Litre Meter VFF Series - FAT Issues; On-Site Flowmeter Calibration; On-Site Calibration; Precautions

Document No LM0670 Issue A Rev 2 November 2017 Page 12 of 15
FAT Issues
TheFactoryAcceptanceTestcanbethefirsttimethemeterisrunafterbeingdespatchedfromthe
factory.Herearesomecommonproble msencounteredandtheirresolution:
1 ThemostfrequentlyusedFATfluidiswater.Thiswon’tdamagethemetersatall,butit
doeshaveaverylow
viscosity.Therearetwosignificanteffects.Firstly,themeterwill
probablynotmeasureaslowastheflowratesachievedattimeoffactorycalibration.
Thecalibrationviscosityistakentobetheviscosityofnormaloperation.Secondly,ifit
doesoperateatthelowestflows,thentheaccuracymay
begreatlyreduced.Itislikely
tounder‐readbyupto30%.ThesolutionistochangetheFATfluid.Theadditionof
glycolorreplacementbyglycolfortheFATisquitecommon.
2 Dirtinthesystemishardtoavoid.Evenwithfiltrationat40or100
micronsitisstill
quiteeasyforpotentiallyblockingparticlestobeheldinthepiping,evenafterflushing.
Wewouldrecommendthemeteristakenoutoflinebeforepipeflushing.Itemslike
PTFEtapeandtheremnantsofthreadlockingcompoundswillpreventtherotorfrom
turning.However,
therotorandchambercanbesimplycleanedbydisassemblyand 
washing.
3 Installationattitudecanbedifferentfromoriginalcalibration.Themetersarenormally
calibratedinahorizontallinewiththemeterinstalledupright.Ifadifferentorientation
isadvisedoruseditwillbenotedonthecalibrationcertificate.
Therewillbesomesmall
functionaldifferencesifthemeterisins talledon verticallyupwardfloworupsidedown.
LitreMeterdonotrecommendthemeterisi nstalledforverticallydownwardflow.
Performanceattheverylowestflowsmaybecompromisedunlesscalibratedinthe
correctorientation.

Anerroranalysis
systemisdescribedindocumentLM0638,VFFFaultFinding.
On-Site Flowmeter Calibration

ThisproceduremustbeintegratedwiththeapprovedHealthandSafetypolicyatsite.

Thepurposeofthissectionistooutlineageneralcalibrationprocedureforvariousflowmeters.Itwillmakespecific
referencetovolumetricflowmetersbutmostoftheprinciplesareequallyapplicabletootherflowmeasurement
technologies.Theimportantconsiderationisthatthereisaccesstothe readingoftheMeterUnderTest(MUT)anda
sufficientlyaccurateunderstandingoftheactualflowrate.

On-Site calibration
Theaimofthiscalibrationtechniqueistoprovidedatatotheusersuch
thattheinstrumentationcanbeadjustedtoshowthecorrectflowrate
and/ortotal

Thiswillbedoneby
o maintainingaknownflowrateand
o monitoringtheoutputoftheMUT

Precautions:
 Flush/Cleanpipingpriortoinstallingthemeterorany
pipeworkchanges
 Ensurethataliquidsystemhasnoairorvapour
entrained
 Ensurethattheflowvariationsduringtestingareata
minimum,usuallybetterthan±1%variation
 Ensuretherearenoprotrudinggasketsupstreamofthe

meter(forturbinemetersetc.)
 Measurethepipingtoensurethatdimensionsand
finisharewithinstandardlimits
 Ensurethatthemeasurementequipmentisinstalledin
accordancewithstandardsortothemanufacturer’s
recommendations

ThisishowLitreMetercalibrateflowmetersin
thefactory:

CALIBRATION
MostLitreMeterflowmetersarecalibrated
usingagravimetricmethod.Aflowrateis
establishedthroughtheflowmeterwiththe
outputflowreturningtothemainreservoir.At
thecommencementoftest,theoutputflowis
divertedintoaweightank.Whensufficient
volumeoffluidhasbeencollectedinrespectof
thatflowrate,theoutputflowisdivertedto
themainreservoironcemore.Thetimefor
thevolumeoffluidtobecollectedisrecorded,
togetherwiththenumberofpulsesproduced
bythetransmitter.Thedensityofthefluidis
determinedattimeofcalibration.Volume
dividedbytimeequalsflowrate.Thenumber
ofpulsesdividedbyvolumeequalsthepulses
perlitreMeterFactor.Thecalibration
certificateispreparedfromatableofthese
values.Ifon‐sitecalibrationisrequiredanda
knownvolumeoffluidflowcanbeestablished,
thenthesamecalculationsapply toreproduce
thecalibrationcertificate.
