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Oxygen sensor / Pressure sensor

Discussion in 'Electronic Design' started by Vincent Himpe, Aug 22, 2004.

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  1. I'm looking for sources of oxygen sensors ( 0 to 100% ) like used in gas
    analysers. I know that these exist as semiconductor devices ( real small )

    Want to make a nitrox analyser for scuba diving.
    Most sensors for DIY analyser i find out there are big and bulky. Can be no
    bigger then a transistor.

    Second thing i'm looking for is a Pressure sensor ( Absolute pressure )
    that can withtstand at last 4000 PSI ( 350 BAR ) and has a threaded
    coupling. No strain gauge type ! has to be semiconductor or capacitive
    type.Preferrable with compensatin electronics inside. Like 0 to 5 volts is
    0 to 5000 PSI. I don't want to deal with non linearities and temperature
    drift of these things. Motorola and Melexis make neat sensors but they
    don't go that high in pressure..

    Anyone know who makes the sensors used in dive computers from suunto /
    Mares / Uwatec ? That is what i am looking for. Has the right connection
    and everything.
  2. Marc H.Popek

    Marc H.Popek Guest

    I don't have any answers yet I am intrigued by the application of real-time
    gas composition and pressure for the scuba market! This could be the
    reason' detre' for a tech/marketing adventure!

    A great deal of the commercial sensors are geared for automotive
    applications, and these may be adapted for your use, or you roll your own.
    for pressure you might be able to electronically "read" an old time analog
    meter movement to extract pressure in a non obtrusive way.

    gaseous sensing can be done with a platimium or palladium thin film
    structure... the surface is heated and allowed to cool, during the cooling
    period the presence of (your gas) is detected by watching the decay....

    For myself I dive with older analog and decidely manual gear. not dive
    computer I do have a dive watch, knife, gloves are very helpful
    sometimes..... underwater flashlight is very important......

    good luck

  3. I don't have any answers yet I am intrigued by the application of
    Nope can't do that. This is not a 'hobby project' Let me explain.

    I have a prototype system that is using sensors bought from various
    suppliers. Problem is that they are big and bulky and need a lot of tubing
    and piping to keep it all together. I want to make a nice thing for the
    final proto.

    Application is a fully automatic nitrox blending station.
    Hook up a scuba tank to the filling whip and key in the end pressure and
    mixture you want . The system reads the pressure of what is currently in
    the tank , takes a sample of the tank and determines current mixture. Then
    it automatically calculates what to add. It then mixes the right amount of
    gas. If the end mix would not be possible due to what is already in the
    tank it will figure out if 'bleeding off' part of the tank would help. If
    so it will do that. IF impossible to reach end it will alert the user
    before the filling process starts.
    At end of fill it samples the gas in the tank and prints a label.

    I can get it accurate to within 0.5% ( verified with independent gas
    analyser )

    Todays fill stations require empty tanks ( or near empty tanks ) as they
    can not 'top off' a half empty tank (which is a waste of nitrox ) Neither
    can they work with non 100% oxygen.

    If you get high oxygen content gas ( lets say 50% or 40%) and you need to
    downmix to 32 % then this is no problem with my system either. At every
    cycle the gas from the sources is sampled and its mix determined.

    You can attach 2 storage tanks : 1 with air and one with oxygen
    After power on it self calibrates

    The system has a Serial and USB port to hook it up to a computer. If
    someone orders a mix in store , the store clerk enters name and mixture
    desired. THe operator who is filling tanks gets one at a time
    automatically. The label printing happens on the machine. So all the
    operator needs to do is hook up a tank , press start , wait for fill to
    complete and affix printed label. The label printer is detachable ( if hte
    fill station is outside you can put the printer inside.

    When the customer comes to pick up his tank he signs off after having done
    an independent analysis using a separate nitrox aalyser ( any brand )
  4. Richard

    Richard Guest

    I sure don't know of any that small. To get one that small, the life span
    would be very short. Citrix sells industrial o2 sensors and so does
    Grainger but they average from $75 to $300 and have a 1 year life span if
    kept dry and clean.

    Pressure Sensors come pretty small but for one that will read up to 5k about
    the smallest I found is 1/2" diameter and about 1-1/2" tall with 1/8 NPT
    threads and they run in the $100 - $250 Range.
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