Vaisala WMT700 Manuel d'utilisateur télécharger pdf (Page 37)

Chapter 3 _______________________________________________________ Functional Description

CHAPTER 3

FUNCTIONAL DESCRIPTION

This chapter describes the functionality of WMT700.

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. This

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.

Figure 11 on page 36 shows how the time shift of the ultrasonic

signals is measured and how tail wind and forward wind affect the

measurement.

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Vaisala WMT700 Manuel d'utilisateur Page 37