Since you are trying to fill the tank to the point where the sub starts to
sink, why not look at the external water level? A simple float inside the
sail or on the top deck could be used to indicate the onset of submersion.
Of course, you will need to filter the signal to reduce wave effects & may
need them fore & aft  but I imagine they could be made very small (opto
interrupters or reed switches?)


Richard P

wrote :-
> Actually the issue is not the depth of the sub (I already have depth
sensors
> using pressure on the sub), this issue is providing closed loop control
over
> the amount of water in the ballast tank.

So why do you need to know the amount of water in the tank?  Isn't this
something the servo controls implicitly in an attempt to maintain the
desired depth?

> Anyway if anyone is interested the current configuration can be seen at
> http://freespace.virgin.net/andy.shaw/subcomsep2000.htm

Pretty cool, Andy!  So when will this be fully operational torpedoing those
annoying jet skis?


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, olin@cognivis.com, http://www.cognivis.com

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