脉冲输出型数字涡街流量计的研究

附录AResearchonpulseoutputmodeldigitalvortexflowmetersThevortexflowmeteriswidelyusedindifferentfieldsduetoitsflexibilitytovariousmedia,non-mobileparts,simplestructureandlonglifeetc.However,ithaspoorperformancewhenoperatingatlowflowratewheretheSignal-to-Noiseratioisverysmalloreventhesignalissubmergedbythenoise.Thetraditionalanalogvortexflowmeterhasbenefitsofsteadysignal,highaccuracyandgoodrealtimeintheregularflowrange,whileitalsohasadisadvantageofweaksignaldifficulttodetectatlowflowrate,whichleadstounsatisfyinglowerlimitandasmallerrangeratioof10:1.Basedonthepreviouseffortsapulseoutputmodeldigitalvortexflowmeterisdevelopedsuccessfully,whichinheritstheadvantagesoftheanalogoneandmakeupitsshortagementionedabove.Thedigitalvortexflowmeterwithitsdouble-corestructurethatmeansacoupleofCPUsmadeupofDSPandMSP430identifiesthevortexsignalsfromnoisesbythefrequencyspectrumanalyzingalgorithminDSPatlowflowratewheretheanalogoneisnotaccurate,orevencan’twork.MeanwhileitworksoutbyitsmicrocontrollerMSP430thefrequencyofthevortexsignalthatissquarewavesoutputfrompre-amplifierforthevortexsignalsintheregularflowrangewheretheSignal-to-Noiseratioisn’ttoomuchsmallandtheanalogoneisaccurateandrealtime.Thisdissertationconsistsoftheory,hardware/softwaredesignandexperiment.Themainpointincludes:1.Theschemecalleddouble-channelworkmodelofthepulseoutputmodeldigitalvortexflowmeterisdesigned.Theprincipleisaswitchoftwodifferentmethodstodetectthevortexsignal.Thatisusingspectrumanalysisofdigitalsignalatlowflowrateandfrequencycountinglikeanalogvortexflowmetersintheregularflowrange.Thecriticalcriterionoftheswitchpointistheuncertaintyofthefrequency.2.Apulseoutputmodeldigitalvortexflowmeterisdevelopedsuccessfully.TheflowmeterisstudiedrespectivelyatDN25andDN50pipelinesofthewaterflowexperimentfacilityandDN50andDN100pipelinesofthegasflowexperimentfacilitythatlocateatProcessDetect&ControlLaboratoryinTianjinUniversity.Andthedatashowsthatthedigitalflowmeterhasthepropertyofabetterlowerlimitthantheanalogoneandabiggerrangeratioof1:28.5～41.3.MassesofexperimentsonthedigitalvortexflowmeterhavebeencarriedoutatthewaterflowexperimentfacilityandthegasflowexperimentfacilityofTianjinUniversityrespectively.Theresultshowsthatthepulseoutputmodeldigitalvortexflowmeterhasasatisfyinglowerlimitthatincreasestherangeratioeffectively,strongabilityandgoodrealtimeandthusitisofgreatpracticability.The21stcenturyisthecenturyinformation,informationandmaterialsandnewtechnologyasthemainpillarofsocietyfromthehumanrevolutionisindustrializationeratoinformationera,astheperception,acquisition,conversion,processingandtransmissionofinformationtechnologyandtheindispensabletestinginstrument,hasbecomeanimportanttechnologyandcomputerequivalentanddailylifeandproductionofallfields.Alongwiththerapiddevelopmentofscienceandtechnology,industrialproductiongetcontinuousdevelopment,thedetectiontechnologyandputsforwardmanynewrequirements,andnewtechnologyandinstrumentappearanceandfurtherpromotethedevelopmentofscienceandtechnology,thedevelopmentdegreeofdetectingtechnologyhasdecidedtoscienceandtechnologylevel,inotherwordsdetectiontechniquesandinstrumentsisthemeasureofmodernscienceandtechnologylevelofamark.Thisone,astestingtechnologyisanimportantpartofflowmeteringwithnationaleconomicandnationaldefense,scienceandtechnology,thecloserelationshipineconomicdevelopmentplaysanimportantposition.Aftercontinuousefforts,andtechnicalworkershavedevelopedpyreticandvariouscharacteristicsofflowmeter.Accordingtothemeasuringmethodandthestructureoftheclassificationmethod,willbedividedintodifferentialpressuremeterflowmeter,volumetricflowmeter,fluidflow,ultrasonicvibrationflowmeter,massflowmeter,insertflowmeteropen-channelflowandotherflowmeter,11kinds.Theresearchofthevortexflowmeterbelongstothehydrodynamicvibrationflowmeterarewidelyused.Vortexflowmeterisaccordingtothefluidvelocityofvibrationfrequencyandthecorrespondingprincipleofwork.Asearlyasin1878strawStrophepublishedaboutfluidvelocityrelationshipwiththevibrationfrequency,straw,vortexfrequencyissaidtostopfeaturesofsimilarsizeandthevelocityoftherelationship.Peopleintheearlyvortexresearchmainlyisthepurposeofprevention.Vortexflowvibrationphenomenonformeasuringthestudybeganinthe1950s,suchaswindmeterandshipspeedgaugeetc,attheendofthe1960sbegantodevelopclosepipelineflow-vortexflowmeter.1970sand1980svortexflowmeterunusuallyquickdevelopment,developmentoutstandingtyperesistancefluidanddetectionmethodsofvortexflowmeter,andmassproduction,suchasthemarketinjustafewshortyearstimetoarrivefromlaboratorybatchproductionprocessofthesampleflowisunique.Vortexflowmeterisafluidvibrationflowmeter,setinthefluidflowvortexhappened(resistancefromvortexhappen)alternatelyonbothsidesofthebodyproducesregularvortex,thespiralcalledCarmenvortex,swirlinginspiralhappenasymmetricalbodydownstream,vortexflowmeterisarrangedbymeasuringthevortexfrequencyandrealizationofflowmeasurement.Vortexflowmeterbysensorsandswitchestwoparts.Sensors(includingvortexflowresistanceoccurs,components,instrument)suchastable,converterincludingpre-amplifier,filteringplasticcircuit,D/Atransformationcircuit,outputinterfacecircuit,terminals,bracketandshields,etc.Inrecentyears,intelligentflowmeteristhemicroprocessor,communicationsandotherfunctionsthatareinstalledinconvertermodule.Accordingtothedetectionmeans,vortexflowmeterstresscanbedivided,capacitiveandthermaltype,typeofultrasonicvibration,strain,andphotoelectricandfiber,etc.Amongthem,stress(alsocalledthepiezoelectric)vortexflowmeterwithitsfastresponseandstrongsignal,workingtemperaturerangewide,strongadaptabilityandhighreliabilityetc,hasbecomethemainproductsvortexflowmetertype.Thisvortexflowmeter,itistotesttheliftinformstresstestingdevices,piezoelectricconversionvariablechargesignal,clinchadealthechargeamplifier,filtering,plasticaftervortexsignal.Piezoelectricsensorsignals,fastresponseandlowcost,manufacturingprocess,butismoresensitivetovibration.Asmentioned,vortexflowmeterhasmanyadvantages,andtherearemanyproblemstobesolved,especiallyinthemeasurementofsmallflow,vortexusefulsignalisveryweak,yiwasdrowned,lownoisesignalunderthevelocitymeasurementcausedgreatdifficulties.Inordertosolvethisproblem,thedomesticandoverseasscholarsandscientificresearchinstitutionsinresearchandapplicationofvarioussolutions,namelyofdigitalsignalprocessingmethodtosolve,butmostjuststayintheresearchonthemethodofhighefficiency,andnotbeappliedalgorithmsupportforproduction.Atpresent,thedomesticproductionofthevortexflowmeterislimitedtotheanalogcircuitapplicationmethodofvortexsignalprocessing(calledsimulationvortexflowmeter),thiscannotsolvethelowSNR,leadingtolowertheproblemthanonlyachievehigh,range1:1scaletheory,farbelowzero.Foreigncompany,YokogawaonlyRosemountandABBhasdevelopedtheapplicationofdigitalsignalprocessingmethodsofsignalprocessingvortex,namelydigitalvortexflowmeter,butspecifictechnologyisnotopen.Inrecentyears,thevortexsignalprocessingmethodsaboutthestudymany(suchaswaveletmethodofadaptiveLMSchanges,etc),thealgorithmoftianjinuniversityprofessorzhangtaopresidedovertheresearchofvortexsensoroutputsignalforexplorationofdigitalsignalprocessingwongreatprogress.LingQingmasteraccordingtothesignalfeaturesandvortexofsignalprocessingmethod,therequirementsformaximumlikelihoodestimationresultsincyclechartareputforwardonthebasisofmoresuitableforrelaxationofthevortexfrequencyestimationmethodofgraph,commitcycleandthesimulationexperiments.Thismethodwithhighresolutionandhighfrequencycharacteristicsofthecalculationefficiency,strongresistancetocomplexnoiseinterferenceability.WuPengmasterbasedonwavelettransform,deposingprincipleofflowmeasurementspecificrequirements,andputsforwardasuitablevortexflowsensorsignalprocessingmethodsofsinglereconstructionfilterisgiven,andthemethodofselecting,filterseriesofthismethodcaneffectivelyexpandvortexflowsensorrange.However,duetotheabovetwomethods,thecomplexityofalgorithm,real-timecomputationisnotguaranteed,andappliedinpractice.AlongwiththeDigitalSignalProcessorDigitalSignalprocessing(DSP)technology,referredtotherapiddevelopmentandwideapplication,makecomplexSignalprocessingalgorithmcanachieveinhardware.DuanRuiFengmasterasetofDSPandMSP430microcontrollercombinationofthevortexdigitalsignalprocessingsystem,usingslacktrappedcyclegraphmethodforcalculatingthevortexflowmetersignalfrequency.Experimentalresultsshowthatthevortexflowdual-coredigitalsignalprocessingsystemcaneffectivelyreducethemeasurementlimit(mmdiametermeasurementcanreachvortexlower0.323m3/h),realizethereal-timedataprocessing.Thistopicisonthebasisofresearchachievementsindomesticproduction,thevortexflowmeterislimitedtosimulatethevortexflowmeter,researchandimplementationofapracticalpulseoutputtypevortexflowmeterfigures.ThepulseoutputtypedigitalvortexflowmeterusingMSP430MCUbasedonDSPandthetwinCPUhardwarestructure,smallflowinlowvelocitybyDSPbasedonfastFouriertransform(FFT)formfast,referredtoasthepowerspectrumestimationisproposedtomeasurevortexfrequencyreal-timepulseoutput,Whentheflowinthenormalflowrangeanaloguecircuit,signalpreprocessingvortex,thenbymicrocontrollerprogramflowcalculations,display,frequency,pulseoutputetc.Thedigitalpulseoutputtypevortexflowmeterintianjinuniversityexperimentdeviceandgasflowfluxondoingalotofexperiments,theresultsshowthattheinstrumenteffectivelyexpandthescaleofthevortex,lowerthanthemeasuringlow,repeatability,stronganti-jammingability,goodreal-time,etc.附录B脉冲输出型数字涡街流量计的研究涡街流量计因其介质适应性强，无可动部件，结构简单、使用寿命长等诸多优点，在许多行业得到了广泛的应用。而在低流速下，涡街测量就显现出了它的不足，涡街信号的信噪比很低，有用信号几乎被噪声淹没。普通的涡街流量计采用模拟信号处理方法，在正常流量范围内，涡街流量信号稳定、测量准确、实时性好；而在小流量下，涡街有用信号微弱、提取困难，导致实际测量下限比较高，量程比小，一般为10：1。鉴于上述模拟涡街流量计具有的优势以及存在的不足，课题在前人研究成果的基础上，研究并成功地实现了一台实用的脉冲输出型数字涡街流量计。该数字涡街流量计采用了基于DSP和MSP430单片机双CPU的硬件结构，在低流速小流量的情况下，由DSP实现频谱分析算法来计算涡街信号频率，有效地克服了模拟涡街在小流量下测量精度不高甚至不能测量的问题；在正常流量范围内，由单片机对涡街信号前置放大电路输出的方波进行计频，具有常规模拟涡街在高信噪比的情况下测量准确、实时性好的优点。本文从原理分析、硬件软件设计和实验研究三方面来研究，主要内容包括：1.设计了脉冲输出型数字涡街流量计的总体方案，尤其是采用了双通道处理的方式，将低流量下数字信号处理的频谱分析功能和正常流量范围内智能涡街的计频功能有机地结合起来，并引入了频率不确定度的概念作为判断涡街有用信号双通道处理方法的依据。2.成功实现了一台脉冲输出型数字涡街流量计。通过在天津大学过程检测和控制实验室的水流量实验装置上进行的25mm口径和50mm口径实验研究，以及在气体实验装置上进行的100mm和50mm口径实验研究的结果表明，本脉冲输出型数字涡街流量计有效地降低了涡街的流量下限，使量程比显著扩大，量程比达到1：28.5～41.3。将此数字涡街分别在天津大学水流量实验装置和气体流量实验装置上做了量的实验，结果表明本脉冲输出型数字涡街流量计具有很低的测量下限，有效扩大了涡街的量程比，抗干扰能力强，实时性好，具有很高的实用价值。21世纪是信息的世纪，以信息、材料和生物为主要支柱的新技术革命正将人类社会从工业化时代推向信息化时代，作为感知、采集、转换、处理和传输各种信息不可缺少的检测技术和仪表，已成为与计算机同等重要的技术而深入日常生活及生产的所有领域。随着科学技术的突飞猛进，工业生产得到不断发展，对检测技术又提出了许多新的要求，而新的检测技术和仪表的出现又进一步推动了科学技术的发展，故检测技术的发展程度决定了科学技术的水平，换句话说检测技术和仪表是衡量现代科学技术水平高低的一个标志。这其中，作为检测技术重要组成部分的流量计量由于与国民经济、国防建设、科学技术的密切关系，在经济发展中占有重要的地位。经过不断的努力和探索，科技工作者已开发出种类繁多、各具特色的流量仪表。按照测量方法和结构的分类方法，将流量计分成差压式流量计、容积式流量计、流体振动式流量计、超声流量计、质量流量计、插入式流量计、明渠流量计和其他流量计共十一大类。本课题研究的涡街流量计属于流体振动式流量计中应用最为广泛的一种。涡街流量计是依据流体振动频率与流速有对应关系的原理进行工作的。早在1878年斯特劳哈（Strophe）就发表了关于流体振动频率与流速关系的文章，斯特劳哈数就是表示涡街频率与阻挡体特征尺寸、流速关系的相似准则。人们早期对涡街的研究主要是防灾的目的。涡街流体振动现象用于测量研究始于20世纪50年代，如风速计和船速计等，60年代末开始研制封闭管道流量计——涡街流量计。70、80年代涡街流量计发展异常迅速，开发出众多类型阻流体及检测方法的涡街流量计，并大量生产投放市场，像这样在短短几年时间内就到达从实验室样机到批量生产过程的流量计还绝无仅有。涡街流量计是一种流体振动式流量计，在流体中设置旋涡发生体（阻流体），从旋涡发生体两侧交替地产生有规律的旋涡，这种旋涡称为卡门涡街，旋涡列在旋涡发生体下游非对称地排列，涡街流量计通过测量其旋涡产生的频率而实现流量计量。涡街流量计由传感器和转换器两部分组成。传感器包括旋涡发生体（阻流体）、检测元件、仪表体等；转换器包括前置放大器、滤波整形电路、D/A转换电路、输出接口电路、端子、支架和防护罩等。近年来智能式流量计还把微处理器、显示通讯及其他功能模块亦装在转换器内。按检测方式划分，涡街流量计可分为应力式、电容式、热敏式、超声式、振动式、应变式、光电式和光纤式等。其中，应力式（又称为压电式）涡街流量计以其响应快、信号强、工作温度范围宽、现场适应性强、可靠性高等优点，已成为涡街流量计的主要产品类型。这种涡街流量计中，它把检测元件受到的升力以应力形式作用在压电检测元件上，转换成交变的电荷信号，经电荷放大、滤波、整形后得到旋涡信号。压电传感器响应快、信号强、工艺性好、制造成本低，但是对振动比较敏感。正如前面所述，涡街流量计具有诸多优点，同时又有许多亟待解决的问题，特别是在测量小流量时，涡街有用信号非常微弱，易被噪声信号淹没，给低流速下的测量造成了很大困难。针对这一问题，国内外学者及科研机构纷纷研究并提出各种解决方案，即应用数字信号处理的方法解决，但大部分只是停留在方法上的研究，而没有将高效率的算法应用于实际服务于生产。目前，国内生产的涡街流量计还限于应用模拟电路的方法对涡街信号进行处理（称为模拟涡街流量计），这样解决不了低信噪比条件下的问题，导致下限太高，量程比只能达到1：10，远低于理论量程1：100。国外也只有Yokogawa公司、Rosemount公司和ABB公司研发出了应用数字信号处理的方法处理涡街信号的涡街，即数字涡街流量计，但是具体的技术并不公开。近几年，关于涡街信号处理方法的研究很多（如小波变化法、自适应LMS算法等），由天津大学张涛教授主持研究的对涡街传感器输出信号进行数字信号处理方面的探索获得了很大的进展。凌箐硕士根据涡街信号的特点及其对信号处理方法的要求，借鉴最大似然谱估计方法的研究成果，在周期图法的基础上提出了更适用于涡街频率估计的松弛陷波周期图法，并进行了仿真实验。该方法兼有高频率分辨率和高计算效率的特点，有很强的抗复杂噪声干扰的能力。吴鹏硕士基于子波变换消噪原理，结合流量测量特定要求，提出了一种适用于涡街流量传感器信号处理的单支重构滤波方法，同时给出了滤波级数的选取方法，这种计数方法能够有效地扩大涡街流量传感器的量程下限