BentlyNevadaP/N140471-01此处不是利用MOSFET的转移特性，而是采用电压反馈的方式进行电流控制。在场效应管的漏极与源极间加上24V的电压(由系统的其它模块提供，限于篇幅不作说明)，与外部所接负载构成回路后，漏极电流便成为电流源的输出电流。设输出电流为I，则U8的引脚3引入的采样电压为10I，经过10倍放大后变为100I引入引脚6，由于5与6处的电压值相等，所以Vstand＝100I(Vstand的***大输出为2.5V，而I要求其输出范围为0～20mA,所以100倍的关系比较合适)，由于Vstand的分辨率＝V2‘‘分辨率＝0.002mV，理论上I的分辨率可以达到0.000002mA，完全可以满足预计的0.001mA分辨率要求(Vstand以0.1mV的步进改变即可)，于是高精度电流源得以实现。测试实验按照以上的高精度电压与电流的产生方法进行硬件设计，再加上键盘与液晶显示器等模块，利用单片机控制，便可构成一个简易的、可以提供高精度直流电压与电流的仪表(限于篇幅，其它模块与程序设计不作说明)。系统定标由于本系统是精密仪表设备。因此，必须采用定标消除系统误差。由于在本设计中MCU采用的是SST公司生产的89E58RC单片机。这种单片机为用户提供了强大的IAP(InApplicationProgram)功能，并有8KflashROM用于存储数据。通过IAP，系统可以提取校准数据，并将数据存储，在仪表输出电压/电流时就可以先提取相应的校准数据进行预处理。这样就保证了该系统的精度。测试试验定标后，采用安捷伦公司的3485A进行测试。表1与表2分别为测试的电压输出与电流输出的实验数据。结语综上分析可知,本文所提出的宽动态范围、高分辨率的高精度直流电压/电流源的设计方法是切实可行的，同时，此设计方法节约了成本。NORGRENK41EA00-KS6KV2*USED*HAYSSEN810A-0100-00AB*USED*ALLENBRADLEY1784-KTSERIESB*USED*SOLONPRESSURESWITCH2PSW1D2*USED*MILBANK12126-HC1*USED*BROOKSFLOWMETER110CM45CMDAA*NICE*HONEYWELLC645A1022PRESSURESWITCH*USED*GENERALELECTRIC5KSP51GL*USED*YAMATAKESL1-ELIMITSWITCH*NEWINABAG*FALK02466551050THUBRSB*NEWINABOX*SPIRAXSARCOVS-206STEAMTRAP3/4"*USED*FARADAY6114B-0-15-120-?60HORN*NEWINABOX*EMERSONFX-455POSITIONINGSERVODRIVE*USEDFESTODSNU-25-15-P-A*NEWOUTOFABOX*WEIDMULLEROSTEG7OPTOCOUPLER24VDC*USED*DANFOSSCI16*USED*GOSWITCH7D-43658-DCAPROXIMITYLIMITSWITCH*USED*MARKEM2050MARPRE-HEATER*USED*WILKERSONL01-02-M00LUBRICATOR1/4"*USED*LOTOF2GENERALELECTRICCOIL15D4G2115V*USED*MILLERFLUIDPOWERCYLINDERA72B2C(RUSTYASPICTURED)...LOTOF3RELIANCEELECTRIC45C60DUAL115VAC,2AOUTPUT...M&P,INC.OILFILTER,FILTERREGULATORL28W-2/CFR60...LOTOF7MERLINGERINC60N2A-TYPEB*USED*STATICORING6NN-Y3-N5-C1A*USED*MAGNETEKJA2N12N#311/25HP115VSHADEDPOLE*USED*ALLENBRADLEY20BD8P0A0AYNAND?0SERIESBPOWERFLEX700*...TRANSDUCERTECHNIQUESTM-2*NEWINBOX*DOMNICKHUNTER2858-5*USED*IFMIF0311*USED*KBELECTRONICSINC.KNMD-240D*USED*PARKERPA36RX21SOLENOIDCOIL53VDC*USED*CSID24170/450016CHANNELMULTIPLEXERBOARD*USED*NO***ON109729A*NEWINBOX*ESCORTMEMORYSYSTEMSCM42*NEWINBOX*BAILEYIMLM01*NEW****CSOLENOIDVALVEVG342-5DZ-04FA*NEWOUTOFBOX*BALLUFFBES516-3005-G-E5-C?-S49*NEWINFACTORYBAG*SPRECHER+SCHUH55-530282G002*USED*SENSUS143-80-2HPNATURALGASREGULATOR*USED*FIREYEE110FLAMEMONITORCHASSIS&COVER,120V*USED*...MARPOSS679200001P*NEWINBOX*SEALEDWILKERSONC18-04-FK00W0-122773CIRCUITBOARD*USED*LAMBDALND-Y-152*USED*GFCPOWERGH0F324-OVPPOWERSUPPLY*NICE*OMEGAPHOM-10ABNOPOWERSUPPLYCORD*USED*PILZPNOZX3SAFETYRELAY*USED*LOTOF12RITTALPS4584*NEWINABOX*PILZPNOZV30S3S1SZ/1?O*NICE*WATLOW93BA-1DD0-00RR*NEWINTHEBOX*ALLENBRADLEY1A11440VCOIL*USED*SWAGELOKSS-Q***-B-4PFK1*NEWINBAG*BELLOFRAM903078000*NEWINABOX*HOFFMAND-AH8001B*NEWINABOX*LENZEEVD533--E*NEWOUTOFABOX*MASTERPNEUMATICDETROITINC.CFR55-1L15(ASPICTURED)...GENERALELECTRICCOIL22D11G45A50V*USED*LOTOF2BALLASTRONIXINC.REPLACEMENTIGNITORKITBMS-...TURCKN120V-G30-ADZ30?X2-B1131*USED*LOTOF3ADVANCECONTROLTECHNOLOGYB40033AFD2B607*USE...***CCLAMPCYLINDERCK1T50-175Y2PN*USED*LOTOF4RELIANCEELECTRIC45***2DUALELECTRONICINPUT...ALLENBRADLEYLOGIX5550PROCESSORUNIT1756-L1SERIES...WEEDINSTRUMENTSSP451-PD.3-J-12?.0-A1.50-2006*USED*SOR6TA-EE5-N4-C2A-?CGRR*USED*NEWPORT400AS-4-A3-D2*USED*120/240VPARKER71315SN2KNJ1N0D?1P1C2*USED*LOTOF2MERLINGERINC60N-84TYPEB*USED*LOTOF2CUTLER-HAMMERWMS3D20415V*USED*MICROSWITCHFE-MLS2EA*NEWOUTOFBOX*MSD,INC.326XBX48PTIMEDELAYRELAY*USEDTELEMECANIQUEXCK-MWITHZCK-M1LIMITSWITCH*USED*FOXBORO763RNA-C763RNA-C-E300-0?-0-0-0-0-0-0-0*NEWIN...FINCOR10428461*USED*CROUSE-HINDSAR-331*USED*PARKERVALVE***-20BAMAC56C-13-501JC*USED*SEW-EURODRIVEFSKF321EPH04/13?/06*NICE*LOTOF2TRI-TRONICSBF-B-36*USED*UNISTATUSIS-120QC*USED*MERCOIDCONTROLDA-41-2-23E*USED*ALLENBRADLEY592-JOV16SERIESB*USED*ALEMITE7118-1*USED*SIGNET3-2720PREAMPLIFIER*USED*WESTINGHOUSEA201K4CA*USED*HONEYWELLC6045D10191*USED*MEASUREMENTTECHNOLOGYMTL221OB*USED*OVCVALVE2-CF8M*NICE*GESNUBBERCARDCF12014AAG01*USED*BAG*)