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The Sonic Surface-Wave Transducer

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The Sonic Surface-Wave Transducer EDITORIALffiruET$ffisAl COpycsPY UNIVERSITYUNIVERSITY OF OF MINNESOTAI\4INMSOTA ST.ST. ANTHONYANTHONY FALLS FAttS HYDRAULICHYDRAUTIC LABORATORYTABORATORY LORENZTORENZ G.G. STRAUB.STRAUB, DirectorDirector TechnicalTechnicql PaperPaper No. No. 23.23, Series Series BB TheThe SonicSonic Surface-Surface-WaveWave TransducerTransducer / Preprint of Paper toto be Presented atct the AmericanAmericcn Towing Tank Conference.Conference, University of California.California, Berkeley Campus.Ccmrpus, AugustAugiust 31 to September 2.2, 1959 by JOHN]OHN M. KILLENKNffiN JulyJuly 19591959 Minnecpolis,Minneapolis. IvlinnesolcrMinnesota / :' UNIVERSITYUNIVERSITY OFOF MINNESOTAMINMSOTA ST.ST. ANTHONYAIiITHONY FALLSFALTS HYDRAULICHYDNAUTIC LABORATORY TABONATORY LORENZtOnENZ G.G. STRAUB,STRAIJB, DirectorDirector TechnicalTechniccl PaperPcrper NoNo.. 23,23, SeriesSeries BB The SonicSonic Surface-Surface-\MaveWave TransducerTransducer Preprint of PaperPcper to be Presented atctt the AmericanAmericcn Towing TankTc"'L Conference, University of California,Cclifornio Berkeley Campus,Ccmpus, August 313l to September 2, 1959lg59 by JOHNIOIIN MM.. KILLENKILI.EN • IulyJuly 1959 Minnecrpolis,Minneapolis, MinnesotcMinnesota .. ABSTRACTastISagS AA wavewave height measuringmeasuring instrumentinstn:ment isis describeddescribed. whichwhieh measuresmeasures thethe height ofof waterwater surfacesurface waveswanes byb;r means ofof aa sonicsonic rangingranging techniquetechnique inin airoair" This systemsystern isis advantageousadvantageous forfor wave amplitude measurementsmeasurernents fromfrom a movingnroving towingtow'ing carriagecarriage since thethe sensing elementselenrents or itsi-ts supportszuppor.ls do not disturb thethe water surface.surface" The?he design operating range of the instrumentinstn:nrent is 2-in.Z-in. to 2-ft wave height.height" The accuracy of measurement depends on the incrementalj-ncremental slope ofoJ the water surfacesrirface at the point of measurement.measurement," An intrinsic erroreror of !0.83O,B per centeent average over the wave would occur for a 2-ft2-fb wave with a slope at mid­nid- height of 0.2. This?his erroremor increasesinereases to !3.2!3,2 perper cent for a 2-in. wave of the same slope.slope, The error is much reduced for both these cond.itionsconditions with less steep waves.rraves. L11iii a { --------CONTENTSCONTENTS Page Abstract.. e. e r o o. e r o o ... r. ! . r r.. taaaa+4+iii Abstract •••••• • • • • • •• 0 • • • • • • • • • • • • • • • • tist of lllustrations List of Illustrations •n •o •. •. •! •••r, . •. •t •. •. •. •| •. •. •. •. •c •toaaav •••• v I.T. INTRODUCTIONfl{tnOSiCTlON •••. •. ..... .,. 0o •c •. •. •o •f •. •••I o e •r •r. • •. •. •o •.. • 11 II.rr" DESCRIPTIOND$scRrPTf0I{0FAPPAnA:Ils OF APPARATUS •r.. • • 0r. • ..o.,.. • .. • •r. • •o •o •o,*... ., • • • •' 1 III.III' ACCURACYAccUBAcT0FI{EAsUns}4s}illf OF MEASUREMENT •. •o.6... • • • • • •o... • • • •o. • '0 ••o.. • •e ..r. 0 2 fV" CIRCUITCffiCUITOE$CHIPTI0I\T DESCRIPTION •" •o I • • • 0 • • • • • • • • • • 0 • • IV. •oo • 0 o r..o o. o,... c. + o.. 5 A. PulserFnlsgr 0o ~D 0o •.. • "40. .. • •ara{ • •• •a. • 0rr.., 0 • • " •r.... • • • • 5 B. ,.SparkSpark CoilCoLl andard Gap .."..c .. d ! 0o •. .0 •. •. •. •o •. •I "o •. •{ •r 5) A C. MicrophoneHlerophorre ••••d o o r 0. 0o. .,• • •i! •c' 0' 0. •o, <> •o •o •* ..r 0o •o •. •. 6 D.D" Amplifierarrplifier and Amplitude^&raplitude Discriminatorlliscriminator .......c . e,, . '"* ••. I 6 A E.E" Phantastron Delay.Delay o 04 .....* * r" ...o + 0a,, •r .,a <I€ ...o, 9 .....6 * i .,* 06 •ir 6 F. BootstrapBootstrap$reep.. Sweep • .,s, ..+ 0,,"o +sn!o .. co .. ..* '"i ..+,r{r. .. .. • e , '"c.}c,,f, .. • .0' 6 G.Or Holding CircuitsCircults •c ""* ..o ..., it ..*, .. ..* ..+l • ... ..e ... +,• • "G "{ ..{ ..{! 6 V. ACKNOWLEDGMENTSAC,K$0HLEDGMEHT$ '0 *,0 .. .i!I"*tr{ 0n,r.}.+*.r, . • .. e' • .. '"$*a*+. ... • • ~ • !}.• •• }. • 7 a... ListIrist of ReferencesHefergnces ...............r + * € r + c oa <I' .," ..* *,6.. ... +..6e' • . " e,'" ., a• {• *.. ••r e i.• • B8 Figuresl.throughl5Figures 1 through 15 .... c "q ......+ . { o.' 0 f• ,0 ae ....*. s ... ...{ . e'* c'" ,..* . '*. c,• • 11l-t PartslistParts List "0e o a.o. o.. o• o• r.0' 0 &.. e• .6.. .. $,i• '" *... *... r'• e... *..,.n• ., • .. ... +... • €• r• G• 27 iviv ... 1&rqr 1ST ogg F -------------MsgSSggrgrgI 1 1 U S T RAT ION S Figure Page 1 PhotographPhotographof of FrontFrontPanel Panel •... • • •r .0r' o ••r... • • 0r. • ..i,..,... ... • • • • 11It 2 Photograph of RangingBanging Head o.o I 0o 00. o .•r 06 •. 0€ 0r •r •c' 0 •. ••., •. 12L2 i =h0ft 3 LargeLargeMechani.calWave Mechanical Wave HH*2ft, 1& 2 ft, .>...\ 1& 40 ft .0.0.. c c o o .c .c. • 13 o = 4 Small$mall Mechanicallfiechanical Wave H 1& 2 in.,i-n., .>...\ = 2 ft •. •. •. •r •. •. •., • 141I+ tr 5 Photographs of Towing Carriage and Mechanical}4echanical Waves •. •. 0o •. •, 15 6 Comparison of Capacitive Wavelfave RecordHecord withl,iith SonicSonie WaveHave Record, - = HI{ 1& 0.6930"693 ft, SteepnessSieepness - 0.055 •. 0o 0. ••. + 0. 0o •. 0., •••••. 1615 7 Comparisonfionrpartson of CapacitiveCapaeitive WaveHave RecordBecord withr'rith Sonic Wavel{ave Record,Eeeord, -O.I25 HI{.Iftr • 1 ft, Steepness 1& 0.125 ••••••••••••••••.. s... r... *...., 17t7 8X Functional BlockHlock DiagramDiagran of Sonic$onic Wave-Profile!{ave-Profile Transducer •. •* 181B 9 MicrophoneHicrophone and PreamplifierPrearnplifier Housing .• •., • •. o0 •{, •. •. oe 0e 0q ••o, 19 10 FrequencyFrequencyResponse Response ofofPreamplifier Preamplifier ,•• o 0& •|, 0 •* •o •c.5 • 0 •r 0! 0r 204U 11 Pulser ••.. •r ·e*... • • • 0c. • •. •••••••••.. r r a.eaao....... 0 ••••••• 212A 12 Delayklay Phantastron and &aplitudeAmplitude Discriminatorliseriminator, • •o .• •c •. •c •. •. 22 13 AmplifiersA:aplifiers •••••••••" f . *.. * d r. '. +• c.. r• 0c e• ,• •+ r• e0 •r.... • • • • c• 23 14T4 Bootstrap$weepandHol-d:ingCircuitsBootstrap Sweep and Holding Circuits .• c• •s.., • • 0 c0 *..• • • o• o0 2b24 1r' 15L} PowgrSuppliesPower Supplies •••••••. r.6 r. I o.0 ••• r. {• !.• • c0 c• f• .• r• r.• • r}.• • 25z, v THE $ON]C -------SURFACE-WAVESU&EAgg-ggsE---- ----------33g,rE!sqg&TRANSDUCER I.1, INTRODUCTIONII{TNOAICTION The use of a wave-profile$ave-profi:e recorder whoseerhose sensing elementsele$ent$ are sub­su^b- mergednerged or partly submerged andand. which is mounted on a towingtoring carriageearriage movingnoving at - high speed$peed produces problems of structuraletrructural ssupport,upport of the element and dis­dis- turbanceturbanee of the liquid surface.surfaee. The wave-profile recorder described in thisthj"s reportreport' is based on the soI1;ic-rangingso4ic-ranging principle in air and appears tot,o overcomeovercms these difficultiesdiffleulties sincesj-nce no part of the instrumenti:rstrunent contactscontaets the waterrrater surfacesurfaeeoo The instrumentinst:rrment is intended to operate withrith wave heights of 2 in.in" to 2 ft,fL, wave lengths of 2 tota 40LO ft, andad an flequivalentneqr::lvalent periodfiperiodlt as short as 1/20t/2O sec.$€cr These?hese operatingoperati^agrang9s ranges aresre presunedpresumed to correspondeorrespond to ranges of interesti-nterrest ini-n laboratory wave studies andanddo do not specifyspecif) the limits of application.application, The?he obt.ainableobtainable accuracyacfiracy is dependent on the incrementalineremental slope and thetbe waveuave heighto Therefore, withrr:th this instrument,i-nsLrnment, as withrrith mostr*ost ''plrysicalphysical measuring instruments,iastnments, , carefulcarefuJ- attention mustrnusb be paidpald to these two mentioned geometriesge*raetries in order to keep errorseruors within the acceptable limitsljm:its for the particular investigation.investigat'ion" IIoII" DESCRIPTIONDBSCAIPTIO}d OF APPARATUSAPPASAfl]S The instrumentj-nstnnent functionsfunciions as follows:fo3*lows: AS" veryve:y $ortshort pulse ofsf sound is transmittedtranrxrltted fromfroyn a point as closeelose as pracbica1-practical to the water surface. The?he sound puSsepulse is reflectedreflLeeted by the watersater surface*rrfaee and sensed byW a microphonenicrophone lo­1o- cated as closeelose as possible tot,o the point of transmissionotransnrissiono Appropriate elec­elec- tronictronie circuitseircuiis measureReafirre the timetjrce ofef travel ofsf the soundsornrd pulse and convert this timetirne intolnts a voltage proportional to the time"tixe" WhenHhen this process is repeatedrrepeated 120 timestjmes a second,seeond, a voltage output results whoser*hose magnitudenagritude varies withsith the changes in the levelIevel of the water surface"sarfaceo On a cathode-raycathede-ray oscillographoseillopraph or light-beamlight-bear* oscillographoscll1ograph whichshich havetrave a high-frequencyhlgh-frcquency response, thisthi-s wave$a?€ pro­pro* filefi1.e will appear composedconposed of a seriesserj.es ofcf smalleffalJ- steps,sLeps, eacheaeh step corresponding to a samplesanrple of the wave profile"profile o On0n mostrnost direct-writingd:irect-writing oscillographs whose frequencyfrequeney responsere$povrse extendsexbends to about 10010O cycles, the wave profile willwiIL appear as a smoothgaooth line"line. 22 TheThe instrnrnentinstrument lsis composedcomposed pf of twotwo parts:parts: aa controlcontrol panel,panel, Fig.Fig. 1,1, andand aa rangingranging head,,head, Fig.Fig. 2,2. InIn prac*iealpractical applicationapplication thethe raagingranging headhead isis placedplaced appro:ci*ratepapproximately 5.55r5 in*in. frosrfrom thethe rnaxj:armmaximum erpectedexpected crestcrest ofof tbethe rrilsY€nrwaves.
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