LSI LASTEM Alpha-Log, Руководство пользователя, Страница: 72 / 116

Alpha-Log – User manual
LSI LASTEM SRL INSTUM_03388 Page 72 / 116
Fig. 35 – Example of calculated measurement configuration of type "Cross wind"
4.2.4
Elaborations
For each acquired or calculated measure, it’s possible to obtain the statistic elaborations with time basis from
1 second to 24 hours. It’s possible to choose one or more of the statistic elements mentioned in the list:
Item Description
Ist Is the last acquired value
Min Is the lower value among those acquired within the time basis
Med Is the average value calculated with the values acquired within the time basis
Max Is the higher value among those acquired within the time basis
DevSt Is the standard deviation calculated with the values acquired within the time basis
Tot Is the total obtained by adding all the values acquired within the time basis
TimeMin Is like Min with the addition of the point in time when it happened
TimeMax Is like Max with the addition of the point in time when it happened
Furthermore, for anemometric measurements, it is possible to choose the following vector calculations:
(Prevailing) average direction
It is the vector angle value calculated as the vector sum of all wind components measured by the data logger
within the selected statical time base, whose module is considered unitary. It provides the most frequent
origin of the wind during the processing period, regardless of the wind intensity.
The formula for calculating
the Prevailing average direction is as follows:
PrevDir =
( ) ( )
)) ( ( )), ( ( atan2 Dir rad Cos Dir rad Sin gra
 
Resulting average direction
Vectorial angle value calculated as the vectorial sum of all wind speed and direction components measured
by the data logger within the selected statistical time base. In other words, it provides the direction of origin
of the wind based even on the individual wind intensities. Below is the formula for calculating the Resulting
average direction.
RisDir =
( ) ( ) ( ) ( )
Vel Dir rad Cos Vel Dir rad Sin gra
   
)) ( ( , )) ( ( atan2
Resulting average speed
It corresponds to the value of the modulus of the vector calculated for the evaluation of RisDir, so it is the
wind intensity resulting from the sum of each individual components. In other words, from the point of view
of the displacement of the air masses, the same result would be obtained in real conditions, if the wind were