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Author Topic: Submersible Pressure Transducer  (Read 894 times)
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Boulder, Colorado
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Hello Arduino Folks!

I'm at the outset of thinking about building a submersible pressure transducer for the purpose of monitoring water levels in wells, behind weirs, in flumes, in tanks, etc.  I will probably model the sensor after the design in some USGS reports: 

A couple of questions:

- are there alternate designs out there that already include interface with an Arduino and a datalogger?  ...haven't encountered anything, but if there's something I'd love to here about it. 

- any experience working with long signal wires that only carry mV output?  ... perhaps I need to think about amplifying the signal.  At least one application could be in a "noisy" environment at an industrial site.  With that in mind, what are the pros/cons of using an integrated transducer that has a 0-5 V output vs wiring up my own signal amplifier?

- I have the arduino uno w/ 0-5 V output, but some of the freescale pressure transducer spec sheets I've looked at have an excitation voltage more akin to a 9V battery.  What are my options for providing a nice stable excitation voltage to the transducer?

As background, I have a soil science background with only beginner/desktop-level electronics experience.  I have the Arduino Uno and recently spent a day in  an intro class put on by a hobbyist electronics vendor (SparkFun).
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Georgina Ontario
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Google is your friend... or Bing or whatever...
http://www.globalw.com/products/levelsensor.html

http://www.google.ca/#hl=en&xhr=t&q=submersible+pressure+sensor&cp=14&pf=p&sclient=psy&aq=0&aqi=&aql=&oq=submersible+pr&pbx=1&fp=ec885af529af1eb0


http://www.alibaba.com/countrysearch/CN/water_pressure_sensor.html

http://www.sensortechnics.com/ssi

You might even be able to use a barometric pressure sensor inside a sealed container...

It looks like a simple data logging application....

You might need to add an RTC DS1307 fer example... if you want the time.

You will have to pay attention to the length of the I2C cable.

I have no idea what long signal wires are... Maybe you can mention expected length or depth or whatever...

As you are another professional, I am sure you have written a specification...no?  smiley
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Just another Hacker

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If this is a hobby project, you might look at hacking a digital tire pressure gauge or getting the transducer out of one.
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Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

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NightTrain

Measuring water behind a weir is a challenge.  Usually the goal is something like determining and totalizing water flow through a V or some other notch.  A tiny bit of error adds up to a huge systematic miscalculation of water flow.  Ice is an enemy.  Cows are really loose cannons. Raccoons are organized vandals.

It is best to build a covered and locked stilling well to the side of the stream and hydraulically connect it below freeze level to the bottom of the stream or pond.  The pipe must be large enough to not get plugged or mashed by cows, and be equipped with a screen that will keep the muskrats out.

I firmly believe that the best level sensor for this application is the old USGS  standard of a multi turn potentiometer with float on one end of a beaded chain and counterweight on the other.  As the water level goes up and down the chain turns a gear on the shaft of the pot.  There are thousands of these around, some must be available for scrounging. The critical repair parts are available for sale

A pressure transducer in this application must be precise and repeatable to a few mm.  Changes to barometric pressure will, so to speak, blow your data out of the water.  If you have one absolute pressure device under water, there must be another one just like it to track BP.

You might roll your own level instrument for modest depths using ultrasonic parts.  Maybe put the sonic device on the bottom of the pond and look up at the water surface.  A fixed target at a known distance would let you recalibrate with each shot.

Successful pressure transmitters installations in wells are generally 4 to 20 milliamp current loop devices.  The current loop does not care if the leads are a mile down and back.  Usually there are power leads to the submersible pump alongside the leads to the transmitter.  This leads to an impossible situation with gathering data from voltage and digital devices.  The two wire current loop cable costs a lot less than a three or four lead shielded cable that you might try to use with a voltage or digital device.  I have been involved with placing hundreds or maybe thousands of pressure transmitters in wells.  Every single one was a current loop.

Good luck with the project

JC

« Last Edit: March 15, 2011, 10:16:22 pm by jcarrr » Logged

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