Pitot Anemometer

2011-01-20 17:22:32.000 – Rebecca Scholand,  Summit Intern

My internship this winter is much different than this past summer. Where I spent most of my time giving tours, working in the museum, and stripping paint off the tower ladders, I am now reading papers and working on my intern project. Different from this past summers multiple projects I have turned in my tool belt for my computer. I am working on the intricate detail that is the pitot-static anemometer and recording devices. On the exterior anyone can see our unique pitot tube mounted to a vane at the top of the tower but it is the complex inner workings that are truly unique and fascinating.

For starters the pitot tube was invented by Henri Pitot in the early 18th century. It is a pressure measurement instrument that is widely used by many industries. Most notably is the aviation industry. On aircraft the pitot tube is used to determine the airspeed of an airplane. By measuring the ram air pressure at the tip of the pitot tube, created by the forward motion of the aircraft moving through the “stationary” atmosphere, and comparing it to the static pressure, measured by a small static port perpendicular to the motion, results in impact pressure. The impact pressure is translated to airspeed through a mechanical calibrated device called an airspeed indicator. The higher the impact pressure the higher the airspeed.

On the summit our pitot-static anemometer works in the same way, but under different conditions. Our pitot tube is mounted at a stationary location and vanes into the wind, as the atmosphere “moves past” the pitot tube a ram air pressure is exerted at the tip of the pitot tube. A static pressure is recorded by a small static port perpendicular to the wind and the difference between ram air pressure and the static pressure yields the impact pressure. The impact pressure is than translated to wind speed by our calibrated wind speed indicator. As the impact pressure increases, so does the wind speed. Instead of measuring the speed of the aircraft you have determined the speed of the “atmosphere” or wind.

This is only a basic description of how we obtain wind speed with our pitot-static anemometer on the mountain. The complex description comes from adding about 100 feet of tubing and multiple instrument connections between the pitot tube and the wind speed indicator. As my internship progresses I will have more to report and explain on our fascinating system.

Rebecca Scholand,  Summit Intern