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2.2.1 Wind Vanes

The conventional wind vane consists of a tail section attached to one end of a horizontal shaft which, in turn, is mounted on a vertical axis; the tail and shaft rotate in a horizonal plane. The wind vane measures the azimuth angle of the wind. Wind vanes and tail fins should be constructed from light weight materials. The starting threshold (lowest speed at which a vane will turn to within 5 o of the true wind direction from an initial displacement of 10  ) should be 0.5 ms -1 . Overshoot must be 25% and the damping ratio should lie between 0.4 and 0.7.

Bi-directional vanes (bivanes) measure both the azimuth and elevation angles of the wind vector. The bivane generally consists of either an annular fin or two flat fins perpendicular to each other, counterbalanced and mounted on a gimbal so that the unit can rotate freely both horizontally and vertically. Bivanes require greater care and are not generally suited for routine monitoring. Data from bivanes, consequently, should only be used on a case by case basis with the approval of the reviewing authority.

2. PRIMARY METEOROLOGICAL VARIABLES 
 2.1 Wind Speed
      2.1.1 Cup Anemometers
      2.1.2 Vane-oriented and Fixed-mount Propeller Anemometers 
      2.1.3 Wind Speed Transducers 
  2.2 Wind Direction 
      2.2.1 Wind Vanes  
      2.2.2 U-V and UVW Systems  
      2.2.3 Wind Direction Transducers 
      2.2.4 Standard Deviation and Turbulence Data  
  2.3 Temperature and Temperature Difference 
      2.3.1 Classes of Temperature Sensors  
      2.3.2 Response Characteristics  
      2.3.3 Temperature Difference 
      2.3.4 Sources of Error 
  2.4 Humidity  
      2.4.1 Humidity Variables  
      2.4.2 Types of Instrumentation  
  2.5 Precipitation 
  2.6 Pressure  
  2.7 Radiation  
  2.8 Recommendations


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