Measure salt water pressure

You don't say how deep you want to go.

http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=MSP3101P2-ND&Site=US

That's a 100 psi pressure sensor, which should be good down to about 175
feet, for $75. You can go deeper for the same price, but you lose
resolution when you do.

It will plug into a standard 5 volt A/D port on a micro-controller, and has
a stainless steel case.

Later,
Jon

--------------------------------------------------------------
   Jon Hylands      Jon@huv.com      http://www.huv.com/jon

  Project: Micro Raptor (Small Biped Velociraptor Robot)
           http://www.huv.com/blog

Sorry, i missed out that little detail...

I`m planning a depth of about 50m which means about 90PSI.



Jon Hylands wrote:

http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=MSP3101P2-ND&Site=US

http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=MSP3101P2-ND&Site=US

Ah Jon....I see another RobotRov member :-)

James,

I'm currently working on the same thing myself (building both an ROV and
AUV). Pressure sensor cost £10GBP and the support/interfacing electronics
cost around £2GBP. Output is analog voltage the same as Jon's recommendation

Pressure sensor:
https://secure3.farnell.com/jsp/endecaSearch/partDetail.jsp?skus1729

If you want some more details like a schematic etc email me @
mmichael@mmhimms.co.uk (turn "mm"s into "m") or clense this address of the
Qs.

Michael

That URL gave me an error about the session timing out.  I just went to the
home page and searched for 731729 and got this URL which might work better
for people since it's not an https: page...

http://export.farnell.com/jsp/endecaSearch/partDetail.jsp?SKUs1729

--
Curt Welch                                            http://CurtWelch.Com/
curt@kcwc.com                                        http://NewsReader.Com/

That doesn't work for me...I have to pick a country.....

Well the part number is 731729 so I guess type that in on the homepage and
you should find it....

Another address:
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKUs1729  though I
expect it'll timeout......

Michael

On 20 Dec 2006 19:59:22 -0800, "James_sgp"


One thing to consider is to seal the sensor in a flexable
container filled with an inert liquid that would be harmless to
the pressure sensor. The inert liquid will transmit the external
water pressure to the sensor. A $6 digital tire pressure guage
from walmart might be an inexpensive pressure sensor source.

Why would you expose the pressure transducer to salt water? ... for
example, small stainless steel tube mounted in the side of the vessel,
rubber diaphragm covering the opening, filled with oil, pressure
transduces on the other end.  The pressure transducer only ever sees oil,
oil is (almost) uncompressible, so the deflection on the diaptragm is
pureley the amount needed to deflect the pressure sensing element.

You need to be sure that if the pressure sensing element fails (ie leaks)
its not going to sink your entire vesssel ...

robin_sz

Well, you need to make sure that if your hose seal fails, its not going to
sink...

Its the same problem, you're just moving it to another component. Most
decent pressure sensors that have stainless steel bodies are rated
(body-wise) for 10,000 psi - they only change the electronics on the inside
to vary the scale for the lower pressure models. They typically also have a
threaded port, with a flange, and a spot for an o-ring to help seal the
whole thing.

The pressure sensor is the last place I would worry about leaks coming
from, if you're using a decent one.

Later,
Jon

--------------------------------------------------------------
   Jon Hylands      Jon@huv.com      http://www.huv.com/jon

  Project: Micro Raptor (Small Biped Velociraptor Robot)
           http://www.huv.com/blog