I still like the idea of having no moving parts and the perspex
device inserted into the liquid, using the reflected infrared
and an analogue sensor. This should give 9 or 10 bits analogue
and that would be fine enough resolution for what you wanted.
I think this idea might even work with a tapered bar rather than
a stepped one?

Maybe if you had to use moving parts I would have a single float
on an "arm" so you only have one pivot bearing, this would give
the most reliable movement and the least stiction. The pivot end
of the arm could have a analogue opto-interuptor going to your A/D
or maybe a reflective opto with reflection amount determined by
the position or angle of the arm. I think measuring pressure is
a recipe for disaster, ie if the sub goes under waves the pressure
will change, or unstable handling may cause the sub to go up/down
as it moves, causing pressure changes. Maybe your design might
later call for valves to close the tanks from the outside water?
I could see this being of use in a research sub.

Seems to me if you want to measure the water level, then measure
that in a way that is secure, if you want to measure pressure to
determine sub depth than by all means use a pressure sensor.
I just think the best way to measure liquid level is to measure
the liquid level! :o)
-Roman


Peter L. Peres wrote:
>
> Andy, you assume that the tank is open to the water and that nothing
> opposes its movement in and out. This is not the way it works on tiny
> subs afaik (but maybe you know better ;-).
>
> The only ACCURATE way to know the volume of water in the tank is to use a
> volumetric pump to fill and empty it and count turns. Assuming there are
> no leaks (hahaha) that will be accurate. But not to 0.3%.
>
> If this is some sort of slow research sub then this will be adequate from
> all points of view, excepting for the pressurized volumetric pump which is
> a chapter for itself. If you want to go fast, use the navy way, blow air
> into the tanks to raise, and vent air out the top to go down. And use
> a valve to close off the water when not changing pressure. Andy, you
> are into this afaik, what kind of ballast control do you use on model subs
> ?
>
> Peter
>
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