Airflow sensor (150PSI/15SCFM)

Discussion in 'General Electronics Chat' started by mcgyvr, Apr 24, 2015.

  1. mcgyvr

    Thread Starter AAC Fanatic!

    Oct 15, 2009
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    Looking for some suggestions on a low cost (sub $100) airflow sensor.. (0-5V analog output would be great)
    Pressures up to 150 PSI and flow rate up to 15 SCFM or so

    Looking to detect the flow profile on some pneumatic nutrunners for cross-thread detection. (hopefully :))
     
  2. Reloadron

    Active Member

    Jan 15, 2015
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    Looking at your price point you may do better looking airflow rotameters and try to fabricate an optical system? My guess here is you are using a pneumatic gun (nut runner) and if a nut goes on cross thread the normal airflow won't be the same. Does the flow increase or decrease when a nut cross threads? I have seen airflow transducers for closed pipe systems but the ones I have seen can be costly, real costly. I would guess you have a supply pressure around 150 PSIG and zero flow till a nut is driven. Then you have a flow and a difference in flow between a nut normally going on and a nut cross threaded. The trick is detecting one from the other. Even with a rotameter around 100 PSIG is no problem but getting above that can be in the inexpensive flavors.

    Just My Take
    Ron
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I'm guessing the airflow is less when cross-threading because of increased back-pressure. There are two basic air flow sensor types, physical mass and thermal mass. Thermal mass types, like hot-wire anemometers, are very sensitive to placement, very non-linear, and just plain cranky. BUT, no moving parts, much smaller size, easier to whip up as a one-off project, and you don't care about the non-linearity because your application is go / no-go than a calibrated measurement of a physical quantity. If you place an NTC platinum bead thermistor in the air stream and pump a little extra current through it to increase the self heating, then a simple analog comparator will light a red LED when the resistance drops because the sensor heats up because the air stream slowed down because the nut driver isn't turning the right speed because the nut is cross threaded. Or something like that.

    ak
     
  4. mcgyvr

    Thread Starter AAC Fanatic!

    Oct 15, 2009
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    Its really all about flow vs time to detect cross threading.
    I intended a "learning" mode to chart the typical flow vs time for a typical rundown then will store that and they becomes the baseline for all further rundowns plus some hysteresis.

    If the nut is cross threaded the flow will stop as the tool is no longer spinning its motor so its not exhausting air.. same when the clutch triggers at a complete rundown. But the time associated with complete vs cross thread will be different.

    I thought about a pressure transducer first but quickly realized that in most situations the pressure will only drop at first but due to the total flowrate of the whole system it will jump right back up before a complete rundown has occurred.. So I must look at flow instead of just pressure drop... I think.. I still need to do a bit more investigating on that.. I can get a pressure sensor for $20..
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Sounds like a job for a MAF sensor from a car?
     
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