Page 352 - Fundamentals of Air Pollution 3E

IV. Dispersion Instrumentation 307

Fig. 19-7. Microvane and three-cup anemometer. Source: Photo courtesy of R. M.
Young Co,

plished by microcircuitry (minicomputer) designed to sample properly the
output from the vane and perform the calculations for both mean wind
and <r a/ taking into account crossover shifts of the wind past the 360° and
0° point.
The elevation angle, and through appropriate data processing <r e, can be
measured with a bivane (a vane pivoted so as to move in the vertical as
well as the horizontal). Bivanes require frequent maintenance and calibra-
tion and are affected by precipitation and formation of dew. A bivane is
therefore more a research instrument than an operational one. Vertical
fluctuations may be measured by sensing vertical velocity w and calculating
<r w from the output of a propeller anemometer mounted on a vertical shaft.