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Air Flow Test Meter

Discussion in 'General Electronics Discussion' started by Kylebeech, Mar 29, 2010.

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  1. Kylebeech

    Kylebeech

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    Mar 29, 2010
    I have been looking at doing this as a project but i want to add an ADC and a 7-segment counter but wouldnt know how to go about it, for example testing it on multisim. Can anyone help me please?


    http://www.aaroncake.net/circuits/airflow.gif is the analogue part
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    That circuit uses the op amp as a comparator. You would need to change that to be a dc amplifier with appropriate gain (and that would probably be achieved by experiment) to give an output voltage that varies with the resistance of the filament.

    Perhaps the easiest way would be to use the analogue input of a pic (or PICAXE) as it could also drive your seven segment display.

    To calibrate it you could stick it out the window of a car on a calm day. and compare the output to the car's speedo.

    It would be easiest to just convert the voltage to increasing numbers and then make up a calibration chart.

    e.g. 0 = calm, 1 = 4 km/h, 2 = 9 km/h, 3 = 13 km/h, etc...
     
  3. Kylebeech

    Kylebeech

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    Mar 29, 2010
    Have you got any idea how this would look on multisim??
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I don't know what multisim is, and I very much doubt it would work (unless multisim knows what happens to light bulb filaments when exposed to moving air).

    Try building it on a breadboard and testing it. That's pretty much the only way to go.
     
  5. 55pilot

    55pilot

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    Feb 23, 2010
    This concept is not going to work reliably with any accuracy. It is just too dependent upon the air temperature and humidity.

    It is used to detect "airflow" to make sure that there is enough cooling air to keep a protected device from over-heating. It works for that because if the combination of flow, temperature and humidity can take away a certain amount of heat from the bulb, it can take away a proportional amount of heat from the device that needs to be cooled. It measures a moving air mass's capability to take away heat. That ability is only loosely related to its airspeed.

    ---55p
     
  6. Kylebeech

    Kylebeech

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    Mar 29, 2010
    Its only a method of displaying it for my college assignment thats all
     
  7. 55pilot

    55pilot

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    Feb 23, 2010
    Looking for help doing your homework?

    ---55p
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    And here I get to correct you for a change ;)

    It's actually a very useful method of measuring wind speed.

    His simple version would lack some of the finesse of commercial equipment, but would still be an interesting project.
     
  9. Kylebeech

    Kylebeech

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    Mar 29, 2010
    It needs to be electronic and that circuit seems to be a good idea,
     
  10. 55pilot

    55pilot

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    Feb 23, 2010
    I hate to have to correct you back :(
    It is indeed quite useful, even the preferred method, but only in a very limited set of circumstances. It is used mainly in lab and wind tunnel situations where the conditions are very controlled. Its biggest advantage is that it is extremely responsive for detecting small changes and is small enough to not interfere too much with the environment it is measuring.

    It is also used in the field for in-flight or on the road aerodynamics. There the air mass is not controlled, but the instantaneous changes are still accurate enough to detect turbulence and boundary layer separation.

    It is also the only game in town when it comes to really low speeds. Not because it is particularly good at those speeds, but because everything else really really sucks there.

    I still maintain that it is not a good method for doing generic airspeed measurement. But for a school project, where you can show a number changing when you stick a device out the window, or blow on it, it is just perfect. Helping students do their school projects.... that is a different discussion for a different day.

    ---55p
     
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