My vote is to use differential pressure sensors, one internal
one external, process the difference. Hey you might even
find out what depth your sub is listing!

----- Original Message -----
From: "M. Adam Davis" <adavis@UBASICS.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, October 16, 2000 1:50 PM
Subject: Re: [EE]: Help water level


> I've found that the 'pretty accurate flow rate meters' require large flows
and
> are expensive.  But it was some time ago when I looked for them, and I
only
> looked at those suited for high flow rates.  Perhaps a bellows type flow
meter
> would work here...
>
> If you don't mind going slowly you could always use a parastaltic (sp?)
pump to
> pump a known quantity in and out of the ballast tank.  Put a pressure
sensor on
> the outside and inside, and use the pressurized air to make the job easy
for the
> pump.
>
> -Adam
>
> Dale Botkin wrote:
> >
> > On Mon, 16 Oct 2000, Andy Shaw wrote:
> >
> > > Just a quick note here. The way I like to run my subs is not to spend
ages
> > > ballasting them so that taking on a full tank of water takes them to a
> > > neutral buoyancy (which is what most people do). Instead what I would
like
> > > to do is to automate this part so that I can just do a simple pond
side
> > > set-up of taking on water until the sub is neutral then store the
value
> > > associated with this state in eeprom. Then I just command the sub to
take on
> > > the same amount of water when I dive. I currently do this open loop
(timing
> > > based) but this tends to be a bit hit and miss as the batteries go
down...
> >
> > Just a thought:  There are available pretty accurate flow meters, as
used
> > in automotive applications to sense fuel flow.  Couldn't you use one of
> > these (or even a home-brewed one using a paddle wheel and slotted disk
or
> > whatever) to measure how much water you pump into and out of the ballast
> > tank?
> >
> > Dale
> > ---
> > The most exciting phrase to hear in science, the one that heralds new
> > discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
> >                 -- Isaac Asimov
> >
> > --
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>

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