NTC热敏电阻分选仪介绍
NTC是负温度系数的英文缩写,所谓NTC热敏电阻分选仪就是负温度系数热敏电阻器。它是以锰、钴、镍和铜等金属氧化物为主要材料,采用陶瓷工艺制造而成的。这些金属氧化物材料都具有半导体性质,因为在导电方式上完全类似锗、硅等半导体材料。温度低时,这些氧化物材料的载流子(电子和孔穴)数目少,所以其电阻值较高;随着温度的升高,载流子数目增加,所以电阻值降低。利用这一特性,可将NTC热敏电阻通过测量其电阻值来确定相应的温度,从而达到检测和控制温度的目的。采用不同的制作工艺方法,结构,形状,可以获得各种各样的NTC热敏电阻,它们广泛应用于温度测量,温度补偿等领域。NTC在生产出来后,每个阻值随温度变化的特性并不一致,这就需要对NTC按照不同的阻值变化范围进行分选。本系统以PIC16F877A芯片作为下位机控制NTC分选过程,采用8位高速单片机C8051F022做为核心的上位机进行数据管理,串行EEPROM芯片来记录数据;并利用CH375芯片将记录数据安全而准确地转储到U盘上,可以方便的对数据进行存储和管理,并配以液晶显示屏,人机交互更友好。该仪表具有分选准确,运行稳定,操作简便,人机界面友好,管理方便的优点。
1.电阻分选仪下位机控制模块
PIC系列单片机是美国微芯推出的CMOS系列单片机,该系列芯片采用精简指令集(RISC),哈佛总线结构,2级流水线取指令方式,具有实用、低价、指令集小、简单易学、低功耗、高速度、体积小、功能强等特点,体现了单片机发展的一种新趋势。PIC16F877A是微芯公司采用14位RISC指令集的中级产品。该芯片内含A/D、内部EEPROM存储器、比较输出、捕捉输入、PWM输出、I2C和SPI接口、LCD驱动、FLASH程序存储器读写等功能,应用十分广泛。PIC16F877A首先通过I2C总线从模/数转换部分获取数据。这里采用了ADS1110芯片进行A/D转换。ADS1110是精密的连续自校准模/数(A/D)转换器带有差分输入和高达16位的分辨率封装为小型SOT23-6。片内2.048V的基准电压提供范围为±2.048V的输入差分电压。ADS1110使用可兼容的I2C串行接口在2.7V至5.5V的单电源下工作。ADS1110可每秒采样15、30、60或240次以进行转换。片内可编程的增益放大器(PGA)提供高达8倍的增益,并且允许以高分辨率对较小的信号进行测量。在单周期转换方式中ADS1110在一次转换之后自动掉电在空闲期间极大地减少了电流消耗。ADS1110的连接电路如图2所示。图中RX为待测电阻,R0为标准电阻,为了保证测量准确,其上所加的2伏电压是由10伏精密电压基准芯片REF102将输入24伏电压转换为10伏电压基准后,再经过电阻分压和电压跟随器隔离后产生的,电压十分的稳定。待测电阻RX两端的电压再经过一个电压跟随器隔离,如图3上OP07所示电路,以防止电路右边的阻抗对测量的影响,然后再经过一个一阶滤波后传输给了ADS1110,这样就排除了外界对检测的干扰,保证了待测电阻RX两端电压稳定,A/D转换的精度极高。[attach]52466[/attach]
3电阻分选仪系统组成及工作原理
本电阻分选仪系统功能由硬件和软件两大部分协调完成,电阻分选仪硬件部分主要完成各个传感器信号的采集、转换,电磁阀的动作,数据的存储及各种信息的显示;软件主要完成信号的处理和控制,数据的管理等功能。软件方面首先由PIC芯片的程序完成信号的转换和控制,同时在C8051F022芯片上移植入SmallRTOS嵌入式操作系统,使其运行的迅速性、实时性和稳定性更高,更好的进行数据的管理和存储。电阻分选仪整个系统的工作原理是首先将待测NTC浸泡在油中来保持其恒温,然后将其两端电压通过串行模/数转换器件ADS1110转换成数字信号后传送给PIC16F877A单片机,接着PIC16F877A将所得的数值与先测得的标准电阻的数值相比较后进行分档,再通过74LS595移位寄存器输出控制电磁阀的动作,从而将NTC正确的分选出来。同时PIC16F877A将分档值通过485通讯传输给C8051F022芯片。C8051F022将数据实时的显示在液晶屏,并把数据存入串行EEPROM芯片24AA512中,操作人员随时可以用U盘将数据拷走保存。C8051F022也可以将输入的一些参数,比如速度,分档值等,保存并传送给PIC16F877,来控制它的运转。
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NTCThermistorSorterdescription
NTCnegativetemperaturecoefficientoftheEnglishabbreviation,theso-calledNTCthermistorSorteristhenegativetemperaturecoefficientthermistor.Itisbasedonmanganese,cobalt,nickelandcopperandothermetaloxidesasthemainmaterial,madeofceramicmanufacturingprocess.Thesemetaloxidematerialshavesemiconductorproperties,becausethewaycompletelysimilartotheconductivegermanium,siliconandothersemiconductormaterials.Lowtemperature,theseoxidesmaterials,carriers(electronsandcavities)thenumberofsmall,soitsresistancevalueishigher;asthetemperatureincreases,thenumberofcarriersincreased,soresistancevaluedecreased.Advantageofthisfeature,NTCthermistorcanbemeasuredbyitsresistancevaluetodeterminetheappropriatetemperature,soastoachievethepurposeofdetectionandcontroloftemperature.Adifferentmethodofproductionprocesses,structure,shape,accesstoawiderangeofNTCthermistors,whicharewidelyusedintemperaturemeasurement,temperaturecompensationandotherfields.NTCcameoutintheproduction,eachchangeinthecharacteristicsofresistancewithtemperatureisnotuniform,whichneedtoNTCresistancechangesaccordingtodifferentscopeofsorting.ThesystemPIC16F877AchipasthenextpositioncontrolNTCseparationprocess,using8-bithigh-speedMCUC8051F022uppermachineasthecoredatamanagement,serialEEPROMchiptorecordthedata;anduseCH375chipwillrecorddatasecurityandaccuratetodumptotheUdisk,itcanbeconvenientfordatastorageandmanagement,andcoupledwithliquidcrystaldisplay,human-computerinteractionmorefriendly.Theinstrumenthasasortingaccuracy,stableoperation,easytooperateman-machineinterfaceisfriendly,easymanagementadvantages.
1.Resistorsorterunderpositioncontrolmodule
PICseriesofmicrocontrollersisintroducedintheUnitedStatesMicrochipCMOSMicrocontroller,thefamilyreducedinstructionsetchip(RISC),Harvardbusarchitecture,2-stagepipelinetotakeorders,withapractical,low-cost,instructionsetissmall,easytolearn,low-power,highspeed,smallsize,functionalityandotherproperties,reflectthedevelopmentofanewtrendmicrocontroller.PIC16F877AistheuseofMicrochips14-bitRISCinstructionsetoftheintermediateproducts.ThechipincludesA/D,theinternalEEPROMmemory,comparetheoutput,captureinput,PWMoutput,I2CandSPIinterfaces,LCDdriver,FLASHprogrammemoryreadandwriteandotherfunctions,iswidelyused.PIC16F877AfirstthroughtheI2CbusfromtheA/Dconversionpartoftheaccesstodata.ADS1110chipusedhere,A/Dconversion.ADS1110isaprecision,continuouslyself-calibratinganalog/digital(A/D)converterwithdifferentialinputsandupto16bitsofresolutionpackageforsmallSOT23-6.On-chip2.048Vreferencevoltagerangeof±2.048Vtoprovidetheinputdifferentialvoltage.ADS1110usingtheI2C-compatibleserialinterfaceat2.7Vto5.5Vsinglesupply.ADS1110canbe15,30,60or240samplespersecond,timestobeconverted.On-chipprogrammablegainamplifier(PGA)gainofuptoeighttimes,andallowshigh-resolutionmeasurementofsmallersignals.Inthesingle-cycleconversionmodesADS1110inaconvertedauto-powerdownduringidleperiods,aftergreatlyreducingcurrentconsumption.ADS1110connectioncircuitshowninFigure2.RXdiagramfortheDUTresistance,R0asastandardresistor,inordertoensuremeasurementaccuracy,onwhichtheincreaseof2voltsfrom10voltprecisionvoltagereferencechipREF102converttheinputvoltageof24Vto10Vvoltagereference,afterthat,throughtheresistordividerandvoltagefollowerarisingafterseparation,thevoltageisverystable.RXvoltageacrosstheresistorundertestandthenthroughavoltagefollowerisolation,asshowninFigure3ontheOP07circuitinordertopreventtherightoftheimpedanceofthecircuitmeasuringtheimpact,andthenfilteredthroughafirst-ordertransmittedtotheADS1110,sothatexcludetheinterferenceoftheoutsideworldtestingtoensurevoltagestabilityacrossRXresistorundertest,A/Dconversionprecision.
3Resistancesortersystemcompositionandworkingprinciple
Theresistorsortersystemfunctionconsistsofhardwareandsoftware,coordinatingthecompletionoftwoparts,resistorsorterhardware,someofthemajorindividualsensorsignalsthecompletionoftheacquisition,conversion,electromagneticvalvemovement,datastorageanddisplayallkindsofinformation;softwarekeythecompletionofsignalprocessingandcontrol,datamanagementandotherfunctions.Software,firstofallproceduresarecompletedbythePICchipsignalconversionandcontrol,whileC8051F022chipimplantedintoSmallRTOSembeddedoperatingsystemtorunasfast,real-timeandstabilityofhigherandbetterdataformanagementandstorage.ResistanceSorterworksbytheentiresystemundertestNTCfirstimmersedinoiltomaintainitstemperature,andthenbothendsofvoltagethroughaserialA/DconverterADS1110devicesconvertthedigitalsignaltransmittedtothePIC16F877AmicrocontrollerthenPIC16F877Avaluesobtainedforthefirstmeasuredwiththestandardresistancevaluescomparedwithafterthesub-file,andthenthroughthe74LS595shiftregisteroutputcontrolsolenoidvalveaction,thussortingoutthecorrectNTC.AtthesametimethevalueofPIC16F877Afilewillbetransmittedthroughthe485communicationstotheC8051F022chip.C8051F022datainrealtimedisplayedontheLCDscreen,andthedataintotheserialEEPROMchip,24AA512,theoperatorcanreadilyuseUdisktocopythedatastoredaway.C8051F022canalsoenteranumberofparameters,suchasspeed,sub-filevalue,etc.,saveandsendtothePIC16F877,tocontrolitsoperation.Formorepleaselogonistoinstrumentnetwork010-63745117/63746117