High-PerformanceFrequency Counter/CalibratorsCNT-85 & CNT-85RUsers ManualII4031 600 85001Third Edition (March 2003)No part of this manual may be copied without the express permission of the copyright owner.All product names are trademarks of their respective companies. 2003 Pendulum Instruments ABAll rights reserved. Printed in Sweden.Contents1 PrefaceIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . 1-2Design Innovations . . . . . . . . . . . . . . . . . . . 1-2New fast SCPI Bus . . . . . . . . . . . . . . . . . . . 1-4Rubidium Counter. . . . . . . . . . . . . . . . . . . . 1-42 Safety InstructionsIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . 2-2Safety Precautions. . . . . . . . . . . . . . . . . . . 2-23 Preparation for UseUnpacking. . . . . . . . . . . . . . . . . . . . . . . . . . 3-2Installation. . . . . . . . . . . . . . . . . . . . . . . . . . 3-24 Using the ControlsAbout This Chapter . . . . . . . . . . . . . . . . . . . 4-2The User Interface. . . . . . . . . . . . . . . . . . . 4-2Default Settings . . . . . . . . . . . . . . . . . . . . . 4-3Basic Controls. . . . . . . . . . . . . . . . . . . . . . . 4-4Input A Controls. . . . . . . . . . . . . . . . . . . . . 4-5Measurement Control Keys . . . . . . . . . . . . 4-6Display Controls. . . . . . . . . . . . . . . . . . . . . 4-7Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8Display. . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9Rear Panel . . . . . . . . . . . . . . . . . . . . . . . .4-10Rear Panel . . . . . . . . . . . . . . . . . . . . . . . .4-11CNT-85R Front Panel . . . . . . . . . . . . . . . . 4-125 Input Signal ConditioningIntroduction to This Chapter . . . . . . . . . . . . 5-2Input A. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2Input C. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6Reducing Noise and Interference . . . . . . . . 5-66 Measuring FunctionsIntroduction to This Chapter . . . . . . . . . . . . 6-2Selecting Function . . . . . . . . . . . . . . . . . . . 6-2Frequency . . . . . . . . . . . . . . . . . . . . . 6-3Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 6-3Burst Frequency and PRF. . . . . . . . . . . . .6-6AM Signals. . . . . . . . . . . . . . . . . . . . . . . .6-10Period . . . . . . . . . . . . . . . . . . . . . . . 6-12Introduction. . . . . . . . . . . . . . . . . . . . . . . .6-12Pulse Width and Duty Factor. . . . . 6-13Introduction . . . . . . . . . . . . . . . . . . . . . . . 6-13Pulse Width A . . . . . . . . . . . . . . . . . . . . . .6-14Duty Factor . . . . . . . . . . . . . . . . . . . . . . . .6-14Totalize. . . . . . . . . . . . . . . . . . . . . . 6-15TOTalize A. . . . . . . . . . . . . . . . . . . . . . . .6-157 Measurement ControlAbout This Chapter . . . . . . . . . . . . . . . . . . . 7-2Measuring Time. . . . . . . . . . . . . . . . . . . . . 7-2Display Hold . . . . . . . . . . . . . . . . . . . . . . . .7-3Arming . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3Digit Blanking. . . . . . . . . . . . . . . . . . . . . . . 7-5Controlling Measurement Timing . . 7-6Arming Setup Time . . . . . . . . . . . . . . . . . . 7-12Arming Examples . . . . . . . . . . . . . 7-13Example #1:. . . . . . . . . . . . . . . . . . . . . . . 7-13Example #2. . . . . . . . . . . . . . . . . . . . . . . .7-16Example #3. . . . . . . . . . . . . . . . . . . . . . . .7-178 ProcessingIntroduction. . . . . . . . . . . . . . . . . . . . . . . . . 8-2Averaging . . . . . . . . . . . . . . . . . . . . . . . . . .8-2Nulling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-29 Auxiliary FunctionsIIIAbout This Chapter. . . . . . . . . . . . . . . . . . .9-2Auxiliary Menu. . . . . . . . . . . . . . . . . . . . . .9-210Performance CheckGeneral Information. . . . . . . . . . . . . . . . .10-2Recommended Test Equipment . . . . . . . .10-2Front Panel Controls. . . . . . . . . . . . . . . . .10-3Short Form Specification Test . . . . . . . . . 10-5Rear Input/Output . . . . . . . . . . . . . . . . . . .10-6Measuring Functions. . . . . . . . . . . . . . . . 10-7Option 10. . . . . . . . . . . . . . . . . . . . . . . . . 10-811 Preventive MaintenanceCalibration and Adjustment. . . . . . . . . . . . 11-2Other Maintenance. . . . . . . . . . . . . . . . . . 11-312SpecificationsMeasuring Functions. . . . . . . . . . . . . . . . 12-2Input and Output Specifications. . . . . . . .12-3Auxiliary Functions. . . . . . . . . . . . . . . . . . .12-4GPIB (Option 80) . . . . . . . . . . . . . . . . . . .12-5Measurement Uncertainties. . . . . . . . . . . 12-7Timebase Options. . . . . . . . . . . . . . . . . . .12-8General Specifications. . . . . . . . . . . . . . .12-9Ordering Information. . . . . . . . . . . . . . . . 12-1013AppendixAppendix 1, Error Messages . . . . . . . . . .13-214Index15ServiceSales and Service office. . . . . . . . . . . . . . 15-IIGUARANTEE STATEMENT. . . . . . . . . . 15-IIIIVVDECLARATION OF CONFORMITYforPendulumFrequency Counters CNT-85 & CNT-85RPendulum Instruments ABKarlsbodavgen 39, Box 20020SE-161 02 BrommaSwedenStatement of ConformityBased on test results using appropriate standards,the product is in conformity withElectromagnetic Compatibility Directive 89/336/EECLow Voltage Directive 73/23/EECSample testsStandards used:EN 61010-1 (1997)Safety Requirementsfor Electrical Equipment for Measurement, Control, and Laboratory UseEN 61326/A1 (1998)EMC Requirements for Electrical Equipment for Measurement, Control, and Laboratory UseThe tests have been performed in atypical configuration.This Conformity is indicated by the symbol ,i.e. Conformit Europenne.Thispageisintentionallyleftblank.VIChapter 1PrefaceIntroductionYour CNT-85 Counter is designed to bring youanewdimensiontoportableandbench-topcounting.Itofferssignificantlyincreasedper-formance compared to traditional counters. TheCounter offers the following advantages:Tendigitsoffrequencyresolutionpersec-ondand250psresolution,asaresultofhigh-resolutioninterpolatingreciprocalcountingA 3.0GHzinputfrequencyoptionA foolproofautotriggerfunctionNew powerful and versatilefunctionsTheuniqueversatileautosensitivityandautowaveformcompensationtakescareofalltrig-gering from 50 Hz and up. It even optimizes it-self to the requirements of different measuringfunctions.Anotheruniquefeatureinyourinstrumentisthebar-graphlevel monitor. It alwaysshowsyou the input signal level on a dBscale to verifyproper signal strength.TheburstfrequencyandPRFfunctionsmea-sure bursts and AM signals without any exter-nal synchronization signal.Tosolveeventoughertasks, thecounterhascompletearmingpossibilitieswhichletsyousynchronize measurements with externalevents.Youcanevendelaythearmingofthecounter(comparetodelayedtimebasetrigger-ing in an oscilloscope). Read more aboutArming in Chapter 7, Measurement Control.No mistakesYouwillsoonfindthatyournewCounterisadelight tooperate. Oneexampleisthebacklight LCDthat shows you measurement results,setting status, and operator messages. TheAUTOfunctiontriggersautomaticallyonanyinputwaveform.Abus-learnmodesimplifiesGPIBprogramming. With bus-learn mode,manualcountersettingscanbetransferredtothe controller for later reprogramming. There isno need to learn code and syntax for each indi-vidualcountersettingifyouareanoccasionalbus user.Design InnovationsState of the art technologygives durable useThis counter and the other models in theCNT-8Xfamilyaredesignedforqualityanddurability. The design is highly integrated. Thedigital countingcircuitryconsists of a cus-tom-designed VLSI-ASIC and a 16-bitmicrocontroller.Thehighintegrationandlowcomponentcountreducespowerconsumptionand results in an MTBF of 30,000 hours. Mod-ernproductionsurface-mounttechnologyen-sures high production quality and a rugged me-chanical construction including a metal cabinetthat withstands mechanical shocks and protectsagainst EMI.High resolutionThe use of reciprocal interpolating counting inthisnew counterresultsinexcellentrelativeresolution:10digitsinonesecondforallfre-quencies, see Figure 1-1.The measurement is synchronized with the in-put cycles insteadof thetimebase. Simulta-neously with the normal digital counting, thecounter makes analog measurements of thetimebetweenthestart/stoptriggereventsandthe next following clock pulse. This is done inPreface1-2 IntroductionPrefacetwo identical circuits by charging an integratingcapacitor with a constant current, starting at thetrigger event. Charging is stopped at the leadingedgeof thefirst followingclockpulse. Thestored charge in the integrating capacitor repre-sents the time difference between the start trig-gereventandtheleadingedgeofthefirstfol-lowing clock pulse.Whenthedigitalpartofthemeasurementisready, the stored charges in both capacitors aremeasured. The capacitors are discharged with aconstantcurrent,whichisonly1/400:thofthechargingcurrent, whichmeans that thedis-charge time will be 400 times the charging time.This400-foldstretchedtimeisdigitallymea-sured by the counter itself, with adequate reso-lution.The counters microcomputer calculates the re-sult after completing all measurements, i.e., thedigital time measurement and the two interpo-lation measurements.Theresultisthatthebasicdigitalresolutionof 1 clock pulse (100 ns) is reduced to 0.25%of a clock pulse cycle, or 250 ps.Since the measurementis synchronized with theinputsignal,theresolu-tionforfrequencymea-surements is veryhighand is independent offrequency.The Counter has 10 display digits to ensure thatthe display does not restrict the display resolu-tion.Italsohasanoverflowfunctionthatletsyou see digit 11 and 12.DesignInnovations1-371 0981 k 1 0k 1 00k 1 M 1 0M 1 00MFrequency(Hz)Measureti me=1 sMeasureti me=1 0msMeasureti me=1 msMeasureti me=1 00ms#of di gi tsFig.1-1 Resolutionofthecounter.New fast SCPI BusThe counter is not only an extremely powerfuland versatile bench-top instrument, it also fea-turesextraordinaryIEEE-488busproperties.To ensure compatibility now and in the future,the Counter incorporates the latest IEEE-488.2busstandardandtheinternationallystandard-ized SCPI Command set (Standard Commandsfor Programmable Instruments). The bus trans-ferrateoftheCounterisupto100measure-mentspersecondovertheIEEE-488bus,and1,600 measurements per second to internalmemory. This very high measurement ratemakes new type of measurements possible. Forexample, youcanperformjitteranalysisonseveral thousands of pulse width measurementsand capture them in seconds. Together with theIEEE-488 interfaces you get an extensive pro-grammingmanual that helpsyouunderstandSCPI and programming of the counter.YougetananalogrecorderoutputasstandardwithallIEEE-488interfaces.Thisoutputpro-vides an analog signal proportional to the valueof anythreeconsecutivedisplaydigits. Theoutputcanbeusedforrecordingsofmeasure-ments on a strip-chart recorder or as a feedbacksignal to an analog control system.The counter is easy to use in IEEE-488 bus en-vironments. Abuilt-in bus-learn mode makes itpossible to set all counter settings manually andtotransferthecompletecountersettingtothecontroller. The response can later be used to re-program the counter to the same settings. Thiseliminatestheneedfortheoccasionalusertolearn all individual programming codes. Com-plete (manually set) counter settings can also bestored in 20 internal memory locations and caneasilyberecalledatalateroccasion.Anotheruser-friendlyfeatureismacro-programming.Youcandefineyourownmnemonicsandde-fine group settings for complex measurements,then reduce them to one macro command.Rubidium CounterThe CNT-85R contains an atomic reso-nance-controlled timebase (Rubidium) thatgivesanewmeaningto10-12digitmeasure-ments.Quicktooperation,thewarm-uptimefortherubidiumcounter is only4-6minutes, com-pared to 10 minutes for an oven-enclosedtimebase.The counter uses a larger cabinet due to the sizeand power requirements of the Rubidiumtimebase.1-4 NewfastSCPIBusPrefaceChapter 2SafetyInstructionsIntroductionRead this page carefully before you install anduse the instrument.ThisinstrumenthasbeendesignedandtestedaccordingtosafetyClass 1requirements ofEN61010-1 and CSA 22.2 No.1010.1, and hasbeensuppliedinasafecondition.Theuserofthisinstrumentmusthavetherequiredknowl-edgeofit. Thisknowledgecanbegainedbythoroughly studying this manual.This instrument is designed to be used bytrained personnel only. Removing the cover forrepair,maintenance,andadjustmentofthein-strumentmustbedonebyqualifiedpersonnelwho are aware of the hazards involved.Safety PrecautionsTo ensure the correct and safe operation of thisinstrument, it is essential that you followgener-allyacceptedsafetyproceduresinadditiontothe safety precautions specified in this manual.Caution and warningstatementsCAUTION:Showswhereincorrectprocedurescancausedamageto,ordestructionofequipmentorotherproperty.WARNING:Showsapotentialdangerthatrequirescorrectproceduresorpracticestopreventpersonalinjury.SymbolsShows where the protective ground ter-minal is connected inside the instrument. Neverremove or loosen this screw.Indicates that the operator should con-sult the manual.Onesuchsymbolisprintedontheinstrument,below the Ainput. It points out that the damagelevel for the input voltage decreases from350Vp to12Vrms whenyouswitchtheinputimpedance from 1 MWto 50 W.Safety Instructions2-2 IntroductionZZZ...SAFETYFig.2-1 Donotoverlookthesafetyinstructions!If in doubt about safetyWheneveryoususpectthatitisunsafetousethe instrument, you must make it inoperative bydoing the following:DisconnectingthelinecordClearlymarkingtheinstrumenttopreventitsfurtheroperationInformingyourPendulumrepresentative.For example, the instrument is likely to be un-safe if it is visibly damaged.Safety InstructionsSafetyPrecautions 2-3ThispageisintentionallyleftblankSafety Instructions2-4 SafetyPrecautionsChapter 3PreparationforUsePreparation for UseUnpackingCheck that the shipment is complete and that nodamagehasoccurredduringtransportation.Ifthecontentsareincompleteordamaged,fileaclaim with the carrier immediately. Also notifyyour local Pendulum sales or service organiza-tionincaserepairorreplacementmaybere-quired.Check listThe shipment should contain the following:TheCNT-85CounterLinecordThisOperatorsManualOptionsyouorderedshouldbeinstalled.SeeIdentification.ProgrammingManual(whenGPIBoptionisinstalled).N-to-BNCAdapter,(onlywithprescaler,option10)IdentificationCheckmarksontherearpanelshowwhatop-tions are installed in your counter, seeFigure 3-2.InstallationSupply voltagen SettingThe Counter may be connected to any AC sup-ply with a voltage rating of 90 to 265 Vrms, 45to 440 Hz. The counter automatically adjusts it-self to the input line voltage.n FuseAn 1.6A/250V slow blow fuse is placed insidethe counter. This fuse rating is used for the fullvoltage range.CAUTION:Ifthisfuseisblown,itislikelythatthepowersupplyisbadlydamaged.Do notreplacethefuse.SendthecountertothelocalServiceCenter.GroundingGroundingfaults in the line voltage supply willmake any instrument connected to it dangerous.Beforeconnectinganyunittothepowerline,you must make sure that the protective groundfunctions correctly. Only then can a unit be con-nectedtothepowerlineandonlybyusingathree-wire line cord. No other method ofgroundingispermitted.Extensioncordsmustalways have a protective ground conductor.CAUTION:Ifaunitismovedfromacoldtoawarmenvironment,condensationmaycauseashockhazard.Ensure,therefore,thatthegroundingrequire-mentsarestrictlymet.3-2 UnpackingFig.3-1 1.6AT5x20mmfusePreparation for UseWARNING:Neverinterruptthegroundingcord.Anyinterruptionoftheprotectivegroundconnec-tioninsideoroutsidetheinstrumentordisconnectionoftheprotectivegroundterminalislikelytomaketheinstrumentdanger-ous.Orientation andcoolingThe counter can be operated in any position de-sired.Makesurethattheairflowthroughtheventilation slots at the top, and side panels is notobstructed.Leave5centimeters(2inches)ofspace around the counter.Fold-down supportFor bench top use, a fold-down support is avail-ableforuseunderneaththecounter.Thissup-port can also be used as a handle to carry the in-strument.Rack-mount adapter(CNT-85R only)Ifyouhaveordereda19-inchrack-mountkitfor your instrument, it has to be assembled afterdelivery of the instrument. The rack-mount kitconsists of the following:2brackets,(short,left;long,right)4screws,M5x84screws,M6x8Installation3-3Fig 3-3 Fold-downsupportforcom-fortablebench-topuse.! !!!!OFFONMade in SwedenG D E16 8421RL1, DC1, DT1, E2SH1, AH1, T5, L4, SR1,IEEE 488/IEC 625 INTERFACEADDRESS90V-265V1.6 ATPRIMARY FUSE INSIDEANALOG OUT10MHz OUT REF IN EXT ARMOPTION 10OPTION 30OPTION 40OPTION 80OPTION __OPTION __OPTION __OPTION __ALL INPUTS MAX 12VRMSUNLESS OTHERWISE SPECIFIEDINCLUDED OPTIONSLR 39484Fig.3-2 Checkmarksonrearpanel showingoptionsincluded.WARNING:Whenyouremovethecoveryouwillexposelivepartsandaccessibleterminalswhichcancausedeath.WARNING:Capacitorsinsidethein-strumentcanholdtheirchargeeveniftheinstrumenthasbeenseparatedfromallvoltagesources.n Assemblingtherack-mountkitMake sure the power cord is disconnected fromthe instrument.Turn the instrument upside down.Loosenthetwoscrews(A)attherearfeet.Gripthefrontpanelandgentlypushattherear.Pulltheinstrumentoutofthecover.Removethefourfeetfromthecover.Use a screwdriver as shown in the following il-lustrationor a pair of pliers toremove thespringsholdingeachfoot, thenpushout thefeet.Removethetwoplasticlidsthatcoverthescrewholesontherightandleftsideofthefrontpanel.Pushtheinstrumentbackintothecover.TurnitupsidedownInstallthetworearfeetwiththescrews(A)totherearpanel.Fastenthebracketsattheleftandrightsidewiththescrewsincludedasillustratedbelow.FastentheCNT-85Rintherackviascrewsinthefourrack-mountingholesn Reversingtherack-mountkitTheinstrument mayalsobemountedtotheright in the rack. To do so, first remove the plateonthelongbracketandfastenitontheshortone, then perform the preceding steps.Preparation for Use3-4 InstallationAAChapter 4UsingtheControlsUsing the ControlsAbout This ChapterThischaptergivesyouaquickintroductiontoall the controls of the counter, the design of theuser interface, and front panel text. For the oc-casional user, the information in this chapter isoftensufficienttosolveameasurementprob-lem.The User InterfaceKeysMostkeysaresimpletogglekeysthatturnonand off the function printed above the key. Mostofthekeyshaveanon/offannunciatorinthedisplay directly over the key. This annunciatoris on when the function is active.Auxiliary menu selectionFunctions which are not so frequently used aregathered together in the AUXMENU. To selectfrom this menu:PressAUXMENUandscrollthroughthefunctionswiththeFUNCTIONkey.PressENTERwhenthefunctionyouarelookingforisdisplayed.Nownewselec-tionsappear.PressDATA ENTRY keysorFUNCTIONtoselect.PressENTERtoconfirmtheselection.Changing numerical valuesYou must enter numerical values when you setthe following:Measuringtime.Armingdelay.Referencevaluesfornulling.Time-out.Scalingfactorfortheanalogoutput(whenGPIBoptionisinstalled).Thecounterhasnonumericalkeypad,soyoumust use the following keys:n CoarseadjustmentPressDATAENTRY p orFUNCTIONtoincrease,andDATA ENTRY q orFUNCTIONtode-creaseavaluein1-2-5steps.n FineadjustmentPressSENS andtheparametertobesetexpandsovertheentiredisplay.A cursorflashestotheleftoftheMSDdigit.Movethiscursortothedigityouwanttochange.Usingthe SENSkeys.ChangethevalueoftheselecteddigitbypressingtheDATA ENTRY keys.Thesign(+or)ischangedwhenthecur-sorflashestotheleftoftheMSD(onlyminusisindicated).Move the cursor to the next digit and repeat theabove procedure until the display shows the de-sired value. Then press ENTERto confirm theselection.4-2 AboutThisChapterUsing the ControlsDefault SettingsPARAMETER VALUE/SETTINGInputA:Sensitivity AUTOTriggerlevel AUTOImpedance 1MWTriggerslope PosFilter OFFArming:Start OFFStartDelay OFFStop OFFMiscellaneous:Function FREQANull/offset OFFTimeout OFFMeasuringtime 0.2sCheck OFFSinglecycle OFFAnalogoutputcontrol OFFAuxiliaryfunctions AllswitchedOFFBlankLSD OFFDefaultSettings 4-3Table 4-1 Settingsdirectlyafterthecounterhasbeenswitchedon,orthecounterhasbeenPRESET.Using the ControlsBasic Controls4-4 BasicControlsFREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER Up and running in no time!TurnonthecounterbypressingtheONkey.Connectasignaltotheinput.SelectfunctionwiththeFUNC-TIONkey.Nowthecounterautomaticallymea-sures with optimum input settings.STAND-BY LEDLit when the counteris off, but power isavailable to an ovenoscillator.STANDBY/ONPress ON and the counter turns on and re-turns to its default (standard) setting. Ifyou want to recall the settings you usedbefore you turned off the counter, pressAUX MENU, then press ENTER twice.Press STAND-BYto turn off the counter.FUNCTIONSelects measuring functionLOCAL/PRESETThe instrumentwill ask De-fault? If youpressENTERthe counterwill return topreset (default)settings (seepage 4-3).If in Remotemode: thecounterswitches to lo-cal operation.INPUT AThis input is used for allmeasuring functions exceptfrequency C and Ratio C/A.It measures signals with fre-quencies between 10 Hz and300 MHz and levels between30 mVpp and 70 Vpp.INPUT CThis input is used for highfrequency measurements.The frequency range isprinted above the connec-tor. This is an option and ifno connector is installedyou do not have this func-tion. The C input is fullyautomatic and no controlsaffect its performance.Using the ControlsInput A ControlsInputAControls4-5FREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER SENSITIVITYIncreases or decreases thesensitivity of the counterwhen the AUTO function isswitched off. The set sensitiv-ity is shown on the bar graphdisplay.If you turn off AUTO bypressing the SENS keys, theselections made by AUTO re-main as fixed settings.WAVEFORMOffsets the trigger level,when the AUTO functionis switched off, for sig-nals with:very low duty cyclenormal duty cyclevery high duty cycleSLOPEThe trigger slope can be set in theAUX MENU; see chapter 9,Auxiliary functions.This selection is intended for neg-ative pulse width and negativeduty factor measurements.The negative slope of the wave-form indicator flashes when thecounter triggers on negativeslopes.AUTOThis key switches on the auto sensi-tivity and auto waveform compensa-tion.AUTO selects 33 % of Vpp as sensi-tivity for input A, and it adjusts tothe waveform more accurately thanthe three choices available via man-ual setting.Both the waveform and the senskeys switches off AUTO.FILTERSwitches on and off the100 kHz low pass filter.This filter removes highfrequency interferencewhen measuring on LFsine wave signals.50 WSwitches between 50 W/1 MWinput impedance.1 MWallows the counter tomeasure without loading downthe measuring signal, while50 Wterminates the cables in50 Wsystems, minimizing re-flections and interreference.Using the ControlsMeasurement Control Keys4-6 MeasurementControl KeysFREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER MEASURING TIMESets measuring time between 100 ns and 15 s.Use FUNCTION key to step up/down the time in 1-2-5steps. The measuring time works like the exposure time ofa camera, a long measuring time captures more informationgiving more details to the result (higher resolution).GATE LEDOn while a measurement proceeds.EXT REFSwitches be-tween the ex-ternal and theinternalTimebaseCHECKConnects the internal10MHz reference to thecounter logic to allow testof all measuring functions.MEAS RESTARTInterrupts the measurement, clears the display, and starts a newmeasurement.Reset the measurement result in TOT AMAN.Arms individual measurements when DISPLAY HOLD is ac-tive.SINGLEWhen on, the result from each mea-surement cycleisdisplayed. Nowthe set measuring time becomes theDisplayTime(timebetweenmea-surements). Whenoff, thecounteraverages all data capturedduringthe set measuring time.ENTERConfirms aselectionAUX MENUGives you accessto additionalfunctions likearming, bursttriggering,save/recall andmuch more. SeeChapter 10Auxiliary Func-tions.DATA ENTRYIncreases and decreases numerical val-ues on the display. Used for MEASTIME, BURST, PRF, ARMSTART/STOP, TIME OUT and ANA-LOG OUT.Display ControlsUsing the Controls4-7 DisplayControlsFREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER DISPLAY HOLDFreezes the display untilyou press the key again.New measurements arearmed every time MEASRESTART is pressed.Starts/stops the measure-ment in TOT AMAN.NULLThe NULLfunction stores thecurrent result on the display, thenshows all the following results asdeviation from that result.You can read and change thestored reference in the AUXMENU.BLANK DIGITEach press on this key blanksout one display digit, startingwith the LSD.Whenalldigitsareblanked,the next press disables theblanking.DISPLAY LIGHTYou can switch on and offthe display back lightingin the AUX MENU.MENUIf you press MENU, thedisplay shows all selectablefunctions and the currentselections blinks.DISPLAY OVERFLOWThe measurement result can con-tain up to 12 digits. With the over-flow function you can see the twoadditional digits that normally arehidden.Using the ControlsDisplay4-8 DisplayFREQA FREQC PERA RATI OA/ E RATIOC/A P WI DTHA TOT A MAN DUTY F ALEVEL A SENSI TIVITY AOFFSETOVERFLOW SINGLEME MORY BURSTPRFAUX ENTE RSREMOTESRQEXTREF CHECKOVERLOADFILTERHOLD150MNULLAUTOTRI GARMSTAARMSTONUMERICALPRESENTATIONA10-digit display used toshow measuring resultsand other values.Thedisplayalwaysshowsbasic units (Hertz, counts orseconds)plusanexponentwhen necessary.ENTERDisplayed when the instrument wantsyou to confirm a selection by pressingENTER.Mantissa Exponent Unit IndicatorINPUT SETTINGSInput settings areshown on the displaydirectly above the keyused for each setting.OFFSETRead more aboutthe offset annuncia-tor on page 5-5 un-der Auto Once.OVERLOADFlashes if you press 50 Wwhen theinput signal is 12 to 24 Vrms.Press 50 Wagain to confirm selec-tion. If OVERLOAD turns off, theinput signal falls below 12 Vrmswhen loaded with 50 W.Caution:Immediatelydiscon-nectthesignalifthisannunciatorison;other-wise,theinputcouldbeseriouslydamage.LEVEL/SENSITIVITYBAR GRAPHShows A-input level between-27 dB and +33 dB(3 dB/bar) when AUTO is on.Level above +33 dB is indi-cated by an arrow at the rightedge of the graph.When AUTO is off, it showssensitivity. Max. Sensitivity,-27 dB= all segments, exceptthe leftmost, are off.NULLOn if the resultis displayedrelative to anulling con-stant.MEASURINGFUNCTIONSThe current mea-suring function isshown on the dis-play.If MENU ispressed, all possibleselections areshown on the dis-play and currentsetting is blinking.DisplayUsing the ControlsDisplay4-9FREQA FREQC PERA RATIOA/E RATIOC/A PWIDTHA TOT A MAN DUTYFALEVEL A S ENSITIVI TY AOFFSETOVERFLOW SI NGLEMEMORY BURSTPRFAUX ENTERSREMOTESRQEXTREF CHECKOVERLOADFILTERHOLD150MNULLAUTOTRIGARMSTAARMSTOREMOTEOn when the instru-ment is controlledfrom the GPIB.Press LOCAL to goto local control.MEMORYThis indicator is onwhen a setting hasbeen recalled from,or saved in mem-ory. MEMORY isonly on until some-thing is changed inthe instrument set-tingOVERFLOWWhen this annunciatoris on, the counter hasmeasured an 11 or 12digit result, and showsthe 10 least significantdigits on the display.The overflow functionis enabled/disabled inthe AUX MENU.BURST andPRFOne of thesesegment are onwhen the instru-ment is set upfor a frequencyburst measure-ment (via AUXMENU).SQROn when the instrument hassent a Service Request viaGPIB but the controller hasnot fetched the message.Reading the status byte viathe controller will showwhat caused the SQR andturn off the annunciator.AUXILIARYDisplayed when an AUXMENU function results in asetting that cannot other-wise be shown on the dis-play.Make it a rule to keep aneye at this indicator.ARMINGIndicates that theArming functionis in use andshows the selec-tion of positive ornegative slope forarming start/stop.Using the ControlsRear PanelGPIB OPTION4-10RearPanel! ! !!OFFONG D E16 8421RL1, DC1, DT1, E2SH1, AH1, T5, L4, SR1,IEEE 488/IEC 625 INTERFACEADDRESS90V-265VPANALOG OUT10MHz OUT REF IN EXT ARMOPTION 10OPTION 30OPTION 40OPTION 80OPTION __OPTION __OPTION __OPTION __ALL INPUTS MAX 1UNLESS OTHERWINCLUDED OPTIONSANALOGOUTPUTOutputs any 3digits on the dis-play as 0 to4.98 V.GPIB ADDRESSSWITCHSelects address between 1and 30. The display showsthe address every time thecounter is turned on.GPIB CONNECTORAstandard IEEE 488.1connector for connectionto a controller.REFERENCE INPUTIf you have an in-house reference or want to run several instru-ments on the same reference, connect 10 MHz here and selectit by pressing the EXT REF key on the front.10 MHz OUTPUTAfrequency reference out-put to be used with otherinstruments.Rear PanelUsing the ControlsRearPanel 4-11! !!!Made in SwedenE1, DT1, E21, T5, L4, SR1,8/IEC 625 INTERFACE90V-265V1.6 ATPRIMARY FUSE INSIDEREF IN EXTARMALL INPUTS MAX 12VRMSUNLESS OTHERWISE SPECIFIEDLR 39484FUSEThere is a 1.6 Aslow-blow pri-mary fuse inside the housing.If blown, the fuse should not bereplaced without a thorough ex-amination of the power supply.POWER SOCKETThe input can handle 90 to265 VACand 45 to 440 Hzwithout any range switching.Just connect and go!ARMING (Input E)An arming input used to startand stop the measurement withexternal signal.Also used as an extra measuringinput for Ratio measurements.Using the Controlsn OperationSwitchonthecounter.LocatetheUNLOCKEDindicatortotherightonthefrontpanel.Aslongasthisin-dicatorislit,thetimebaseiswarmingup.Whentheindicatorturnsoff,startus-ingthecounter.ApartfromthisUNLOCKEDindica-tor,thecounterworkslikeanormalCNT-85.4-12 CNT-85RFrontPanelFREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85RFREQUENCYCOUNTER/CAL BRATOR uNL0CKE0FRE0uENCYA0Ju3TRUBIDIUMATOMICCLOCKuNL0CKE0FRE0uENCYA0Ju3TRUBIDIUMATOMICCLOCKCNT-85R Front PanelChapter 5InputSignalConditioningIntroduction to ThisChapterThis chapter describes how the input amplifieroperates, and when and how to set its controls.Input AThe input amplifier adapts the measuring signalto the measuring logic of the counter.The built in microprocessor automatically con-trolsthetriggerlevel,sensitivity,andattenua-tion of the input amplifier. This AUTOfunctionissopowerfulthatyouscarcelyeverneedtoturn it off. At four measurements per second itis quickenoughtoenable real-time adjust-ments, and it works down to 50 Hz.The AUTOfunction even adapts itself to differ-ent measurements. It givesfrequency-relatedmeasurementsawidehysteresisbandthatre-ducesnoiseandgivestimemeasurementsthenarrow band they need to minimize trigger er-ror. AUTO ON is the recommended setting for99 % of all measurements.YoucaneasilyswitchofftheAUTOfunction,but to successfully set these parameters manu-ally,itisessentialtounderstandhowthecon-trolsworkwiththeAC-couplingoftheinput.Readmoreabout it further onunder AUTOOFF.Theblockdiagramshowstheorderinwhichthe different controls are connected. This is notacompletetechnical diagram; it is onlyin-tended to help in understanding the controls.Input Signal Conditioning5-2 IntroductiontoThisChapterACAUTOMAT CATTENT ONF XEDACCOUPL1 00kHzLPF LTERMEASUR NGLOG CSLOPE,ARM NG,SYNC,DELAYETC.MI CRO- CONTROLLERI MPManuAlSENSONAUTOSENSNULL,D SP,HOLDETCSENS T V TYWAVEFORMCOMPENSAT ONDACOFFFig.5-1 CNT-85Signal ConditioningBlockDiagram.Triggeringn AUTOONAUTO The AUTO key turns theauto function on. Switchingon the power always acti-vates AUTO.The auto triggering function of the counter con-trols boththesensitivity(alsocalledtriggerwindow or hysteresis) and the waveform com-pensation(alsocalledtriggerlevel offset, ordutyfactorcompensation).Auto measuresthepeak-to-peak levels of the input signal and setstheupperlevelofthehysteresisbandto66%andthelowerlevelto33%ofthatvalue(forpulse width and duty factor measurements,both levels are set to 50 %). AUTO accuratelysets the waveformcompensation to compensatefor duty factors other than 50 %. The waveformindicator shows the symbol that is closest to theauto-selection made.+Auto sets the waveform compen-sation much more accuratelythan is possible manually. So it islikely that the auto trigger canhandle signals that are impossi-ble to trigger manually.Ifthedutyfactorofthesignal changesverymuch, the autofunctioncanfollowa slowchange, but signals with rapidly changing dutyfactorsarebestmeasuredwithaDC-coupledtimer/counter, such as the CNT-80.+Turn off AUTO:- If the input frequency is 2 * * prescaling factor period.For instance when measuring 1 GHz burst fre-quenciesusinginputC,thedelaytimeshouldbe> = > 2 64 1 128 * * ns ns.Thus,themini-mum delay of 200 ns is OK.n HowdoIsetupmymeasurement?Use arming with time delay as described in theprevious example.Setupacorrectburstfrequencymeasurementas follows:ConnectburstsignaltoinputC.ConnectexternalSYNCtoinputE.UsetheFUNCTIONkeytoselectFREQC.Setameasuringtimeshorterthantheburstduration.PresstheAUXMENU key,selectARMSTART,andpositiveslope(ARMSTA+).PressENTER.EnteradelaytimeandpressENTER.Measure.AM SignalsThe counter can usually measure both the car-rier wave frequency and modulation frequencyof AM signals. These measurements are muchlike the burst measurements described earlier inthis manual.Carrier wave frequencyThecarrierwave(CW)isonlycontinuouslypresentinanarrowbandinthemiddleofthesignal.Ifthesensitivityistoolow,cycleswillbe lost, and the measurement ruined.To measure the CW frequency:Selectameasuringtimethatgivesyoutheresolutionyouwant.TurnoffAUTO.Pressthewaveformkeyandselectsym-metricalsignals.Press tSENStoselectthehighestsensi-tivityandthendecreasethesensitivityun-tilthemeasurementresultisnolongersta-ble.IncreasethesensitivityacoupleofdBsandmeasure.6-10AMSignalsABFig.6-11 Effectsofdifferentsensitiv-itywhenmeasuringtheCWFrequencyofanAMsignal.Measuring FunctionsModulating frequencyThe easiest way to measure the modulating fre-quency is after demodulation. If no suitable de-modulator is available, use the PRF function tomeasure the modulation frequency in the sameway as when measuring Burst PRF.PressMEASTIMEandenterameasuringtimethatgivesyoutheresolutionyouwant.SwitchoffSINGLE.PressAUXMENU,selectPRF,andpressENTER.SelectinputA asmeasurementinput,andpressENTERSetasyncdelayofapproximately75%ofthemodulatingperiod.SeeFigure6-7.PressENTERtoleavetheAUXMENU.SwitchoffAUTO.Pressthewaveformkeytoselectsymmet-ricalsignal.PressSENS u untilthecounterstopstrig-gering.IncreasethesensitivityacoupleofdBsandmeasure.RatioTo find the ratio between two input frequencies,thecountercountsthecyclesontwochannelssimultaneously and divides the result on the pri-marychannelwiththeresultonthesecondarychannel.Ratio can be measured between Aand E inputsor between C and Ainputs.+The input frequency range of in-put E is limited to 50 MHz.Note also that the resolution cal-culations are very different ascompared to frequency measure-ments.AMSignals6-11Sync. del ayMeasuredcycl esFig.6-12 Effectsofdifferentsensitiv-itywhenmeasuringtheCWFrequencyofanAMsignal.Measuring FunctionsPeriodIntroductionFromameasuringpoint of view, theperiodfunction is identical to the frequency function.This is because the period of a cyclic signal hasthe reciprocal value of the frequency (1f).In practice there is a minor difference.1. Where the counter calculatesFREQUENCY as:fnumber of cyclesactual gate time=it calculates PERIOD as:pactual gate timenumber ofcycles=2.InthePERIODmode,thecounterusesnoprescaler, resultingina160MHzmaximum frequency.Allotherfunctionsandfeaturesasdescribedearlier under Frequency apply to Period mea-surements.6-12IntroductionMeasuring FunctionsPulseWidthandDutyFactorIntroductionThis counter canmeasure Pulse WidthandDuty Factor.TriggeringIfAUTOisonwhenthesefunctionsarese-lected, the counter sets a 50 % trigger level andthe highest possible sensitivity.The set trigger level and trigger slope define thestart andstoptriggering. Themanual triggerfunction of the counter allows only three triggerlevelsettings.Thislimitedselectionmakesitpossibletotrigger correctlyonlyonsignalswith very steep slopes.+Always use AUTO or AUTOONCE when measuring PulseWidth and Duty Factor.n HysteresisIn pulse width measurements the trigger hyster-esis, among other things, causes measuring er-rors. Actual triggering does not occur when theinput signal crosses the trigger level at 50 per-cent of the amplitude, but when the input signalhas crossed the entire hysteresis band. At maxi-mum sensitivity, the hysteresis band is as smallas possible, about 10 mV.Introduction 6-130VtTri ggerpoi ntsResetpoi ntsHysteresi sband(SENS)Tri ggerl evel offsetFig.6-13 Timeismeasuredbe-tweenthetriggerpointandtheresetpoint.Accuratemeasurementsarepossibleonlyifthehysteresisbandisnar-rowandcenteredaround50%oftheam-plitude.Measuring FunctionsPulse Width AThe counter measures pulse width on input A.Normallythe counter measures the positivepulsewidth.Ifyouwanttomeasurethenega-tive pulse width, you must select negative trig-ger slope in the AUXMENU. The selected trig-gerslopecontrolsthestarttriggerslope.Thecounter automatically selects an inverse polar-ity as stop slope. Thus, a selected positive slopelets the counter start measuring on the first posi-tiveslopetriggering;thereafter,thefirstnega-tive slope trigger event stops the counting.Duty FactorAduty factor (or duty cycle) measurement con-sists of twomeasurements: onepulsewidthmeasurement and one period measurement.The duty factor is then calculated as:Duty factorPulse widthPeriod=+This takes 2x the set measuringtime6-14PulseWidthAMeasuring FunctionsTotalizeTOTalize AThismodeenablesyoutototalize(count)thenumberoftriggereventsonchannelA. Startandstopof the totalizingis manuallycon-trolled.The counting capability is1 1014* events at ratesto 100 MHz.FUNCTION Select TOT A MAN with theFUNCTION key.DISPLHOLDStart and stop thetotalization manually bypressing the DISPLAYHOLD key.Repetitive start/stopscauses the counter to accu-mulate the number ofevents.MEASRESTARTPress the RESTART keywhen you want to reset thetotal sum to zero.+AUTO is switched off duringtotalize. You must always setmanual trigger level.TOTalizeA 6-15Measuring Functions6-16TOTalizeAThispageisintentionallyleftblank.Chapter 7MeasurementControlAbout This ChapterThis chapter explains how you can control thestartandstopofmeasurementsandwhatyoucan obtain by doing that. The chapter starts byexplainingthekeysandthefunctionsbehindthem, then gives some theory, and ends with ac-tual measurement examples.Measuring TimeMEASTIMEThe measuring time is pre-set to 200ms. This givesnine digits on the display,and four measurementseach second.Increasing the measuring time gives more dig-its, but fewer measurements per second.To change the measuring time:PresstheMEASTIME key.Increase/decreasethevaluebypressingtheFUNCTIONkey.ConfirmyourselectionbypressingMEASTIMEagain.Themeasuringtimeischangedin1/2/5stepsfrom 100 ns to 15 s. Default and preset value is200 ms.+If you select SINGLE, the setMeasuring Time becomes theDisplay Time (time betweenmeasurements).n Fine-tuningthemeasuringtimeFortimesabove50ms,youcansetyourownmeasuring time as follows:PressMEASTIME.PressSENSu andtheparametertobesetexpandsovertheentiredisplay.A cursorflashestotheleftoftheMSDdigit.Movethiscursortothedigityouwanttochange.Usingthe t SENSukeys.ChangethevalueoftheselecteddigitbypressingtheDATA ENTRY keys p andq.Movethecursortothenextdigitandre-peattheaboveprocedureuntilthedisplayshowsthedesiredvalue.ThenpressENTERtoconfirmtheselection.SINGLE When SINGLE is on, thecounter shows the resultsfrom a single measurementcycle.When SINGLEis off (default setting), thecountermakesanaveragemeasurementoverthe set measuring time.UseSINGLEwhenyouwanttomeasureonsingle-shotphenomenaorwhenyoujustwantfast results without the need for many digits.The number of input periods in a SINGLEmea-surement depends on the prescaler factor of theinput and which function is selected as follows:Measurement Control7-2 AboutThisChapterFREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER All functions using Input A except DUTYFACTOR:The result is from one period.DUTY FACTOR:Thecountermakesacompositemeasurement,one PERIOD and one PULSE WIDTH.All functions using Input C:Theprescalingfactorsetsthenumberofperi-ods used:64 for option 10 Gate indicatorThe GATE LED is on when the counter is busycounting input cycles.Display HoldDISPLAYHOLDPressing DISPLAY HOLDfreezes the result on thedisplay. The display is notfrozen until one measure-ment has been completedafter DISPLAY HOLD hasbeen pressed.MEASRESTARTMEAS RESTARTinitiates anew measurement.ArmingAUXMENUExternal arming gives youthe opportunity to start andstop a measurement whenan external qualifier eventoccurs.Start and stop of the arming function can be setindependently to positive slope, negative slope,or OFF.Input E on the rear panel is the arming input.Arming is somewhat complicated, so study theexampleslaterinthischaptertoseewhatyoucan do. There is normally no need to use armingexcept whenmeasuringoncomplexsignals(non-continuous wave).Measurement ControlDisplayHold7-3FREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER Measurement ControlStart armingStart arming acts like an EXT TRIGGER on anoscilloscope. It allowsthestart oftheactualmeasurement to be synchronized to an externaltrigger event.Inacomplexsignal,youmaywanttoselectacertainpart,wheretoperformmeasurements.For this purpose, there is an arming delay func-tionwhichdelaystheactualstartofmeasure-ment, with respect to the arming pulse, in a sim-ilar way as a ``delayed timebase does in an os-cilloscope.Activate start arming as follows:PressAUXMENU;usethe FUNCTIONkeytoselectAR.START andpressENTER.SelectPOS orNEG triggerslopewiththeDATA ENTRY keys,andpressENTER.SelectDELAY ONorOFFwiththe DATAENTRY keysandpressENTER.Ifyouenableddelay,selectdelaytimefromthepredefinedtimesusingtheDATAENTRY keys.Youcanalsoenteradelayofyourownbyselectingadigitwiththet SENS u keysandincreasing/decreas-ingthatdigitwiththeDATA ENTRYkeys.Continuewithotherdigitsuntilthedisplayshowsthedesireddelay.EndbypressingENTER.Startarmingcanbeusedforallfunctionsex-ceptburstandPRF.Ifyouusestartarmingtoarmanaveragemeasurement,itonlycontrolsthe start of the first sample.Stop armingStoparmingpreventsthestopofameasure-mentuntilthecounterdetectsalevelshiftonthe E input. Combining Start and Stop Armingresults in an external gate function which de-termines the duration of the measurement.Activate stop arming as follows:PressAUXMENU,selectAR.STOP withtheFUNCTIONkey,andpressENTER.SelectPOS orNEG triggerslopewiththeDATA ENTRY keys,andpressENTER.Stop arming can be used for all functions exceptpulse width, duty factor, burst, and PRF.7-4 ArmingMeasurement ControlDigit BlankingBLANKDIGITSBlanking switches off un-necessary digits on the dis-play. Press BLANK DIGITonce for each digit youwant blanked.Toturnoff blanking, press BLANKDIGITonce after you have blanked all digits.n TwomethodstoreducethenumberofdigitsReadinga10digit displaywhenyoudonotneed more than five or six takes more time thannecessary,andmakestheresultmoredifficultto read.Reducing the measuring time gives fewer digitson the display. However, it also means that eachresultisshownforashortertime, withmoredisplay updates per second. If the display is tobe easy to read, it should not be updated morethan a few times per second as with the defaultmeasuringtime,whichgivesfourdisplayup-dates each second.Digit blanking on the other hand, decreases thenumber of digits on the display without increas-ingthedisplayupdatefrequency. Itmakesitpossible to switch off any number of digits be-tween zero and ten. This means that the numberof digits displayed is zero to ten less than as cal-culated by the counters truncation algorithm.DigitBlanking7-5FREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER Fig.7-1 EachpressontheBLANKDIGITSkeyremovesonedigit.ControllingMeasurementTimingThe measurement processBasicfree-runningmeasurementsSincethecounterusesthereciprocalcountingtechnique, it always synchronizes the start andstop of the actual measuring period to the inputsignaltriggerevents. Infree-runningmodeanewmeasurement automaticallystarts whenthepreviousmeasurementisfinished.Thisisideal for continuos wave signals.Thestartofameasurement takesplacewhenthe following conditions have been met (in or-der):Thecounterhasfullyprocessedtheprevi-ousmeasurement.IfthecountermakesSINGLEmeasure-ments,thedisplaytime(=setmeasuringtime)musthaveexpired.Allpreparationsforanewmeasurementaremade.Theinputsignaltriggersthecountersmeasuringinput.Themeasurementendswhentheinputsignalmeets the stop trigger conditions. That happensdirectly after one of the following events:Thesetmeasuringtimehasexpired(infrequencymeasurements,forexample).InSINGLE,themeasurementstopsimme-diatelywhentheinputsignalfulfilsthestoptriggerconditions(whichisnormallywhenitpassesthetriggerwindowthesec-ondtime).Measuring time andmeasurement ratesThe set measuring time decides the length of ameasurementinall averagetypesofmeasure-ments.Inasingle-shottypeofmeasurement,however,themeasuringtimeinsteadactsasadisplaytimesetting.Forexample,ifamea-suringtimeof500msissetinasingleperiodmeasurement, and the period is 100 ns, the dis-play will show the result for 500 ms before thenext measurement can start.Thisisimportanttoknowwhenyouwanttomakefast measurements, forexample, whenusing the GPIB bus.Measurement Control7-6 DigitBlanking+To get ahigh measuring speed, itis not enough to set the counterfor single-cycle measurements.You should also set the measur-ing time to the minimum value.The time between the stop of one measurementand the start of the next one can be below 1 msin free-running mode if you do the following:DonotuseAUTO.DonotuseNULL.SwitchoffthedisplayviaGPIB.Additional controls over start and stopofmeasurementsFree-running measurements may be easy to un-derstand, but measurements can get more com-plex.Besidesinputsignaltriggering, thestart ofameasurementisfurthercontrolledbythefol-lowing elements:Manual MEASRESTART,ifDisplayHoldisselected.GPIBtriggering(or*TRG),ifbustriggeringisselected.Externalarmingsignal,ifStartArmingisselected.Expiredstartarmingdelay,ifArmingDe-layisselected.In addition to expired measuring time and stopsignal triggering, thestopofmeasurement isfurther controlled by:Externalarmingsignaltriggering,ifStopArmingisselected.GPIBtriggeringisdescribedintheProgram-mersmanual.Nowletslookdeeperintotheconcept of arming.Resolution as function ofmeasuring timeThe quantization error and the number of digitsonthedisplaymainlydefinetheresolutionofthe counter, that is the least significant digit dis-played.As explainedonpage6-4under ReciprocalCounting, the calculated frequency f is:fntg=whiletherelativermsquantizationerror= 250ps/tg.The counter calculates the mantissa of f with upto15digits.However,thenumberofjustifieddigitsdependsontheselectedmeasuringtimeand the measured frequency, and is much morelimited.Thecountertruncatesirrelevantdigitssothatthermsquantizationresolutioncannotchangethe LSD(least-significant digit) more than2.5 units. This is when the displayed value is99999999,andthequantizationerrorisworstcase.+1 unit in 99999999 (=1E8)means 10 times more relativeresolution than1 unit in10000000 (=1E7), despite thesame number of digits.In practice, the quantization error is two to threetimesbetterthanthespecifiedvalue, andthemeasuredvaluecanrangefrom10000000to99999999. Therefore, in practice thequantization uncertainty shown as instability inthe LSDcan range from0.25 to 2.5 LSDunits.A gradualincreaseofthemeasuringtimere-ducestheinstabilityintheLSDcausedbythequantization uncertainty. At a specific measur-ingtimesetting,thecounterisjustifiedtodis-playonemoredigit.ThatoneadditionaldigitMeasurement ControlDigitBlanking7-7suddenlygivestentimesmoredisplayresolu-tion, but not a ten times less quantization uncer-tainty. Consequently, ameasuringtimethatgivesjustonemoredisplaydigitshowsmorevisual uncertainty in the last digit.For a stable LSD read out, the maximum mea-suringtimeselectedshouldbeonethat stillgives the required number of digits. Such opti-mization of the measuring time enables the totalresolution to be equal to the quantization reso-lution. This is shown in Figure 7-2as a functionof the selected measuring time.What is arming?Armingisapretriggercondition(qualifier)that must be fulfilled before the counter allowsameasurementtostart.Thepretriggercondi-tion can be compared to using a gun. When youuse a gun, you must first armthe gun before youcan pull the trigger.Arming can also be used to qualify the stop of ameasurement.Thisiscalledstoparmingasopposed to the more commons start arming.When you use arming, you disable the normalfree-runmode, i.e., individual measurementsmust be preceded by a valid start arming signaltransition.Measurement Control7-8 DigitBlankingQUANT ZAT ONRESOLUT ONRel ati veQuanti zati onErrorMeasuri ngTi mei ns1 01 01 01 01 01 01 01 01 0-3 -4 -5 -6 -7 -8 -9 -1 0 -1 10-1 -2-3-4-5-6-7+1 +2 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0Fig.7-2 Resolutionasafunctionofmeasuringtime.If you use start arming and stop arming togetheryou get an externally controlled measuringtime.n ManualarmingThecounter has a manual arming functioncalled DISPLAY HOLD.Hereyoumanuallyarmindividual measurementsone-by-onebypressing the RESTART key.Usethismanualarmingmodetomeasure sin-gle-shot phenomena, which are either triggeredmanuallyoroccurat longintervals. Anotherreason for using this manual arming could sim-ply be to allowsufficient time to write down in-dividual results.n WhendoIusestartarming?Start arming is useful for measurements of fre-quency in signals, such as the following:Singleshoteventsornon-cyclicsignals.Burstsignals.Signalswithfrequencyvariationsversustime(profiling).A selectedpartofacomplexwaveformsignal.Signal sources that generate complex waveformslikepulsedRF,pulsebursts,tvlinesig-nals,orsweepsignals,usuallyalsoproduceasyncsignal that coincideswiththestart ofasweep, length of an RF burst, or the start of a tvline. These sync signals can be used to arm thecounter. See Figure 7-3.n WhendoIusestoparming?Younormallyusestoparmingtogether withstart arming. That means that the externalgating signal controls both the start and the stopof the measurement. Such a gating signal can beusedtoforcethecountertomeasurethefre-quency of a pulsed RF signal. Here the positionof the external gate must be inside a burst. SeeFigure 7-4.n TheArminginputInputEisthearminginput.Thisinputissuit-ableforarming(sync)signalsthathaveTTLlevels.Thetriggerlevelisfixedat1.4Vandcannot be changed. The trigger slope can be setto positive or negative.n WhendoIusearmingwithdelay?Youcandelaythestartarmingpointwithre-spect tothearmingsignal. Usethisfunctionwhen the external arming signal does not coin-cide with the part of the signal that you are in-terested in.The range for time delay is 200 ns to 1.6 s with asetting resolution of 100 ns.Measurement ControlDigitBlanking7-9SyncPul seSi gnalFig.7-3 Asynchronizationsignalstartsthemeasurementwhenstartarmingisused.StopArm StartArmExtGateBurstSi gnalFig.7-4 Startandstoparmingto-getherisusedforburstsig-nal gating.Measurement Controln GettingthewholepictureTheflowchart inFigure7-5 illustrateshowarming enables precise control of the start andstop of the actual measurement when you oper-ate the counter from the front panel. If you usethe counter via the GPIB, read more about busarming and triggering under the heading Howto use the trigger system in Chapter 18, Trig-ger Subsystem of theGPIBProgrammingManual.7-10DigitBlankingMeasurement ControlDigitBlanking7-11D SPLAYHOLDPRESSRESTARTSTARTARM NGWA TFOREXT. S GNALDELAY?WA TFOR NPUT S GNALTOTR GGERSTARTOFMEASUREMENTSTOPARM NG?WA TFOREXT. S GNALENDOFPRESETMEASUR NGT MEWA TFOR NPUTS GNALTOTR GGERSTOPMEASUREMENTPROCESSRESULT&D SPLAYnoyesyesyesnoouiyesnonoyesnoWA TPRESETT MES GNALDETECTED?AUTOON?SHOW"NOS GNAL"SHOW"NOTR G"Fig.7-5 Measurementcontrol flowdiagram.Arming Setup TimeThe arming logic needs a set up time of about 5nanoseconds before the counter is really armed;see Figure 7-6.When arming delay is selected, the set up timeis different; see Figure 7-7. It illustrates the ef-fect of the 100ns delay resolution.Figure 7-7 shows that a start trigger signal maybe detected although it appears 60 ns before theprogrammedtimedelayhasexpired.Thestarttriggersignalmustcome40nsafterthepro-grammedtimedelayhasexpiredtoguaranteecorrect start of the measurement.Measurement Control7-12ArmingSetupTimeArmi ngSi gnalSetupTi meMeasuredSi gnalFig.7-6 Timefromactiveexternalcontrol edgebeforethemeasurementisarmed:Echannel .5nsSyncEStartArmi ng nputAFig.7-10 Synchronizationusingstartarming.SyncEDel ay nputAFig.7-11 Synchronizationusingstartarmingwithtimedelay.Measurement ControlDo the following steps to start signal synchroni-zation using start arming with time delay:ConnectSYNCtoinputE.ConnecttheburstsignaltoinputA.Adjustthemanualsensitivityandwave-formuntiltheburstsignaltriggersthecountercorrectly.PresstheAUXMENU,selectARMSTART,andarmingonpositiveslope(ARMSTA+),andpressENTER.SelectdelayON usingDATA ENTRYkeysandpressENTER.Enterasuitabledelay,andconfirmwithENTER.UseFUNCTIONkeytoselectPulseWidth.PressMEASTIME,andsetashortmea-suringtime.SelectSINGLEmeasuringmode,andmeasure.Example#1: 7-15Example #2Measuring frequency intwo-tone burstsSonarburstscanconsistoftwodifferentfre-quencieswithdifferentdurations. SeeFigure7-12To measure the frequency of the first part is nor-mallynoproblem. Becauseofthereciprocalmeasurement, thecounterautomaticallysyn-chronize the measurement with the start of theburst. And for fool-proof synchronization, startarming can be used, as in Figure 7-13. The mea-suring time should of course be short enough.To measure the frequency of the second half re-quires the use of arming delay. The delay timeshould be set to a value slightly longer than theduration of the first tone in the two-tone burst.See Figure 7-14.Measurement Control7-16Example#2SYNC nputAorCsi gnalFig.7-12 Atwo-toneburstwithitssync-pulse.Armi ngi nput nputAorCsi gnalMeasuri ng ti meFig.7-13 Autosyncorexternal armingmakesitpossibletomea-surethefirsttoneintheburst.Armi ngi nputArmi ngdel ay nputAorCsi gnalMeasuri ngti meFig.7-14 AddadelaytotheExternalarming,andthesecondtonecanbemeasured.Example #3ProfilingProfilingmeansmeasuringfrequencyversustime. Examples are measuring warm up drift insignal sources over hours, measuring the linear-ity of a frequency sweep during seconds, VCOswitchingcharacteristicsduringmilliseconds,or the frequency changes inside a chirp radarpulseduringmicroseconds. Thecounter canhandle many profiling measurement situations.Profilingcantheoreticallybedonemanually,i.e., by reading individual measurement resultsand plotting in a graph. However, to avoid get-tingboredlongbeforereachingyour800thorsomeasurement result, youmust use somecomputing power and a counter with GPIB in-terface.Inprofilingapplications,counteractsasafast, highresolutionsamplingfrontend,storing results in its internal memory. These re-sultsarelatertransferredtothecontrollerforanalysis and graphical presentation.Youmust distinguishbetweentwodifferenttypeofmeasurementscalled free-runningandrepetitive sampling.n Free-runningmeasurementsFree-running measurements are performedover a longer period, e.g., to measure the stabil-ity over 24 hours of oscillators, to measure ini-tial drift of a generator duringa 30-minutewarm-up time, or to measure short-term stabil-ityduring1or10s. Inthesecases, measure-mentsareperformedat intervalsfromhalfamillisecondandupwards.Inotherwords,themaximumsamplingrateis1.6kHz.Thereareseveraldifferentwaysofperformingthemea-surements at regular intervals.Single-cycle measurements usingmeasuringtimesettingforpacingWhen single measurements are set on the coun-ter, the measuring time acts as a measurementholdtime. Bysettingthemeasuringtimeto10sfor example, single-cyclemeasurementsare automatically made at 10s intervals.UsingacontrolleraspacerWithfairlylargeintervalssuchassecondsbe-tween individual samples, the timer in the con-troller canbeusedfor pacingtheindividualmeasurements.Usingexternal armingsignalsExternal armingsignalscanalsobeusedforpacing.Forexamplewithanarmingsignalconsisting of 10 Hz pulses, individual measure-ments are armed at 100 ms intervals.LettingthecounterrunfreeWhenthecounterisfree-running,theshortestdistance between measurements is approxi-mately 600 ms plus set measuring time. For ex-ample when a measuring time of 2 ms is set, thetimebetweeneachsampleis approximately2.6ms.Youhavetoperformsomespecialac-tionsinsearchofthathighspeed,forinstanceblanking the display. This is described in Chap-ter 19 of the Programming Manual.n RepetitivesamplingprofilingThe measurement setup just described will notworkwhenthe profilingdemands less than600 ms intervals between samples.Measurement ControlExample#37-17Measurement ControlHowtodoVCOstepresponseprofil-ingWith100samplesduringatimeof10ms, i.e., 100msbetweensam-ples.This measurement scenario requires arepetitiveinputstepsignal,andyouhavetorepeatyourmeasurement 100 times, taking one sample perswitch period. And every newsample should bedelayed 100ms with respect to the previous one.Thisiseasiest controlledbyacontroller, al-though it is possible but tedious to manually setand perform all 100 measurements.The following are required to set up a measure-ment:A repetitiveinputsignal(e.g.,frequencyoutputofVCO).AnexternalSYNCsignal(e.g.,stepvolt-ageinputtoVCO).Useofarmingdelayedbyapresettime(e.g.,100,200,300 ms).See Figures 7-15 and 7-16.Whenall100measurementshavebeenmade,the results can be used to plot frequency versustime. Notethat theabsoluteaccuracyof thetimescaleisdependentontheinputsignalit-self.Althoughthemeasurementsarearmed at100ms100nsintervals, theactual start ofmeasurement is always synchronized to the firstinput signal trigger event after arming.7-18Example#3 nputE, EXTARM nputAVol tagestep generatorVCOFig.7-15 Setupfortransientprofil-ingofaVCO.Fig.7-16 Resultsfromatransientprofilingmeasurement.Chapter 8ProcessingIntroductionTwo different ways to process a measuring re-sult are available: Averaging and Nulling.AveragingSINGLE If SINGLE is switched off,the counter makes a multi-ple period average. Thatmeans that it averages alldata captured during theset measuring time and dis-plays the result.NullingNULL One press on the NULLkey stores the current bydisplayed result, thenshows all the following re-sults as deviation from thatresult.+It can be difficult to freeze thedisplay in exactly the right mo-ment when all ten digits show thedesired value. Dont worry, youcan display and change the nullvalue by entering the AUXMENU.To show the stored nulling value:PressAUXMENU,selectNULL withtheFUNCTIONkeyandpressENTER.To change the value:Pressthe< SENS>keystoselectthedigityouwanttochangeandpresstheDATA ENTRY stkeystochangethevalue.PressENTER,andthenewvalueisstored.n ManuallyenteringanullvalueWhen nulling is off:Processing8-2 IntroductionFREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER FREQA FREQC RATIOA/E RATIOC/A P WIDTH A TOTAMAN DUTYF AEXTREF CHECKAUX ENTERHz+0. 1 -2. Z0lz509VAX5vrrs350vp-1 V90C-300Vlz)1 2vrrs-509VAXVENuAuXVENu 3l N0LE8LANK0l 0l TL0CALPRE3ET3TAN0-8YEXTREF ClECK0NFl LTERNuLL3EN3ENTER0ATEl0L0AuT0 5099FuNCTl 0Nl NPuTARE3TART 0ATA ENTRYVEA3Tl VE1 0rv 1 00rv 1 v 1 0vrrsCNT-85FREQUENCYCOUNTER ProcessingPresstheAUXMENU keySelectNULL withtheFUNCTIONkeyPressENTERandthedisplayshowsthepreviousNullvalue(ifany).Tousetheshownvalue,pressENTER.Tochangethevalue,pressthekeystoselectthedigityouwanttochange,andincrease/decreasethedigitwiththeDATA ENTRY stkeys.Re-peatthesestepsforalldigitsyouwanttochange,thenexittheAUXMENUbypressingENTER.The NULL annunciator on the display isswitchedonandthedisplayshowsthedevia-tion from the entered value.Nulling8-3Thispageisintentionallyleftblank.Processing8-4 NullingChapter 9AuxiliaryFunctionsAuxiliary FunctionsAbout This ChapterThis chapter describes less commonlyusedfunctions that are hidden inthe auxiliarymenu.Auxiliary MenuIntroductionAll the counters measuring logic and input set-tings are computer controlled. The ability to se-lect, combine, and add new functions is limitedonlybythenumber of controlsonthefrontpanel.To keep the normal operation of the counter assimpleas possible, theuseof dual or triplefunctionkeyshasbeenavoided.Forthesamereason the number of keys has been restricted,however,thecountercontainsmanyhiddenfeatures.TheAUXMENU keygivesyouac-cess to all the extras that are not generally foundin a traditional counter.If you frequently need to use some AUXMENUfunctions, we recommend that you saveyour favorite complete front panel setup in oneof the 20 memory locations for easy recall later.Youcanusesuchpreprogrammedsettingsasdefault settings for your particular applications,from which you can manually modify the vari-ous individual control settings.When you select something in the AUXMENU, that cannot otherwise be indicated, anAUXannunciator on the display is switched on.+The AUX annunciator showsonly that a change has beenmade in the AUX MENU. Theunique settings that have beenmade are not shown on the dis-play.9-2 AboutThisChapterAuxiliary FunctionsAuxiliaryMenu 9-3AUXMENUENTERFUNCT OND SPLAYBACKL GHTON/OFFNULLRead/ChangeD SPLAYOVERFLOWON/OFFANALOGOUTPUTON/OFF+Control Scal i ngGP B-ADDRESSReadT MEOUTsetTi meOut, 1 00msto25. 5sandOFFTESTSel ectSel f TestPROGRAM DENT FYCounterandGP BprogramsRECALLMEMORYSAVEMEMORYPROTECTMEMORYTR GGERSLOPEPosi ti veornegati veARM NGSTARTON/OFF/DELAYARM NGSTOPON/OFFBURSTCWA, CandOFFPRFA, CandOFFARM NGDELAYTi me200nsto1 . 67sSYNCDELAYTi me200nsto1 . 67sFig.9-1 Youwill entertheAUXMENUatthesameselectionasyouusedtheprevioustime,exceptafterpower-onwhenyouenterthemenuatRE-CALL.Plain English AUX MENUcommandsAUXMENUFUNCTIONENTERThe selection of functionsfrom the menu that you findwhen you press theAUXMENUkey is simple. Justscroll through the list withthe FUNCTION key untilyou find the function youare locking for. PressingENTERwill select the func-tion or take you to asubmenu with more selec-tions.The texts on the display are messages in abbre-viated English. However, the ability to expressoneself using ten, 7-segment indicators issomewhatlimited.Hereisalistofalldisplaymessages with explanations.Analog OutAnalog output ON/OFF and scaling factorar. startArming Startar. stOpArming StopbUrstBurst FrequencybUs 1.23Identity of the GPIB firmwaredisp. lIghtDisplay lightdisp. Ofl.Display overflowErr. ProtecYou tried to save a front panel setting while thememory was protectedgpIb AddrGPIB Address Read/SetInstr. 1.23Identity of the Instrument firmwareNegNegativeNo bUSNo GPIB interface is installedNULLNullOFFOffOnOnPOSPositivePrFPRF Pulse Repetition FrequencyProg. Id.n.Program IdentityProtectMemory Protect MenurecallRecall from memory position 0 to 19.SAVESave in memory position 0 to 19Sync. dly.Synchronization delaytestEnter the test submenutest allAuxiliary Functions9-4 AuxiliaryMenuAll tests in sequencetest asICTest of measurement logictest dISPDisplay testtest ra.Internal RAM testtest rO.Internal ROM testti. OutTime-out menutrig SLOPETrigger slopeRecallRecallsoneofthe20previouslystoredfrontpanelsettings.Press AUXMENU,selectRE-CALLand press ENTER, then select onememory location from 0 to 19, with the DATAENTRY keys and confirm by pressingENTER.The memory annunciator is on as long as the re-called setting remains unchanged.SaveSavesthecurrentfrontpanelsettinginoneofthe 20front panel memorylocations. PressAUXMENU, select SAVE and pressENTER,thenusethe DATA ENTRYkeystoselectanunusedmemorylocationbetween0and19.Confirm by pressing ENTER.+The MEMORY annunciator isonly on as long as no changesfrom the saved setting havebeen made.Memory protectProtectsmemory10-19fromaccidentalover-write,justlikethewrite-protecttabonadis-kette.Trig slopeSelectswhatslopethecountershouldtriggeron. The default trigger slope is positive.Changing to negative trigger slope enables youtomeasurenegativepulsewidthanddutyfac-tor.Changingslopemakesnormallynosenseinfrequency, period or ratio measurements.Arming startSelectsifthecountershouldfree-run, orifaseparate signal must arm the start of each mea-surement. Press AUX MENU, selectAR.START,pressENTER,selectPOS,NEGor OFF, and press ENTER. If you select POS orNEG,thedisplayshowsDELAY OFF.SelectON and you can enter a delay from the arrivalofthearmstartsignalandtheactualstartofameasurement. Press ENTER to exit the menu.Arming stopSelectsifthecountershouldstopmeasuringwhen the measuring time expires, or if a sepa-rate signal must arm the stop of each measure-ment. PressAUXMENU, select AR.STOP,andpressENTER.SelectPOS,NEGorOFFand pressENTER.Burst frequencyTurns the burst frequency function on or off andselect measuring input. Read the explanation ofthis function in the Chapter 6 Measuring Func-tions.Auxiliary FunctionsAuxiliaryMenu 9-5PRFTurns the burst PRF function on or off and se-lectmeasuringinput.Readtheexplanationofthis function in the Chapter 6 Measuring Func-tions.Program identityShowsthefirmwareversionoftheinstrumentand the GPIB interface.TestIntheTestmenu,youcanchoosetoruntestsused in the power up test one at a time:SelectthetestsubmenubypressingtheFUNCTIONkeyuntilthedisplayshowsTEST.EnterthetestmenubypressingtheENTERkey.Selections for internal self-tests are as follows:test all (the four tests below in sequence)test disp (Display Test)test logic (Measuring Logic)test ra (RAM)test ro (ROM)Ifanyfaultisdetected,anerrormessagewillappearonthedisplayandtheprogramhalts.Possible error messages are as follows:InternalROMtestfailed.InternalRAMtestfailed.Thehex-addresswhereanerrorisdetectedisshown.Testofmeasuringlogicfailed.+The display test turns on all seg-ments of the display for a visualinspection. No failure is reported.Press ENTER to end the test.If an error message is displayed, press any keyto make the instrument continue even though anerror was detected. Contact your Local ServiceCenter for repair.Time-outTurns thetime-out onandoff for measure-ments. Use the DATAENTRYkeys to change.IfyouselectON,youenterasubmenuwhereyou can set the value of the time-out. Time-outisaprogrammablestopforameasurementinprogress. The time-out starts when the counterstarts a measurement, and it interrupts the mea-surement if aresult is not readywithinthetime-out period.The range is 100 ms to 25.5 s. Preset time-out isOFF.+The time-out is mainly used forGPIB applications.GPIB addressShows and changes the GPIBaddress. The newaddress is stored in nonvolatile memory and re-mainsuntilchangedagainviathismenu, theaddress switches on the rear panel or via a buscommand.This means that the ad-dress of the counter candifferfromtheaddressindicated by theswitches on the rearpanel.+The last set address is the validaddress whether it is set via theaux menu, address switches orGPIB command.The counter shows the used address during thepower-up test.Auxiliary Functions9-6 AuxiliaryMenuAuxiliary FunctionsAnalog output (GPIB optiononly)The analog output is turned off as a default. Youturniton/offandsetthescalingfactorunderANALOG OUT in the aux menu.n ScalingfactorThe scaling factor has two functions:ItsexponentselectswhichdigitstooutputontheanalogoutputItsvaluesetswhatreadingshouldrepre-sentfullscaleAsdefault,thescalingfactoris1(1E0).Thismeans that the full scale value is 0.999 and theanalog output converts the fraction (digits to theright of the decimal point) to a voltage.The scaling factor should be:Scaling factorfull scale value=1where full scale value is the value for which youwant the analog output to output its maximumvoltage (5 V).Example:Takeameasurementresult,forinstance:12.34567890E+6HzRepresentthisresultwithoutexponent:12345678.90HzMultiplythisvaluewiththescalingfactor,forinstance0.001.12345.67890Takethefractionalpartoftheresult:.67890Thisisthevaluethatwilldeterminetheoutputvoltage,.00willgive0V and.99willgive5V.thismeansthatourread-ingwillgive.67890*5=3.3945V.Thisisoutputas3.38V duetothe0.02Vresolutionoftheanalogoutput.AuxiliaryMenu 9-7Fig.9-2 Theanalogoutputfunc-tion.Default scaling factor = 1Scaling factor = 1E-6Fig.9-3 Tousetheshowndecimalpointasreference;settheexponentofthescalingfactortothesamevalueastheexponentofthemeasurementresultbutwithoppositesign.Sameexponent,oppositesignAuxiliary Functionsn ResolutionThe analog output range is 0 to 5 Vin 250 steps,so one step is 0.02 V. If the scaling factor is 1,onesuchstepistakeneachtimethedisplaychanges with X.004, and if the scaling factor is4, one stepis takeneachtime the displaychanges with X.001.The X in the above paragraph can be any digitand does not influence the output voltage. If thedisplaychangesfrom0.996to1.000,thevolt-agedropsfrom4.98Vto0V. If thedisplayvalue increases further, the output voltage startsto increase again, see Figure 9-4.Display overflowDisplay overflowmakes 12-digit measure-mentspossible.WhenOVERFLOW isonandthemeasurementjustifies11or12digits,theOVERFLOWannunciator turns on, andthecounter truncates one or two MSD:s and showsoneortwoextraLSD:sinstead. Youhavetokeep track of the decimal point yourself, com-pare the values with overflow on and off to seeifoneortwooverflowdigitsareshownwhenthe OVERFLOW annunciator is on.UsingOVERFLOWwithdisplayholdWhen display hold is active, The enter key tog-glesoverflowon/off.Ifthecounterhasmea-sured a result with more than 10 digits and youpress ENTER,theOVERFLOW annunciatorwillswitchonandthedisplayshowtheaddi-tionaldigits.ThecounterisdesignedthiswaybecauseswitchingonoverflowintheAUXMENUwill initiate a newmeasurement. This isundesirableifyouwanttostudyasingleshotphenomena or a long term totalizing.In totalizing the result can be up to 1017, that is17 digits, but overflow will not show more than12 digits.NullThe null function stores the result currently dis-played,thenshowsallthefollowingresultsasdeviations from that result.You store the current display reading by press-ing the NULLkey on the front panel. You canreadandchangethestoredresultintheAUXMENU.When NULL is on:PressAUXMENUSelectNULL withtheFUNCTIONkey.PressENTERandthedisplaywillshowthestoredvalue.9-8 AuxiliaryMenu4. 98V0. 00V0.0000. 9961 . 0001 . 9962. 0004. 98V0. 00V0. 00020mV20mV0.2490.4990.5000. 0010.2500. 004Outputvol tageval ueDi spl ayed Outputvol tageval ueDi spl ayed ScaI i ngfactor1ScaI i ngfactor4Fig.9-4 Outputvoltageversusdisplayedvaluefortwodifferentscalingfactors.Change the value in 1-2-5 steps with the DATAENTRY keys, or select what digit you want tochange with the SENSkeys and change it withthe DATAENTRYkeys.Whenthedisplayshowsthedesiredvalue,pressENTER.Asdefaultthenullvalueisnegativeandsub-tracted from the new readings, but you can alsoenter a positive null value.Turn off the nulling by pressing NULL again.Ifyouwanttoturnonnullingwithoutstoringthecurrentlydisplayedvaluebutkeeptheoldone, press AUXMENU, select NULLandpress ENTER twice.Display lightYou can turn the display backlighting on or off:PressAUXMENUSelectDISP LIGHT withtheFUNCTIONkeyPressENTERSelectONorOFFwiththeDATA EN-TRYkeysPressENTERagaintoexittheauxmenu.Auxiliary FunctionsAuxiliaryMenu 9-9Auxiliary FunctionsThispageisintentionallyleftblank.9-10AuxiliaryMenuChapter 10PerformanceCheckGeneral InformationWARNING:Beforeturningonthein-strument,ensurethatithasbeeninstalledinaccordancewiththein-stallationinstructionsoutlinedinChapter3ofthismanual.Thisperformanceprocedureisintendedtodothe following:Checktheinstrumentsspecification.Beusedforincominginspectiontodeter-minetheacceptabilityofnewlypurchasedinstrumentsandrecentlyrecalibratedin-struments.Checkthenecessityofrecalibrationafterthespecifiedrecalibrationintervals.+The procedure does not checkevery facet of the instrumentscalibration; rather, it is concernedprimarily with those parts of theinstrument which are essentialfor determining the function ofthe instrument.It is not necessary to remove the cover of the in-strument to perform this procedure.Ifthetestisstartedlessthan30minutesafterturning on the instrument, results may be out ofspecification, due to insufficient warm-up time.Recommended TestEquipmentTypeofin-strumentRequiredSpecificationsSuggestedInstrumentLFSynthe-sizerSquare;Sineupto10MHzPowerSplitter50 W PM9584/02T-pieceTermination 50 W PM9585Referenceoscillator10MHz0.1Hzforstandardoscil-latorPendulum6688,oracounterwithcali-bratedop-tion3010MHz0.01Hzforoptions30and40.Pendulum6689,CNT-85RorCNT-81R10MHz0.0001HzforCNT-85RPendulumGPS-89orCesiumStandardHFsignalgenerator500MHz(nopresc.option)3.3GHz(op-tion10)PulseGen-erator125MHzOscillo-scopew.probes350MHzBNC-cables 5-7cables*)Performance Check10-2General InformationTable10-1 Recomm.TestEquipment*)Twoofthecablesmusthave10nsdif-ferenceindelay,forexample:5nsand15ns.PreparationsPowerupyourinstrumentsatleast 30 minutes before begin-ning the performance check tolet theinstrument reachnor-mal operating temperature.Failure to do so may result in certain test stepsnot meeting equipment specifications.Front Panel ControlsPower-ON testAt power-on the counter performs an automaticself-test of the following:MicroprocessorRAMROMMeasuringcircuitsDisplayIfaGPIBinterfaceisinstalled,theGPIBad-dress is displayed.If there are any test failures, an error message isshown.Turnonyourcounterandcheckthatallsegmentslightuponthedisplayandthatnoerrormessageappears.Internal self-testsThebuilt-intestprogramsfromthepower-ontest can also be activated fromthe front panel asfollows:EntertheAuxiliaryMenubypressingAUXMENU.SelectthetestsubmenubypressingDATAENTRY upordown.EnterthetestmenubypressingtheENTERkey.Selections for internal self-tests are as follows:1 TEST RO (ROM)2 TEST RA (RAM)3 TEST ASIC (Measuring Logic)4 TEST DISP (Display Test)5 TEST ALL (Test 1 to 4 in sequence)UseDATA ENTRY up/downtoselectTEST ALL,thenpressENTER.Ifanyfaultisdetected,anerrormessageappearsonthedisplayandtheprogramhalts.Ifnofaultsaredetected,theprogramre-turnstomeasuringmode.Keyboard testThekeyboardtestverifiesthatthecounterre-spondswhenyoupressanykey.TocheckthePerformance CheckFrontPanel Controls10-3FREQA FREQC PERA RATI OA/E RATIOC/A P WI DTHA TOTA MAN DUTY FALEVEL A SENSITI VITY AOFFSETOVERFLOW SINGLEMEMORY BURSTPRFAUX ENTERSREMOTESRQEXTREF CHECKOVERLOADFI LTERHOLD150MNULLAUTOTRI GARMSTAARMSTOFig.10-1 Textonthedisplayfunctionbehindthekeys,seethetestsfurtheron in this chapter.Pressthekeysasdescribedintheleftcolumnand look on the display for the text, as describedin the second column. Some keys change moretext on the display than described here. The dis-play text mentioned here is the text mostly asso-ciated with the selected key.Fortheinstrumenttorespondcorrectly, thistestmustbecarriedoutinsequence,andyoumust start with the preset (power on) setting.Key(s) Display Note Pass/ FailStandby DisplayOff RedLEDbesidethekeyOnON Back light onPRESETLocalDEFAULT?NO SIGNALDefaultsettingExtRef EXTREFInputAFilter FILTER50W 50 WAuto AUTO TRIGdisappearsTRGLVL(2times)Sens (2times)Bargraph:zzzzzzzzSens (2times)Bargraph:zzzzzzzzzzOtherPRESETLocalDEFAULT?NO SIGNALDefaultsettingMeasTime200.03sDATAENTRY500.03sDATAENTRY200.03sEnter NO SIGNALKey(s) Display Note Pass/FailMEASUREHoldHOLDMEASUREHoldSingle SINGLEFUNCTIONDUTYFAFUNCTIONTOTAMANFUNCTIONDUTYFAFUNCTIONFREQAAuxMenuRECALLMEASURERestartNO SIGNALPRESETLocalDEFAULT?NO SIGNALDefaultsettingNullNO SIGNALCheck 10.000000006Hz *Startcount-ingBlank(3times)10.00000..6Hz *Menu Displaysallavailablefunctions,processesandinputcontrols.Se-lecteditemsareblink-ing.PRESETLocalDEFAULT?NO SIGNAL**DefaultsettingPerformance Check10-4FrontPanel ControlsTable10-2 Keyboardtest.*TheLSDdigitmayvary.**MENUisnotdisabledbysettingDE-FAULT;pressmenuagain.Short FormSpecification TestSensitivity and frequencyrangePressthePRESETkeytosetthecounterinthedefaultsetting.ThenconfirmbypressingENTER.TurnoffAUTO.Select50W /InputA andmaximumsensi-tivity.ConnecttheoutputfromanHFgeneratortoaBNCpowersplitter.Connectthepowersplittertoyourcounterandanoscilloscope.Setinputimpedanceto50W ontheoscil-loscope.Adjusttheamplitudeaccordingtothefol-lowingtable.Readthelevelontheoscillo-scope.TheCountershoulddisplaythecor-rectfrequency.Freq Level Pass/FailMHz mVPPmVRMSdBm InputA1 30 10 2750 30 10 27100 45 15 23150 60 20 21200 90 50 17300 150 50 13Reference oscillatorsCrystal oscillators are affected by a number ofexternalconditionssuchasambienttempera-ture and supply voltage but also by aging.Therefore, itishardtogivelimitsfortheal-lowedfrequencydeviation. Youmust decidethelimitsdependingonyourapplication,andrecalibrate the oscillator accordingly. SeeChapter 11 Preventive Maintenance.Oscilla-torMax.tem-peraturedepend-enceMax.agingpermonthMax.ag-ingperyearStandard 100Hz 5Hz 50HzOption300.05Hz 0.1Hz 0.75HzOption400.025Hz 0.03Hz 0.2HzRubid-ium0.003Hz 0.0005Hz0.002HzTochecktheaccuracyof theoscillator, youmust have a calibrated reference signal that is atleastfivetimesasstableastheoscillatorthatyou are testing. See the following table.SetthecountertodefaultsettingsbypressingPRESETand ENTER.ConnectthereferencetoinputAChecktheread-outagainsttheaccuracyrequirementsofyourapplication.Performance CheckShortFormSpecificationTest 10-5Table10-3 SensitivityforinputAatvariousfrequencies.Table10-4 Deviation(foroption30andoption40after48hourswarm-uptime).n AcceptancetestAs an acceptance test the following table givesaworst casereadout figureafter30minuteswarm-up time. All deviations that can occur ina year are added together.Oscilla-torFrequencyread-outSuitablereferencePass/FailStandard 10.000000006120HzOption30or40Option3010.0000000061Hz6689,CNT-85RorCNT-81ROption4010.0000000060.25Hzn Acceptancetest,CNT-85RTofullytesttheaccuracyoftheCNT-85R,anextremely high stability reference signal isneeded.Examplesofsuchreferencesare Ce-sium Atomic references, or transmitted signalsfromanationallyorinternationallytraceablesource.RecommendedTestEquipmentType Stability Model10MHzreference1x10-10910Rwithsatellitecon-tactduringthelast72hours.TestprocedureConnectthecountertothelinepower.CheckthattheUNLOCKindicatorturnson,andthenturnsoffagainwithin6min-utesafterconnectinglinepower.Connectthe10MHzreferencesignaltoinputA ofthecounter.SelectFREQUENCY A measurement.Select2smeasuringtime.Checkthatthedisplayedfrequencyis10.00000000MHz0.1Hz