Just one more thought on this for me today...

I have seen commercial dive computers that have no port, tube or balloons
visible, and yet they are amazingly accurate in sensing depth. I have
searched and phoned sensor makers, foguring that someone must have a
chip-scale sensing element, but have found nothing of the sort. Has anyone
ever seen what I'm talking about? Know a way to sense pressure or depth
without porting water or bagging air? This thread has me thinking of
re-inventing my own rather small wheel...

Chris

-----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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