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.
Reply to
James_sgp
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You don't say how deep you want to go.
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?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
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Project: Micro Raptor (Small Biped Velociraptor Robot)
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Reply to
Jon Hylands
Sorry, i missed out that little detail...
I`m planning a depth of about 50m which means about 90PSI.
J> >
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?Name=MSP3101P2-ND&Site=US>
Reply to
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.
Reply to
Si Ballenger
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?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:
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If you want some more details like a schematic etc email me @ snipped-for-privacy@mmhimms.co.uk (turn "mm"s into "m") or clense this address of the Qs.
Michael
Reply to
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...
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Reply to
Curt Welch
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:
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though I expect it'll timeout......
Michael
Reply to
Michael
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
Reply to
robin
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
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Project: Micro Raptor (Small Biped Velociraptor Robot)
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Reply to
Jon Hylands

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