Measure salt water pressure

I`m building an underwater robot, and need a method to measure the water pressure (to determine depth). I have got a Motorola pressure
sensor, but they say it may not survivie long in slat water. Any other suggestions/ideas, I did think about a FSR (force sensing resistor) but not sure how they will do in salt water either...
I`m working on a small budget so I don`t want to spend hundreds of dollars on a sensor.
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wrote:

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 snipped-for-privacy@huv.com http://www.huv.com/jon
Project: Micro Raptor (Small Biped Velociraptor Robot) http://www.huv.com/blog
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(turn "mm"s into "m") or clense this address of the Qs.
Michael
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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
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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
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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.
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On Wed, 20 Dec 2006 19:59:22 -0800, James_sgp wrote:

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
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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 snipped-for-privacy@huv.com http://www.huv.com/jon
Project: Micro Raptor (Small Biped Velociraptor Robot) http://www.huv.com/blog
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