Test Knotmeter transducer?

[sal...@salnick.cac.washington.edu]

Can anyone tell me if I can test a knotmeter transducer (for a Standard SL10) with a VOM? I suspect that I may have a broken wire somewhere and would like to rule out this possibility.

[SAIL LOCO]

Can't you just spin it and see if it gives a reading on the instrument?
"Trains are a winter sport"

[Jim - SBSC]

>From: sal...@salnick.cac.washington.edu

>Can anyone tell me if I can test a knotmeter transducer (for a Standard
>SL10) with a VOM?

As I recall, a knotmeter paddlewheel puts out a modified sine-wave of varying
frequency and the amplitude is on the order of 5 to 25 millivolts. For this it
is best viewed on an oscilloscope hooked to the paddlewheel cable at the
instrument jack end, while the wheel is spun.

Jim
Visit the Southern Bay Sailing Club website:
http://hometown.aol.com/winchkid/myhomepage/sports.html

To reply to my postings, you must remove "NOSPAM" from my e-mail address.

[Alan]

Bob

Every knotmeter transducer I've seen can be removed from within the hull and
replaced with a plug. Is your's permanently mounted?

Alan

sal...@salnick.cac.washington.edu wrote:

> Would that I could. It is on the hull, almost 6 feet down into the
> cold, cold pacific ocean.
>
> I was hoping for a method that I could use from inside the boat...
>
> bob

[sal...@salnick.cac.washington.edu]

[RW Salnick]

Thanks for the comment Jim...

My memory seems to contain the words 'hall effect' associated with the
transducers... I presume that this means that they must be powered to
produce any output... right?

bob

from the wet coast,
bob
--
RW Salnick | bsal...@cac.washington.edu
(206) 221-4677 | http://staff.washington.edu/bsalnick
S/V Eolian | http://www.realityplus.com/intangible/eolian/index.html

[sal...@salnick.cac.washington.edu]

I have the same experience. However, my boat did not come with the
plugs (I have two knotmeters), and the transducers are located in a very
narrow bilge, right at the very bottom probably 5 feet below the
waterline, and beneath the engine. It is a very awkward position, and
because of this I would be reluctant to pull the transducers, even if I
had the plugs, fearing that I might not be able to get the plug in
against the firehose spraying in my face. I am not even certain that
there is enough clearance to pull them. I would prefer to postpone
removal of the transducers until the boat is on the hard, and there is
no risk. I am probably 6 mo to a year from this.

I was hoping for a method to at least test the integrity of the wiring
between the transducers and the display heads... perhaps to even see if
the paddle wheels were spinning when the tidal flow brings water through
the moorage.

Initially, I suspected that barnacles (sp?) had taken up residence in
the transducers, but after asking a passing diver to check, he said no,
they both seemed to spin freely...

bob

Alan wrote:
>
> Bob
>
> Every knotmeter transducer I've seen can be removed from within the hull and
> replaced with a plug. Is your's permanently mounted?
>
> Alan
>
> sal...@salnick.cac.washington.edu wrote:
>

[Alan]

I see. In this case, I suspect the best way would be to do as Jim suggested and
disconnect the transducer wire from the gauge and monitor the output during the
tidal flow with an oscilloscope. If you can't get your hands on a scope, you
could use a DVM, set to measure AC mV. Compare measurements in still water vs.
tidal flow.

I've also found that the impeller wheels can sometimes bind when either the axle
or impeller gets worn. They will spin fine by hand, but will freeze up while
underway. Replacement (and in your case, relocation) is usually the best
solution.

Alan

[Al Gunther]

bsal...@cac.washington.edu wrote:

> Thanks for the comment Jim...
>
> My memory seems to contain the words 'hall effect' associated with the
> transducers... I presume that this means that they must be powered to
> produce any output... right?
>
> bob

The paddlewheel ones have magnets in the paddle blades with a coil in the
base. The magnets passing the coil produce alternating current. Your volt
meter may not read ac voltage that low and in dc, the plusses will cancel
out the minuses so it will probably show zero voltage. But you might get a
flicker in either. If I'm not mistaken, the only ships power going to mine
is for the instrument light.

--
Al Gunther, Kingston, WA <---- 47° 48.1'N, 122° 30.0'W
http://www.silverlink.net/~agunther/

[JGarner]

My volt meter has an AC setting in the 250 mV range. Should work for
this type of application. Good luck Salnick.

[Dave]

The Standard impellers use hall effect devices. Some of the Signet
impellers had a coil that generated a low voltage AC signal.
Dave

In article <agunther-251...@silver173-81.silverlink.net>,

agun...@silverlink.net (Al Gunther) wrote:
> bsal...@cac.washington.edu wrote:
>
> > Thanks for the comment Jim...
> >
> > My memory seems to contain the words 'hall effect' associated with
the
> > transducers... I presume that this means that they must be powered
to
> > produce any output... right?
> >
> > bob
>
> The paddlewheel ones have magnets in the paddle blades with a coil in
the
> base. The magnets passing the coil produce alternating current. Your
volt
> meter may not read ac voltage that low and in dc, the plusses will
cancel
> out the minuses so it will probably show zero voltage. But you might
get a
> flicker in either. If I'm not mistaken, the only ships power going to
mine
> is for the instrument light.
>
> --
> Al Gunther, Kingston, WA <---- 47° 48.1'N, 122° 30.0'W
> http://www.silverlink.net/~agunther/
>

Sent via Deja.com http://www.deja.com/
Before you buy.

[Jerry Twomey]

>
>
> My memory seems to contain the words 'hall effect' associated with the
> transducers... I presume that this means that they must be powered to
> produce any output... right?

Hall sensor = moving magnetic field (the little paddle thing has magnets in it)

and a coil (in the body of the transducer) in the thru-hull.

Check continuity of wires with a VOM, the transducer output should be able to be
looked at with
a O-scope.

Most of the time these things get gunked up with growth and junk, causing the wheel
to not move.
that is where the problem is most of the time

jerry

[sal...@salnick.cac.washington.edu]

I was able to confirm last night that the Signet knotmeter, which is a
magnet/coil type is OK. The nice part about this design is that I can
do a continuity check on the wiring to the transducer and the transducer
itself with a VOM. It doesn't produce speed readings, so it most likely
has a barnacle on it, or some bottom paint.

The Standard Horizon unit is definitely a magnet/hall-effect design -
much harder to test. In fact, I can't think of any way to test it that
doesn't involve me going swimming (not likely in Puget Sound) to spin
the paddle wheel. Even testing the display head is not simple - it
wants a 37.5 Hz square wave applied to the transducer connection...

Perhaps somebody deeper in electronic design can explain to me why they
would eschew the simplicity of the magnet/coil design (which produces AC
pulses) for the more complex (and untestable without special tools)
hall-effect design (which also produces AC pulses).

Hmmm... maybe I could simply install a coil-based transducer...

bob

Dave wrote:
>
> The Standard impellers use hall effect devices. Some of the Signet
> impellers had a coil that generated a low voltage AC signal.
> Dave
>
> In article <agunther-251...@silver173-81.silverlink.net>,
> agun...@silverlink.net (Al Gunther) wrote:
> > bsal...@cac.washington.edu wrote:
> >
> > > Thanks for the comment Jim...
> > >

> > > My memory seems to contain the words 'hall effect' associated with
> the
> > > transducers... I presume that this means that they must be powered
> to
> > > produce any output... right?
> > >

[Alan]

Bob

I'm not really a circuit designer, but I can think of a couple of reasons to
use a hall effect device instead of a coil. First, the amplitude of the
signal from the hall effect device (and associated amplifier) would be
constant with speed, whereas the the output of the coil would be lower at
slow speed and higher at high speed. Also, the output of the hall effect
transducer would be less affected by the loading of longer cable runs than a
coil.

Alan

[Jean-Marie Houle]

In article <381753A0...@irsi.com>, Alan <al...@irsi.com> wrote:

> Bob
>
> I'm not really a circuit designer, but I can think of a couple of reasons to
> use a hall effect device instead of a coil. First, the amplitude of the
> signal from the hall effect device (and associated amplifier) would be
> constant with speed, whereas the the output of the coil would be lower at
> slow speed and higher at high speed. Also, the output of the hall effect
> transducer would be less affected by the loading of longer cable runs than a
> coil.
>

Also, the hall effect transducer does not load the paddle-weel as the coil
does. You can feel it when turning the weel by hand. It allows a more
sensitive measurement. It will start working at a lower speed.

Jean-Marie VE2AEY

[sal...@salnick.cac.washington.edu]

Aha!

NOw THAT is a good reason to go for the Hall effect.

Thanks
bob