Post on 19-Apr-2018
BT-77 Bearing Tester with Non-Contact Tacho
Operating Instruction Manual
KOHTECT BT-77
CONTENT
PageINTRODUCTION................................................................................1
1.0BT-77INSTRUMENTDISCRIPTIONANDFUNCTION............11.1Specification1.1.1StandardConditionforOperation1.1.2SystemSpecification1.2OverviewonRollingBearingConditionMonitoring1.3UnderstandingShockInduced“Carpetvalue”and“Maximumvalue”1.4Tachometer1.5DesignofBT-771.5.1OperationKeys
2.0TAKINGMEASUREMENTWITHTHEINSTRUMENT..............72.1.Instrumentdisplayandmeasuringmodes2.1.1Settingthesystemrealtimeanddate2.2TakingBearingDiagnosisMeasurements2.2.1Selectionandsettingupthemeasuringpoints2.2.2Setupinitialparameter&takingbearingmeasurements2.2.3Takingbearingdiagnosismeasurementandsave2.2.4Fileformatandopenmeasuredfile2.3EvaluationoftheMeasuringResults2.4MeasuringRPMbyTachometer2.4.1SetupinstrumentandmeasuringRPM2.4.2MeasuringRPMbytheTachometer
3.0ROLLERBEARINGCONDITIONMONITORINGBYTHE SHOCKPULSEMETHOD(MEASUREMENTMETHOD)......14
3.1WhatisShockPulseMethod(SPM)anditbasis3.2HowShockPulseMeasuredandEvaluatedforRollingBearing3.3EvaluationofBearingConditionwithBT773.4Methodandmeasurementlocationofthebearing
4.0DELIVERY.................................................................................19
KOHTECT BT-77
KOHTECT BT-77
INTRODUCTION
ThismanualisintendedforthestudyoftheBT-77bearingconditiontester.Themanual
containsdescriptionof theBT-77bearing checkeroperatingprinciple, operating
proceduresoftheintendeduseandbearingshockpulseevaluationconcept.
1.0 BT-77INSTRUMENTDISCRIPTIONANDFUNCTION
1.1 Specification
1.1.1StandardConditionsforOperation:
Operatingtemperature(device&sensor),-10to55°С,(±5)°С;
Relativehumidity80%attemperature30°С;
Atmosphericpressure,84to106.7KPa(630-800mmHg);
Resonancefrequency,32kHz;
Measurementunit,dBi,dBc,dBm;
Range,max.99dB;
Resolution,1dB;
Accuracy,±5%;
Operatingtemperature(tacho),10to55°С,(±5)°С;
Tachometerrange,50-30,000rpm;
Tachometerresolution,1rpm;
Tachometersensingdistance,upto1m;
Memorycapacity,2MB;
PCcommunicationport,USB;
1.1.2SystemSpecification
Power supply, 3.6�� �iMH rechargeable battery.Powersupply,3.6���iMHrechargeablebattery.
Continuous operation on batteries, not less than 10 hours.Continuousoperationonbatteries,notlessthan10hours.
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KOHTECT BT-77
Current consumption 220��, 50 Hz AC, not more than 5��A.Currentconsumption220��,50HzAC,notmorethan5��A.
The limits of complementary error of the instrument at voltage changing fromThelimitsofcomplementaryerroroftheinstrumentatvoltagechangingfrom
3.6��oltsto2.8��olts.
Probabilityofno-failureoperation,notlessthan0.92per2000hrs.
Theaverageinstrumentlife,notlessthan10years.
Failuretime,1000hours.Theaveragefailuretimeissetforstan-dardconditions
foroperation.
Dimensions,notmorethan60х110х30(mm).
Weight,notmorethan210gram.
1.2 OverviewonRollingBearingConditionMonitoring
Ideally, rollingbearingelementsareseparatedbyaprotective lubricantfilm,which
impedes their collision. However,manufacturingdefects, damages,whichappear
duringoperation,dirtinthebearing,insufficientorincorrectlubrication–allthese
factorscause thecollisionof thebearingelementsand,asa result, acoustic
oscillationsofawidespectrumaregeneratedinthebearingbody.
Aspeciallydesignedtransducer(patent№18652)isusedtofilteroutthepartofthis
spectrumthatcarriesinformationonthebearingfaultsdetection.Thetransducerfilters
thoseacousticoscillationswhicharegeneratedbythebearingdefects,andconverts
themintoelectronicsignalproportionaltothemagnitudeofshockpulsesignal,thatis
amplifiedandmeasuredby theBT-77electronicunit in therelativeunitsofdecibels
(dB).
Arealnewbearingisjustfromthebeginningofitsuse,asourceofinducedvibration,
theamplitudeoftheshockpulseofwhichisdBi.
ThedBi,initialvaluedependsonthelargenumberoffactors;however,inpracticeitis
possibletolimitthemtodiameterD(mm)oftheneckanditsrotatingspeed�(rpm).The
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KOHTECT BT-77
valueofdBifeaturestheconditionofanewcorrectlyinstalledandlubricatedbearing.
The shockpulseamplitude increasesasa result ofwear and improper use.Shock
accelerationamplitudeoverrunningthevalueofdBi -dBsvfeaturesadamage,andis
usedfortheevaluationofbearingcondition.
ThisenableBT-77totellthedifferenceofshockpulsevaluesinduceislowshockand
highshock,anormalizedmeasurementscalecalldBnisuses,seebeneathTable-1.0.
dBn = 0-25 Goodcondition
dBn = 25-40 Satisfactorycondition
dBn > 40 Poorcondition,breakdownrisk
Table-1.0
Fig-1.0
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KOHTECT BT-77
50 -
-dBa-absolutevalueatmeasuringpoint
40 -
- dBsv-valuefeaturesbearingfailure(dBa-dBi)
30 -
20 -
-dBi-originalvalueoftheshockaccelerationamplitude
10 -
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0 -responsethresholdofthebearingchecker
-5 -
-10 -
Figure-1.1-Anexampleofthesevaluesratio.
Patternoftheinducedoscillations,whichareregisteredbyBT-77,changesaccording
tothebearingfaults.
1.3 UnderstandingShockInduced“Carpetvalue”and“Maximumvalue”
Atthemeasurements,thebearingcheckerallowstofilteroutandmeasuretwospecified
valuesoftheshockaccelerationamplitude:theCarpetvalue(dBc)andtheMax.value
(dBm).
ThedBcbackgroundvalue (theCarpetvalue) refers to the frequentcollisionsof the
bearingsurfaceroughness,dBcitgivesimportantinformationregardtothelubrication
ofthebearings,howwellthebearinghavebeenmountedandthewayinwhichthey
arebeenloaded,andisindicatedbythecontinuouslightofLED.ThedBmMax��alue
referstotheseparateshocks,characterizingthefaultslevel,andisindicatedbyseparate
LEDflashes.
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KOHTECT BT-77
Forinstance,attheshockaccelerationamplitudemeasuringofawelllubricatedand
correctly installed bearing, the dBm is only slightly higher than dBc. But when one
measuresshockaccelerationamplitudeofabearinghaving faults, these faultsare
detectedbydBmmaximumvalues,atthat,thebackgrounddBcvaluedependsonthe
lubrication condition, and can grow increase substantially when there is insufficient
lubricationfollowedbyfrequentmetal-to-metalcontacts.
IncreaseofdBcbackgroundvaluemaybecausedbyotherreasonsaswell,e.g.atthe
drivecouplingmisalignment.Itiseasytodistinguishbetweenthesecases–withthe
couplingmisalignmenttherewillbethesamepictureforthebearingsonthebothsides
ofthecoupling.
Resultsoftheshockaccelerationamplitudemeasurementfordrivesbearingscanbe
influencedbyshocksproducedduring the running inofagearmesh,whichcanbe
transferredontothebearings.However,mostlythegearteethhumissolowthatdoes
notimpedethemeasurement.
Withtheshocks,originatedbythegearwheelsdefects,thedBmMax��alueincreases
sharplyforthetwobearingssimultaneously(onbothsidesofgear).
Thegreatesteffect from the technicalstatemonitoringofbearings is reachedwhen
measuringresultsarebeingputongraphagainstthetimefactor.Atthis,aforecastof
thetechnicalstatebecomespossible.Exampleofthemeasurementsresultsprocessing
isgiveninTable-1.0.
1.4 Tachometer
TheTI-7tachometeroperationisbasedonthemeasurementoffrequencyofinfrared
rayreturnfromthereflectivetape(oranothermarker)fixedontheturningshaft.Awhite
markerpenisprovidesinthepackagesothatusercanmarktherotortogetgood
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KOHTECT BT-77
contrastwhentakingRPMmeasurement.
ThemeasuredRPMreadingcanalsobesavedwithinthedevicewithfilenameendby
“tac”extension.
1.5 DesignofBT77
ConstructivelyBT-77BearingTester is designed ina light andstrongalloy casing
protectedbysiliconsleevewiththerechargeableinternalbatterypowersupply,socket
forthemeasuringprobeandUSBportfortachometersensorsorfileuploadtoPCfor
datamanagement.ThecontrolsandconnectorslocationisshownontheFig.1.2a&
Fig.1.2b.
Fig.1.2a Fig-1.2bTopviewofBT-77
1.BT-77device
2.Bearingshockpulsemeasuringprobe
3.Tachometersensorandmagneticstand
4.Socketformeasuringprobe
5.USBportforTachometersensor/PCcom
6.SocketforACcharger
7.Softmembranepushpadforoperation
8.Back-litemonochromeLCDdisplay
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KOHTECT BT-77
1.5.1OperationKeys
TurnO� Entersetupmenu
OK/Start Return/backtoearlierstep Adjustuporincrease Adjustdownordecrease/OFF(pressandhold)
2.0 TAKINGMEAUSREMENTWITHTHEINSTRUEMNT
Beforeusingtheinstrument,itisagoodpracticestocheckpropermechanicalfunctioning
ofthecontrols,connectorsandpowerstatewhenswitchon.
Note the device automatically switches off after 150 seconds when no further
operation.
2.1 InstrumentDisplayandMeasuringModes
Toswitch“O�”theBT-77bearingtester,press .Thedeviceperformselftest
asshowninFig-2.1andautomaticallyenterthefirstdefaultoperationmode-USB
interface,Fig-2.2.
ToconnectdevicetoPCforreportprintandview,makesuredeviceissetinUSB
interfacemodeandpress to ready for interface.Connect theUSBcable
betweendeviceandPCviatheUSBport.
Togo toothermode,presseither or to scroll through the fouroperating
modeoption.
Fig-2.1Fig-2.2
B e a r i n g Te s t e r
K o H T E C T B T - 7 7
( c ) 0 7 0 1 0 8 v 3 . 0 1 c
N o . 1 2 3 4 4 5 5
w w w . k o h t e c t . c o m
U S B i n t e r f a c e
* 3 . 0 2 v2 5 m a r 0 7 1 4 : 3 0 : 5 0
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KOHTECT BT-77
2.1.1Settingthesystemrealtimeanddate
Atanyoperationmodedisplay,press toenterdate/timemenufollowby
toseesetitems.
Press and tosettheminutesandfollow toconfirmcorrectinput
setting.Thescreenproceedsandshowsubsequencesettingforhours,day,date,
monthandyeartobesetinsameway.
Whenalldateandtimesettingsarecorrectlyinput,press twicetoreturn
operationmodedisplaytobeginnewtask.
2.2 TakingBearingDiagnosisMeasurements
2.2.1Selectionandsettingupthemeasuringpoints
Whileselectingthemeasuringpoints,takeintoaccountthefollowingandseeFig3-3:
Metalcolumnbetweentheprobetipandbearingmustbe,ifpossible,straight
(don’ttakereadingsfromthecapthatcoversthebearinghousing).
Itiscriticalthatthemeasuringpointtobeselectedascloseaspossibleto
thebearing.
Whilemonitoringthebearing,usethesamemeasuringpoint.
Settingupmeasuringpoint:
Measuringpointsshouldbefreeofpaintanddirt;
Mount thestationaryextenders (pinsorbolts6-8mm)ofdesired lengthor
provideholes formeasuringprobeaccess in thebearinghousings located
behindthemachineprotectivegearsorcaps.
ATTENTION! Keep the probe location and the force the same during the measuring
cycle!
TheBT-77Tester automatically switches off after 150 secondswhen no further
operation.
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KOHTECT BT-77
2.2.2Setupinitialparameter&takebearingmeasurements
Press toturnonBT-77,press keytoswitchdisplaytobearingdiagnosis
measurementmodeshowsinFig-2.3.
Press tobeginnewmeasurementshowninFig-2.4andpress again
tostarttakingreading.
Fig-2.3Fig-2.4
Ifparametersonscreenare�OTcorrectsetandneedtobechange,press
twicetodisplaychangeofdBi setting(see note below for dBi setting).
IfdBiisunknown,press againtochangeD(diameterofshaftorbearingI/Ddia)
byusing or keytosetandpress toconfirmtheDinputvalueand
gotonextsettingparameters.
ScreenwilldisplayRPM(shaftrotatingspeed)setting,sameusing or
keytosetandpress toconfirm.
Thedisplaynowshows“Single”“Average”or“Contin”,setting.Tochangethe
calculationmethodbyusing or keytoset.
�owpress twicetoviewthenewlycalculateddBivaluewithchangedinput
parameters.
Ifallparameterhavesetcorrectly,press toreturnreadyformeasurement
screen,Fig-2.4.
Tobeginnewmeasurement,press tostarttakingreading.Waitformeasured
todisplaywithevaluationasshowninFig-2.5b
Note: dBi can be input manually or calculate by device after input of the bearing inner
B e a r i n g s 7 7 D 1 1
* 2 . 7 7 v2 5 m a r 0 7 1 7 : 3 0 : 5 9
= = = = = = = = = = = = = = = =D = 2 5 N = 3 0 0 0d b i = 3 0 A v e r a g e
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KOHTECT BT-77
diameter or shaft diameter “D” and RPM, “N” speed for the machine.
ATTENTION!
Measurement calculation method:
single reading with dBi taken into account. Result – normalized value of
dBm, dBc for condition evaluation based on the technology developed
by the Central Research & Design Institute of Navy.
continuous reading with dBi taken into account. Result updates every
seconds. Press “STOP” button to end the procedure.
five readings are taken with dBi taken into account; the result is their
arithmetic mean value.
2.2.3Takingbearingdiagnosismeasurementandsave
After identified themeasuringpointonmachine,place theprobefirmlyagainst the
machineatthedesiredmeasurementlocationandreadytotakereading.
Press andwaituntilbearingreadingisdisplayed.Whiletakingthereading,
displayshow“busy…”message,Fig.2.5a,andthemeasuringcycleis
approximately30-40secondif“Average”methodisselected.
Oncemeasurementfinish,thedisplayshowsFig-5b,themeasuringresults:the
Maxvalue,Carpetvalue(dBmanddBc)andconditionofthebearingevaluated
ondBnchartasfinalresult.
Fig-2.5aFig-2.5b
Tosavethereading,Press follow OKkeytoentermaindirectory.
Press again tomakenewdirectory, save, read or delete folder or press
Single-
Cont.-
Average-
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d B m = 2 9 S a t i s f .d B c = 1 8
= = = = = = = = = = = = = = = =D = 2 5 N = 3 0 0 0d b i = 3 0 A v e r a g e
Max. valueBearing evaluationCarpet value
Input info
B u s y . .
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KOHTECT BT-77
or toselectdesireddirectory(directorylineareshowswith)series of
numeric without “xxx.b77”or “xxx.tac” extension)tobesaved,seeFig-2.6in
section2.2.4savemeasuredfile.
Press toconfirmdatasaved.
2.2.4Fileformatandopenmeasuredfile
ForBT-77,anymeasured readingondisplay reading is savedwithin thedevice in
standardformatwithselfdevicegenerateddirectoryorfilenamesintermofdateand
time(“0325”mean25Marchand“165301”mean16hrs,53mins,01sec) followby
“b77”extensionformatfordatafile,seeFig-2.6.
Fig-2.6
Toopendatafileforreview,press or togotomydocumentsscreen
andpress toseefileanddirectoryasFig-2.6.
Press or tomovecursortodatafile(withb77extension)andpress
toopenforview.
2.3 EvaluationoftheMeasuringResults
BearingconditionisdefinedbytheshockaccelerationmagnitudedBn.
0...25dBn -goodcondition,optimaloperatingconditions;
25...40dBn -satisfactorycondition,themeasurementsaretakeninshort
timeintervaltoevaluatethetypeofcoming;
>40dBn -poorcondition,visiblefailuresappear,operatingconditionsbe
cameworse,accidentmayhappen.
/ 0 3 2 4 _ 1 7 0 4 0 5. .0 3 2 5 _ 1 6 5 2 1 10 3 2 5 _ 1 6 5 3 0 1 . b 7 7
1 6 bD a t a s a v e d
Main directory nameBack to earlier directorySub-dir nameData file name saved
File size
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KOHTECT BT-77
Themeasuring results are recorded into the report. While continuouslymonitoring the
equipmentcondition,itisrecommendedtousetherecordsasgraphicaldatarepresentation
toshowclearlythetendencyofconditionchangeatthemeasuringpoints.
Table-2
DiagramsintheTable-2showasfollows:
Bearing№1isingoodtechnicalcondition
Afterthemeasurementdated15.02.90thelubricationwasreplacedinthebearing
№2,presentlythisbearingisingoodconditionandneedsclosemonitoring(more
frequentmeasurements).
Bearing№3isingoodtechnicalcondition.
Conditionofbearing№4isgettingworse,afterthemeasurementdated15.03.90
the lubricationwas replaced,nopositive resultswereshown, it isadvisable to
replace the bearing to avoid any serious faults (bending of the shaft, impeller
break-away,etc.).
2.4 MeasuringRPMbytheTachometer
2.4.1SetupinstrumentandmeasuringRPM
Applyreflectingtapeormarkontheshaftwhichrotationfrequencyshouldbemeasured.
Themarkshouldbecontrastagainsttheshaftmaterial(a lightmark-onthedark
Pump inventory numbe1121r Bearing № 1 Bearing № 2 Bearing № 3 Bearing № 4Date 10 30 50 10 30 50 10 30 50 10 30 50
18.01.9031.02.9015.02.9022.02.9001.03.9015.03.9022.03.9028.03.90
1.
2.
3.
4.
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KOHTECT BT-77
background,adarkmark–onalightbackground).
Reflectivemarkingshouldnotlessthan20mmlengthonshaftfortachosensortotake
speedreading.
Placethetachometersothatyoufollowtherecommendationsonpositioningawayfrom
themeasuredobject.Selectthelocationofthetachometerthatwillprovidethereliable
andstableresponsefromthemark.Itisrecommendedtoplacethetachometeratthe
angledifferentfrom90degreesand10-20cmawaytothemarksurface–thiswill
decreasefaultresponsefromthesurfaceoftheshaftsurface.Useretro-reflecting
tapeasamark.(Itispossibletousethecorrectionfluid“Stroke”toapplythemark).
2.4.2MeasuringRPMbytheTachometer
Press to turnonBT-77,press key toswitchdisplay toTachometer
measurementmodeshowsinFig-2.7a.
Fig-2.7aFig-2.7b
Press twotimestostartrpmmeasurement.
Press torecordmachinerotatingspeedanddisplayRPMreading,Fig-2.7b.
When finishmeasuring, press save result or press to return to
programmodeoptionwhenRPMnoted.
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Ta c h o m e t e r
* 2 . 7 7 v2 4 m a r 0 7 1 7 : 3 0 : 4 7
Ta c h o E P C = 1
R P M 3 0 0 4 . 8 1
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KOHTECT BT-77
3.0 ROLLER BEARING CONDITION MONITORING BY THE SHOCK PULSE
METHOD(MEAUREMENTMETHOD)
3.1 WhatisShockPulseMethod(SPM)anditbasis
DesignationoftheShockPulseMethod(SPM)isasignalprocessingtechniqueused
tomeasure rollingbearingconditionand thequalityof their lubrication in themotor,
pumps,separators,turbocompressorsfordieselboost,etc.Usingtheinstrumentsto
measureshockpulses,onecandetermine theairorgas leaksvia looseness in the
high-pressurevesselsorpipes.TheresearchworkconductedatCentralResearch&
Design Institute of �avy allowed expanding the performance capabilities of the
instruments.Shockpulsecheckershavesettobeusedfortheevaluationofcondition
ofhigh-pressurefuelpumps,dieselinjectors,valvesofpistoncompressors.
TheShockPulseMethod (SPM)wasdevelopedbyaSwedish instrumentcompany
andbasedonmonitoringandanalyzingofhighfrequencycompression(shock)waves
causedbymechanicalimpact.Accelerationofmaterialparticlesgeneratespressureor
shockwavethatpropagatesasultra-sonicfrequencybandthroughtheobject.Inthe
initialphaseofimpact,theaccelerationofmaterialparticlesdependsonimpactvelocity
andisindependentofthemassofcollidingobjects.Withinshortperiodandthereisno
evidentdeformation.Thevaluewaveshockistheimpactvelocityofcollidingobjects.
In the secondphaseof the collision, the surfacesof twoobjectsaredeformed; the
energymovementdeclinestheobjectandgeneratesvibrationsthatarediagnosedby
thevibrationanalysis.
Piezoelectrictransducerisusedtomeasureshockpulse;vibrationandnoisebackground
donoteffectonit.Thetransducerselectricallyandmechanicallytuneto28…32kHz.
Shockwavecausedbythemechanicalimpactgeneratesthedecayingshockvibrations
intransducer.Themaximummagnitudeofthisdecayingvibrationisrelativetothevelocityof
theimpact(v).Sincethedecayingtransientiswelldefinedandhasconstantdecayvalue,it
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KOHTECT BT-77
canbeeasilyfilteredoutallothervibrations,i.e.vibrationfrequencies.Theshockpulse
methodinvolvesmonitoringandanalyzingthedecayingtransientprocess.
3.2 HowShockPulseMeasuredandEvaluatedforRollingBearing
Theouterracewaysofthebearingalwaysfeatureroughness.Thereforeabearingunder
normaloperatingundergoesthemechanicalimpactsandcreatesshockpulses.Shock
pulsevalueisdependentonthebearingsurfaceconditionandtheperipheralcondition
ofthebearing.Shockpulsevalueoftheregularbearingfeatures1000timesincrease
sincethetimeabearingisnewuptothemomentwhenabearingneedsreplacement.
Becauseof the very largedynamic rangeshockpulsesaremeasuredonadecibel
scale.
Empirical tests showed that even the newand lubricatedbearing generates shock
pulses.ThevalueofthisinitialimpactissetasdBi(dB,initialvalue).Asthebearing
wears,thevaluedBa(averageshockpulsevalue)increases.�ormalizedvaluedBnfor
thebearingcanbeshownasfollowsdBn=dBa-dBi
(BearingLife)
Fig-3.1.depictsdBnandbearingliferatio.
Inorderfortheshockpulsesreadingtobequicklyandeasytoevalutatedonthebearing
condition,insimpleunderstandingscaledBnhasbeenderived.Itcategoriesthebearing
condition into threedifferent zonesby indicating theextentofbearingdamage from
goodtopoorcondition,Fig-3.1:
100%0 50
20
40
60dBn
100%0 50
20
40
60dBn
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KOHTECT BT-77
dBn < 20 Goodcondition
dBn = 20-40 Satisfactorycondition
dBn > 40 Poorcondition(i.e.bearingneedreplacement)
Table-3
3.3 EvaluationofBearingConditionwithBT-77
Technicalconditionofthebearingismainlydeterminedbythelevelandrelationoftwo
measuringvaluesdBmanddBc.
dBm-maximumvalueofnormalizedsignalindecibel.
dBc-carpetvalueofnormalizedsignalindecibel(backgroundofthebearing).
However, under thework of the bearing the peak strikes have not only varying
magnitudes, but frequencies aswell. Fig-3.2 shows the typical examples of the
evaluationofbearingconditionandoperatingconditions(installation,rollerbearing
fit,alignment,lubrication)basedontherelationofshockmagnitudevalue(reading
ofscaledBc)andfrequencyvalue(numberofshocksperminute):
Fig-3.2
dBm
60
40
20
0 TimedBc
dBndBn
60
40
20
0Time
dBm
dBc
dBn60
40
20
0Time
dBm
dBc
dBm
dBc
60
40
20
0Time
dBn
dBc
60
40
20
0Time
dBm
dBdBn
dBm
dBc
60
40
20
0 Time
dBdBn
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KOHTECT BT-77
1.Goodbearinggeneratesmainlyshocksintheinterfacebetweentheloadedrolling
element and the raceway.These shocks create normal background levelwith low
carpetvalue(dBc<10)andrandomstrikeswithmaximumvaluedBm<20dB.
2.Whenthedefectsoccurontheouterracewayofabearingorabearingelement,the
generalbackgroundfeaturespeaksignalswithMax��aluedBm>40dB.Thecollisions
happensrandomly,quiteoftentheircarpetvaluesstandwithinthelimitsdBc<20dB.
Thoughwhenthebearingfailureoccurs,thecarpetvaluecanbedecreased.Asarule,
agreatdifferencebetweendBmanddBcvaluesoccurs.
3.Whenthereisnolubricationsupplyortight(loose)rollerbearingfit,theCarpet��alue
willreflectthisbyincreasing(dBc>10),eventherearenotanydefectsontheouter
racewayofathebearing.TheMax��alueandtheCarpet��aluearerelativelyclose(dBm
=30,dBc=20).
4. Under pump cavitation both backgrounds feature highmagnitude value. Shock
pulsestandardsonpumpcavitationarepublished.Themeasurementsare takenon
thepumpcase.Beawarethatthecurvedsurfacesdampshockpulsesoutofcavitation.
ThedifferencebetweentheMax��alueandtheCarpet��alueisquitesmall(forexample,
dBm=38dB,dBc=30dB).
5.Mechanicalcontactbetweentherotatingandstationarypartsofthemechanismnext
tothebearingcreaterhythmic(periodic)ahighamplitudeburstofShockPulsewaves.
6.Ifthebearingundergoestheshockload,forexample,astheresultofpistonstroke
inthecompressionpump,theshockpulseswillberhythmic(periodic)withrespectto
theoperatingmodeofthemachine,sotheCarpet��alue(dBc)andtheMax��alue(dBm)
areeasilydefined.
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KOHTECT BT-77
Drivinggearfailureinthegearboxalsocancausetheperiodicstrikes.Thesestrikes
willberhythmicinrespecttotheshaftspeed(onallbearingsinstalledinthegearbox).
Don’ttakemeasurementswhenyoustartthemotororyoujustappliedthelubrication
(completeitin15minutes).
Table-3.2 showsmentionedaboveandother possible cases of increased values of
shock impulses. Itmayhappen thatanewbearingmayhave theCarpet��aluedBc
morethan20dB.Ifthesevaluesarestablewithinsometimeinterval,bearingcondition
isacceptable.
3.4 Methodandmeasurementlocationofthebearings
Shockpulsemeasurementsshouldbecompletedonthebearinghousing.Whenfree
accesstothebearinghousing,usethemeasuringprobeasshowninFig-3.3a,3.3b
3.3candFig-3.3d.
Beforeshockpulsemeasurementitmaybenecessarytoconsultdesigndrawingsto
seehowthemachineisconstructedandcheckthemeasuringpointsbasedonsignal
path.Thesurfaceatthemeasurementpointshouldbeplane.Ifthepaintlayeristhick,
clearoffpaintonmeasuringspot.Fittheproberadicallytothecheckedsurface.
Fig-3.3aBearingloademissionFig.-3.3b.Shockpulsezones.
window(loadZone)
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KOHTECT BT-77
Fig-3.3cShockpulsezones.1-��ibrationmeasuringprobe
2-Bearinghousing
3-Stresswavepropagation
4-Defectiverollingbearing
5-Shockpulsemeasuring
zones(Bearingloadzone)
Fig-3.3d
4.0DeliverySet
№ Description Qty �ote
1. BT-77w/rechargeablebatteryinserted 1
2. Bearing��ibrationmeasuringprobe 1
3. IRTachometerw/mountingstand 1
4. ACCharger,220-230��olts 1
5.Liquidmaker 1
6. CarryingCasewithFoam-insert 1
7. OperatingInstructionsManualinCD-ROM 1
8. CD-ROMPCsoftware 1
9. USBPCcommunicationcable 1
10. Makercalibrationcertificate 1
Table4.0
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