Vibration5

8/11/2019 Vibration5

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LESSON

4LECTURE

VIBRATION AND NOISEMEASUREMENT

SUB - OBJECTIVE

At the end of the lesson the Trainee ill !e a!le to de"onstrate an #nderstandin$ ofVi!ration and Noise Meas#re"ent%

&%' INTRODUCTION

Electronic instruments for measuring machinery noise and vibration are generallyclassified as METERS, MONTORS or !N!L"#ERS$ The vibration Meter, %ig$ &'(,is a small )ortable instrument used to ta*e )eriodic vibration chec*s on rotatingmachinery to determine the +overall vibration level$ The vibration-sound level metersho.n in %ig$ &'/ may be used to ta*e or noise level readings$

! vibration monitor, %ig$ &'0 is similar to a vibration meter but is )ermanently orsemi')ermanently installed to )rovide continuous )rotection from e1cessivemachinery vibration$ 2ibration monitors normally incor)orate alarm relays incon3unction .ith )reset vibration levels to .arn .hen vibration has increasedbeyond a given level$ Some monitors may actually trigger the shutdo.n se4uence ifvibration becomes critical$

The analy5er, %ig$ &'&, includes a tunable filter for se)arating the individualfre4uencies of com)le1 noise and vibration$ ! strobosco)ic light .hich is triggeredin synchronism .ith the vibration of noise is also included and is a valuable aid inanaly5ing machinery )roblems and for dynamic balancing$

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E (


2/56

(i$% 4-&% A )i!ration "eter is #sed to ta*e +eriodi, ,he,*s of "a,hine )i!rationto dete,t de)elo+in$ tro#!le%

(i$% 4-% This )i!ration.so#nd le)el "eter is #sed to "eas#re !oth noise and)i!ration%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E / 28R!TON !N!L"SS 9 CORRECTON


3/56

(i$% 4-/% Vi!ration "onitors are +er"anentl0 installed to +ro)ide ,ontin#o#s 4ho#r +rote,tion of ,riti,al "a,hiner0%

(i$% 4-4% A )i!ration anal01er has all the +ro)isions needed to dia$nose"a,hiner0 +ro!le"s and +erfor" in-+la,e d0na"i, !alan,in$%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E 0


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TRANSDUCERS 23ICU3S5

Regardless of .hich ty)e of instrument is used to measure the vibration or noise


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Even though the sensitivity falls off at lo. fre4uencies, the standard velocity )ic*u)is still 4uite usable$ This dro) in sensitivity .ill have little or no effect on the use ofyour instrument for balancing or for detecting increases in machinery vibration asre4uired in a )reventive maintenance )rogram$ 7o.ever, for those .ho must ta*ereadings for com)arison .ith s)ecific criteria, the dro)'off in sensitivity is reasonably)redictable, and accurate data can be obtained by using the correction factor chart,%ig$ &'$ !ll readings a))lied to the chart must be filtered am)litude readingsobtained using the filter of your vibration analy5er instrument$ Overall or filter outreadings such as those obtained .ith the vibration meter should not be a))lied tothe chart$

To use the chart, sim)ly note the fre4uency of the vibration on the hori5ontal scaleat the bottom of the chart$ %rom this )oint, move u).ard to intersect the curve, andcross over to the vertical a1is on the left side and read the value of the correctionfactor from the scale$ Ne1t, sim)ly multi)ly the observed am)litude meter readingtimes, the correction factor to obtain the true am)litude of vibration$

MOUNTIN: T6E 3ICU3

Li*e most vibration )ic*u)s, the Mechanalysis velocity )ic*u) is sensitive only tovibration occurring in the direction in .hich it is )ointed n addition, the )ic*u) maybe )laced in any )osition .ithout affecting its o)eration or accuracy$

There are several methods .hich can be used to a))ly the vibration )ic*u) asillustrated in %ig$ &'F$ Each of the methods sho.n .ill hold the )ic*u) in )lace.ithout distorting the actual vibration, but only over a limited fre4uency range$ %ig$&'D lists the highest recommended fre4uency for each mounting method$ 2ibrationreadings ta*en at higher fre4uencies may be sub3ect to error$

The fact to consider .hen mounting the vibration )ic*u) is that any ob3ect


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6AND 6ELD 8IT6OUT A 3ROBE

The hand held )ic*u) .ithout )robe is 4uite satisfactory for most )eriodic vibrationchec*s and analysis a))lications$ The )ic*u) should be held against a reasonablyflat surface$ @hen a))lying the )ic*u) to curved or irregular surfaces, *ee) in mindthat the )ic*u) measures vibration only in the direction )arallel to the )ic*u) a1is,and any unsteadiness of the hand .hich allo.s the direction of the a1is to vary mayresult in unsteady vibration readings$

Use only enough )ressure to *ee) the )ic*u) from chattering or +.al*ing on thesurface$ @hen the vibration )ic*u) is hand held, a tingling sensation in the handindicates the )resence of the a high fre4uency vibration and the need for more)ressure$

6AND 6ELD 8IT6 STANDARD ;< 3ROBE

The standard G ho.ever, cautionshould be e1ercised .here vibration fre4uencies are above (, C:M$

VISE :RI3 3LIERS

The vise gri) )liers re4uire a firm mounting, )referably .ith the 3a.s in contact .iththe mounting surface along their entire length$ !ctually, vise gri)s are items ofconvenience for use during in )lace balancing, and are not recommended forvibration analysis )ur)oses because of their very limited fre4uency range$

MA:NETIC 3ICU3 6OLDER

The magnetic )ic*u) holder should be mounted on a reasonably flat, smooth, clean

surface$ 6irt or grease bet.een the magnet and the mounting surface reduces theholding )o.er of the magnet and conse4uently the ma1imum usable fre4uency$ fthe magnetic surface is not flush .ith the mounting surface, the holder may roc* atsome un)redictable lo. fre4uency, )roducing erroneous readings$ @hen )ro)erlya))lied, the magnetic holder )roduces good results as a vibration )ic*u) holder$

Sometimes a machine .ill re4uire a s)ecial )ic*u) mounting brac*et or ada)ter$ Or,)erha)s a longer )robe is needed to reach out of the .ay )laces$ @here theusable fre4uency range is in 4uestion, a 4uic* com)arison chec* .ill usually revealany )roblems$ Sim)ly select an accessible )oint on the machine .ith vibrationcharacteristics similar to those .here measurement .ill be ta*en$ Measure thevibration first .ith the )ic*u) hand held .ithout the )robe, and then measure the

vibration at the same )oint using the selected brac*et or )robe$ !ny difference inthe t.o sets of readings .ill )robably be due to the selected mounting$

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E 28R!TON !N!L"SS 9 CORRECTON


7/56

(i$% 4-=% Basi, ,onstr#,tion of the seis"i,-)elo,it0 )i!ration +i,*#+%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E F


8/56

(i$% 4->% 8hen #sin$ the IRD Seis"i, Velo,it0 3i,*#+ at fre?#en,ies !elo >''

C3M@ if re?#ired@ "ore +re,ise a"+lit#de readin$s "a0 !e o!tained !0"#lti+l0in$ the o!ser)ed readin$ !0 the "#lti+li,ation fa,tor o!tained fro" the

,hart a!o)e% Onl0 (ilter In readin$s sho#ld !e a++lied to the ,hart%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E D 28R!TON !N!L"SS 9 CORRECTON


9/56


10/56

The fish'tail sha)e )rovides t.o )oints of contact needed to *ee) the shaft stic* onthe circumference of a rotating shaft, and also )ermits the use of the stic* .ithalmost any diameter shaft or roll$ n addition, the end of the stic* is ta)ered to)rovide a smaller contact area .ith the shaft in order to reduce friction and )reventchatter$

Shafts must be reasonably smooth, )referably smooth, )referably turned or ground$!))lying the shaft stic* to shafts .ith rust, dents, )its or an other.ise rough surface.ill )roduce 4uestionable information and may also damage the stic*$ Tuning theanaly5er filter to the rotating s)eed fre4uency .ill normally im)rove the results$!lso, ta*e care to avoid *eys and *ey.ays, set scre.s and lubrication holes$

(i$% 4-% Re,o""ended fre?#en,0 li"its for different +i,*#+ atta,h"ent"ethods%

(i$% 4-;% The entire fa,e of the st#d-"o#nted +i,*#+ sho#ld !e in ,onta,t iththe "eas#red s#rfa,e% Mo#ntin$ the +i,*#+ at an an$le 2B5 or o)erhan$in$the "eas#red s#rfa,e 2C5 "a0 res#lt in errors% Mo#ntin$ ith an o)erl0 lon$

st#d that !otto"s in the +i,*#+ end ,a+ 2D5 "a0 not onl0 affe,t 0o#r readin$s!#t "a0 also res#lt in da"a$e to the +i,*#+%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E ( 28R!TON !N!L"SS 9 CORRECTON


11/56

(i$% 4-&'% The shaft sti,* #sed ith the +i,*#+ for "eas#rin$ shaft )i!ration a )al#a!le tool for "an0 anal0sis and !alan,in$ a++li,ations%

%or shaft s)eeds in e1cess of 0 R:M, avoid holding the stic* against the shaftfor any length of time$ 7eat build'u) from friction may burn the stic* or actuallycause scoring of the shaft$ %re4uent a))lications of a medium .eight lubricating oilis recommended to reduce friction and heat build'u) on high's)eed shafts$ Shaftstic* readings are not recommended at shaft s)eeds above (/, R:M$

T.o hand are normally re4uired to a))ly the shaft stic*> one hand one the stic* to

)revent .al*ing u) and do.n the shaft and the other hand on the )ic*u) to regulate)ressure and control the angular )osition of the )ic*u)$ @hen a))lying the shaftstic*, use only sufficient )ressure to )revent the stic* from chattering$ ! tinglingsensation in the hand accom)anied by a distinctive s4ueal or gro.l indicates the)resence of chatter and the need for more )ressure$ Maintaining a constant)ressure is im)ortant also$ Studies ho. that varying the )ressure significantly mayaffect the accuracy of readings$ This is )articularly im)ortant in balancing or.herever a com)arison of shaft stic* readings is im)ortant$

n the same .ay that the shaft stic* senses shaft vibration, it also senses any out ofroundness or eccentricity of the shaft$ Normally the influence from shaft runout is4uite small and not a cause for concern$ !gain, the use of the analy5erHs filter tunedto rotating s)eed fre4uency .ill usually im)rove the validity of your readings$ Onshafts, cou)lings, )ulleys or .herever runout is sus)ected, a visual chec* .ith a dialindicator or micrometer is recommended$

!lthough there may be sources of error in shaft stic* measurement fromirregularities in shaft geometry, variations in a))lied )ressure and angular )osition,the shaft stic* is a very valuable tool for analysis and in )lace balancing$

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E ((


12/56

S6A(T RIDER ACCESSOR7

!lthough the shaft stic* is 4uite suitable for )eriodic vibration chec*s, analysis andin )lace balancing, .here it is desired to continually monitor absolute shaft vibrationthe R6 Mechanalysis Shaft Rider !ccessory, %ig$ &'((, is used$

(i$% 4-&&% IRD Me,hanal0sis Shaft Rider A,,essor0%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E (/ 28R!TON !N!L"SS 9 CORRECTON


13/56

The shaft rider accessory is )ermanently installed in the machine bearing housingand consists of a s)ring loaded )robe held firmly against the rotating shaft toaccurately follo. shaft motion$ The )robe is fitted .ith a long'.earing non'metallicti) .hich is installed .ithin the bearing area to )rovide ti) lubrication$ ! velocity)ic*u) or accelerometer mounted to the shaft rider )rovides an electrical out)ut)ro)ortional to the absolute shaft vibration


14/56

! tem)orary solution to overcome the )roblems of magnetic interference is to use along e1tension )robe$ The long )robe sim)ly locates the vibration )ic*u) a.ay fromthe magnetic field, thus reducing the interference level$ The limitation of thistechni4ue is a reduction in the usable fre4uency range of the measurement system$

T6E DIRECT 3ROD VELOCIT7 3ICU3

Many times it is necessary to measure the vibration of a small, light'.eight )art orstructure$ 7o.ever, holding or attaching the standard velocity )ic*u) to a small )artmay actually reduce the vibration$ To overcome this )roblem, the direct )rodvibration )ic*u), %ig$ &'(&, may be used$

The direct )rod )ic*u) is 4uite similar in construction and o)eration to the seismicvelocity )ic*u)$ 7o.ever, the direct )rod )ic*u) includes a )rod e1tending throughthe end'ca) of the )ic*u) and directly attached to the movable coil inside$

Toe measure vibration using the direct )rod )ic*u), the )rod of the )ic*u) is broughtinto contact .ith the vibrating )art .hile the case of the )ic*u) is rigidly held ormounted as a fi1ed reference$ The )rod may be attached to the )art using thethreaded ti), or it may beheld in )lace by a s)ecial magnetic ti)$

The normal )ractice is to mechanically mount the direct )rod )ic*u) ho.ever it canbe hand'held if s)ecial care is ta*en$ @hen hand holding the )ic*u) it is usuallynecessary to tune the analy5er filter to the vibration fre4uency of interest$

This .ill )revent errors in your readings resulting from the natural movement of thehand$ n addition, be sure that the )robe and )ic*u) coil are free to move .ithin thelimits of travel at all times$

@hen using the direct )rod velocity )ic*u), only the .eight of the )rod and movingcoil is added to the vibrating )art$ This ma*es the )ic*u) es)ecially useful on small,light'.eight ob3ects .here the added .eight of a seismic velocity )ic*u) may affect

the actual vibration$

n addition, since the )ic*u) coil is mechanically moved, the out)ut of the direct )rod)ic*u) is virtually unaffected at the lo. fre4uencies$

Thus, this )ic*u) is .ell suited for measuring lo. fre4uency vibration and is oftenselected for use on balancing machines .here )arts may be balanced at s)eeds aslo. as ? R:M .ith e1cellent results$

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E (& 28R!TON !N!L"SS 9 CORRECTON


15/56

(i$% 4-&% The effe,t of "a$neti, interferen,e ,an !e easil0 deter"ined !0

si"+l0 s#s+endin$ the )elo,it0 +i,*#+ !0 its ,a!le in the area here )i!rationreadin$s are nor"all0 "ade%

(i$% 4-&/% The effe,ts of "a$neti, interferen,e are $reatl0 red#,ed !0installin$ the )elo,it0 +i,*#+ in a "a$neti, shield%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E (?


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17/56

The out)ut of accelerometers is usually small .hen com)ared to the normal out)utof velocity ty)e )ic*u)s$ %or this reason, )re'am)lification of the accelerometerout)ut is usually re4uired before a usable signal is obtained$ The accelerometer)ictured in %ig$ &'(F has its o.n am)lifier built in$ this has the advantage ofeliminating many )roblems such as limited cable length or cable interchangeability$The accelerometer in %ig$ &'(? does not have a built'in am)lifier, but has theadvantage of higher o)erating tem)erature and some.hat smaller si5e and .eightmagnetic field .hich in turn )roduces a )ro)ortional reduction in the am)litude ofthe carrier signal$

@hen the distance bet.een the )ic*u) ti) and the metal ob3ect


18/56

(i$% 4-&>% Blo,* dia$ra" Non-Conta,t 3i,*#+ o+eration%

Non'contact )ic*u)s are installed in the machine .ith the )ic*u) ti) in close)ro1imity to the rotating shaft$ The distance bet.een the ti) and shaft is referred toas the ga)$ Ty)ical ga) settings are $/, 0, $?, $ and $($ 7o.ever,the s)ecific ga) setting for a )ic*u) .ill de)end on the ty)e of )ic*u), shaft materialand system calibration$

To facilitate installing the non'contact )ic*u) and to )rovide assurance that the)ic*u) ga) is )ro)erly ad3usted at all times, the ga) meter on the accessoryinstrument or monitor indicates )ic*u) ga)$

;a) readings can be ta*en .hen the shaft is rotating


19/56

To )rovide ma1imum )rotection from cable damage, some cables may havearmored covers$ %ig$ &'(F illustrates only a fe. of the many styles of non'contact)ic*u)s .hich are available to match individual installation re4uirements$

Non'contact )ic*u)s are normally installed in holes drilled and ta))ed in themachine case or bearing ca) as sho.n in %ig$ &'(D$ N some cases, the machinerymanufacturer may have already made the necessary )rovisions for installing thenon'contact )ic*u)s, in .hich case installation is a sim)le matter of inserting the)ic*u)s in the )rovided locations and ad3usting for the )ro)er ga)$

%or field installations .here there are no )rovisions for mounting the )ic*u)s in thebearing, the )ic*u) may be mounted in a rigid brac*et or ada)ter as sho.n in %ig$&'(G$ @henever ada)ters are used to mount the )ic*u), care must be ta*en toinsure that ada)ters are securely fastened to the machine$ !da)ters must be *e)tshort and massive to minimi5e any vibration of the mounting$

(i$% 4-% IRD Me,hanal0sis Non-Conta,t 3i,*#+s are a)aila!le in a )ariet0 ofst0les to "eet indi)id#al installation re?#ire"ents%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E (G


20/56

(i$% 4-&% Non-Conta,t 3i,*#+s "a0 !e installed in holes drilled and ta++ed inthe "a,hine ,ase or !earin$ ,a+% 2note The !earin$ ill#strated here has !een

,#t aa0 to re)eal details of installation5%

T6E MICRO36ONE

There are several ty)es of micro)hones commercially available> ho.ever, they alluse a dia)hragm arrangement .hich serves to convert the air )ressure oscillations


21/56

(i$% 4-&;% The Non-Conta,t 3i,*#+ "a0 !e "o#nted on a ri$id !ra,*et fir"l0

atta,hed to the !earin$ ,a+%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E /(


22/56

(i$% 4-'% A ,era"i, "i,ro+hone is +ro)ided ith "ost IRD Me,hanal0sisinstr#"ents

3OSITIONIN: T6E MICRO36ONE

Unli*e vibration )ic*u)s .hich sense vibration only in the direction they are )ointed,the micro)hone )rovided .ith your R6 Mechanalysis instrument is Omni'directional$This means that the micro)hone is sensitive to noise coming at it from vitally anydirection$ Even though the micro)hone is sensitive to noise coming from alldirections, some care must be e1ercised .hen )ositioning the micro)hone in orderto obtain reliable data$ %or e1am)le, Cha)ter discussed the )resence of three)ossible sound fields, NE!R, %!R and RE2ER8E!R!NT, and the effect each hason the noise levels measured$ %urther more, you .ill recall from Cha)ter thatnoise sources are usually directional in nature and may re4uire more than 3ust onemeasurement$

The )ositions selected for noise measurement often de)end on the )ur)ose of themeasurement$ %or e1am)le, some government regulations re4uire measurementsat )ositions .hich .ill re)resent the location of the .or*erHs ear, since their )ur)oseis to determine the amount of noise to .hich the .or*er is e1)osed$

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E // 28R!TON !N!L"SS 9 CORRECTON


23/56

Other standards re4uire measurement at a number of fi1ed )ositions


24/56

$ Once micro)hone )osition has been established for 4uadrant I (, it shouldbe )ermanently located by a suitable mar* on the floor and by dimensioningthe )osition on your data sheet$

F$ Re)eat ste)s 0 through above to establish suitable micro)hone )ositionsfor 4uadrants /,0 and &$

D$ f there are o)erator stations near the machine, noise level measurementsshould also be ta*en at these locations$ The micro)hone should be locatedat the a))ro1imate )osition of the o)eratorHs ear as illustrated in %ig$ &'//$The machine o)erator should not be near the micro)hone .hen themeasurement is ta*en$

(i$% 4-&% Mi,ro+hone +osition is +ro+erl0 di"ensioned@ to +er"it relo,ation for,o"+ara!le readin$s later%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E /& 28R!TON !N!L"SS 9 CORRECTON


25/56

(i$% 4-% So#nd "eas#re"ents are also "ade at o+erator stations at thea++roi"ate +osition of the o+eratorFs ear%

3OSITIONIN: T6E O( T6E INSTRUMENT O3ERATOR

@hen the instrument o)erator is near the micro)hone, as .ould be the case .henhe is holding the $to ma*e a measurement, his)resence can affect the measured results by as much as d8$ %or this reason, it is.orth.hile to follo. )rocedures .hich minimi5e this effect$ The o)erator shouldstand .ith one micro)hone e1tended .ell in front of him .ith the a))arent noisesource either to his right or left$ The micro)hone should not left$ The micro)honeshould not be )ointed directly to.ard the source$ See %ig$ &'/0$

7and holding the micro)hone is generally satisfactory .hen overall soundmeasurements are being ta*en$ 7o.ever, .hen an analysis of the noise is to bemade, the micro)hone should be held by a clam) and the instrument o)eratormoved ? or ( feet a.ay$

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E /?


26/56

(i$% 4-/% The instr#"ent o+erator sho#ld stand ith the "i,ro+hone helda!o#t feet in front of hi" ith the so#nd so#r,e at his left or ri$ht% The

"i,ro+hone sho#ld +oint aa0 fro" the o+erator@ !#t not toard the so#r,e%

INSTRUMENT O3ERATION

This section outlines the basic features and o)eration of the instruments used tomeasure and analy5e noise and vibration and for dynamic balancing$ Theinstruments illustrated here are ty)ical meters and analy5ers$ %or more detailedinformation, refer to the instruction and o)eration manual furnished .ith yours)ecific instrument$

(IBRATION AND SOUND LEVEL METERS

The meters sho.n in %ig$ ($ !nd / are used for measuring overall vibration andnoise am)litudes$ The 2ibration Meter, %ig$ (, both dis)lacement and velocity$ Thevibration-Sound Level Meter, %ig$ /, measures vibration and also )rovides ameasure of noise levels in d8 utili5ing the standard !, 8 and C .eighting net.or*s$

Some regulations on hearing conservation re4uire that a chec* of instrumentaccuracy be made before and-or after conducting a noise level survey$ Such achec* can be made 4uic*ly and easily in the field using an o)tional sound levelcalibrator such as the unit sho.n in %ig$ &'/&$ The sound level calibrator illustratedis battery )o.ered and generates a )recise sound )ressure$ Sim)ly sim)ly fittingthe calibrator over the micro)hone and com)aring the resulting am)litude meterreading to the )re'established level noted on the calibrator chec*s instrumento)eration$

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E / 28R!TON !N!L"SS 9 CORRECTON


27/56

(i$% 4-4% A so#nd le)el ,ali!rator is #sed to +eriodi,all0 ,he,* instr#"enta,,#ra,0%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E /F


28/56

MEASURIN: MAC6INER7 VIBRATION

To measure machinery vibration, first connect one end of the )ic*u) cable to thevibration )ic*u) and connect the other end of the cable to the )ic*u) in)utrece)tacle on the instrument$

Test the instrument batteries using the +TEST )rovisions of the instrument$8atteries .hich read lo. should be re)laced immediately$

To measure the vibration, .e must )lace the )ic*u) at various )oints on themachine .here .e can gain the most useful information$ Often the )osition andlocation of the vibration )ic*u) .ill be dictated by the )hysical sha)e of themachine$ n general, ho.ever, $$near as )ossibleto the machineHs bearing because it is through the bearings that the vibration forcesare being transmitted$

t should be remembered that the vibration )ic*u) measures only the vibrationoccurring in the direction in .hich it is )ointed$ %or this reasons, it is necessary toidentify the )osition of the )ic*u) for all vibration measurements$ 2ibration readingsare normally ta*en .ith the )ic*u) in the 7OR#ONT!L, 2ERTC!L or !!Ldirection as illustrated in %ig$ &'/?$ 2ertical and hori5ontal readings are ta*en .iththe )ic*u) )er)endicular to the machineHs shaft centerline and are generally calledradial vibration measurements$ !1ial vibration readings are those ta*en .ith the)ic*u) )arallel to the centerline of the shaft of the machine$ n either case, the)ic*u) should be )laced on the bearing housing as near to the shaft as )ossible$:roceed to measure the vibration as follo.sK

($ :lace the vibration )ic*u) on the machine in the vertical, hori5ontal or a1ialdirection$ The )ic*u) may be hand'held .ith or .ithout the standard )robe,or it may be attached by )liers or magnetic holder as illustrated )reviously infig$ &0$ @hen hand holding the )ic*u), the )ic*u) should be held firmlyagainst the machine .ith 3ust enough )ressure to )revent it from chattering$

7old the )ic*u) as steady as you can to insure accurate readings$

/$ Select the 6S:L!CEMENT of the 2ELOCT" of the vibration formeasurement using the 6S:L!CEMENT'2ELOCT" SELECTOR$ See %ig$&'/$

0$ Starting at the least sensitive full'scale range


29/56


30/56

NOTEK

6onHt .orry if you ha))en to turn the am)litude range selector too far such that theam)litude meter goes off scale$ Overload )rotection is built into the meter circuits sothat the meter .ill not be burned out or harmed if it goes off scale$ Sim)ly turn theam)litude range selector bac* until the meter reads in the u))er t.o'thirds of the meterscale$

"ou .ill note that the am)litude meter has t.o scalesK the to) meter scale reads from to ( and the bottom scale from to 0$ The t.o scales on the meter are designed so thatan u)'scale reading of at least one'third full scale is )ossible for all vibrationmeasurements$ This minimi5es inherent meter error$

The setting of the am)litude range selector determines .hich scale a))lies$ f theselector is set to a range .hich begins .ith ( such as (, (, (, etc$, use the to) scale.hen reading the meter, )lacing the decimal )oint as indicated by the am)litude rangeselected$

%or e1am)le, on the ( setting, the full scale am)litude on the meter becomes ( mils


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(i$% 4-% T0+i,al )i!ration a"+lit#de "eter readin$s%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E 0(


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&' Starting .ith the !M:LTU6E R!N;E SELECTOR in the least sensitiverange


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Of course, the analy5er .ill only read the vibration from the one )ic*u) at a time$The )ic*u) rece)tacle connected tot he instrument is determined by the :CBU:SELECTOR S@TC7 located on the front )anel of the analy5er, %ig$ &'F$

Other vibration )ic*u)s such as non'contact and accelerometer )ic*u)s may beused .ith the analy5er using available accessories$ Or, the analy5er may beconnected directly to a )ermanently installed vibration monitor instrument .hichuses either velocity, non'contact or accelerometer )ic*u)s$ !ll R6 Mechanalysismonitors feature a s)ecial !N!L"#ER Q!CB for this )ur)ose$ See fig$ &'0/$

%or analysis of machinery noise, the vibration-sound level meter may be connecteddirectly to the analy5er as sho.n in %ig$ &'00$ The standard )ic*u) cable is used forthis )ur)ose$

(i$% 4-/'% To +i,*#+s ,an !e ,onne,ted to the anal01er to s+eed anal0sis and!alan,in$%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E 0& 28R!TON !N!L"SS 9 CORRECTON


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(i$% 4-/&% 3i,*#+ sele,tor sit,h%

(i$% 4-/% Vi!ration anal01er ,onne,ted to the ANAL7GER JAC lo,ated on thefront +anel of all IRD Me,hanal0sis )i!ration Monitors%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E 0?


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(i$% 4-//% To anal01e "a,hiner0 noise@ si"+l0 ,onne,t the )i!ration.so#ndle)el "eter to the anal01er%

T6E AM3LITUDE METER

The am)litude of vibration is read from the analy5erHs !M:LTU6E METER, &'0&$This meter is identical to the am)litude meter used on the vibration- sound levelmeters, and uses the same to ( to) scale and to 0 bottom scale$ 7ere also, thefull scale range of the meter and the scale to use


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T6E (RE9UENC7 METER

The fre4uency of the vibration or noise being measured is indicated on theanaly5erHs %REUENC" METER, %ig$ &'0&$ 2ibration and noise fre4uencies areread directly from the meter in cycles )er minute


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The cut off fre4uencies above and belo. the tuned center fre4uency, .here theres)onse to a signal is a))ro1imately 0 less than ma1imum res)onse$ n other.ords, at the cut'off fre4uency a signal .ould be reduced by 0 of its realam)litude$ 8eyond the cut'off fre4uencies the signal .ill be reduced byconsiderably more$

The band.idth of a filter is usually e1)ressed as the )ercentage bet.een the filterHsturned center fre4uency and the u))er and lo.er cut'off fre4uencies$ %or e1am)le,

the band.idth of the filter in %ig$ &'0 is ?, .hich means that the filter band.idth

e1tends ? above


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&$ Select either dis)lacement or velocity for measurement using the6S:L!CEMENT A 2ELOCT" SELECTOR$

?$ Turn the !M:LTU6E R!N;E SELECTOR to a range .hich gives anam)litude meter reading )referably in the u))er /-0rds of the meter scale$

$ Roc* the filter tuning *nob by turning it slo.ly bac* and forth .hile observingthe am)litude metre$ N this fashion, ma*e minor ad3ustments to obtain thema1imum or )ea* reading on the am)litude meter$

This techni4ues of tuning the filter to obtain the )ea* am)litude is very similar totuning your radio to a )articular station to get the clearest rece)tion$ @ith the filter)ro)erly ad3usted, the fre4uency meter should read steady at the tuned fre4uency$

TUNIN: T6E (ILTER TO (IND UNNO8N (RE9UENCIES

@hen machinery noise and vibration are com)le1, i$e$, consisting of t.o or morefre4uencies, the analy5erHs tunable filter must be used to determine .hichfre4uencies are )resent$ t is in this regard that the fre4uency meter is of greatvalue$

@hen see*ing un*no.n noise and vibration fre4uencies, the analy5erHs fre4uencyrange is scanned .ith the tunable filter$

@hen there is no )articular vibration or noise )resent at the fre4uency to .hich thefilter is tuned, the fre4uency meter )ointer .ill move u) and do.n the meter scale ina random manner$

7o.ever, as soon as the filter a))roaches a )articular vibration or sound fre4uency,the fre4uency meter )ointer .ill loc* on to that fre4uency and cease its .anderingover the scale$

This is the first indication that a )articular fre4uency is )resent$ %ine ad3ustment ofthe filter'tuning dial is then made to obtain a )ea* reading on the analy5er am)litudemeter$

This method of tuning the filter to discover the various fre4uencies of noise orvibration is outlined in more detail in the follo.ing ste)'by'ste) )rocedureK

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E 0G


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ABOVE LE(TThe fre4uency range selector is set on the ? A ? C:M range$Therefore, the indicated meter reading is> &/ C:M$

ABOVE RI:6TThe fre4uency range selector is set on the ? A ?B C:M range$Therefore, the indicated meter reading is (DC:M$

BELO8 LE(TThe fre4uency range selector is set on the ?B A ? C:M R!N;E$Therefore, the indicated meter reading is D C:M$

BELO8 RI:6T The fre4uency meter indication is unsteady, indicating that there isno vibration )resent at the fre4uency to .hich the filter is tuned$ n the +%ilter Outmode this .ould indicate that there is no )redominate vibration fre4uency$

(i$% 4-/=% Sa"+le fre?#en,0 "eter readin$s%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E & 28R!TON !N!L"SS 9 CORRECTON


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(i$% 4-/>% T0+i,al filter res+onse%

(i$% 4-/% 8ith this "otor.fan #nit@ so"e )i!ration ill li*el0 o,,#r at "otorR3M 2&''5 and fan R3M 2''5

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E &(


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($ Turn the %LTER SELECTOR to the 8OR!6 )osition$ The 8RO!6 )ositionis selected because it allo.s us to scan the fre4uency ranges 4uic*ly$Scanning .ith the S7!R: filter .ould ta*e more time and is usually reservedfor analysis of very com)le1 noise or vibration$

/$ Turn the %REUENC" R!N;E SELECTOR to the lo.est fre4uency range)osition$ %or the analy5er in %ig$ &'0&, this range is ?'? C:M$


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T6E STROBE LI:6T

The strobosco)ic light of STRO8 L;7T furnished .ith your analy5er is a high'intensity light .hich flashes on and off in synchronism .ith the vibration or noisefre4uency being measured$ The light is connected to the analy5er by the STRO8C!8LE su))lied$

To illustrate the o)eration of the strobe light, su))ose the (D R:M motor in fig$ &'0D is out of balance$ This .ill cause a vibration at a fre4uency of (D C:M or oncefor each revolution of the shaft, and the strobe light .ill be fired at the same rate$!s the motor )ulley rotates, the strobe light flashes each time the )art reaches acertain )osition$

%or the motor in %ig$ &'0D, the strobe light flashes .hen the reference mar* on the)ulley reaches a )osition of /K oHcloc*$ The motor )ulley is illuminated briefly atthat time$ 6uring the rest of the )ulleyHs rotation, the light is off and then the )ulleyis again illuminated .hen the mar* is at /K oHcloc*$ This action ma*es the eyebelieve that the )ulley is standing still$

The use of the strobe light to )in)oint the source of vibration or noise is veryim)ortant$ "ou .ill recall from cha)ter that the fre4uency of vibration and noise isusually e4ual to or a multi)le of the rotating s)eed of the )at at fault$ Since thestrobe light flash rate is determined by the fre4uency of noise or vibration, the )artcausing the )roblem .ill often a))ear to stand still under the light$

The motor )ulley in %ig$ &'0D is standing still .ith one mar* visible under the strobelight because the vibration fre4uency is ( 1 R:M$ f the vibration or noise fre4uencyoccurs at / R:M, say due to mechanical looseness, you may see the )ulleystanding still .ith the reference mar* in t.o )ositions as illustrated in %ig$ &'0G$

%ig$ &'& sho.s the reference mar* fro5en in three )ositions .hich could occur ifthe fre4uency .as 0 1 R:M$

Sometimes the rotor .ill not a))ear to stand still under the strobe light$ The imagemay be erratic li*e the one in %ig$ &'&($ This occurs .hen the vibration or noise isunsteady or com)le1$ Or, )erha)s the vibration or noise is coming from anothersource$ f this occurs, the tunable filter should be used$

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E &0


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(i$% 4-/% The stro!e li$ht flashes in s0n,hronis" ith the )i!ration% Thereferen,e "ar* is ill#"inated !riefl0 ea,h re)ol#tion hen it rea,hes the ''

oF,lo,* +osition to "a*e the +#lle0 a++ear to stand still%

(i$% 4-/;% Vi!ration at R3M "a0 sho to referen,e "ar*s #nder thestro!e li$ht%

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E && 28R!TON !N!L"SS 9 CORRECTON


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(i$% 4-4'% Referen,e "ar* fro1en< in three +ositions%

(i$% 4-4&% An errati, stro!e i"a$e #s#all0 "eans the noise or )i!ration is#nstead0@ ,o"+le or@ +erha+s ,o"in$ fro" another so#r,e%

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E &?


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MAHIMUM STROBE (LAS6

RATE

The ma1imum flash rate of the strobe light is normally limited in order to conservebulb life$ Some analy5ers have a ma1imum strobe flash rate of (?, flashes )erminute .hile others are limited to ? flashes )er minute$ %or noise and vibrationfre4uencies above the ma1imum flash rate, the analy5er ma1imum flash rate, theanaly5er .ill automatically cause the strobe light to flash at sub'multi)le rates of thefre4uency> i$e$, (-0, W , etc$

The im)ortance of this fact can be illustrated by the follo.ing e1am)leK !ssume thatthe ma1imum flash rate of your strobe light is ? flashes )er minute, and therotating s)eed


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7o.ever, if the fre4uency being measured is not e1actly the same as shaft s)eed orsome multi)le of shaft s)eed, then the shaft .ill not a))ear to stand still under thestrobe light$ %or e1am)le, if the noise or vibration is a actually coming from another)art of the machine or )erha)s from a nearby machine, the strobe image maya))ear erratic li*e that in %ig$ &'&(> or the reference mar* may a))ear to rotateslo.ly$

USIN: T6E STROBE LI:6T TO MEASURE 36ASE

!nother common use of the strobe light is to measure the )hase of vibration$:hase measurements are often essential in vibration analysis to diagnose s)ecificmachine )roblems$ n addition )hase measurements are )articularly use full forbalancing rotating )arts$ The )osition of the reference mar* changes .hen the)osition of the unbalance is changed$ The )osition of the reference mar* can beused then to determine the correct )lace for ma*ing .eight corrections$

The use of )hase measurements for analysis is discussed in Cha)ter 2, anddynamic balancing using )hase measurements is outlined in detail Cha)ter 2

The first ste) in using the strobe light to measure )hase is to establish a commonreference to .hich all )hase measurements .ill be made$ Normally, a referencemar* is )ut on one end of the shaft .hich can be vie.ed under the strobe light$ !reference mar* can be made .ith chal* or )aint, or an e1isting *ey or *ey .ay canbe used$ n some cases .here the machine cannot be shut do.n and .here no *eyor *ey is visible, a distinguishing blemish, nic*, rust s)ot or grease s)ot on the shaftmay be used$

! common )ractice is to vie. the end of the shaft as an imaginary cloc* face, in.hich case the )hase of the vibration measured in %ig$ &'0D .ould be /K oHcloc*$The cloc* face reference system is most commonly used .hen )hase is observedfor general com)arison )ur)oses$

@hen it is desirable to measure )hase very accurately


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T6E INTERNAL OSCILLATOR

Standard R6 Mechanalysis !naly5ers are )rovided .ith an ad3ustable NTERN!LOSCLL!TOR$ The internal oscillator is a se)arate means of flashing the strobelight, and is com)letely inde)endent of the vibration or noise source$

The internal oscillator is )ut into o)eration by s.itching the %LTER SELECTOR tothe +OSC )osition$ See %ig$ &'0&$

The rate at .hich the internal oscillation fires the strobe light is ad3ustable over theentire fre4uency range of the analy5er> ho.ever, the strobe light flash rate .illautomatically be sub'divided above the strobeHs ma1imum flash rate 3ust as it is forvibration or noise fre4uencies$

The oscillator is ad3usted by the %LTER TUNN; BNO8, and the oscillatorfre4uency .ill be indicated on the fre4uency meter$ @hen the internal oscillator is ino)eration, the am)litude meter .ill read 5ero$

The internal oscillator used in con3unction .ith the strobe light offers three im)ortantusesK

($ :erform slo. motion studies$

/$ %acilitate filter tuning$

0$ 6etermine the rotating s)eed


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TUNIN: T6E (ILTER 8IT6 T6E INTERNAL OSCILLATOR

f the rotating s)eed of a machine is *no.n, the oscillator can be used to 4uic*lyand accurately tune the filter to rotating s)eed and multi)les of rotating s)eed$

%or e1am)le, su))ose .e .anted to tune the filter to a fre4uency e4ual to therotating s)eed


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Recordings of am)litude versus time can be hel)ful in many .ays$ 6$C$ recordersare often used .ith )ermanently installed vibration monitors$ 8y continuallyrecording vibration am)litude levels, it is )ossible to determine .hether machinery)roblem has develo)ed suddenly or gradually over a )eriod of time$ Suchinformation may be an im)ortant factor .hen ma*ing the decision to shut do.n anim)ortant machine$

2ibration and noise am)litude recordings can be a valuable aid in diagnosing certainmachinery )roblems$

%or e1am)le, one )a)er manufacturer .as e1)eriencing re)eated bearing failures inthe dryer section of a )a)er machine for no a))arent reason$ ! vibration analy5er.as brought in, ho.ever, the am)litude readings$ta*en at the time .ere very lo.,indicating that no significant mechanical )roblems e1isted$

!fter e1hausting all realistic )ossibilities, the decision .as made to connect a 6$C$recorder to the analy5er and record the vibration am)litude for a fe. days to see ifanything could be learned$

The ne1t day, an e1amination of the chart recording revealed several brief )eriodsof very high am)litude$ Since the starting time of the recording as .ell as the charts)eed .ere *no.n, it .as an easy matter to establish the a))ro1imate time of daythat each severe vibration occurred$ @ith this information, an investigation .asunderta*en to determine .hat might have occurred at these times to cause the highvibration$

t .as learned that the )eriods of high vibration corres)onded )recisely .ith theschedule of trains running on a nearby trac*$ Stiffening the dryer structure theneliminated e1cessive vibration in the )a)er dryer section caused by the )assingtrains$ This eliminated the re)eated bearing failures$

Time history recordings of noise levels may be necessary to establish com)liance

.ith legislation dealing .ith hearing conservation$ !lthough hearing conservationla.s normally s)ecify the )ermissible e1)osure time for constant levels of noise,consideration is also given to those situations .here the noise level is not constant$

@here the level varies, it is necessary to record the noise am)litude during a normal.or*ing day to determine the levels encountered and the duration of each level$This information is then used in a formula to calculate the e4uivalent e1)osure$Such recordings serve as valuable documentation of a hearing conservation)rogram and are then *e)t on file as evidence of com)liance$

!62!NCE6 COURSE MEC7!NC!L M!NTEN!NCE28R!TON !N!L"SS 9 CORRECTON LESSON & :!;E ?(


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(i$% 4-44% A%D%C% stri+ ,hart re,order@ shon here !ein$ #sed to re,ord noisele)els@ ,an also !e ,onne,ted dire,tl0 to the anal01er for re,ordin$ )i!ration

a"+lit#de o)er lon$ +eriods of ti"e%

OSCILLOSCO3E RECE3TACLE

The OSCLLOSCO:E RECE:T!CLE found on all R6 Mechanalysis analy5ers)rovides an !$C$ signal .hich is an e1act re)roduction of the mechanical vibration orsound )ressure$ 8y connecting an oscillosco)e& to the rece)tacle, the vibration ornoise .aveform can be observed$ 2irtually any general )ur)ose oscillosco)e canbe used for this )ur)ose>$ Consult the sco)e manufacturerHs instruction manual fordetails on the o)eration of your )articular oscillosco)e$

2ie.ing the vibration or sound )ressure .aveform on an oscillosco)e can )rovidemuch useful information$ Many machinery troubles can be identified by thecharacteristic vibration .aveforms they )roduce$ %or e1am)le, normal conditions ofunbalance and misalignment .ill generate a common sine'.ave as illustrated in %ig$&'&?!$ 7o.ever, these )roblems accom)anied by mechanical looseness often)roduce a .aveform li*e that illustrated in fig$ &'&?8$ The .aveform in %ig$ &'&?C isthe result of oil .hirl$ %ig$ &'&?6 is characteristic of a faulty antifriction bearing$

MEC7!NC!L M!NTEN!NCE !62!NCE6 COURSELESSON & :!;E ?/ 28R!TON !N!L"SS 9 CORRECTON


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!nother a))lication for the oscillosco)e is measuring im)act or transient noise andvibration$ Measuring short'*lived noise or vibration is often very difficult using thestandard analy5er or vibration-sound level meter because built'in dam)ingre)resents the meter from res)onding to the true )ea* values$

Since the oscillosco)e does not have this built in dam)ing, it .ill res)ond instantlyand is often used .ith the analy5er or vibration->sound level meter for this )ur)ose$

The oscillosco)e is also a valuable aid for evaluating data obtained from non'contact )ic*u)s$ Earlier, it .as mentioned that scratches on a shaft .ill sometimescause misleading vibration am)litude and fre4uency readings$ Connecting anoscillosco)e to the instrument .ill 4uic*ly reveal the )resence of scratches by thes)i*e'li*e signals they generate on the .aveform$

The oscillosco)e rece)tacle on your vibration analy5er can be used for othera))lications$ %or e1am)le, .hen analy5ing machinery noise


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(i$% 4-4% An os,illo$ra+h ,onne,ted to the anal01er os,illos,o+e a,*+ro)ides hi$h s+eed re,ordin$ of the )i!ration or noise a)efor"%

REVIE8

The another has all the necessary features for measuring and analy5ing machineryvibration or noise$ The features and o)eration of the analy5er are covered in somedetail in this cha)ter and in your instrument instruction manual$

Of course, reading about the analy5er is one thing, but there is no substitute for first

hand e1)erience$ Therefore, if you have not already done so, set u) your analy5erand become as thoroughly familiar .ith it as you can$ 7oo* it u)$ Measurevibration or noise am)litude and fre4uency$ 8E SURE "OU UN6ERST!N6 7O@TO RE!6 T7E METERS CORRECTL"$ Use the tunable filter, the strobe light andinternal oscillator$ Using a small electric motor or a device similar to the oneillustrated in %ig$ (&'0' , .e suggest you conduct the follo.ing e1ercises$

($ %ind the rotating s)eed


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