Whitepaper 002

8/2/2019 Whitepaper 002

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TechnologyReviewWhitePaper

WhitePaper Copyright2009CougarIndustries, Inc.

BinLevelIndicationApplicationsinGrainElevators


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Introduction Grainelevatorsarefacilitiesusedforstorageofawidevarietyofgrains. Asapartofthedistributionsystemforwholegrainsfromthefarmto processorsofgrainthesestoragefacilitiesperformavitalrole. Th einitialintroductionofgrainelevatorsissaidto havebeeninBuffalo,NYin1842. ItwasJosephDartwho firstinventedasteam-poweredmechanismcalledamarinelegthatwasusedto scoopgrainfrombargesandships

andloadthegrainintostoragesilos. Eventuallythemodernbucketelevatoremergedforliftinggrainupto thetopofthestoragesilosforfillingpurposes.Earlyon inthehistoryofgrainelevatorstheywereconstructedfromwood,andwereproneto fire. Sincetheearlypartofthetwentieth centuryconcretewasintroducedasabuildingmaterialan dcorrugatedsteelisalsoused. Infarmingcommunitieseachtownhadoneormoregrainelevatorsandmanystilldo.However,inmorerecenttimesimprovedtransportation centralizedgrainstorageandmuchlargergrainelevatorsnowservemultiplecommunitiesandfarms.Aninterestingproblemthatoldgrainelevatorshadwasthatofsiloexplosions. Graindustcanbeveryexplosiveinenclosedareas.Electricalareaclassification istypicallyClassII,Division1whereexplosivedustexistscontinuously. Finepowderfromthemillionsofgrainparticlespassingthroughthefacilitywouldmixwiththeoxygenintheair. Eventheslightestsparkcouldcausean explosionasasparkspreadsfromonetinydustparticletoanotherwitharesultingchainreactionthatcanbedevastatingto thefacilityandakillerofpersonnel. Whileitisnotasprevalent,thishazardandproblemstillexiststoday. Forthisreasonall electricaldevicesmustbeproperlycertified,installedandoperated. Ventilationhasbeenimprovedandmanycomponents,suchasbearingswithinthebucketelevators,areconstantlymonitoredforexcessheatandfriction.

Figure2:1928 BurrusElevator(slipformconcretesteelreinforced)in Lubbock, TX justbeforedemolition in2004contains123 silos.

Figure 1: Firstgrainelevatorin western Canadacirca1879


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Bin LevelIndicatorUsageTw oprimaryapplicationsexistforlevelindicators. Th efirstisacriticalapplicationtoensurethateachsiloisnotoverfilled. Bin levelindicatorsareusedto detectahighlevelconditionwithineachsilochamber. Inadditionto indicatingafullconditioninthesilo,thisdevicealsopreventsoverfilling. Th esecondapplicationofbin levelindicatorsisforinventorymonitoringpurposes. Inthissituationabin levelindicatordeviceisusedtomeasurethelevelofthegrainineachsilo. However,thesedevicesforinventorymonitoringaremuchmoreexpensivethanhighleveldetectorsandthereforefewergrainelevatorshaveemployedinventorymonitorswithineachsilo.HighLevelDetectors:Thisapplication monitorsthepresenceandabsenceofmaterialat a predeterminedhighpointwithineachsilostructure. Th eoutputistypicallyarelaycontactclosureorelectricalswitchclosureto indicatematerialhighlevel. However,thereverseca nalsobeused(switch/contactopeninguponhighleveldetection).Th etechnologybestsuitedfortheseapplicationsistheTiltSwitchandtheRotaryPaddlebin levelindicator. Asummaryfollows.TheTiltSwitchissuspendedbyacabletoapointwherethehighleveldetectionisrequired. Anelectricalcableisalsoextendedbetweentheswitchandthecontrolpoint(remotecontrolunitorplant-widecontrolsystem). Thetiltswitchmustnotbesuspendedbytheelectricalcable. ATiltSwitchsuitableforhazardouslocationsbybeingintrinsicallysafemustbeused. Th is mayrequiretheuseofaremotecontrolunitwiththeappropriate intrinsicallysafepowersourceandinputcircuitryorthesamefromyourcontrolsystem.TiltSwitchunitsareactuatedbyatiltsensorwithintheswitchprobe. Therearethreetypesoftiltsensortechnologiesinuse. Th efirstismechanicalactivation. Inthiscaseasteelballdepressesan electricalswitchwhentheTiltSwitchprobeissuspendedandinaplumbposition. Whenmaterialcomesupto thelocationoftheTiltSwitchandbeginsto tilttheprobe,theballwillfallofftheelectricalswitchwhentheprobeistiltedbetween15-17degrees. Thisopenstheelectricalswitchcontact. Whenthegrainfallsaway,theTiltSwitchprobewillgo backto theplumbpositionandtheballwillseatbackovertheelectricalswitchandcloseitscontactagain.Th esecondmethodofactuationistheuseofamercuryswitchencapsulatedwithintheTiltSwitchprobe. Th emercuryswitchcontactstatechangeswhentheprobeistiltedbythepresence ofthematerial15degreesfromplumb. Th emercuryswitchcontactwillrevertbacktoitsnormalstatewhenthegrainfallsawayandtheTiltSwitchproberevertsto itsnormalplumbposition.


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Th ethirdactuationmethodusesmercury-freetiltsensors,opticalorothertype,oraccelerometers. ThesesensortypesofTiltSwitchesofferthesamesimpleprincipleofoperation whileeliminatingthemechanicalormercury-ladentypesensor. Themercury-freesensorisstillencapsulatedforprotectionandusesacabletoconnectwithitsremotecontrolunit. Outputfromthecontrolunitsineachcasearepotentiallythesame.Table1:ComparisonofTiltSwitch sensortechniques AdvantagesandDisadvantagesTiltSwitchSensorType Advantages Disadvantages

Mechanical Simpledesign Lowestcost Notoxicmercury

Mechanical,movingparts

Notsuitableforhazardousexplosivedustenvironments

Typicallybaremetalprobes

No

remote control unitavailable

MercurySwitch Industrystandardformanyyears

Hasremotecontrolunitorcanbedirectlywiredtocontrolsystem

Mercuryistoxicmaterial

Highercostthanmechanicalswitches

Solidstate(mercury-free)Switch Solidstate Notoxicmercury Highercost Donotcurrentlywork

withouttheirremotecontrolunit

RotaryPaddlebinlevelindicatorsarealsousedforhighleveldetectioningrainelevators. Inthiscasean assemblyincluding theRotaryPaddlepowerpack,flexiblecoupling,extensionshaft,extensionguardandpaddleareused. Th eRotaryPaddleassemblyistopmountedon thesilo. Th eextensionshaftextendsthemonitoringpoint(thepaddle)intothesilotothedesiredhighleveldetectionpoint. Th eflexible shaft couplinghelpsprotectthepowerpackoutputdriveshaftfromdamageduetosideloadingfromflowingandshiftingmaterial. Theshaftguardprotectstheextensionshaftfrombendingandalsoprotectstheoutputdriveshaftfromdamage.

Figure 3: Rotary Paddle bin levelindicatorassemblyfor top mountingandhighleveldetection


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The Rotary Paddlebinlevelindicatorconsistsofasmallsynchronousmotorwhichturnsat1rpm. Withmaterialabsentatthehighleveldetectionpoint,theshaftrotatesthepaddlefreelyinair. Whenthesilofillsandgrainreachesupto thepaddle,theweightofthegrainwillresistthepaddlerotationandstopitfromturning. Th edrivemotorinsidetheRotaryPaddlebin levelindicatorwillrotateon itsmountingplateandactivatetheunitscontroloutput. Subsequently,anotherswitchwillbeactivatedthatwillturnpowerofftothedrivemotor. Thedrivemotormountingplateisspringloadedandwhenthegrainintheelevatorsilofallsawayorrecedesfromthehighleveldetectionpointatthepaddle,thedrivemotorwillrotatebacktoitsnormalpointandreactivatetheswitchthatturnspoweron to thedrivemotoran dalsoreactivate theotherswitchthatreversesthecontrol/alarmoutputstate.ForfurtherinformationaboutRotaryPaddlebinlevelindicators,TiltSwitchesandotherpointlevelmonitoringtechnologiesreferto theWhitePapertitledApplication ConsiderationsforPointLevelMonitoringofPowderandBulkSolids.InventoryMonitoringinGrainElevators: Graininventorymonitoring(determiningtheamountofmaterial)isusuallybasedon measuringthelevelofgrainineachsilo. Oftenthisisnotdonebecauseoftheexpenseofinstalling alevelsensorof$1300-3000ineachsilo. Thisisasizeableexpensewhenyouhave50,70,100ormoresilosinthegrainelevatorfacility. Manyfacilitieswillfilleachsilountilthehighlevelpointisreachedandweighouttheamountofmaterialwhendischarging. Whenreal-timeinventorymonitoringisemployedalevelsensorisusedthatwillmeasuretheemptyspacedistancebetweenthesensoran dthematerialsurfaceandrelatethisdistanceto theoverallheightofthesilotoobtaintherelativelevelofgraininthesilo. Calculationscanthenbemadeto estimatetheamountofgraininbushels,poundsortons.Th esensorsmostcommonlyusedforgrainsiloinventorymonitoringistheweight&cable,ultrasonicandeventheopen-airradartypeofdevices. However,theweight&cablesystem(a.k.a.smartplumb-bob, yo-yo,and bin-bob)isusuallythemosteffectiveasitisagoodbalancebetweencostandmeasurementperformance. RefertoTable2foraquickcomparisonofthetechnologies. Also,referto theWhitePapertitledApplicationConsiderationsforContinuousLevelMonitoringofPowderandBulkSolids.Allthreetechnologiescanbetieddirectlyintotheelevatorcontrolsystemformonitoringofsiloinventory. Th esmartweight&cablesystemsca nalsobeprovidedwiththeirow nstandaloneoperatorinterfacethatcanbeeitherawallmountedalphanumericdisplayorPC software.


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Smart weight & cabledevicesarecapableofcalculatingvolumesandweightsforcylindricalandrectangularsilos. Theyevenincludeacapableweighttablefitthatcanallowyouto customizetheconversionfromlevelto weightbysettingupalinearizationtable,sometimeswithupto 100datapairs.Table2:Comparisonoftop inventory monitoringtechnologies for grainelevatorapplication ContinuousLevelTechnology Advantages Disadvantages

Weight&Cable Moderate cost($1300+) Mostly solid-statewith

modernversions Ruggedenoughfor

grainsiloapplications Can measureupto 150

feetevenwithdust Standaloneorwiththeir

ownoperatorinterface

Not non-contact Nottypicallyusedfor

measuringduringfilling

Nottruecontinuous,more intermittentmeasurement(sampleratecanbeset to withineverfew minutes

Ultrasonic Non-contact Moderate cost($1600+) Notreliablewithheavydust

Notreliableforlongrangemeasuringdevicesfor100+feet

Mustbetiedintoelevatorcontrolsystemfor operatorinterface

Radar(open-air) Non-contact Goodindustladenair Betterreliabilitythan

ultrasonic Rangemaybelimited

to 80-100feet Mostexpensiveof

threetechnologies,e.g.$2500+

Weight&Cabledevicesmeasurethedistanceofcableasitisloweredintothesilountilitcontactsthematerialsurface. Th edistancemeasurementisalsomadeasthemotorreversesandretractstheweight&cable. Th emeasureddistanceisreportedto thecontrolsystemoroperatorinterfaceviaaRS-485 digitalcommunicationconnection.Cablesaretypically3/16diameterstainlesssteelwithaplastic jacket. Smartmotorcontrol,opticalsensingfordistancemeasurementandsmartweight&cablecontrolaspectsofthemodernweight&cablesensor.


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Ultrasoniccontinuouslevelsensorsmeasurethedistancebydeterminingthetime-of-flightofsoundenergyemittedfromthesensorandreflectedoffthematerialsurface. Assuch,itisneverincontactwiththematerial,however,soundenergycanbeeasilyabsorbedbyinternalsilodustandtheenergydissipatesastherangegetslongerandlonger,asinan emptyornearemptysilo.Open-AirRadarcontinuouslevelsensorsmeasuredistancebydeterminingthetime-of-flightofradarenergyreflectingoffthematerialsurface. Radartechniquesaremoretolerantofdustinthesiloatmosphere,buttheyareexpensiveandmaybelimitedinmeasuringrangeto 80-100feetatthemost.Conclusion Bin levelindicatorsarean integralpartoftheoperation ofgrainelevatorsandhavebeenfordecades. Whetherprotecting againstsilooverfilling,controllingfillingoperations

or

monitoring

inventory

in

silos,

they

are

an

important

part

of

the

grain

elevatoroperation. TiltSwitch,RotaryPaddle,Weight&Cable,UltrasonicorRadartechnologiesarewhataretypicallyemployedingrainelevatorsfortheseimportantbin levelapplications.

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