Controlling measurement instruments via GPIB 通过GPIB控制仪器.docx

Controlling measurement instruments via GPIB 通过GPIB控制仪器.docx

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ControllingmeasurementinstrumentsviaGPIB通过GPIB控制仪器

ControllingmeasurementinstrumentsviaGPIB

IntroductiontoGPIB

GPIB（GeneralPurposeInterfaceBus）isaninterfacestandardforconnectingcomputersandperipherals,whichsupportsthefollowinginternationalstandards:

IEEE488.1,IEC-625,IEEE488.2,andJIS-C1901.TheGPIBinterfaceallowsyoutocontrolvariousinstrumentsfromanexternalcomputer.ThecomputersendscommandsandinstructionstotheinstrumentsandreceivesdatasentfromtheinstrumentsviaGPIB.

Beforesettinguptheinstrumentforremotecommunicationsusingtheelectronic（physical）GPIBinterface,youshouldfamiliarizeyourselfwiththefollowingGPIBrequirements:

▪Auniquedeviceaddressmustbeassignedtoeachdeviceonthebus.

▪Notwodevicescansharethesamedeviceaddress.

▪Nomorethan15devicescanbeconnectedtoanyoneline.

▪Onedeviceshouldbeconnectedforevery6feet（2meters）ofcableused.

▪Nomorethan65feet（20meters）ofcableshouldbeusedtoconnectdevicestoabus.

▪Atleasttwo-thirdsofthedevicesonthenetworkshouldbepoweredonwhileusingthenetwork.

▪Connectthedevicesonthenetworkinastarorlinearconfiguration.Donotuselooporparallelconfigurations.

ThefollowingfigureillustratesatypicalGPIBinterfacesystem.

Figure1:

atypicalGPIBinterfacesystem

Ifnecessary,theGPIBconnectorscanbestackedasshowninthefollowingfigure:

Figure2:

stackofGPIBconnectors

IntroductiontoSCPI

SCPI（StandardCommandsforProgrammableInstruments）isaprogramminglanguageforcontrollinginstrumentfunctionsovertheGPIB（GeneralPurposeInterfaceBus,IEEE488）instrumentbus.SCPIisintendedtofunctionwithstandardGPIBhardwareandconformstotheIEEEStandardDigitalInterfaceforProgrammableInstrumentation.SCPIislayeredontopofthehardwareportionofIEEE488.2.

ThesameSCPIcommandsandparameterscontrolthesamefunctionsindifferentclassesofinstruments.Foreachinstrumentfunction,SCPIdefinesaspecificcommandset.TheadvantageofSCPIisthatprogramminganinstrumentisonlyfunctiondependentandnolongerinstrumentdependent.Severaldifferenttypesofinstruments,forexampleanoscilloscope,acounterandamultimeter,cancarryoutthesamefunction,suchasfrequencymeasurement.IftheseinstrumentsareSCPIcompatible,youcanusethesamecommandstomeasurethefrequencyonallthreeinstruments,althoughtheremaybedifferencesinaccuracy,resolution,speed,etc.

FunctionalityofaSCPIinstrument

ThefunctionsinsideaninstrumentthatcontroltheoperationprovideSCPIcompatibility.

Figure3showsasimplifiedlogicalmodelofthemessageflowinsideaSCPIinstrument.

WhenthecontrollersendsamessagetoaSCPIinstrument,roughlythefollowinghappens:

–TheGPIBcontrolleraddressestheinstrumentaslistener.

–TheGPIBinterfacefunctionplacesthemessageintheInputBuffer.

–TheParserfetchesthemessagefromtheInputBuffer,parses（decodes）themessage,andchecksforthecorrectsyntax.Theinstrumentreportsincorrectsyntaxbysendingcommanderrorsviathestatussystemtothecontroller.Moreover,theparserwilldetectifthecontrollerrequiresaresponse.Thisisthecasewhentheinputmessageisaquery（commandwitha“?

”appended）.

TheParserwilltransfertheexecutablemessagestotheExecutionControlblockintokenform（internalcodes）.TheExecutionControlblockwillgathertheinformationrequiredforadeviceactionandwillinitiatetherequestedtaskattheappropriatetime.TheinstrumentreportsexecutionerrorsviathestatussystemovertheGPIBandplacesthemintheErrorQueue.

–Whenthecontrolleraddressestheinstrumentastalker,theinstrumenttakesdatafromtheOutputQueueandsendsitovertheGPIBtothecontroller.

SCPIcommandsaresentasASCIIoutputstringswithintheprogramminglanguagestatements,theSCPIsyntaxisindependentofbothprogramminglanguageandinterface.

Figure3:

OverviewofthefirmwareinaSCPIinstrument

TypesofSCPICommands

SCPIhastwotypesofcommands,commonandsubsystem.

CommonCommands

Commoncommandsgenerallyarenotrelatedtospecificoperationbuttocontrollingoverallinstrumentfunctions,suchasreset,status,andsynchronization.Allcommoncommandsconsistofathree-lettermnemonicprecededbyanasterisk:

*RST*IDN?

*SRE8

Figure4:

CommonCommandsSyntaxDiagram

*Fordetails,referto“Agilent_DSA90604A_Infiniiumoscilloscope_programmingguide.pdf”,page26-33

SubsystemCommands

Subsystemcommandsperformspecificinstrumentfunctions.

SCPIisanASCII-basedinstrumentcommandlanguagedesignedfortestandmeasurementinstruments.SCPIcommandsarebasedonahierarchicalstructure,alsoknownasatreesystem.Inthissystem,associatedcommandsaregroupedtogetherunderacommonnodeorroot,thusformingsubsystems.Subsystemcommandsperformspecificpowersupplyfunctions.AportionoftheSOURcesubsystemisshownbelowtoillustratethetreesystem.

SOURceistherootkeywordofthecommand,CURRentisasecond-levelkeyword,LEVelandPROTectionarethird-levelkeywords,andIMMediate,TRIGgeredandSTATearefourth-levelkeywords.Colons（:

）separatehigher-levelfromlower-levelkeywords.

Figure5isatreediagramofthesubsystemcommandsforDCpowersupply6674A.Commandsfollowedbyaquestionmark（?

）takeonlythequeryform.Exceptasnotedinthesyntaxdescriptions,allothercommandstakeboththecommandandqueryform.Thecommandsarelistedinalphabeticalorderandthecommandswithineachsubsystemaregroupedalphabeticallyunderthesubsystem.

Figure5:

SubsystemCommandsTreeDiagram

StructureofaSCPIMessage

SCPImessagesconsistofoneormoremessageunitsendinginamessageterminator.Theterminatorisnotpartofthesyntax,butimplicitinthewayyourprogramminglanguageindicatestheendofaline（suchasanewlineorend-of-linecharacter）.

TheMessageUnit

ThesimplestSCPIcommandisasinglemessageunitconsistingofacommandheader（orkeyword）followedbyamessageterminator.

ABOR

VOLT?

Themessageunitmayincludeaparameteraftertheheader.Theparameterusuallyisnumeric,butitcanbeastring:

VOLT20

VOLTMAX

CombiningMessageUnits

Thefollowingcommandmessage（seeFigure6）isbrieflydescribedhere,withmoredetailsinsubsequentparagraphs.

VOLT:

LEV4.5;PROT4.8;:

CURR?

Figure6:

CommandMessageStructure

ThebasicpartsofthemessageinFigure6are:

MessageComponentExample

HeadersVOLTLEVPROTCURR

HeaderSeparatorThecoloninVOLT:

LEV

Data4.54.8

DataSeparatorThespaceinVOLT4.5andPROT4.8

MessageUnitsVOLT:

LEV4.5PROT4.8CURR?

MessageUnitSeparatorThesemicolonsinVOLT:

LEV4.5;andPROT4.8;

RootSpecifierThecoloninPROT4.8;:

CURR?

QueryIndicatorThequestionmarkinCURR?

MessageTerminatorThe（newline）indicator.Terminatorsarenot

partoftheSCPIsyntax.

GPIBsettingandSCPIcommandsforinstruments

GPIBAddressSettingforinstruments

FortheGPIBinterface,messagesareplacedonthebususinganoutputcommandandpassingthedeviceaddress,programmessage,andaterminator.PassingthedeviceaddressensuresthattheprogrammessageissenttothecorrectGPIBinterfaceandGPIBdevice.

ProcessforsettingGPIBaddressforinstrumentsis:

Oscilloscope

−TectronixDSA73304D

oThedefaultsettingsfortheGPIBconfigurationare:

GPIBAddress1.

oTochangeeitheroftheGPIBsettings,dothefollowing:

SelectGPIBConfigurationfromtheUtilitiesmenuonfrontpanel.

−AgilentDSA90604A

oDeviceAddress=（InterfaceSelectCode*100）+OscilloscopeAddress

oEachinterfacecardhasauniqueinterfaceselectcode.Thiscodeisusedbythecomputertodirectcommandsandcommunicationstotheproperinterface.Thedefaultistypically"7"fortheGPIBinterfacecards

oEachoscilloscopeontheGPIBmusthaveauniqueoscilloscopeaddressbetweendecimal0and30.Thisoscilloscopeaddressisusedbythecomputertodirectcommandsandcommunicationstotheproperoscilloscopeonaninterface.Thedefaultistypically"7"forthisoscilloscope.YoucanchangetheoscilloscopeaddressintheUtilities,RemoteInterfacedialogbox.

oDoNotUseAddress21foranOscilloscopeAddress,Address21isusuallyreservedfortheComputerinterfaceTalk/Listenaddress,andshouldnotbeusedasanoscilloscopeaddress.

Signalsourceanalyzer

−AgilentE5052B

oPressSystem>MiscSetup>GPIBSetup>Talker/ListenerAddress.

oEntertheaddressusingtheENTRYblockkeysonthefrontpanel.

DCpowersupply

−AgilentN5745A

oThepowersupplyisshippedwithitsGPIBaddresssetto5.UsethefrontpanelmenuifyouneedtochangetheGPIBaddress.

aPressandholdtheOCP/488buttonforaboutthreeseconds.TheDCVOLTSdisplaywillshowthepresentGPIBaddress.

bTochangetheGPIBaddress,turnthevoltageknobuntilthedesiredGPIBaddressappearsinthedisplay.ValidGPIBaddressesareintherangeof0to30.

−HPAgilent6674A（HPIB）

oThepowersupplyaddresscannotbesetremotely;itmustbesetfromthefrontpanel.Oncetheaddressisset,youcanassignitinsideprograms.

oUsetheADDRESSkeyandnumericalkeypadforenteringaddresses.Thepowersupplyisshippedwitha5stand-aloneaddressasthedefault.Thegeneralprocedureforsettinganaddressis:

Frequencycalibrator/analyzer

−PendulumCNT-91R

oTheaddressofthecounterissetto10whenitisdelivered

oSetGPIBAddressviathefrontpanelUSEROPTmenu

onumberbetween0and30

Warmbox

−VotschWEISSTECHNIKC7-600

oNOTAVEAIIBLE!

!

oUseGPIB-RS232converter（forexampleFT7130GPIB-RS232）

SCPICommandsforinstruments

Osc