Simrad ES70 Manual De Usuario página 136

Simrad ES70
entonces conocidos por la ecosonda, y el software en la ecosonda se asegurará que no se
genera demasiada potencia. Si utiliza un transductor de otro fabricante, debe comprobar
manualmente que la potencia de salida de la Simrad ES70 no supere la potencia nominal.
Nota
Si se envía demasiada potencia al transductor se dañará irreparablemente – igual que
un altavoz.
Si el transductor recibe demasiada potencia desde la ecosonda, también cavitará. Éste
es un fenómeno físico que produce la aparición de burbujas de gas justo por debajo
de la superficie del transductor. Cuando ésto ocurre apenas se transmite energía en el
agua, y la cara del transductor es susceptible de dañarse. La cavitación depende de la
potencia aplicada, el tamaño de la superficie del transductor, la profundidad de montaje
del transductor, y la cantidad de contaminación (aire y partículas) bajo la cara del
transductor. Los transductores con una superficie grande pueden aceptar más potencia.
Near sea level, minute bubbles of micron or submicron size are always present in
the ocean. When the rarefaction tension phase of an acoustic wave is great enough,
the medium ruptures or "cavitates". For sound sources near the sea surface, the
ever-present cavitation nuclei permit rupture to occur at pressure swings of the
order of 1 atm (0.1 MPa), depending on the frequency, duration, and repetition
rate of the sound pulse. Cavitation bubbles may also be produced by Bernoulli
pressure drops associated with the tips of high-speed underwater propellers. Natural
cavitation is created by photosynthesis.
Several extraordinary physical phenomena are associated with acoustic cavitation.
Chemical reactions can be initiated or increased in activity; living cells and
macromolecules can be ruptured; violently oscillating bubbles close to a solid
surface can erode the toughest of metals or plastics; light may be produced
by cavitation (sonoluminescence). The high pressures and high temperatures
(calculated to be 30,000° Kelvin) at the inteior during the collapsing phase of
cavitating single bubbles can cause emission of a reproducible pulse of light of
duration less than 50 picoseconds.
Of direct importance to the use of sound sources at sea is the fact that, as the sound
pressure amplitude increases, ambient bubbles begin to oscillate nonlinearly, and
harmonics are generated. At sea level, the amplitude of the second harmonic is
less than 1 percent of the fundamental as long as the pressure amplitude of the
fundamental of a CW wave is less than about 0.01 atm rms (l kPa) (Rusby 1970).
This increases to about 5 percent harmonic distortion when the signal is about 10
kPa.
When the peak pressure amplitude is somewhat greater than 1 atm, the absolute
pressure for a sound source at sea level will be less than zero during the rarefaction
part of the cycle. In using CW below 10 kHz, this negative pressure, or tension, is
the trigger for a sharply increased level of harmonic distortion and the issuance of
broadband noise. Any attempt to increase the sound pressure amplitude appreciably
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