Vaisala WS425 - Manual (Page 15)

Chapter 2 __________________________________________________________ Product Overview
VAISALA _______________________________________________________________________ 15
CHAPTER 2
PRODUCT OVERVIEW
This chapter describes the features of the WS425 Ultrasonic Wind
Sensors.
Introduction to WS425
Measuring Principle
The WS425 Ultrasonic Wind Sensor has an on-board microcontroller that
captures and processes data and performs serial communications.
The wind sensor has an array of three equally spaced ultrasonic
transducers on a horizontal plane. The sensor measures transit time, the
time that it takes the ultrasound to travel from one transducer to another.
The transit time is measured in both directions.
The transit time depends on the wind velocity along the ultrasonic path.
For zero wind velocity, both the forward and reverse transit times are the
same. With wind along the sound path, the up-wind transit time increases
and the down-wind transit time decreases.
The microprocessor of the microcontroller calculates the wind speed
from the transit times using the following formula:
) t / 1 (1/t L 5 . 0 V
r f W
− ⋅ ⋅ =
where:
V
w
= Wind velocity
L = The distance between two transducers
t
f
= The transit time in the forward direction
t
r
= The transit time in the reverse direction.