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Topic: Modern Devices Rev P Wind Sensor Mathematics (Read 1 time) previous topic - next topic

acarp

Hi, 

We are using the subject anemometer with an Arduino Uno and trying to read temperature and especially wind speed.  The parts and arduino work like a charm--no problem with libraries, and below is the lines of code we used to calculate the wind speed from the pin reading:

 float windMPH =  pow((((float)windADunits - 264.0) / 85.6814), 3.36814);
    Serial.print(windMPH);
    Serial.print(" MPH\t");   

One can guess the problem--no datasheet anywhere from Modern Devices, and the wind speed it serial prints is switching back and forth from 7 mph to 1500 mph when we blow on it.

Does anyone here have experience with this part and have a hint at how to change the math on this line to get reasonable readings??  We can play with the numbers on our own, but that yields inconsistent results when we for instance divide everything by 1500 etc....

UKHeliBob

Code: [Select]

 float windMPH =  pow((((float)windADunits - 264.0) / 85.6814), 3.36814);

Where did those "magic" numbers come from ?
Please do not send me PMs asking for help.  Post in the forum then everyone will benefit from seeing the questions and answers.

PaulS

Quote
below is the lines of code
Some of them, anyway.

If the value in windADunits varies in a meaningful way when you manipulate the sensor, then the problem is in the way that you implemented the equation or in the equation itself.

If the value in windADunits does not vary in a meaningful way, the problem isn't the equation or its implementation.

So, what is the problem?
The art of getting good answers lies in asking good questions.

vaj4088

Have you printed the output from the sensors, and windADunits, to verify that you are getting reasonable results?

MarkT

[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

jremington

I experimented with an earlier version of that sensor, and it is completely useless.

Your only hope for making any use of it is to have a friend with a fully calibrated, temperature controlled wind tunnel perform a calibration run and work out a mathematical model for the response (plan on a full day or more of work).

acarp

Thanks for posting website...that is in fact the part.  Investigating today the WindADunits.  If we get reasonable values (0-3.3v) from that we will experiment with changing the math.  That line of code was taken from the sketch posted on their site based on their "wind tunnel" tests...

Thanks!

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