Rigol DS6104 Administrator Guide

RIGOL TECHNOLOGIES USA INC

877-4-RIGOL-1 How-To Guide

[email protected]m

www.rigolna.com



Oscilloscope

SignalAnalysis

UsingFFTs

Application Notes

Comparison Guides

FAQs

How-To Guides

Programming Manuals

Quick Start Guides

Support Information

User’s Guides

RIGOL TECHNOLOGIES USA INC

877-4-RIGOL-1 How-To Guide

[email protected]

www.rigolna.com



FastFourierTransformswithRigolOscilloscopes



FFT(FastFourierTransform)isaprocesswhichconvertsatime‐domain

signalintoitsfrequencydomainequivalent.Commonapplicationsforusage

ofFFTwaveformsare:



zMeasuringharmoniccontentanddistortioninsystems

zCharacterizingnoiseinDCpowersupplies

zAnalyzingvibration



Howtoobtainawaveform'sFFT?



InthisexampleanFFTwillbegeneratedforthe1KHzsquare

waveacquiredonChannel1asseenbelow.Thissignalcanbe

duplicatedonanyRigolscopebyattachingtheprobetothesquare

wavegeneratorportonthefrontoftheinstrument.Onceyoudo

that,pushAUTOthenyouwillseethis:



RIGOL TECHNOLOGIES USA INC

877-4-RIGOL-1 How-To Guide

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

Pressthe“MATH”button,amenuwillappearontheside,thenselectFFT

andsetthesourcetoChannel1:



AFastFourierTransformofthecurrentsignalonChannel1willappearinthe

Purplecolorbelowthesquarewave.



RIGOL TECHNOLOGIES USA INC

877-4-RIGOL-1 How-To Guide

[email protected]

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

TheFFTcanbedisplayedfullscreenwiththechannelaswellbyadjusting

theWINDOWsetting.However,youliketoviewittakenoticeofthe

separateVERT/divandHORIZ/divsettingsshowninpurple.Youcanadjust

thesebypushingtheMATHbuttonandthenusingthehorizontaland

verticalscaleknobs.IftheFFTisn’tshownonthescreen,movetheVERTICAL

positionknobuntilyouseethezeropointandthenthesignal.



TherearetwooptionsforverticalunitsontheFFT:mVrmsand

dBVrms.Whenlookingtoviewsmallsignalsalongwithmuchlargersignals

dBVrmsisbeneficialbecauseitprovidesalogscale.Forthosenotusedto

logarithmicscalinglookatthescreenshotabove.Inthesplitscreenmode

shownthereare8verticaldivisionsdedicatedtotheFFT.Herearethevalues

atthetopofeachdivisiongiventhe200mVrms/divsettingandtheposition

ofthezeromarkerontheleftatthetopofthebottomdivision:



DivisionsdownfromtopofFFT

screen

Valueattopofthatdivision

0(topofpurpledisplay)1.4Vrms

11.2Vrms

21Vrms

3800mVrms

4600mVrms

5400mVrms

6200mVrms

70mVrms

8(verybottomofthescreen) ‐200(negativenumbersarenotused

byamVrmsscale)



So,inthismodetheFFThasabout1.4Vrmsoftotalrangecapability.Youcan

changethesensitivity,butifyouwantedtoseea10Vrmsfundamentalanda

10mVrmsharmonicatthesametimeitisn’tpossibleonalinearscale.

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877-4-RIGOL-1 How-To Guide

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

IfyouchangetheunitstodBVrms,herearethevalues:



Whenthesettingsare20dBVrms/divandthereferenceismovedtoone

divisiondownfromthetopoftheFFTdisplay:



Divisionsdownfromtop

ofFFTscreen

dBVrmsfromposition

marker

Valueattopofthat

division

0+10dBVrms 3.16Vrms

10dBVrms 1Vrms(attheposition

marker)

2‐10dBVrms .316Vrms

3‐20dBVrms .1Vrms

4‐30dBVrms .0316 Vrms

5‐40dBVrms .01 Vrms

6‐50dBVrms .00316mVrms

7‐60dBVrms .001mVrms

8‐70dBVrms .000316mVrms



Tounderstandthisfully,theformulatoderivethedBVrmsvalueisasfollows:

dBVrms=20*log(Vrms/VREF)



whereVREFinthiscaseis1Vrms,soitcanbesimplifiedto:



dBVrms=20*log(Vrms)



Consequently,whenlookingataspotonthescreenthatisknowntobeX

dBVrmstheactualVrmsvalueexpressedbysignalatthatlocationis:



Vrms=10^(X/20)

Forexample,‐20dBVrms=10^‐1=0.1Vrms

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877-4-RIGOL-1 How-To Guide

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

Sointhiscaseevery20dBisafactorof10xthevoltage.Usually,dBisused

intermsofWattsormilliWatts(dBm)inwhichcaseevery10dBisafactorof

10xthepower,butbecauseoftherelationshipbetweenpowerandvoltage

notethat20dBisafactorof10onyourscopesdisplay.



ThehorizontalunitsperdivisionoftheFFTarealwaysinfrequency.The

abovescreenshotshows1.25KHzperdivision.Inthisdisplay,theleftsideof

thescreenisalwaysatDCor0Hz.Eachdivisiontotherightthenmarksthe

setvalue.Inthiscasethedivisionswouldbe0Hz,1.25KHz,2.5KHz,3.75

KHz,5KHz,andsoon.



Howtosaveawaveform'sFFT?



TosaveanFFTtothescopeoraUSBdrive,theFFTmustbesavedasa

referencewave“REF”asinthefollowingprocedure:

Pressthe“REF”button.Whenthesidemenuappears,setthesourcetobe

theFFT.Thenusethe“Save”optioninthemenutosavelocallyorexternally.



RIGOL TECHNOLOGIES USA INC

877-4-RIGOL-1 How-To Guide

[email protected]

www.rigolna.com



Tosavethewaveform,selectsave.



TosavetheFFTwaveformtoaUSBdrivepressthe

“Location”buttontheLocationnowswitchesto

“External”asinthefigurebelow:



Uponselecting“Save”selectthefiletosavethewaveformtoandthenexit

uponcompletion.



Referencewaveformscanthenberecalledatalatertimetocomparesignals.

RIGOL TECHNOLOGIES USA INC

877-4-RIGOL-1 How-To Guide

[email protected]

www.rigolna.com



Insummary,whilenotasaccurateasaspectrumanalyzerorwithasmuch

range,theFFTfunctionoftheoscilloscopecanbeusedtoviewthe

frequencydomaininformationforasignal.Withavarietyofcapabilitiesto

changeranges,units,anddisplaymodeaswellassavingandrecalling

waveforms,Rigoloscilloscopescanmakefrequencymeasurementseasily

andquicklyusingtheincludedFFTfunction.



Formoreinformationorquestionscontactusdirectlyat:



RigolTechnologiesUSA

7401FirstPlace

SuiteN

OakwoodVillage,OH44146



Youcanreachusdirectlyat:

(440)232‐4488

877‐4‐RIGOL‐1

inf[email protected]om

www.rigolna.com(RigolNorthAmericawebsite)



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