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 Catalina/Capri 25/250 Sailor's Forums
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 Are speed logs just inductively coupled?		  New Topic  Topic Locked
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delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts
Initially Posted - 07/12/2013 :  19:38:32  Show Profile  Visit delliottg's Homepage
I installed an older Humminbird fishfinder on SL the other day, using the toilet wax method. It also came with a thermometer / speed wheel designed to be mounted on the transom. I unscewed the speed wheel portion to see if the temperature part would read if I stuck it in the wax as well, which it did. There were no electrical connections between the two, so they must be inductively coupled, right? Now I'm wondering if i could have set it next to the old speed log (which still works just fine), and whether it could sense the magnetic pulses from it? If so, I could remove the Bidata display entirely, and replace it with the fishfinder.
David
C-250 Mainsheet Editor


Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --
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Voyager
Master Marine Consultant

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USA
5371 Posts
Response Posted - 07/13/2013 :  06:54:47  Show Profile
Some are, some aren't. Many RPM sensors use a small permanent magnet in the rotor or spindle and a magnetic reed switch or "Hall Effect" semiconductor in the pickup. When the magnet passes the sensor it creates a series of pulses and the circuit counts the pulses. Thru the magic of TTL circuitry and math it displays a speed on a display.
The rotor passes within a few mm of the sensor.
Not sure but I don't think 2 speed sensors nearby one another would interact - they might - might be worth a try.
Edited by - Voyager on 07/13/2013 07:14:27
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.