Coh herence). Th he data is easily trransferred to the vb8 Asc cent database e software as a pre e-formatted series s of plots s, and can be e exported as a Universal File Format F (UFF) file for those who have access to ME’scope for animation n. No, the app plication is not perfe ect, thus the reasoning behind a “beta” test, but it is abund dantly appare ent that consid derable upfro ont thought and eng gineering wass applied. It is a nice fit fo or the suite of firmw ware diagnostic applications s. The app plication is sch heduled to be e ready for release later this yea ar. Sometime es big things really r do com me in small package es. For mo ore information contact Commtest directly.

Full Specttrum Diagnosticss has no financia al connection witth any of the books, pa apers, reference materials, or application notes reviewed in this newssletter. All of th he reviews of th hese materials are a first-hand opinions of o Full Spectrum Diagnostics’ ana alysts and instrucctors.

ng Elemen nt Bearings: Failurre Mode “Rollin Identiffication and Vibration Analysis Poc cket Guide” is now w available at a the Reliab bility Solution ns and Full Spectru um Diagnostics websites. This pu ublication is packed p with information i frrom bearing lubrication, nomenclature, de esign and fits to contam mination and vibration failu ure modes. The unique background of the author, a Toma as Brown, inccludes years of pracctical experie ence in the paper p industryy and as a design engineer for f a large bearing ma anufacturing corpora ation. There are a a lot of pu ublications pro ovided by rollling element bearing g manufacture ers, but none that merge th he technical and pra actical aspectts in a single concise guide e. The guides retail for $19.95 each plus postage & handlin ng. More information n can be found at www.R and, or by phone at 218-729-4646 and 612--875-9959, re espectively.



IN-PLANT COURSES AVAILABLE Tuition: $ 945.00 / 2-day Format Proficiency Test: Included

For In-Plant Training: Tuition: $ 1,595.00 / 3-day Format One Month ME’scope Software Included




Tuition: $ 945.00 / 2-day Format Proficiency Test: Included

Tuition: $ 945.00 / 2-day Format Proficiency Test: Included


Charlotte, NC 2012-VA1-05 New Orleans, LA 2012-VA1-06

Tuition: $ 1,295.00 / 3-day Format Certification Exam: $ 200.00

VIBRATION ANLAYSIS II SEP 25-28 Cedar Rapids, IA 2012-VA2-06

NOV 27-28 Chillicothe, OH 2012-TWF-02



Tuition: $ 945.00 / 2-day Format Proficiency Test: Included

CONCENTRATED PHASE ANALYSIS IN-PLANT COURSES AVAILABLE Tuition: $ 945.00 / 2-day Format Hands-on Exercises: Included

Tuition: $ 1,395.00 / 3-day Format Certification Exam: $ 200.00



OCT 16-17 Cedar Rapids, IA 2012-BGA-01

IN-PLANT COURSES AVAILABLE Tuition: $ 1,595.00 / 4-day Format Certification Exam: $ 200.00

Tuition: $ 945.00 / 2-day Format Proficiency Test: Included


PRACTICAL VIBREATION ANALYSIS IIIb IN-PLANT COURSES AVAILABLE Tuition: $ 1,595.00 / 4-day Format Certification Exam: $ 200.00

St. Paul, MN


Tuition: $ 1,295.00 / 3-day Format Hands-on Exercises: Included


!!! NEW !!!

NOV 13-14 Wheeling, WV 2012-BAL-04 Tuition: $ 945.00 / 2-day Format Hands-on Exercises: Included

THE VIBRATIO V ON FAUL LT GUIDE E The Vib bration Faultt Guide is a 110-page indispensable asse et for every vibration v ana alyst, as well as a helpful too ol to bridge the t gap betw ween the analystt and his management staff. Some 45 4 Rotating Machinery Faults F are Identified and deffined. Convveniently des signed at 3” x 6”, it easily fits f in your po ocket for eve eryday use!

GUÍA A DE FALLAS DE VIBRACIÓ V ÓN Este manual m constta de 110 pá áginas y fue compila ado por Full Spectrum Diagnostics D c como referen ncia rápida para p la indus stria de Manten nimiento Pre edictivo y Mo onitoreo de Condicción. La guía a incluye eje emplos de espectros, formas de onda, de efiniciones de e fallos y reglasde análisis de fase parra aproxim madamente unos 45 pro oblemas que e se pueden n presentar en e maquinarria rotativa. Tambié én incluimoss varios estándares de especifficaciones de vibración, guías para definiciión de banda as de alarma as, fórmulass y definiciiones de Pro ocesamiento o de Señaless. Es suficien ntemente pe equeño como o para llevarrlo en la bolsa a de su cam misa ( 3.5” X 6.0”), pero su s contenido es tan grande que podría ser conside erado como una guía de e referencia esencia al para la ind dustria del Monitoreo M de e Condicción.

THE VIBRATIO V ON TECH HNIQUES GUIDE The Vib bration Ana alysis Techn niques Guid de is a 108-pag ge pocket siized informa ation treasure e trove. Informa ation on doze ens of analy ysis techniqu ues, specificcations and data d presenttation formats are included. ur next If you liked the Vibrration Faultt Guide, you hould be the Vibration educatiional step sh Analys sis Techniqu ues Guide get g yours no ow at:

n at: http p:// e.html Order now Or by Phone P @ (763) 577-995 59


THE VIBRATIION ANALYSIS WALL W CHA ART The Vibration V Ana alysis Wall Chart C is a 46 6” x 36” Full-Color Laminated Referrence for you ur drab officce wall. The e overall Alarm cha arts in the center of th he chart are e surrounde ed by group pings of ove er 40 dominant rotating g machinery faults.. The faultt groupings include fre equency con ntent and dominant d dirrectional ressponse thatt he analyst to o “narrow-do own” the pottential source es and zero-in on curren nt vibration problem. p effectively allow th n combined with the Vib bration Fault Guide, the e Vibration Analysis Wall W Chart co ompletes the e diagnosticc When analyssis loop. We eather you require r one chart c or a ne eed to wall-p paper your office, we can n help!

Orderr now at: Htttp:// ore.html Or byy Phone @ (763) 577-99 959


THE VIBRAT TION ANA ALYSIS PERIODIC P C TABLE Thiss Full Color Laminated L 13 x 17 inch card-stock table provide es a “quicck-look” metthod of distin nguishing on ne machinerry fault from another and suggests Diagnostic Tests T or form mula that ma ay be used to t build a e and make the call! case Thiss Chart is a “Logical” “ ana alysis tool th hat classifiess vibration prroblems by Frequency F C Content and Directional Response. R T potentia The al vibra ation source es are instan ntly reduced based on th he analyst’s current c mea asurement data. The Ta able “forces” the user to think logicallly and classify faults acccordingly. Indivvidual Faultss are Foot Note Referen nced to the Vibration V Fa ault Guid de for a morre detailed re eview. If you think the Vibration V Fa ault Guid de is valuab ble, your nex xt educationa al step shou uld be the Vib bration Ana alysis Periodic Table! Get yours now at: a, or o by phone at a 763-577-9 9959



Full Spectrum Diagnostics’ Lead Instructor & Seminar Author is Dan Ambre. Dan is a graduate of The University of Iowa with a Bachelor’s degree in Mechanical Engineering, and has completed additional graduate level course work in Engineering Dynamics from The University of Illinois at Chicago, and Florida Atlantic University. Dan is a Certified Vibration Analysis Level III Instructor (Category IV) with over 16 years of Vibration Training and Certification Experience. Dan’s 25+ years of vibration experience in the Aviation & Aerospace Industries comes from positions at Sundstrand Aviation Corporation and Pratt & Whitney (United Technologies Corporation). This fieldwork includes Vibration & Acoustic testing, Rotor Dynamics analysis of high speed Rotor Systems, Experimental Modal, and Finite Element Analysis. His consulting experience base comes from positions at Technical Associates and Full Spectrum Diagnostics, which he founded in June of 2000. He is a Registered Professional Engineer in the States of North Carolina and Minnesota.

In 2004, after years of close association, Louis G. Pagliaro joined Full Spectrum Diagnostics. Lou fulfills multiple roles as our Seminar Sales Coordinator, Senior Instructor and course content co-author. Lou is a certified Level III Vibration Analyst (since 1996) and was recently re-certified by American Society of Nondestructive Testing as an ASNT PdM Level III in Vibration Analysis (Category IV). He has over 30 years of varied industrial experience, including Maintenance Management, Vibration Analysis, Vibration Training, Certification, and course development in areas of Noise Control, Precision Maintenance, Precision Alignment, Preventive Maintenance, and Maintenance Skills Enhancement. His worldwide teaching credentials include instruction of TAC, Update International, CSI, Entek and SKF customers in eight countries. Louis is a graduate of Niagara College in Welland, Canada. Lou can be contacted by phone at (704) 577-3953, or via Email at

Dan can be contacted by phone at (612) 875-9959, or via Email at

Email Tips Volume 87  

Varaible Frequency Drive Vibration Issues

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