![]() Electronic circuits inside measure the time it takes for Transmitter constantly beams high-frequency sound to its respective Receivers mounted at right angles to one another. (generally above the range humans can hear).Īn ultrasonic anemometer has two or three pairs of sound transmitters and ![]() The same idea is used in an ingenious way in ultrasonic anemometers, which measure wind speed using high-frequency sound Sound waves they generate have to fight against the wind to reach Shout back, you'll hear their voice slightly later-because the Than they would if there were no wind at all. Of where you're standing, you'll hear their voice slightly sooner If you're shouting to a friend who's down-wind It's fairly obvious that the speed of the wind affects You probably know that sound travels by making air molecules moveīack and forth. Photo by Spencer Roberts courtesy of US Navy. The case is made of lightweight aluminum. Photo: The main parts of the handheld, optoelectronic Ames anemometers used by the US Navy. Made by Ames of Slovenia, work in roughly this way. The anemometers shown in our photos up above, An electronic circuit times the pulses and uses them to calculate the wind speed. Each time the paddle wheel rotates, it breaks a light beam and generates a pulse of current. In another design, known as optoelectronic, spinning cups turn a kind of paddle wheel inside the metal canister underneath. Peet II, November 8, 1994, courtesy US Patent and Trademark Office. US Patent 5,361,633: Method and apparatus for wind speed and direction measurement by William J. These send impulses to a circuit that calculates the wind speed. As the wind spins the cups, the magnet rotates past a couple of reed switches (orange) mounted in the stationary bottom section (green). In the red cup section, there's a magnet built into one side (yellow). You can see it's divided into three main parts: the vane on top (blue), which indicates the wind direction the rotating cups (red) and the stationary housing that you hold underneath (green). This kind ofĪnemometer effectively makes a series of electric pulses at a rate that is proportional to the wind speed.Ĭount how often the pulses come in and you can figure out the wind speed from that.Īrtwork: How a simple reed-switch anemometer works. When a magnet is nearby, the reed switch closes and generates a brief pulse ofĮlectric current, before opening again when the magnet goes away. In one typical design, some of the fan blades have tiny magnets mounted on them and, each time they make a single rotation, they move past a magnetic detector called a reed switch. The cups or fan blades rotate each second. Some cup-style anemometers dispense with the electricity generator and, instead, count how many times The display also indicates how strong the wind is on the Beaufort scale. The fan at the top generates magnetic impulses, which electronic circuits inside convert into a precise wind speed. ![]() Photo: A handheld digital anemometer from La Crosse Technology. The generator is connected to an electronic circuit that gives an instant readout of the wind speed on a digital display. ![]() As the wind blows, it spins the fan blades and a tiny generator to which they're attached, which works a bit like a bicycle dynamo. Some anemometers have what looks like a small fan in place of the cups or propeller. Like miniature wind turbines, they use small propellers to power their generators instead of spinning cups. Propeller anemometers work in much the same way. On top of the axle, there are several large cups that catch the wind and make the generator spin around. They're little more than an electricity generator mounted in a sealed-up metal cylinder with an axle protruding upward from it. Some of the simplest anemometers work in exactly this way. You figure out the mathematical relationship between wind speed andĮlectric current so you could figure out the speed of an unknown wind Much current is generated by a few winds of known speed. Instrument like this before you use it, of course. So if you measure the current, you have a basic way of measuring the Motor wired up backwards so it makes an electric current when you spin its centralīlades turn, the quicker the generator spins, and the higher the electric current it will produce. Suppose you build yourself a miniature, table-top wind turbine andĬonnect it to an electricity generator (effectively an electric But it's certainly true that wind turbines turn Turbines are fitted with brakes that stopīlows too hard (and they have built-in anemometers to measure the speedĪs well). Unsafe because gales and storms could make them
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