Glossary /­ FAQs /­ LexiconWind measuring technology

The acoustic virtual temperature is the air temperature referred to dry air without any portion of water vapour.
It is acquired by propagation measurements of sonic pulses. After respective correction of the humidity influence the procedure exceeds the accuracy of the classic procedures of the temperature measurement in a weather and thermal radiation shield.

The quotient from the sum of all the individual values and the number of values within the mean value time.

The damping coefficient characterises the oscillations of the wind vane. It is an important characteristic quantity for the qualitative evaluation of the wind vane. The damping coefficient is determined from the ­amplitudes of two successive excursions and is calculated by means of an equation.

Measure for the damping of wind vanes. It represents the ratio between the consecutive damped deflection amplitudes (for example 3^rd ­amplitude to 1^st amplitude) in one direction.

The path covered by the wind which is reached when, after a sudden change in wind speed, the speed reaches 63% of its end value.

The lowest value of wind speed and wind direction at which a stable value sets in.

The mean value which is updated as the mean value time at short time intervals
(for example the 10 min.-mean value is updated once a second).

One-increment binary code, on the changeover of one value to the next one only one single data bit modifies each to the previous and the next value respectively. The Gray-code is used for the digital determination of distances, for ex. the wind direction of a wind vane.
The code can be set up by means of any number of digits, it depends only on the required accuracy of resolution.

A straight line standing vertically to another straight line. By arranging two measurement distances standing vertically on each others you achieve the amount and angle of the wind velocity vector in the form of rectangular components. After measurement of the rectangular wind velocity components the amount and angle of the wind velocity can be calculated.

Wind velocity amount without indication of direction.

The serial-synchronous interface is a unidirectional two-wire-interface with Thies specifications. It allows the connection between Thies wind sensors with serial-synchronous output and respective periphery (for ex. display instruments)

Spatial Path Averaging is a physical measurement principle used in ultrasonic wind measurement. Instead of measuring the flow at a single point, it integrates the flow along a defined measurement path. Instead of using just a single measurement point in the flow, the wind is measured along a spatial path. This results in an averaged measurement value that takes into account multiple local flow components. This is particularly important for large wind turbines, where the air is often highly turbulent. In this case, large-scale wind movements overlap with small-scale turbulence structures and wake effects.

Influence of the Measurement Path Length:
The effectiveness of spatial path averaging depends significantly on the length of the measurement path.
• Short measurement paths:
greater sensitivity to local microturbulence and short-term fluctuations
• Longer measurement paths:
greater spatial integration of multiple flow components → more stable output signal

Significance for wind measurement:
Spatial averaging can improve the representativeness of the measurement signal. This contributes to a more stable measurement of the average wind direction, particularly in applications such as the yaw control of wind turbines.

Application in ultrasonic wind sensors:
In ultrasonic wind sensors, spatial path averaging is achieved through the geometric design of the measurement path.

The wind speed at which a cup anemometer respectively the wind vane starts to move.

Maximum allowable wind speed at which no damage occurs on the wind measuring instruments.

The range within which wind direction has changed within the ­preceding 10 minutes (in accordance with ICAO).

Method of calculation: The individual vectors, measured as wind speed and direction, are decomposed into rectangular components.
The components are averaged arithmetically, these mean values are then composed into a vectorial mean value.

Only used for wind direction. A constant wind speed is assumed for the individual vectors.

Information on the direction from which the wind is coming.
Information appears clockwise from North to East (90°), South (180°), West (270°) and North (360°).

”Beaufort“ (bft) classes for certain wind speed ranges.

The path covered by the wind for a certain period of time.

The most common units of measurement are: 1 m/­s = 3.6 km/­h = 1.9455 knots.

The wind direction (0 … 360 °) is converted into an 8-bit Gray code (Thies special) and transmitted. The resolution is 2.5 °, 144 increments per ­revolution.
Increment 0 = 0 ° = North and corresponds to the sector 0 … 2.5 °
Increment 143 = 357.5 ° corresponds to the sector 357.5 … 0 °.