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Operating Manual V25/09.2019
Ventus / Ventus-X / V200A
Chapter 6 Equipment Description
8
The orthogonal arrangement of the measurement sections allows to evaluate the x and y
components (resp. North-south and east-west components) of the air flow.
Basically the sonic velocity, and with it the time of flight of the ultrasonic pulse packets, will be
influenced by air temperature and air humidity. The alternating measurement (north->south /
south->north, west->east / east->west) compensates this influence.
The differences of the time of flight are averaged over a number of measurements, then the
wind speed and wind direction is evaluated from the average.
The design of the sensor head protects, to a large extend, the measurement sections against
rain and snow. The heating of the sensor prevents icing of the ultrasonic transceivers.
The aerodynamic design of the sensor head minimizes influences on the wind flow. Remaining
deviations are evaluated during device calibration so that they are compensated during the
calculation of wind speed and wind direction.
6.2 Virtual Temperature
Due to the physical relationship between the velocity of propagation of sound and the air
temperature, the approximate ambient temperature can be determined with the aid of
ultrasound sensors.
6.3 Air Pressure
The air pressure is measured by an integrated air pressure sensor
6.3.1 Air Density
Air density is calculated from the measured air pressure, virtual temperature and relative
humidity. The
Ventus
doe
sn‘t measure relative humidity so a constant value, which can be
adjusted through ConfigTool.NET, is applied. Factory setting is 75%.
6.4 Heating
For winter operation
Ventus
has got 2 heating elements (one element only on plastic version) to
keep the sensor free of snow and ice. One element is in the cover (metal version only) and the
other is built into the ultrasonic sensors.
To reduce the maximum operating current of the device, upper and lower heating can be
switched alternatingly.
Separate measurement channels are available for the surveillance of the temperatures of upper
and lower heater.
By default the heating is set in automatic mode and full capacity. This is the recommended
heating mode of the sensor.
Figure 2 Influence of Wind on Time of Flight