Simrad ST90 - Self Noise

78
442703/B
•Acousticnoisefromotherhydroacousticsystems
BThetransducercableislong,andmaypickupelectricnoisefromgenerators,
pumps,coolingsystemsandotherelectricorelectromechanicaldevices.
CThepreampliersareverysensitive,andtheycaneasilypickupelectricalnoise
frominternalandexternalpowersupplies.Thepreampliersarealsovulnerablefor
analoguenoisecreatedbytheirownelectroniccircuitry.Digitalnoisecreatedby
theconverterandprocessingcircuitrycanalsocreateproblems.
DConverterstransformtheanalogueechoestodigitalformat.
ESignalprocessingcircuitrycancreatedigitalnoise.
Relatedtopics
Acousticnoise,page76
Selfnoise
Anyvesselequippedwithahydroacousticsystem(forexampleechosounderorsonar)
willproducemoreorlessselfnoise.
Therearemanysourcesofsuchselfnoise.Wewillheregointosomedetailsinorderto
analysethedifferentsourcesofselfnoiseonavesselandhowtheymayinuenceupon
thenoiselevelofthehydroacousticinstruments.
Machinerynoise
Themaincontributortomachinerynoiseisusuallythemainengineonboardthevessel.
Thecontributionfromauxiliarymachinerymay,however,beconsiderable,especiallyif
itisinpoorshape.Themachinerynoisecanbetransmittedtothetransduceras:
•Structure-bornenoisethroughtheshipstructureandthetransducermountings
•Water-bornenoisethroughthehullintothewatertothetransducer
Electricalnoise
Modernvesselsarenormallyequippedwithalotofelectricinstrumentssuchas
hydroacousticsystems,radars,navigationsystems,andcommunicationequipment.
Anyelectricinstrumentsmayinsomecasescauseelectricalinterferenceandnoise.
Internationalregulationsandcerticationsareusedtocontrolandreducethis,buteven
thesearelimitediftheelectricalsystemsarepoorlyinstalledand/ormaintained.
Propellernoise
Propellernoiseisoftenthemainsourceofnoiseathighervesselspeeds.Variablepitch
propellersorfastmovingpropellersusuallymakemorenoisethanxedpropellersor
slowmovingpropellers.
Propellernoiseisusuallywater-borne.Insomecases,however,shaftvibrationsor
vibrationsinthehullnearthepropellermaybestructure-bornetothetransducer.Ifa
propellerbladeisdamaged,thismayincreasethenoiseconsiderably.
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