Brookfield DV2T - Special Considerations; Low Viscosity Measurement Limits; Accessory Impact on Accuracy

Brookeld Engineering Labs., Inc. Page 66 Manual No. M13-167
Special Considerations
IntakingviscositymeasurementswiththeDV2TViscometer,therearetwoconsiderationswhich
pertaintothelowviscositylimitofeffectivemeasurement.
1) Viscositymeasurementsshouldbeacceptedwithintheequivalent%TorqueRangefrom
10%to100%foranycombinationofspindle/speedrotation.
2) Viscositymeasurementsshouldbetakenunderlaminarowconditions,notunderturbulent
owconditions.
Therstconsiderationhastodowiththeprecisionoftheinstrument.AllDV2TViscometershave
anaccuracyof+/-1%oftherangeinuseforanystandardspindleorcone/platespindle.(Notethat
accuracyvaluesmaybehigherthan1%whenusingaccessorydeviceswiththeDV2T).Wediscourage
takingreadingsbelow10%ofrangebecausethepotentialviscosityerrorof+/-1%isarelatively
highnumbercomparedtotheinstrumentreading.
Thesecondconsiderationinvolvesthemechanicsofuidow.Allrheologicalmeasurementsof
uidowpropertiesshouldbemadeunderlaminarowconditions.Laminarowisowwherein
allparticlemovementisinlayersdirectedbytheshearingforce.Forrotationalsystems,thismeans
alluidmovementmustbecircumferential.Whentheinertialforcesontheuidbecometoogreat,
theuid can break into turbulentowwhereinthe movement of uid particlesbecomesrandom
andtheowcannotbeanalyzedwithstandardmathmodels.Thisturbulencecreatesafalselyhigh
viscometerreadingwith thedegreeofnon-linear increaseinreadingbeingdirectly relatedtothe
degreeofturbulenceintheuid.
Forthefollowinggeometries,wehavefoundthatanapproximatetransitionpointtoturbulentow
occurs:
1) No.1LVSpindle: 15cPat60RPM
2) No.2LVSpindle: 100cPat200RPM
3) No.1RVSpindle: 100cPat50RPM
4) ULAdapter:   0.85cPat60RPM
TurbulentconditionswillexistinthesesituationswhenevertheRPM/cPratioexceeds thevalues
listed above.
Eect on accuracy when using accessory devices
TheBrookeldviscometerhasastatedaccuracyof+/-1%oftherangeinuse.Thisstatedaccuracy
applieswhentheviscometer is used in accordancewiththeoperatinginstructionsdetailedin the
instrumentinstructionmanualandthecalibrationtestuidisusedinaccordancewiththeinstructions
providedbytheuidsupplier(includingthecriticalparametersoftemperaturecontrolandstateduid
accuracy).Brookeld’saccuracystatementof+/-1%oftherangeinuseappliestotheBrookeld
rotationalviscometerwhenusedwiththestandardspindlessuppliedwiththeinstrument,including
LVspindles1through4(suppliedwithLVseriesviscometers),RVspindles2through7(supplied
withRVseriesviscometers),andHVseriesspindles2through7(suppliedwithHAseriesviscometers
andHBseriesviscometers)ina600mLlowformGrifnbeaker.
Brookeld offers a range of accessories for use with the Brookeld viscometer to accommodate
specialmeasurementcircumstances.Theseaccessories,whileofferingaddedcapabilitytotheuser,
alsocontributetoanexpandedmeasurementtolerancebeyondtheinstrumentaccuracyof+/-1%of
therangeinuse.Thisexpandedmeasurementtoleranceisafunctionofmanyparametersincluding
spindlegeometry,accessoryalignmentaccuracy,samplevolumerequirement,andsampleintroduction
techniques.Theeffectoftheseelementsonmeasurementtolerancemustbeconsideredwhenverifying
thecalibrationofyourBrookeldviscometer.Sampletemperatureinalltestcircumstancesisvery
important,andwillalsoaddanadditionalexpandedtolerancedependingonthetemperaturecontrol
systemandthecalibrationvericationtestsbeginwiththestandardviscometerspindlesasdetailed
above.  Once the calibration of the viscometer itselfis conrmed, theexpanded tolerance ofthe
measurementsystem maybedetermined usingaccessorydevices. Inmany cases,thisadditional
tolerancewillbeveryminimal,butasageneralstatement,theadditionof+/-1%oftherangeinuse
is reasonable for accessories.