If you need to brush up on magnetic declination, visit Wikipedia.īefore erecting a tower or mast for your anemometer, check for possible height restrictions set by local ordinances and homeowner's association covenants. Do not use a GPS to make the determination, the magnetic compass is a more accurate tool to determine true north. Visit the National Geophysical Data Center (NGDC) page that will calculate it for your location. The best way to locate magnetic north is by using a magnetic compass and correct to true north by the magnetic declination for your area. The mast can easily be leveled using a carpenter's bubble level, but orientation to true north is a bit more problematic. Other requirements for the proper installation of an anemometer include mounting the mast absolutely vertical and orienting the wind direction indicator to true north for accurate wind direction readings.
#Home wind speed indicator how to
Unfortunately this is the reality of taking wind measurements and the choice of how to deal with it is ultimately yours. Local obstructions like nearby mature trees, houses and buildings all have the potential of impacting anemometer readings. Accuracy of the wind speed indicator is not just a matter of height. For a rooftop installation, the minimum height to avoid anomalous winds caused by the roof itself is 3 meters (10 feet) above the most exposed part. So what are your alternatives? Part of the answer to that is how accurate you want your measurements to be? Wind observations taken at 7 meters (23 feet) are accurate enough for the National Weather Service to accept. For most home weather stations installations, striking a compromise is likely the best alternative. Attaining this height can not only be difficult but expensive as well. The World Meteorological Organization has set the international standard height for wind measurement devices at 10 meters (33 feet) above ground, with no obstructions at or above this level.
The wind speed indicated by the rotary anemometer in gusty wind is generally too high (the average error produced is about 10%).The goal of installing a wind speed meter (anemometer) is to position it in a location where the wind flows freely and is not influenced by nearby objects. When the wind speed decreases, due to the influence of inertia, the speed However, it cannot drop immediately. When the wind speed increases, the rotor cup can quickly increase the speed to adapt to the airflow speed. At present, the new type rotor anemometer adopts three cups, and the performance of the cone cup is better than that of the hemispherical cup. The pulse signal is counted by a counter, and the actual wind speed value can be obtained after conversion. When the wind cup rotates, it drives the coaxial multi-tooth cutting disc or magnetic rod to rotate, and the pulse signal proportional to the speed of the wind cup is obtained through the circuit. In this way, the wind speed can be determined according to the speed of the wind cup (the number of turns per second). After a period of time (when the wind speed is constant), when the partial pressure difference acting on the three wind cups is zero, the wind cups will rotate at a uniform speed. Rotating in the clockwise direction, the greater the wind speed, the greater the initial pressure difference, the greater the acceleration generated, and the faster the wind cup rotates.Īfter the wind cup starts to rotate, because the cup 2 rotates in the direction of the wind, the pressure of the wind is relatively reduced, while the cup 3 rotates at the same speed against the wind, the wind pressure is relatively increased, and the wind pressure difference is continuously reduced. The wind cup starts to go smoothly due to the pressure difference between the wind cup 2 and the wind cup 3 in the direction perpendicular to the axis of the wind cup.
The wind cup 3 has a convex surface facing the wind, and the effect of the wind makes the wind pressure received by the wind cup 2 smaller than that of the wind cup 2. For wind cup 2, its concave surface faces the wind and bears the greatest wind pressure. Wind cups 2 and 3 intersect with the wind direction at an angle of 60 degrees. When the wind blows from the left, the wind cup 1 is parallel to the wind direction, and the force component of the wind pressure on the wind cup 1 in the direction most straight to the axis of the wind cup is approximately zero.
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