Litre Meter VFF Series - Flying Start and Finish; Standing Start and Finish; Installation; Commence the Test

Document No LM0670 Issue A Rev 2 November 2017 Page 13 of 15
 Avoidpulsatingflowandcavitationtohavemeaningfulresults
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Prepare a weigh tank . Thetankshouldofsufficientsizetocontainavolumeoffluidrunningatthe
requiredrangeofflowsforaminuteorso.Forexample,ifthemeterhasaflowrangefrom1to30litresper
minutethena30litretankwouldbeappropriate.Asthetank
maybedifficulttoemptycompletelyhavingita
littlelargerisadvisable;careshouldbetakenthatitisdeepenoughorsoshapedthatsplashingoutsideofthe
tankdoesn’toccur.Thetankneedstobeweighedbeforeandafterthetesttosufficientaccuracy.Forlower
flow
ratesthereisnotnecessarilyarequirementtomeasure30litreseachtime.Thiswilldependonother
factorssuchasweighscaleresolution,accuracyofweighscale,accuracyofflowmeterandaccuracyofdensity
determination.Thismethodisnormallyusedforwaterwherethedensityiswellknownasitmeasuresmass

butwillbeappliedtovolumetricflowmeters.AsguidanceLitreMeterrecommendsaweighscalewitha
resolution10,000timessmallerthanthemaximumweightandadensitometeraccuratetothe±0.001g/cm³(if
waterisn’tused).Insomeinstances,avolumetrictankcouldbeusedwherethevolumeis
accuratelyknown. 

Prepare start and end of test. Therearetwooptions:

Flying start and finish
Thismethodisverywidelyusedwhenflowratemetersmustbecalibratedwithwater.Itisperhapsless
appropriateforthecalibrationofvolumetricmeters,orformeterswhicharebeingcalibratedwithoilsorfuels.
Themassflowrateiscalculatedbydividingthemasscollectedinthetank
bythediversiontime,andthiscan
beconvertedtoavolumetricflowratebydividingitbythedensityattheappropriatetemperature.Adiversion
iscausedbyswitchingthestreamoffluidintoaweightankatthestartofthetestandreversingtheswitchat
the
endofthetest.Accuracyofcalibrationisobtainedbyensuringthetimingerroratthestartandendis
minimisedbybothgoodtechniqueandbyrelativelylongtestperiods(atleast60seconds,forexample)and
repeatable,quickdiversion.

Standing start and finish
Issimplerthanflyingstartbutthefollowingerrorscanoccur:
 EnsurethattheMUTisfullpriortotesting;arushofaircanleadtolargeerrors.
 Ifthestartsystemisrelativelyslowtheremaybeasignificantpartofthetestwhichisata
varyingflowrate–the
sameappliesfortheendportion.Timingmaybehardtocalculate.
Ifitisintendedtouseastanding‐start‐and‐finishmethodofcalibration,itisprobablybettertouseaweighscaleifthetest
fluidiswateroraviscousoil(above,say,5cSt),andtouseavolumetrictankwithlowviscosityhydrocarbons(below,say,5
cSt).
Installation
 Ifnotalreadyinstalled;install
MUTintopiping.Tightenall
pipes/flangestoavoidleaks.
Selectappropriatepipeworkfor
eachmeterstyle;usemarkings
onmeterforflowdirectionand
orientation.Ensuremeteris
centredwithinpipework.
 Ifnotalreadyconnected
electronically; connect
displaytometer.Ensuredisplay
is
settoshoweither
 totalor
 flowrate
 Alternativelypulsesoran
analoguesignalcanbe
measured
 Beforecommencingtestmake
sureweightankisemptyor
nearlyempty.Closevalveand
tarescalestoshowzero.
 Switchonpumpandcontrol
flow
 Reset
totalondisplay(ifonly
flowratedisplayisavailable,
notethevaluefortheduration
ofthetestandcalculatethe
averageattheendofthetest)
Commence the test
 Eitherdiverttheflowor
commencetheflow.
 Whenthetankhasreachedthe
specifiedweight(ortime)then
diverttheflowbackorstopthe
flow.Recordthe
weight/volume,emptytankas
necessary,resttheweighscale.
 Repeatforeachflowrateas
required–factorycalibration
normally
coversfromminimum
flowratetomaximumflowrate
in8stepsbutiftheusageis
overadifferentorreduced
rangethanthatshouldbe
reflectedinthecalibrationflow
rates.Additionalconfidence
canbegainedbyrepeatingthe
testsateachflowrate.
 Finishcalibration

AssessMUTperformance

Calculations
 Compareeither:theactualflow
ratei.e.themassorvolume
dividedbythelengthofthetest
againstthedisplayedflowrate
 Or:thetotalcollectedagainst
thedisplayedtotalorcalculated
total.
 Createatableofresultsover
therangeofflowratesused.
 Using
themanufacturers
originalcalibrationcertificate
recalculateanydataintonew
‘points’.Thisassumesthataset
oflinearizationdatahasbeen
enteredoriginallyintothe
instrumentation.(Insome
cases,asinglemeterfactoris
used.Thetableofresultscan
beusedtoprovideanaverage
meterfactoroverthe
rangeof
flowratestestedwhichwill
provideabetterseriesof
readingsoncemodified.)
 Enterthenewdataintothe
instrumentation
 Ideally,runthetestsagainto
checktheresultsoverafewof
theflowratesandconfirmthe
calculations.


Calculationexamplescanbe
foundonthenextpage: