13 Replies Latest reply on Dec 14, 2020 1:14 PM by gekkoscamp

# Looking for a way to calibrate an anemometer in order to measure the wind speed

Hello guys,

(My first post on this forum, so ill introduce myself post scriptum)

To get into smart home systems and arduino, I am currently building a weather station measuring temperature, humidity and all kinds of funny stuff.

I am ALSO measuring the rotations of a self built 3d printed anemometer. I know the dimensions of the "flaps/cups", i know the rotations/frequency with which the thing is spinning

but i simply cant think of how to calculate the windspeed, given rotations and the drag value of a half sphere (in German its called Cw-Wert).

The actual spinning part consists of 3 equally spaced "arms" of length d each with a half sphere with diameter a.

How do I calculate the Windspeed, given those parameters?

Any hints are super appreciated.

----

Hi, this seems like a really cool and friendly forum so i decided to sign up.

My Name is Michael, studying engineering in Germany, eager to learn the basics of electronics and programming.

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

Hi Michael,

Welcome to element14.

What accuracy are you hoping to attain with your anemometer?

A simple test is to put it on your car and drive at various speeds on a calm day.

You can run through a series of theoretical calculations for the rotation of the device, but you still need to know the level of friction is inherent in the system.

See if you can rent a calibrated anemometer to use beside your new unit to see how well they correlate.

DAB

6 of 6 people found this helpful
• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

I've seen it done from a car but better on the back of a motor bike if you have a friend to give you a ride.

It's easier to hold the sensor out of the slipstream on a bike.

If it were me I'd put it on a long pole and attach it to backof the cab on my truck.

I think you will need to get the end of the pole at least 2m from the vehicle, and ideally more.

MK

5 of 5 people found this helpful
• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

John

4 of 4 people found this helpful
• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

My G-d what is with all of you trining to redesign the world. I have a Fieldpiece AAV3 head for my EHDL1   >

Ft/mi or M/s

MPH or KM/hr

~~Cris

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

I can't speak for anyone else but for me it is fun to try to do it the hard way sometimes.

John

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

and this tends to be the best way to learn.

Gosh, even Elon Musk (Tesla) points this out when he was reported as saying "(to) Make better products, seek negative feedback and ditch those PowerPoints presentations (or as I interpret, ditch those product brochures)."

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

Nice - but how do you calibrate it

MK

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

michaelkellett , The Factory of course! LOL This calls for a blond joke ( and I still have some in my hair but you have to look.

gekkoscamp Reinventing the wheel

Disclaimer: I live in a glass house and most of my windows are broken.

therefore I can throw stones too.

~~Cris

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

hey guys, thanks for the great input.
As some mentioned friction, very correctly, doesnt behave linearly which would overcomplicate a very accrate complication.

And i lack of the tools to measure at the moment.

But i love the idea of calibrating it by giving it a rough reference speed by car or another vehicle and do it this way.

My uni does have a windtunnel tho, so i am thinking of continuing with the rest of the project until i have the opportunity to test it there... or a car if that doesnt work.

@christina, as John pointed out. I enjoy it building it myself.

Thanks again for all the hints.

Stay healthy and have great holidays!

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

Hi gekkoscamp,

I was curious how you are measuring the fan rotations. Are you using a counter or is it a dynamo?

John

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

I am using hall efect sensors.

The rotating part has two light weight permanent magnets embedded in its housing while i mounted a hallsensor on the stationary axis.

every second time a magnet passes the hallsensor i measure the time delta between the previous time-measurement and the new one and from there I form the frequency.

this is implemented as a interupt service routine at the moment but i am thinking of overhauling the hole concept.

Cant find the time to reinvent that before i havent figured out my calibration problem.

Hope i could help.

3 of 3 people found this helpful
• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

Some great suggestions above for you.

More so for the test from a motorbike, make sure its either very secure with a secondary safety lanyard or can completely break free i.e. a weak point in the head to Arduino wiring. Being extra cautious I'd also not post any pictures of my setup until after the tests and definitely don't add the sticker stating "If lost please return to..."

• ###### Re: Looking for a way to calibrate an anemometer in order to measure the wind speed

You could try swinging it at a known and constant rotational speed at the end of a stick or string.

You might get a crude calibration by using a fan and measuring the speed of a feather in the flow.

1 of 1 people found this helpful