Hello Chris,

Thanks for the info.  I'm only looking at a depth of only 10 feet.  Right
now I am using the Motorola MPX5050 (a differential pressure sensor) and am
*hoping* that the sub will not change volumetrically at shallow depths so I
can get an accurate differential pressure.  Was your scuba computer is a
rigid vessel?  Why was it deforming in shallow water?

Regards,
Donovan


> This is similar to a scuba computer that I did recently. The vessel will
> deform and change volumetrically at fairly shallow depths - this is
> something one learns
> during the earliest scuba cert training. I wouldn't want to even try to
> calibrate a system
> with a differential sensor inside the vessel.
> What max depth will your sub run at? for shallow depths (<100 ft.)I think
> the most convenient,
> reliable, and simplest solution for this may be a
> Motorola gauge type pressure sensor. According to the data sheets they are
> only for use in air,
> but since they have a fluorosilicone gel covering the chip, I have found
> that they have a
>  pretty long life in fresh water, even in chlorinated pool water. These
are
> very small devices,
> approx 20mm round by 6 thick. 5V analog output models are very easily
> scaled. The device can be
> inside the sub with it's barbed fitting through the outer hull with a
small
> o-ring.
> They are fairly linear. The hardest part of working with them is
> themperature compensation.
> f your water temp is pretty regular, say within =/- 10C, it will be no
> problem getting accurate readings
> to within about 1/2 ft, down to about 100 ft.
> You might want to check out the MPS5700 family.
>
> Chris
>
> Alternately
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Donovan Parks
> Sent: Saturday, February 02, 2002 1:13 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [OT]: Measuring Depth of Submarine using Differential Pressure
>
>
> Hello,
>
> Here is the setup.  I have a submarine with a differential pressure
sensor.
> The high pressure end of the sensor will be placed in a 'ballon' that is
in
> the water and the low pressure end will be in the interior of the sub.
For
> technical reasons I can't run a tub up to the surface of the water.
>
> How do I can this differential pressure into a measurement of the subs
> depth?  Since the submarnie was sealed at the water surface pressure (i.e.
1
> atm) and is rigid I am assuming the pressure in the submarnie will remain
1
> atm regardless of the depth of the submarnie.  Now, the pressure of the
> 'ballon' will change will change will depth as it is non-rigid, but what
is
> the conversion factor from differential pressure to depth?  I have a book
> (which I don't have access to right now) that gives the relationship, but
I
> don't really trust the source and it is to 0 decimal places of accuracy!
I
> will be using the sub in FRESH water.  (A search of the Internet has been
> unfruitful - likely because I am not sure what I should be searching for.)
>
> Regards,
> Donovan
>
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