Vaisala WINDCAP WS425 User's Guide download pdf (Page 27)

Chapter 3 ______________________________________________________ Functional Description

VAISALA _______________________________________________________________________ 25

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 WS 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 up-wind direction transit time increases and the down-

wind transit time decreases.

Figure 6 on page 26 shows how the time shift of the ultrasonic signals is

easured and how tail wind and forward wind affect measurement.

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Vaisala WINDCAP WS425 User's Guide Page 27