Join Date: Feb 2000
Location: Annapolis, Md
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Re: For Pete's sake! I just want a speed transducer!
Knotmeter transducers do not send NMEA information. They either send an electrical pulse or voltage reading. The Display head or 'black box' takes that pulse frequency or voltage, crunches the numbers and converts that to useful data such as a read out on an instrument or a NMEA sentence. Some of the newer systems use a 'smart transducer' but those do not work with older equipment.
Since different manufacturers, or even different models of equipment from the same manufacturer use different transducers which produce different pulse rates or voltages, its extremely difficult to find alternate transducers for any given display head, even if you do know the transducer manufacturer.
One of the things which has happened with great frequency is that the design of transducers has changed over time. Manufacturers claim that these changes have resulted in more reliability or better functionality. So with every new upgrade to the display heads, the transducers seem to change as well. But with each change, the transducer in your hull and possibly thru-hull in your boat, will no longer be correct for the replacement black box or display head.
My best suggestion would be to start with the company that made your display head. Find out what the input characteristics need to be to work properly with by your instruments. Failing that, find out the specific model number for the transducer that was used by your display. Once you have that information, Airmar (or who ever made your transducer) should be able to tell you whether they have other transducers with the output characteristics of the specific transducer that you are replacing.
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Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay
Last edited by Jeff_H; 03-26-2018 at 11:36 AM.