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Anemometer (handheld) with the prop 1 — Parallax Forums

Anemometer (handheld) with the prop 1

mikeologistmikeologist Posts: 337
in Customer Projects
Hi All;
I lost most everything in a flood a few years back, including a significant amount of tools and test equipment. I've managed to replace most of it as needed for jobs. One tool that I really miss and have not needed to replace for a job is my handheld anemometer. It was a Kestrel 5500 which is actually a full weather station, but I primarily used it as an anemometer.

Instead of buying one, I thought I'd make one.
I searched before making this and I couldn't find a thread about making one completely from scratch.

My plan is to use a 120mm computer fan. Not a brushless model.
Then to connect that to an ADC then to the prop 1.

I have a few questions before I get the parts:
1) What kind of resolution do I need for my ADC?
2) Besides Not brushless are there any other parametrics for the computer fan that are suited to this application?
3) I'd like to use a 120mm fan for a larger sampling area, is this a mistake?
4a) What do I need to do to protect the ADC and prop from surges, or is this even an issue?
4b) If I can't connect the fan directly to the ADC, what do I need to read to figure out how to connect it, please?

I appreciate any help here and I'll be happy to share my results.
Follow-up projects will include the other features of the 5500, I've got a box full of sensors that I'm itching to use.

Comments

  • iseriesiseries Posts: 1,492
    I built one using 3D printed parts.

    As the unit spins I mounted a magnet on the shaft with a Hall effect switch. Now I just count the rotations per minute.

    The problem I faced was that the device has too much resistance and does not turn freely enough to get an accurate reading.


    Mike
  • iseriesiseries Posts: 1,492
    Also I purchased one of these to test my weather station data.

    Weather Flow

    Mike
  • ceptimusceptimus Posts: 135
    You can make a solid state anemometer with some of those ultrasonic ping modules. Basically you use them to measure the speed of sound in two axes at right angles to each other, and ideally in both directions on each axis. The speeds differ when the air between the modules is moving. A few trigonometric calculations then give the speed and direction of the wind.
  • mikeologistmikeologist Posts: 337
    iseries wrote: »
    I built one using 3D printed parts.

    As the unit spins I mounted a magnet on the shaft with a Hall effect switch. Now I just count the rotations per minute.

    The problem I faced was that the device has too much resistance and does not turn freely enough to get an accurate reading.


    Mike

    The problem you had with free rotation is one of the two reasons why I've chosen a readymade fan specifically.
    I would do exactly that for a larger weather station model though as it makes sense on a collector that is easy to balance.

    Your second suggestion is cool though, and I bet it'd be a breeze (pun completely intended) to hook it up.

    Putting that one on the board, Thank you.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    You can get plastic fan blades from Grainger:

    https://www.grainger.com/category/plastic-fan-blades/fan-blades-and-propellers/hvac-and-refrigeration/ecatalog/N-jrc?suggestConfigId=2

    I used the 4" ones in a wind gage I built many years ago. They spin on a polished shaft with very little resistance.

    -Phil
  • Tracy AllenTracy Allen Posts: 6,664
    Electronic Goldmine has 5" propeller blades on sale,
    http://www.goldmine-elec-products.com/prodinfo.asp?number=G19443A
    You can buy replacement cups from Davis Instruments, or find DIY plans online for that sort of cups. The thing about cups is that they are omnidirectional, whereas a fan has to be oriented into the wind manually or by mounting on a pivot with a vane. Okay if direction is known, as in HVAC.

    I took out a 6" AC fan and found that it took a lot of air to put it in motion. Too sticky to be useful I think. Maybe a different brand. I have an ancient anemometer in the photo, calibrated with velocity in units of feet, actually wind run, and you have to divide the feet in a measured number of seconds. The thing is exquisitely sensitive with the tubeaxial blades. Slowly walking across a still room adds up the distance travelled.


    IMG_3019.JPG
    576 x 432 - 62K
  • mikeologistmikeologist Posts: 337
    edited 2018-02-16 22:41
    That's a fine looking machine. Thanks for posting it.
    I'm not really interested in a weather vane design. I'd much prefer something like what you've posted.
    That's why I'm leaning towards a DC fan. I don't know how to read from an AC fan, but most Not brushless DC fans should produce some current proportional to their speed, right? Plus it's already in a case and balanced.
    I know how to produce pretty accurate volumes of gas under specified pressure so I can get a descent calibration. I'm sure there's a temperature variant that I'd need to figure out.

    I have dozens of DC fans on hand, could you recommend a method of connecting one to an ADC, please?
  • iseriesiseries Posts: 1,492
    The problem I see is that there are magnets all around the outside of the brushless motor that prevent it from turning.

    This resistance is going to effect the speed of the fan as the air moves through it.

    It would be better to remove all the windings and metal from the inside of the fan and replace it with a hall-effect switch and count the pules.

    Mike
  • mikeologistmikeologist Posts: 337
    iseries wrote: »
    The problem I see is that there are magnets all around the outside of the brushless motor that prevent it from turning.

    This resistance is going to effect the speed of the fan as the air moves through it.

    It would be better to remove all the windings and metal from the inside of the fan and replace it with a hall-effect switch and count the pules.

    Mike

    Got it, now I see.
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