Delta OHM HD32MT.3, Operating Manual

Page: 24 / 62

HD32MT.3
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V1.2
7 MEASURING WIND DIRECTION AND SPEED
7.1 D
EAD BAND OF WIND VANE
The data logger considers a fixed dead band of ±4° around zero of the vane, that is to say that
the value recorded by the data logger is zero if the measurement of the vane is included in the
ranges 0...4° and 356...359.9°. Therefore, it is advisable to direct the zero indicator of the
vane in the direction of less interest and correct the measurement direction with respect to the
North by setting an offset with the appropriate command WINDVANEOFFS (see paragraph
11.7) or with the aid of the software Meteo Studio.
7.2 A
VERAGE WIND DIRECTION AND SPEED
The data logger can record the average of direction and wind speed by using various methods of
calculating the average. The calculation method most appropriate depends on the information that
you want to achieve and the environmental conditions of the installation site (for example, if it is
an exposed place in which the wind direction can vary considerably sudden or if it is a place where
the wind has a prevailing direction, as in a gallery).
The average is calculated over a 10-second interval for the measurements recorded in the files of
type T1 and over the set logging interval for the measurements recorded in the files of type T3 and
T4.
Below are described the possible methods. The indices of the measures listed below are those of
the command MEASUREMAP used for the definition of the tables in memory (see paragraph 11.6).
Scalar average
The average intensity is calculated as the average of intensity regardless of the direction (corre-
sponds to the average of the modules of velocity vectors). The mean direction is calculated as the
average of the directions without taking into account the intensity of the wind in various directions.
The scaling method can be used in places where the wind has a prevailing direction, as for exam-
ple in a tunnel. In an area exposed, the method has the disadvantage of not providing an indica-
tion about the direction in which the wind blew with greater intensity.
The average direction may be even wrong if the wind comes predominantly from the north but
sometimes the direction is slightly to the North-East (direction equal to some degrees) and some
other times it is from the North-West (direction equal to a value close to 360 °). Under these con-
ditions, the scalar average of the directions results next to 180°, as if the wind is coming from the
South, it means from the opposite direction.
Fig. 7.1: wind directions
The scalar average is calculated by the data logger HD32MT3 recording measures of direction
(measures with index 2 or 8) and speed (measures with index 3 or 7) with the storage type of in-
dex 2 (mean value).
If you are using an anemometer of the series HD52.3D…, you can get the scalar average calculat-
ed directly from the anemometer, in a configurable interval from 1 to 9 seconds, recording the
measures with index 17 and 18 and configuring the anemometer to use the scalar method for the
calculation of the average (not the default method, please refer to the manual of HD52.3D ...).