Vaisala WINDCAP WMT700 Series, User Manual

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3. Functional Description
3.1 Operating Principle
WMT700 uses the Vaisala WINDCAP ultrasonic sensor technology in wind measurement.
The sensor has an onboard microcontroller that captures and processes data and
communicates over serial interfaces.
The wind sensor has an array of three equally spaced ultrasonic transducers on a horizontal
plane. Wind speed (WS) and wind direction (WD) are determined by measuring the time it
takes the ultrasound to travel from each transducer to the other two.
The wind sensor measures the transit time (in both directions) along the three paths
established by the array of transducers. The transit time depends on wind speed along the
ultrasonic path. For zero wind speed, both the forward and reverse transit times are the
same. With wind along the sound path, the upwind direction transit time increases and the
downwind transit time decreases.
The following figure shows how the time shift of the ultrasonic signals is measured and how
tail wind and forward wind affect the measurement.
Chapter 3 – Functional Description
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