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How to make an anemometer

  1. Nov 21, 2016 #1
    Hello,
    I need an anemometer that is fairly accurate, but there are no anemometers available around where I live. Thus, I am trying to make one.
    I know there is a model that can be made with rotating cups, such that the wind speed is proportional to the rotational speed of the device. However, to find the rotational speed in this design, I would need to know the number of rotations it makes.
    The problem is that if it is rotating very quickly, it will be hard to measure the number of rotations by eye. So I am asking if there is a way to make an anemometer such that I don't need to measure the number of rotations, or that I don't need to measure them by eye.
    If there is no way to do so, is there a way to measure wind speed other than by using anemometers. I need to measure the windspeed for something on the lift force generated by wind, so perhaps another way of doing that could work too.
    Thanks for the answers
     
  2. jcsd
  3. Nov 21, 2016 #2
    There are also ultrasonic anemometers, if you are less mechanically minded these might be an alternative. They don't work well in wet weather though.
     
  4. Nov 21, 2016 #3
    I meant to say, with a mechanical anemometer we used a hall effect switch to measure the rotations and just attached it to the + button of a cheap reverse polish calculator. Put 1 into the calculator and it counts the rotations. Wind is generally measured in "wind run" which is in metres, i.e. the circumference of the anemometer multiplied by the number of rotations.
     
  5. Nov 21, 2016 #4

    Bystander

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    Cup anemometers have a "slip correction" of anywhere from ~ 1.5 - 2.0 depending on number and shape of cups. Longer arms give a slower rotation for given wind speed.
     
  6. Nov 21, 2016 #5

    boneh3ad

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    There are many ways to measure wind speed and they can basically all be automated. Which method is best depends on your needs. It's not clear exactly what you are trying to do. I'd be surprised if a cup anemometer was your best option, though.
     
  7. Nov 21, 2016 #6
    I'm trying to measure the speed of the current created by a electric fan.
    I had a look at ultrasonic ammeters. I'm not sure I will be able to make one, because it looks quite complicated. That's why I was slanted towards mechnical ones, since those are quite easy to make.
    Any ideas of what sort of store would sell things like the Hall effect sensor?
     
  8. Nov 21, 2016 #7

    davenn

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    Farnell, digi-key, mouser are 3 of the common component places
     
  9. Nov 21, 2016 #8
    If you'd like to buy an anemometer, there are a few available at mcmaster.com, omega.com, and dwyer-inst.com.
    Whether you're set on building an anemometer or would like to buy one, I recommend a hot-wire anemometer if you'd like to avoid mechanical problems like needing to count number of rotations or dealing with slip. They are fairly simple to make and are highly accurate. No moving parts, just an exposed wire. The change in resistance in the wire is proportional to the velocity of flow over the wire; this change can be used to determine the velocity of the flow.
    You could also use a Pitot tube with a manometer, although depending on how low of a velocity you're dealing with this may not be a very accurate method. Pitot tubes are usually better for mid-to-high velocity flows.
     
  10. Nov 22, 2016 #9
    Hot wires are very accurate, but they are not simple to make without losing a lot of accuracy. If accuracy is not that important, you could make one from the wire of a small light bulb, some googling will give you some tutorials on this (basically smash the glass of a light bulb without braking the wire and then calibrate against known windspeeds). You could also create a vane anemometer from an old CPU fan or a propeller from a model airplane.
     
  11. Nov 22, 2016 #10
    Ah, I didn't realize there was considerable loss of accuracy in building one yourself. I assumed you could make the rest of the circuit and buy the hot wire itself, then incorporate it into your circuit (I've never built one myself, only worked with them, but had heard they were simple to build).
    Using a CPU fan would also be a good idea. You don't need to count the number of rotations since the motor inside the fan will generate a voltage when the fan is rotated by air blowing through it. Calibrate it at a few different velocities and you can just measure that voltage to get the velocity, then compare it to your calibration curve.
     
  12. Nov 22, 2016 #11

    boneh3ad

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    It depends on the sort of hot-wire anemometer you want to build. The operating principle is pretty simple. The probe is conceptually simple. Realizing them isn't always simple.
     
  13. Nov 22, 2016 #12

    Baluncore

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    You might use a digital movie camera with a known frame rate. Drop a piece of confetti into the air stream and measure the distance travelled between two frames of the movie.
     
  14. Nov 22, 2016 #13

    rbelli1

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    Track the locations and you get air flow patterns (3d if you use two cameras) as well.

    BoB
     
  15. Nov 24, 2016 #14
    The MAF sensor in modern motor vehicles is basically a hot wire anemometer.
     
  16. Dec 5, 2016 #15
    Alright thanks for the answers. I was able to make a hot-wire one.
     
  17. Dec 12, 2016 #16
    Perhaps you could connect the anemometer to a small dc motor. Have someone hold the device out a car window on a still day and record the voltage at different speeds.
     
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