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B & G Sonic Speed, pulses per nautical mile

Discussion in 'Boat Electronics' started by Moonshadow, Oct 11, 2009.

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  1. Moonshadow

    Moonshadow Guest

    Can anyone please tell me how many pulses per nautical mile are
    delivered by the B & G Sonic Speed system.
     
  2. I am very curious why you ask. This system has been out of production for a long time now. I too am a fond user, so I am also
    concerned about the availability of spares to keep it running. It is much more accurate than the impeller type because it measures
    water velocity beyond the turbulent hull boundary layer and it won't foul and wear out as the impeller type does.. I hope you
    realize that it is designed to produce the same pulse train rate of the conventional impeller, as the electronics beyond the speed
    box are interchangeable. So it shouldn't be rocket science, once the impeller pitch is measured. Please post your findings when
    you have them. Currently, Sperry Marine make a much more sophisticated version for ships. That system measures flow in both the x
    and y direction and can have multiple sensors on the hull. Its purpose is primarily used to measure water currents when inshore.
    Steve
     
  3. Moonshadow

    Moonshadow Guest

    We will be using them to measure water currents past our jetty due to
    passing shipping.

    They are an old design, but we've just bought two so they are still
    available.
    We don't have a conventional impeller to measure, and I can't find info
    regarding its ppnm rate anywhere either.
    Hmmm. Pity I didn't know about that earlier. Too late - I must use what
    I've got.

    Thanks for your comments.
     
  4. You couldn't afford the Sperry unit anyway.......it is very expensive. From your comment, I assume you don't have the rest of the
    system (processor and display) How are you going to use it? I will find an impeller measure it and get back to you.
    Steve
     
  5. Moonshadow

    Moonshadow Guest

    Thanks Steve.

    I will design and build a PIC-based interface which will deliver
    NMEA-formatted proprietary sentences containing the current rates from
    the two Sonic Speed systems. Others will organise for these data to get
    to our servers via various boxes of tricks and WiFi. The data from these
    will be logged, and probably be made available in real time via the
    Internet.
     
  6. Paul

    Paul Guest

    The B&G "Network" paddlewheel puts out a nominal 6.25Hz per Knot (at least
    6.25 Hz is the factory-standard calibration setting). That would work out
    to 6.25 x 3600 = 22,500 pulses per nautical mile. This is very likely the
    same paddlewheel sensor that the Sonic unit is emulating.
     
  7. Moonshadow

    Moonshadow Guest

    Thank you Paul.
     
  8. Paul

    Paul Guest

    For depth sounders it's a lot more complicated. The transducer is a
    piezoelectric element, often with a seperate temperature sensor. These are
    both analog devices, at least the types I've seen. The electronics in the
    display head (or possibly a central processor unit) send a high-power signal
    in the high kilohertz range, then listens for the weak echo returned by the
    bottom. It is possible to swap out the basic transducer if the frequency it
    is designed for matches the old unit, but I don't know what the temperature
    measurement interface looks like.

    I've seen transducer frequencies of 50KHz and 200KHz, but I don't know what
    frequency the B&G units use.
     
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