lecroy 18_LTXXX-OM-E_Ch14 电路图.pdf

LTXXX-OM-E Rev BISSUED: January2002191 CH A P T E RFO U R T E E NMaking Histograms CreateandViewaHistogram Createyour histogram as youwouldanyother Mathfunction: bydefiningtraceA, B, C, or D as thefunction. Havingconnectedyour signal toaWaverunner channel (Channel 1 inthis example), dothefollowing: 1.Press 1 toselect CHANNEL 1 anddisplaythebasic Waverunner menus. 2.Press thebuttontoand A tomakeTraceA azoom of Channel 1. 3.Press thebuttonforandselecttodisplaySETUP OF A. 4.Usetheseandthemenus onthefollowingpages to set upyour histogram. Toselect for math. Toselect Histogram. Toselect parameters andfurther configurethehistogram (seenext page). For calculatingoptimal center- andbin-widthvalues for the histogram. Toselect theparameter linetobeusedinthehistogram. Toselect usingbutton or knob thenumber of values inthehistogram. Whenthemaximum of two billionvalues is exceeded, theparameter results will scroll off thehistogram. RadioFans.CN 收音机爱 好者资料库 H I S T O G R A M S 192ISSUED: January2002LTXXX-OM-E Rev B T TI IP P: : As withanyothertrace, position and expand yourhistogramusing POSITION and ZOOM knobs POSITION ZOOMZOOM POSITION Toadjust either thehistogram binningor scalesettings. When Binning is selected, themenus shown hereappear. N NO OT TE E: : Whenusing these knobs, values inthe “Center” and “Width” menus do not change, since theydetermine the range of the histogramand cannot be used todetermine the parametervalue range of a particularbin. If the histogramis repositioned using the horizontalPOSITION knob the histograms centerwillbe moved fromthe centerof the screen. (MEASURE TOOLS should thenbe used. ) Toaccess theCHANGE PARAM menus andselect or configurea parameter for histogramming. SeeChapter 11, “Parameter Analysis.” For calculatingoptimal center- andbin-widthvalues for the histogram. For choosingthenumber of bins intowhichthe parameter events aretobeclassified, or distributed. RadioFans.CN 收音机爱 好者资料库 CH A P T E RFO U R T E E N:Making Histograms LTXXX-OM-E Rev BISSUED: January2002193 Toadjust either thehistogram binningor scalesettings. WhenScale is selected, themenus shownhereappear (seepage197). For settingtheverticalscale: Linearsetsalinear verticalscale,Log a logarithmicverticalscale,and LinConstMaxtheverticalscalingtoa linear valuethat usesclosetothefullverticaldisplaycapabilityof the instrument. Waverunner automaticallyincreases thevertical scalesettingas required, ensuringthat thehighest histogram bar does not exceedthe vertical screendisplaylimit. Toselect parameters andconfigurethehistogram. For calculatingoptimal center- andbin-widthvalues for the histogram. Toset thehistogram center value. Toset thehistogram widthvalueper division. The widthper divisionmultipliedbythenumber of horizontal displaydivisions (ten)determines therange of parameter values centeredonthenumber inthe “Center” menu, usedtocreatethehistogram. RadioFans.CN 收音机爱 好者资料库 H I S T O G R A M S 194ISSUED: January2002LTXXX-OM-E Rev B Figure2.1, below , shows thedisplaywhen“Histogram” is selectedfrom the“MathType” menu. Thefreq parameter onlyhas beendefined. Todefineadditional parameters, select from the“Histogram custom line” menu. Figure 2.1 Eachtimeawaveform parameter valueis calculatedyoucanplaceit inahistogram bin. Themaximum number of suchvalues is selectedfrom the“usingupto” menu. Pressingtheassociatedmenubuttonor turningthe knoballows youto select arangefrom 20 totwobillionparameter valuecalculations for histogram display. CH A P T E RFO U R T E E N:Making Histograms LTXXX-OM-E Rev BISSUED: January2002195 5.Now , press A todisplaythehistogram, for adisplaysimilar tothat showninFigure2.2. 2 1 Figure 2.2 Eachhistogram is set tocaptureparameter values fallingwithinaspecifiedrange. As thescopecaptures the values inthis rangethebincounts will increase. Thosevalues not fallingwithintherangearenot usedinthe histogram. Informationonthehistogram is providedintheDisplayedtracefield(Item )for theselectedtrace, which shows: Thecurrent horizontal per divisionsettingfor thehistogram (“1 Hz” inthis example). Theunit typeused is determinedbythewaveform parameter typeonwhichthehistogram is based. Thevertical scalein#bincounts per division(here, “200 m”). Thenumber of parameter values that fall withintherange(“inside0”) Thepercentagethat fall below(“0%”) Thepercentageof values abovetherange(“100%”). H I S T O G R A M S 196ISSUED: January2002LTXXX-OM-E Rev B Theprevious figureshows that 100% of thecapturedevents areabovetherangeof binvalues set for the histogram. As aresult, thebaselineof thehistogram graph ()is displayed, but novalues appear. Selectingthe“FIND CENTER AND WIDTH” menucalculates theoptimal center andbin-widthvalues, basedontheup-to-the-most-recent parameter values calculated. Choosethenumber of parameter calculations with the“usingupto” menu(or 20 000 values if this is greater than20 000). Figure2.3 shows atypical result. 1 Figure 2.3 If thetraceonwhichyouhavemadethehistogram is not azoom, all bins withevents will bedisplayed. Otherwise, youcanpress RESET toreset thetraceanddisplayall histogram events. TheInformation Window(Item )at thebottom of theprevious figureshows ahistogram of thefreq parameter for Channel 1 (designatedas “A:Hfreq(1)”)for TraceA. The“1000 100 pts” inthewindow indicates that thesignal onChannel 1 has 1000 waveform acquisitionsamples per sweepandis beingmapped into100 histogram bins. SETTING BINNING AND SCALE The“Setup” menuallows modificationof either the“Binning” or thehistogram “Scale” settings. If “Binning” is selected, the“classifyinto” menuappears, as showninthefigureabove. CH A P T E RFO U R T E E N:Making Histograms LTXXX-OM-E Rev BISSUED: January2002197 Thenumber of bins usedcanbeset from arangeof 20 to2000 ina1-2-5 sequence, bypressingthe correspondingmenubuttonor turningtheassociatedknob. If “Scale” is selectedfrom the“Setup” menu, ascreensimilar to that of Figure2.4 will bedisplayed. Figure 2.4 Thefollowingoptions areofferedbythe“vertical” menufor settingthevertical scale: Linearsets thevertical scaleas linear. Thebaselineof thehistogram designates abinvalueof 0. As the bincounts increasebeyondthat whichcanbedisplayedonscreenusingthecurrent vertical scale, this scale is automaticallyincreasedina1-2-5 sequence. H I S T O G R A M S 198ISSUED: January2002LTXXX-OM-E Rev B Log sets thevertical scaleas logarithmic (Fig. 2.5). Becauseavalueof 0 cannot bespecified logarithmically, no baselineis provided. Figure 2.5 CH A P T E RFO U R T E E N:Making Histograms LTXXX-OM-E Rev BISSUED: January2002199 LinConstMaxsets thevertical scalingtoalinear valuethat uses nearlythefull vertical displaycapabilityof thescope(Fig. 2.6). Theheight of thehistogram will remainalmost constant. 1 3 2 Figure 2.6 For anyof theseoptions, thescopeautomaticallyincreases thevertical scalesettingas required, ensuringthe highest histogram bindoes not exceedthevertical screendisplaylimit. The“Center” and“Width” menus allowyoutospecifythehistogram center valueandwidthper division. The widthper divisiontimes thenumber of horizontal displaydivisions (10)determines therangeof parameter values centeredonthenumber intheCentermenu, usedtocreatethehistogram. Intheprevious figure, thewidth per divisionis 2.000 103(Item ). As thehistogram is of afrequency parameter, themeasurement parameter is inhertz. Therangeof parameter values containedinthehistogram is thus (2 kHz/division)x(10 divisions)= 20 kHz, withacenter of 2.02 E+05 Hz (). Inthis example, all freqparameter values within202 kHz 10 kHz from 192 kHz to212 kHz areused increatingthehistogram. Therangeis subdividedbythenumber of bins set bytheuser. Here, therangeis 20 kHz, as calculatedabove, andthenumber of bins is 100. Therefore, therangeof eachbinis: 20 kHz / 100 bins, or 0.2 kHz per bin. H I S T O G R A M S 200ISSUED: January2002LTXXX-OM-E Rev B The“Center” menuallows youtomodifythecenter values mantissa here2.02 exponent (E+05), or the number of digits used inspecifyingthemantissa(three). Thedisplayscaleof 1 kHz/division, showninthe TraceDisplayField, is indicatedby. This scalehas beenset usingthehorizontal zoom control andcan expandthescalefor visual examination of thehistogram trace. Theuseof zoom inthis waydoes not modifytherangeof dataacquisitionfor thehistogram, onlythedisplay scale. Therangeof measurement acquisitionfor thehistogram remains basedonthecenter andwidthscale, resultinginarangeof 202 kHz 10 kHz for dataacquisition. Thewidthor divisioncanbeincrementedina1-2-5 sequencebyselecting“Width.” CHOOSING HISTOGRAM PARAMETERS Onceyouhavecreatedthehistogram, youcanselect additional parameter values for measuringparticular attributes of thehistogram itself. 6.Press thebuttontoselectandaccess theCHANGE PARAM menus (Fig. 2.7). 1 Figure 2.7 CH A P T E RFO U R T E E N:Making Histograms LTXXX-OM-E Rev BISSUED: January2002201 Youcan nowselect newparameters modifythosealreadyselected. Inthefigureontheprevious page, the histogram parameters maxpandmode(Item )havebeenselected. Thesedeterminethecount for thebin with thehighest peak, andthecorrespondinghorizontal axis valueof that bins center. Notethat both“maxp” and“mode” arefollowedby“(A)” onthedisplay. This designates themeasurements as beingmadeon thesignal onTraceA. Alsoof note: Thevalueof “maxp(A)” is “110 #”, indicatingthehighest binhas acount of 110 events. Thevalueof mode(A)is “203.90 kHz”, indicatingthat this binis at 203.90 kHz. Theicontotheleft of “mode” and“maxp” parameters indicates that theparameter is beingmadeona tracedefinedas ahistogram. However, if theseparameters weretobeinadvertentlyset for atracewith nohistogram theywouldshow-. USING MEASUREMENT CURSORS Youcanusecursors (seeChapter 4)toselect asectionof ahistogram onwhichaparameter is to becalculated. Figure2.8 belowshows theaverage, “avg(A)” (Item )of thedistributionbetweentheparameter cursors for a histogram of thefrequency(“freq”)parameter of awaveform. Theparameter cursors ()areset “from” 4.70 divisions ()“to” 9.20 divisions ()of thedisplay. 1 3 2 4 Figure 2.8 H I S T O G R A M S 202ISSUED: January2002LTXXX-OM-E Rev B NOTE: It is recommended that you use cursors onlyafterthe input waveformacquisitionhas been completed. Otherwise, the cursors willalsoselect the portionof the input waveformused to calculate the parameterduring acquisition, creating a histogramwithonlythe localparameter values forthe selected waveformportion. Cursors areuseful for determiningthevalueandpopulationof selectedbins. Figure2.9 shows anabsolutetime cursor (Item )positionedonaselectedhistogram bin. Thevalueof thebin()andthepopulationof thebin ()arealsoshown. 1 3 2 4 Figure 2.9 A histograms rangeis representedbythehorizontal widthof thehistogram baseline. As thehistogram is repositionedverticallytheleft andright sides of the baselinecanbeseen. Intheabovefigure, theleft edgeof therangeis visible(). TIP: Press CLEAR SWEEPS At anytime toclearall histogramevents inthe 20-kparameterbuffer at the same time. CH A P T E RFO U R T E E N:Making Histograms LTXXX-OM-E Rev BISSUED: January2002203 ZOOMING SEGMENTED TRACES Youcanalsodisplayhistograms of traces that arezooms of segmentedwaveforms. Whenasegment from a zoomedtraceis selected, thehistogram for that segment will appear. Onlytheportionof thesegment displayedandbetweentheparameter cursors will beusedincreatingthehistogram. Therespectivedisplayed tracefieldwill showthenumber of events capturedfor thesegment. H I S T O G R A M S 204ISSUED: January2002LTXXX-OM-E Rev B BLANK PAGE