> For the complete documentation index, see [llms.txt](https://3dpaws.comet.ucar.edu/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://3dpaws.comet.ucar.edu/building-3d-paws/building-the-core-instruments/anemometer.md).

# Anemometer

### How the Sensor Works

The three-cup anemometer measures **wind speed** using a **Hall effect sensor (SS451A)** that detects rotations. Two magnets on the anemometer generate 2 interrupts per revolution, enabling precise tracking of rotational speed. Wind speed is sampled **every second** by recording interrupt counts and millisecond durations. These 1-second samples are converted into instantaneous wind speeds using the anemometer’s calibration factor. Observations are logged every minute, with:

* **Wind Speed**: Average of 60 consecutive 1-second samples.
* **Wind Gust**: Highest 3-second average (three consecutive samples).

Wind speed is calculated using:<br>

$$
\text{Speed (m/s)} = \left( \frac{\frac{\text{interrupts}}{2} \cdot 2\pi \cdot \text{radius}}{\text{time (s)}} \right) \cdot \text{calibration factor}
$$

* **Radius**: 0.079 meters (distance from center to cup)
* **Calibration factor**: 2.64 (empirically determined from wind tunnel testing)

### Instruction Slides for Assembling the Anemometer

{% embed url="<https://docs.google.com/presentation/d/1hDxI2VXYWU8e3g-MxkWPEuZZY1h1np-v/edit?ouid=117036005519516778359&rtpof=true&sd=true&usp=sharing>" %}

### Tutorial Videos for Assembling the Anemometer

This video playlist demonstrates the entire assembly of the Anemometer. **It demonstrates the glue in version of the bearing housing and hub using Qwiic cables. Please follow the manual instructions if using the twist version of the bearing housing or M5 stack Grove cables.**

This video playlist demonstrates the entire assembly of the instrument. You can toggle between assembly videos using the "fast forward" and "rewind" buttons.

{% embed url="<https://youtube.com/playlist?list=PL_rvcKZhmIf0pVc3sgLi5L2UCpbDumTmw&si=yCZf57mjFfVSm7Mz>" %}


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