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Airmar
is a little shy about calling this transducer “new” because
it was originally introduced several years ago. It even won a prize for
innovation, but full production had to be curtailed until some RF interference
issues could be resolved to comply with strict European standards. Perhaps
the CS4500, now encased in protective bronze and fully certified, is better
termed “newly available.” At any rate, it has no moving parts
to foul, claims an accurate range from 0.1 to 40 knots, and also manages
to skip over the boundary-layer effect that can mess up a conventional
paddle wheel’s precision.
The
unit works by sending out twin beams of acoustic energy, much like a sounder,
but at a very high 4.5-MHz frequency capable of generating super fast
and microscopically narrow returns from passing air bubbles, plankton,
etc. The signals are first “range-gated” to include only those
three to five inches away (bye-bye boundary layer), then pattern-analyzed
and timed to generate a speed value every half second (see inset). The
ultrasonic insert includes a temperature sensor and can be had with a
choice of housings. It can also be retrofitted into most two-inch paddle
wheel housings, and its “pulsed” output format will work with
many existing instrument systems. It sells for about $600.
Airmar
Phone: (603) 673-9570. www.airmar.com.
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