Microcontrollers In Recirculating Aquaculture Systems

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Microcontrollers In Recirculating Aquaculture Systems
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Fowler, P.
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University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
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"EES-326"

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EES-326 April1994MicrocontrollersinRecirculatingAquacultureSystems1 P.Fowler,D.Baird,R.Bucklin,S.Yerlan,C.Watson&F.Chapman2Closed-systemaquaculturepresentsanewand expandingcommercialopportunity;however,presently therearefewprofitablecommercialoperations. Intensiveaquaculturesystemsrequireasufficient supplyofoxygenandnutrientsintemperaturecontrolledwaterwithameansofremovingwastes fromthesystem.Inproperlycontrolledrecirculating aquaculturesystems,stockingratesofuptoone-half poundoffishpergallonofwatercanbeobtained. However,sincefailureofanycomponentcancause catastrophiclosseswithinashortperiodoftime,the systemmustbereliableandconstantlymonitored. Thus,precisemeasurementsandcontrolsare necessaryforthesuccessofanintensiverecirculating aquaculturesystem. Animportantcomponentofclosed-system aquacultureisthecontrolsystemwhichmustmeasure andcontrolallofthecriticalsystemparameters. Recentdevelopmentsincontroltechnologyand microcomputersmayrevolutionizetheoperationand controlofmanyagriculturalandbiologicalproduction systems.Aproperly-controlledsystemwillalsobe energyefficientsinceproductioncanbeoptimized withrespecttothevariousinputs.SYSTEMPARAMETERSThemostimportantparameterstobemonitored andcontrolledinanaquaculturesystemarerelatedto waterquality,sincetheydirectlyaffectanimalhealth, feedutilization,growthratesandcarryingcapacities. Theprimarywaterqualityparametersinclude temperature,dissolvedoxygen(DO),pH,ammonia, nitrites,nitrates,suspendedsolids,salinity,alkalinity, biochemicaloxygendemand(BOD),andwaterflow rate.Waterlevels,availabilityofelectricpower, meansofdetectingfire,smokeandtheintrusionof vandalsshouldalsobemonitored. Duetothecostand/orunreliabilityofsensorsand associatedequipment,mostautomatedaquaculture systemsdonotattempttomonitorandcontrolallof theseparameters.Itisrecommendedthat temperature,DO,pHandwaterflowratebe monitoreddirectlyonacontinuousbasissincethey tendtochangerapidlyandhaveasignificantadverse effectonthesystemifallowedtooperateout-ofrange.Otherparameterschangeslowlyandtendto stayinrangeifproperflowrateismaintained.For example,ammoniaisusuallynotaproblemifthe biologicalfiltersareproperlysizedfortheloading rateandifadequateflowismaintained.Inthiscase, 1.ThisdocumentisEES-326,aseriesoftheFloridaEnergyExtensionService,aseriesoftheFloridaEnergyExtensionService,Florida CooperativeExtensionService,InstituteofFoodandAgriculturalSciences,UniversityofFlorida.Publicationdate:April1994. 2.P.Fowler,GraduateAssistant;D.Baird,Professor;R.Bucklin,AssociateProfessor,AgriculturalEngineeringDepartment;S.Yerlan,Associate Professor,Industrial&SystemsEngineeringDepartment;C.Watson,AquacultureExtensionAgentII,HillsboroughCounty;F.Chapman, AssistantProfessor,FisheriesandAquaculture,CooperativeExtensionService,InstituteofFoodandAgriculturalSciences,Universityof Florida,GainesvilleFL32611. TheFloridaEnergyExtensionServicereceivesfundingfromtheEnergyOffice,DepartmentofCommunityAffairs,andis operatedbytheUniversityofFlorida'sInstituteofFoodandAgriculturalSciencesthroughtheCooperativeExtensionService. TheinformationcontainedhereinistheproductoftheFloridaEnergyExtensionServiceanddoesnotnecessarilyreflectthe viewoftheFloridaEnergyoffice. TheInstituteofFoodandAgriculturalSciencesisanequalopportunity/affirmativeactionemployerauthorizedtoprovideresearch,educational informationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithoutregardtorace,color,sex,age,handicap,ornational origin.Forinformationonobtainingotherextensionpublications,contactyourcountyCooperativeExtensionServiceoffice. FloridaCooperativeExtensionService/InstituteofFoodandAgriculturalSciences/UniversityofFlorida/JohnT.Woeste,Dean

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MicrocontrollersinRecirculatingAquacultureSystems Page2flowrateisthecriticalparameterthatshouldbe Table1. Waterqualitystandardsforfishculture. Alkalinity(asCaCO3) 10to100 Nitrogen(N) <110%totalgaspressure <103%asnitrogengas Aluminum(Al) <0.02 Nitrate(NO3) 0-3.0 Arsenic(As) <0.05 Nitrite(NO2) 0.1insoftwater Barium(Ba) 5 Nickel(Ni) <0.1 Cadmium Alkalinity<100ppm Alkalinity>100ppm 0.0005 0.005 PCB(polychlorinated biphenyls) 0.002 Calcium(Ca) 4to160 pH 6.5-8.0 Carbondioxide(CO2)0to10 Potassium(K) <5.0 Chlorine(Cl) <0.003 Salinity <5% Chromium(Cr) 0.03 Selenium(Se) <0.01 Copper Alkalinity<100ppm Alkalinity>100ppm 0.006 0.03 Silver(Ag) <0.003 Dissolvedoxygen(DO)5tosaturation Sodium(Na) 75 Hardness,total 10to400 Sulfate(SO4) <50 Hydrogencyanide(HCN)<0.005 Sulfur(S) <1.0 Hydrogensulfide(H2S) <0.003 Totaldissolvedsolids (TDS) <400 Iron(Fe) <0.1 Totalsuspendedsolids (TSS) <80 Lead(Pb) <0.02 Uranium(U) <0.1 Magnesium(Mg) <15 Vanadium(V) <0.1 Manganese(Mn) <0.01 Zinc(Zn) <0.005 Mercury(Hg) <0.2 Zirconium(Z) <0.01 Source:U.S.EnvironmentalProtectionAgency1979-80 Note:Valuesareinmilligramsperliterunlessotherwisenoted.monitoredcontinuously,takingonlyperiodic measurementsofammonia.Table1givesthegeneral rangeofwaterqualitystandardsforfishculture. Inordertomaximizeproduction,water temperaturemustbepreciselycontrolled.Therange oftemperatureforoptimumaquaculturalproduction dependsonthespeciesbeingcultured.Somespecies requireavariablerangeinordertopropagate. However,temperaturevariationcanbedetrimentalto somespeciesand,inmostcases,arelativelyconstant temperatureisthegoal.Thelargerthevolumeof water,theeasieritistocontrolthetemperature, becausethehighspecificheatofwatercreatesahigh thermalmassthatresistsrapidchangesin temperature. Allaquaculturespeciesdependonoxygenforlife andgrowth.Theconcentrationofmolecularoxygen inthewater(normallymeasuredinmg/liter)iscalled dissolvedoxygen(DO)anddependsonthe temperatureofthewaterandthebiologicaldemand ofthesystem.Dissolvedoxygenisthemostcritical parameterinaclosedrecirculatingsystemsinceitcan changerapidly.FishkillsresultifDOisallowedto

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MicrocontrollersinRecirculatingAquacultureSystems Page3dropbelowacriticallevel.DOshouldbemonitored verycloselyatalltimesandthereshouldbeabackup sourceofoxygenincasetheprimarysupplyis interrupted.Ifaerationequipmentisusedtosupply oxygen,theairpressuresuppliedtotheaeration equipmentcanbemonitoredinsteadofdirectly measuringdissolvedoxygen.However,sincethisis suchanimportantparameter,itwouldbeadvisableto measureboth,thusprovidingabackupinthesystem. Ammoniaisawasteproductofprotein metabolism.Inwater,itispresentintwoforms, ionized(NH4 +)andunionized(NH3).Unionized ammoniaistoxictomostaquaticorganismsand occursingreaterproportionathighpHandwarmer temperatures.Thetoxicityoftheunionizedformis harmfulatlevelsaslowas0.05milligramsperliter. Nitriteisabyproductofthebiologicaloxidationof ammonia.Mostaquaticorganismscantoleratesome tracesofnitrites,butasthelevelincreases, productivitygoesdown.Generally,nitrateisnottoxic tofishandisusedbyplantsforfood.Nitriteisa difficultparametertomeasureandcontrol. Ammoniaisalsodifficulttomeasurewithsensors. However,ammoniaisusuallynotaproblemoncethe biologicalfiltershavebeenproperlysizedandan adequateflowratedetermined.Also,ammonialevels tendtochangeslowly,makingperiodicmeasurements sufficient.SENSORSANDINSTRUMENTATIONRecirculatingaquaculturesystemscommonly includecontrolstomonitorthewaterquality parametersoftemperature,dissolvedoxygen,pH,and waterflowrateeitherdirectlyorbymonitoring equipmentwhichmaintainstheparameter.Inthe past,onlythemostsophisticatedandexpensive instrumentswereadequateformonitoringand controllingaquaculturesystems.However,today therearemanynewdevelopmentsinsolidstate electronicswhicharebringingdownthecostand increasingthereliabilityofsensorsandinstruments. Thefollowingisareviewofseveralofthesensorsand instrumentsusedtomonitorsomeoftheparameters ofanaquaculturalsystem.Liquid-FilledThermometerTheliquid-filledglassthermometeristhesimplest andmosteconomicalwaytomeasuretemperature. Thethermometerindicatestemperaturebythe expansionandcontractionofmercuryoralcoholina sealedglasscolumn.Acommontypeusedin aquacultureisasealedunitthatfloatsinwater. Thesethermometersareaccurate,simpleandreliable, butarealsopronetobreakageandcannotbe interfacedwithacontrolsystem.Theyaremost appropriatelyusedasaback-uptoothertemperature indicatorsandforcalibrationofothertemperature sensors.BimetallicandGasBulbThermometersBothofthesethermometersaremechanicaland canbeusedtoindicatetemperatureonadialorused toeitheropenorcloseanelectricalswitchsuchas thoseusedonmostcommonthermostats.These typesofthermometersareverysimple,reliableand canbeinterfacedwithelectroniccontrolsystems.ThermocoupleTwowiresofdissimilarmetalsconnectedateach endgenerateavoltagerelatedtothetemperature differencebetweenthetwojunctions.Therearesix commontypesofthermocouplesdependinguponthe kindsofmetalsusedtomakethem.Theyhavewide operatingrangesbuthaveverylowDCvoltage outputs.Duetothislowvoltage,inthepast thermocouplescouldonlybeusedwithveryexpensive instrumentation;however,advancesinsolidstate electronicshavegreatlyreducedthepriceof instrumentationtothepointwhereitisapractical methodofmeasuringtemperaturetoday.These sensorsareveryinexpensiveifyoumakeyourown. Simplycutthewiretothelengthdesiredandsolder orweldtheendstogether.Thermocouplesarevery practicalwhenyouwanttomeasuretemperatureata numberoflocations.ResistantTemperatureDetectors(RTDs)and ThermistorsResistanttemperaturedetectorsandthermistors workontheprincipleofchangeofresistancewitha changeintemperature.Thisresistancecanbe measuredandcalibratedtoatemperaturescalewhich canbeelectronicallydisplayed.Althoughthe principleofoperationiscompletelydifferent,RTDs andthermocouplesareverysimilarfromauserspoint ofview.Thermocouplesusuallyaremoreflexiblein applicationandhaveabetterlong-termstabilitythan doRTDs.However,RTDsandthermistorshavea muchhighertemperaturesensitivitythan thermocouples,thusrequiringlesssophisticated electronics.

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MicrocontrollersinRecirculatingAquacultureSystems Page4IntegratedCircuit(IC)TransducerAnintegratedcircuittransducerisasolid-state microelectroniccircuitthatiscontainedina transistor-likehousingandhasanoutputvoltageor currentproportionaltoitstemperaturewhensupplied withaconstantcurrentorvoltage.ICtransducersare veryreliableandsimpletouseandinterfacewith controlcircuits.Theyhavetheadvantageofbeinga completelypackagedtemperatureindicatorin comparisontothermocouplesandRTDswhichmust beconnectedtosomeelectroniccircuit.IC transducers,sometimescalledICsensors,arevery linear,areprecalibratedandcostaboutthesameas RTDsandthermocouples.Theydohavealimited temperaturerange(minus85to125Celsius). However,thisshouldnotbeaproblemwith aquacultureoperations.pHMeasurementThepHmeasurementismadeeitherchemically orelectronically.Thechemicalmethodisextremely simple.Areagentisaddedtoasampleandthe resultingcolorchangecorrespondstothepHvalue. Theelectronicmethodusesanelectrodethatis placedinthewaterandhasanoutputvoltagewhich iscorrelatedtopH.Theseunitsarecommercially availableatamoderatecostandcanbeinterfaced withcontrolsystems.DissolvedOxygenMeasurementDissolvedoxygen(DO)canbemeasuredboth chemicallyandelectronically.Theelectronic measurementforDOsimplyrequirestheplacement oftheprobeinthewater.TheDOprobeconsistsof agoldorplatinumelementthatissurroundedbya reagentsolution.Thissolutionisseparatedfrom waterbyamembranewhichallowsthepassageof oxygenintothesolutionwhereitreactswiththe elementandgeneratesavoltagethatcanbemeasured anddisplayed.TheDOprobecanbeinterfacedwith anelectroniccontrolsystembuthasthedisadvantage ofhighcostandhighmaintenance.ENVIRONMENTANDELECTRONICSAnimportantconsiderationinaquacultural controlsystemsistheenvironmentinwhichtheyare used.Thecorrosivenessofthewaterinwhichthe probesareplacedcanrapidlydegradetheir effectiveness.Probescanalsobefouledbymicrobial growth.Aregularscheduleofmaintenanceand calibrationmustbeusedtoinsurethattheprobesare functioningproperly.Somemethodoffaultdetection shouldbeusedforeachprobetodetermineitsstatus andcalibration.Theelectronicsmustbeisolated fromthehighhumidityandconstantwetenvironment oftheproductionfacility. Lowvoltageshouldbeusedforcontrol componentswherepossibleandagroundfaultsystem shouldbeprovidedasasafetyprecautionforthe highervoltagecomponentsofthesystem.Thisis neededforprotectionofpersonnelaswellasthe aquaticanimals.AUTOMATICCONTROLFeedbackisanimportantconceptinsystems control.Asanexample,consideraheatedwatertank inwhichameasurementistakentodetermineifthe waterisatthedesiredtemperature.Thecontroller wouldinterpretthefeedbackasfollows:waterabove desiredtemperatureturnheateroff;waterbelow desiredtemperatureturnheateron.Thecommon thermostatoperatesinthismanner;however,itis usuallyanon-offdevicewhichcausestemperature fluctuationsinthesystem. Abettersystemisonethatsuppliesheat proportionaltothatwhichisneeded,thusminimizing thefluctuations.Thisiscalledproportionalcontrol. Therearealsomoresophisticatedcontrolfunctions knownasderivativeandintegralcontrolfunctions whichfurtherminimizeoscillationsinthesystem. Theyaccomplishthisbysensingtherateatwhichthe parameterischangingandbydeterminingthe deviationofthemeasuredparameterfromthedesired setpoint.Thistypeofcontrolsystemisusually referredtoasPID(proportional-integral-derivative). Thesetypesofcontrollershavebeenavailablefor manyyearsbuthavebeenveryexpensiveandusually wereusedonlyinsophisticatedindustrialoperations. ThecostofPIDcontrollersisfalling,buttheymay notbeagoodchoiceformostagriculturaloperations sincePIDcontrollersarebasedoncomplex mathematicsandrequireconsiderableexpertisein ordertodesign,modifyandapplytoaspecific operation. Analternativetotraditionalcontrolsystemtheory isbasedonwhatiscalled"fuzzylogic".Itsstrengthin processcontrolliesinitsabilitytomanipulatesystems thatarecomplex,nonlinearand,mostimportantly, lackanymathematicalmodel.Moreover,theinputto

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MicrocontrollersinRecirculatingAquacultureSystems Page5fuzzylogiccontrolisasetofruleswrittenwith linguisticvariables,statedinplainEnglish.Thus,no specialprogrammingskillsarerequiredifafuzzy logiccontrolcodegeneratororcompilerisused.This exotictechniquehasfoundahomeinapplications rangingfromautofocuscamerastostockportfolio management.Italsolendsitselfverywellto applicationsinaquaculturesinceitisbasedona simplesystemof'if'and'then'statements.For example,ifconditionAandconditionBexist,then takeactionC.Thisbasisforcontrolmakesitmuch easierfortheaquaculturiststocommunicatewiththe engineersandthecomputerscientists.Thisnew controltechnology,microcomputersandanew programminglanguagemayrevolutionizethe operationandcontrolofmanyagriculturaland biologicalproductionsystems.MICROCONTROLLERSIndustrialautomaticcontrollershavebeen availableforyearsbuthaveapricetaginthe thousandsofdollars.Inaddition,theyarenotvery adaptabletoaquaculturaloperationsduetothe severeenvironmentinwhichtheyoperateandthe changingrequirementsofagriculturalcontrolsystems. Ontheotherhand,microcontrollerchipsarevery inexpensive,usuallycostingmuchlessthan$100. Theyareverysmall,canoperateunderverysevere environmentalconditions,andlendthemselvesto new,simplifiedprogrammingprocedures.These featuresmakethemicrocontrollerthepreferred choiceforembeddedcontrol,suchasthatusedin appliances,automotiveenginecontrol,camera exposurecontrolandindustrialautomation. Amicrocontrollerisanenhancedmicroprocessor. Inadditiontothemicroprocessor,amicrocontroller typicallycontainsseveralparallelandserialports, systemclockgenerators,dataandprogrammemory, timers,counters,interruptlogic,analog-to-digital converters,digital-to-analogconverters,andeven digitalsignalprocessingsubsystemsonthesamechip. Thus,asingle-chipmicrocontrollermaybeplacedin anapplicationtoperformasanembeddedcontroller withnoothersupportchips.Onlywithinthelastfew yearshavemicrocontrollersadvancedtothepointthat theycanhandlealargenumberofinputsandoutputs andaccommodateenoughmemoryandprocessing powertocontrolacomplexsystemsuchasthoseused inaquaculturalproduction. Microcontrollersthatcanbeprogrammedby meansofaninterviewwiththeaquaculturistmaybe availablesoon.Thisisduetoanewvisual programminglanguagebeingdevelopedbythe IndustrialandSystemsEngineeringDepartmentat theUniversityofFlorida.Thisnewvisual programminglanguageallowstheenduser (aquaculturist)tositdownatacomputeratsome convenientlocation,suchasthecountyExtension office,anddescribewhatparametersaretobe controlled,whattypeofcontroldeviceswillbeused, andtellexactlyhowthesystemshouldoperate.This visualprogramminglanguageprovidesamenuof choicesforallofthesystemandcontrolparameters. Oncethechoiceshavebeenmadeandinstructions given,thecomputerautomaticallywritesallofthe computerprogram(sourcecode)forthecontrol system.Moredetailedinformationonthevisual programminglanguagecanbefoundin AVisual LanguageforMicrocontrollers ,S.Yerlan,etal., ResearchReport93-4,IndustrialandSystems Engineering,UniversityofFlorida. Asanexampleofhowthevisualprogramming languageworks,consideramicrocontrollersystem (Figure1)inwhichtemperature,dissolvedoxygen, pH,waterlevel,andwaterflowratearetobe monitoredand/orcontrolled.Usingthevisual programmingsoftware,theaquaculturistscanselect theseparametersandtellhoweachiscontrolled.For example,thetemperatureiscontrolledbyaheat pumpwhichcanheatorcoolthewater.The dissolvedoxygenleveliscontrolledbyoxygen injection,thewaterleveliscontrolledbyavalve connectedtothemainsupplyline,theflowrateis controlledbythepumpspeedandthepHis monitoredbutnotcontrolled.Theupperandlower limitsofeachparameterandthesamplingratefor eachcanbeselected.Oncealltheinputshavebeen made,theoperationofthesystemmaybesimulated bythesoftwaretoinsurethatitoperatesastheuser intended.Next,thevisualprogrammingsoftware writesallofthesourcecodeintheappropriate computercontrollanguage,thentheelectronic controlcircuitisdrawnbythecomputerwhichcan thenbeburnedoretchedintothemicrocontroller. Themicrocontrolleristhenreadytobeinstalledinto theautomaticcontrolsystem,wheretheinputsensors areconnectedandtheoutputsignalsaresenttothe controldevices(pumps,valves,heatpumps,etc.). Thehardwareandsoftwaretoaccomplishthe tasksjustdescribedarestillbeingdeveloped,but shouldbeavailableinthenearfuture.Inthe meantime,microcontrollerscanstillbedevelopedto

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MicrocontrollersinRecirculatingAquacultureSystems Page6monitorandcontrolmostparametersinan aquacultureproductionfacility,butmayrequirea considerablecooperativeeffortamongthe aquaculturist,engineerandhardwareandsoftware suppliers.POTENTIALFORENERGYSAVINGSAsmorereliableandeffectivesensorsbecome availabletomeasureaquaculturalsystemparameters, moremicrocontrollerswillbeusedtooptimize aquaculturalproduction.Anoptimizedsystemisboth energyefficientandcosteffective.Presently,most systemcomponentsareoverdesignedbecauseprecise measurementandcontrolarenotbeingutilized.For example,aerationsystemsusuallymovealotmoreair andusemoreenergythanisnecessarybecause dissolvedoxygenisnotbeingdirectlymeasuredand controlled.Inaddition,biologicalfiltersmaybe overdesignedandusehigherwaterflowratesand, hencemoreenergythan necessarybecausetheammonialevelisnotbeing directlymonitoredandcontrolled. Microcontrollersallowlargeamountsofrealtime datatobecollected,providingabasisforimproving theefficiencyoftheproductionsystemasitoperates. Aprecisely-controlledenvironmentminimizesstress ontheaquaticorganismandreducesthegrowout period.Italsoreducesthequantityofenergy,labor andwaterusedperproductionunit.Forexample,if thesystemiscompletelyautomatedwith microcontrollers,includingthemonitoringoffeed, growthrateoffishandenergyutilization,simple experimentscanberuntodeterminewhetheritis economicallyfeasibletoincreasethewater temperatureinordertoincreasethegrowthrate.In otherwords,theaquaculturistcancontinuallyimprove theefficiencyoftheoperationbyobservingits performanceunderdifferentoperatingconditions. Microcontrollerscanalsobeutilizedtoactivate otherdevicessuchasswitchingonback-uppower whenthemainpowerfails,soundingalarmsand makingphonecallswhensystemparametersareout ofrangeorwhenintrusion,smoke,fireorhigh temperaturesensorsareactivated.Tobepractical, themonitoringandnotificationsystemshouldallow theproductionmanagertofollowanormaldaily routine,includingtravelawayfromtheproduction facility,whileremaininginformedaboutthesystem's operation.Thistypeofmonitoringandresponsemay providethebasisforthegreatestenergysavings, becausesystemfailuresresultininstantlossofthe energysequesteredintheaquaticanimal. Aconservativeestimateofenergysavingsfora properlymonitoredandcontrolledaquaculturesystem of20%wouldresultintenbillionBtusofenergy savedannuallyfromornamentalfishproduction alone.Thisisbasedonenergyconsumptionas reportedfrom"TheFloridaEnergyConsumption Model"whichindicatesthat4.46x1011Btusofenergy areconsumedannuallyinaquaculturalproductionin Florida,with1.16x1011Btusofthatusedin ornamentalfishproduction.

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MicrocontrollersinRecirculatingAquacultureSystems Page7 Figure1.Microcontrolledaquaculturesystem.