Vaisala WS425 - Manual (Page 35)

Chapter 4 ________________________________________________________________ Operation
VAISALA _______________________________________________________________________ 35
CHAPTER 4
OPERATION
This chapter explains the operation and programming of WS425.
Analog Mode
The WS425 Ultrasonic Wind Sensor can be used as a conventional wind
set that gives instantaneous readings. The sensor is normally powered
down. When power is first turned on, it takes about two seconds for the
sensor to initialize and stabilize. Then the sensor takes a 0.35-second
measurement and synthesizes the analog outputs of wind speed and wind
direction. The cycle is repeated every second until power is turned off.
Wind Speed
The factory sets the wind speed unit of the analog mode to miles per
hour. This is the only option available for the analog mode.
The wind speed output at pin 14 is 0 to 12 V pulsed output with a
frequency proportional to wind speed. Every mile per hour adds 5 Hz to
the frequency. In SI units, a change of 0.894 m/s adds 10 Hz to the
frequency. A frequency counter is required to count the output in Hz and
the calculation that scales the result to appropriate units.