Air flow measurement sensor

Discussion in 'The Projects Forum' started by embpic, Aug 16, 2014.

  1. embpic

    Thread Starter Member

    May 29, 2013
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    I need any air flow measurement sensor/circuit so i could measure the amount air is flow.
    I searched on google but i got air flow detector using opamp but i need measurement of air flow.
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    What velocity of air flow are you wanting to measure? HVAC? Wind? Breath?

    Ken
     
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
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  6. gixxer50

    New Member

    Aug 17, 2014
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    Mass Airflow Meter from a car ? Sorry, im a mechanic by trade.
     
  7. cork_ie

    Member

    Oct 8, 2011
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    Absolutely the best way to measure airflow in an engine is to use a second MAF (Mass airflow meter) as a MAF will give you a far more accurate and linear output than any alternative. Automotive MAFs have specially circuitary built in to compensate for changes in density and are designed to be linear for the kind of air flow ranges in an engine.There are two main types
    1) linear 0-5V output for stated range.
    2) Variable frequency types - output signal frequency is depenant on airflow. If you look at a workshop manual for the type you intend to use it will generall give you figures for the signal voltage or frequency V's airflow in g/s or Kg/hr
     
  8. ep.hobbyiest

    Member

    Aug 26, 2014
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    Thank and sorry for late reply.
    i want to measure the air flow of exhaust fans.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    The biggest problem you have is that the flow rate is not constant across the area the flow is passing through (a duct?). It has a velocity profile that depends on position. This is not as bad a problem if you only need to watch relative changes, but it's a huge problem if you need an actual volume estimation, cfm for instance.

    What are you trying to do?
     
  10. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    @ep.hobbyiest:

    You are not the thread starter.
    How come you reply for him?

    Bertus
     
    sirch2 likes this.
  11. sirch2

    Well-Known Member

    Jan 21, 2013
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    Bertus, my thoughts exactly. I've done quite a lot of work on measuring low velocity airflows over the last 6 months and was planning on posting some details but I usually look through to see if the OP has bothered to reply to anyone before I put a lot of effort into a post.

    So I'm happy to post what I have if the OP or anyone else expresses an interest.
     
  12. pilko

    Active Member

    Dec 8, 2008
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  13. sirch2

    Well-Known Member

    Jan 21, 2013
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    OK, I tried one of those and wasn't that impressed so I rolled my own. I'll get some details together and post something later.
     
  14. wayneh

    Expert

    Sep 9, 2010
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    I'll say it again: Measuring a point velocity alone is almost useless in measuring flow (the word chosen by the OP). They are not the same thing. Could be a language problem here, it's hard to tell.
     
  15. sirch2

    Well-Known Member

    Jan 21, 2013
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    wayneh - I don't think anyone is disagreeing with you, but sampling across the airflow and averaging is one approach.

    For pilko I have attached a schematic of a thermistor based anemometer. It uses self heating of a thermistor in one leg of a bridge (TR2). TR1 is there for ambient temperature compensation which works OK for small variations but it is hard to get thermistors with the same coefficient of resistance for 10k and 220R so the bridge does go out of balance if the temp changes too much. Half of U1 and T2 form a constant current supply for the bridge. U2 is an instrumentation amp to amplify the bridge output. U3 is just there to allow a MCU to switch the unit on and off and could be left out. The other half of U1 drives an LED to indicate bridge balance and if airflow is detected. Basically I adjust the bridge via R5 until the LED lights and then back it off until it just goes off. This means the output of U2 is at around 0.6V, the voltage being set by the junction of D1, I found this to be good for my application which was detecting very slight drafts.

    Was going to attach the Eagle schematic and board files but they don't seem to be allowed formats
     
  16. wayneh

    Expert

    Sep 9, 2010
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    I'm just pointing out that we're blind without more info from the OP about what he needs. The best solution might be a streamer hanging from the grill of his fan, a wind sock. Or he may need a temperature and pressure compensated sensor array and a microprocessor.
     
  17. pilko

    Active Member

    Dec 8, 2008
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    @ sirch2,
    Thanks for the info --- will study it.
    What was bad about the Modern Devices sensor?
     
  18. sirch2

    Well-Known Member

    Jan 21, 2013
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    I found the Modern devices wind sensor quite noisy when detecting low velocity flows so it was hard separate draft from noise and I wanted to input the data to an MCU so wanted 0-5V at the output in the range of flows (around 0.3m/s) that I was interested in.
     
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