Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 190

Section 7. Installation 7.8.5.1 OutputOpt Parameters In the CR800 WindVector() instruction, the OutputOpt parameter defines the processed data that are stored. All output options result in an array of values, the elements of which have _WVc(n) as a suffix, where n is the element number. The array uses the name of the Speed/East variable as its base. table OutputOpt Options (p. 190) lists and describes OutputOpt options. Table 29. OutputOpt Options Option Description (WVc() is the Output Array) WVc(1): Mean horizontal wind speed (S) WVc(2): Unit vector mean wind direction (Θ1) 0 WVc(3): Standard deviation of wind direction σ(Θ1). Standard deviation is calculated using the Yamartino algorithm. This option complies with EPA guidelines for use with straight-line Gaussian dispersion models to model plume transport. WVc(1): Mean horizontal wind speed (S) 1 WVc(2): Unit vector mean wind direction (Θ1) WVc(1): Mean horizontal wind speed (S) WVc(2): Resultant mean horizontal wind speed (U) WVc(3): Resultant mean wind direction (Θu) 2 WVc(4): Standard deviation of wind direction σ(Θu). This standard deviation is calculated using Campbell Scientific's wind speed weighted algorithm. Use of the resultant mean horizontal wind direction is not recommended for straight-line Gaussian dispersion models, but may be used to model transport direction in a variable-trajectory model. 3 WVc(1): Unit vector mean wind direction (Θ1) WVc(1): Unit vector mean wind direction (Θ1) WVc(2): Standard deviation of wind direction σ(Θu). This standard deviation is 4 calculated using Campbell Scientific's wind speed weighted algorithm. Use of the resultant mean horizontal wind direction is not recommended for straight-line Gaussian dispersion models, but may be used to model transport direction in a variable-trajectory model. 7.8.5.2 Wind Vector Processing WindVector() uses a zero-wind-speed measurement when processing scalar wind speed only. Measurements at zero wind speed are not used in vector speed or direction calculations (vectors require magnitude and direction). This means, for example, that manually-computed hourly vector directions from 15-minute vector directions will not agree with CR800-computed hourly vector directions. Correct manual calculation of hourly vector direction from 15-minute vector directions requires proper weighting of the 15-minute vector directions by the number of valid (non-zero wind speed) wind direction samples. Note Cup anemometers typically have a mechanical offset which is added to each measurement. A numeric offset is usually encoded in the CRBasic program to compensate for the mechanical offset. When this is done, a measurement will equal the offset only when wind speed is zero; consequently, additional code is 190