Gill Instruments Ltd
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WindObserver II Page 29 Issue 18
Doc. No. 1390-PS-0004 January 2009
8.4. Units
The wind speed can be set to any of the following units:
Unit Abbreviation
Metres per sec m/s
Knots knots
Miles per hour MPH
Kilometres per hour kph
Feet per minute fpm
8.5. Output rate
The output frequency can be set between 1 and 10 per second. The wind speed is sampled
every 25ms, each axis being sampled sequentially. The following Table lists the possible
outputs per second and the corresponding number of averaged samples. A 25ms sample
period is used to process and output the results.
Outputs per Second Sample Average
1 39
2 19
4 9
5 7
8 4
10 3
8.6. Averaging (Digital Data)
The Averaging Period can be set from zero to 3600 secs. (1 hour). The default setting is
zero. When averaging is enabled, data is output at a rate determined by the averaging
period. The data is an average of valid data collected during the averaging period. If G is
set to zero then averaging settings will be disabled.
8.7. Options
Speed of Sound (SOS) and Temperature
Either or both of these parameters can be selected or disabled
Note that neither of these parameters is available in Tunnel or NMEA formats.
SOS is useful for calculating air temperature with a rapid response. Sonic temperature is
derived from the SOS, based on an assumption of the composition of the atmosphere.
Humidity will affect the result.
True temperature can be calculated by:
T = Ts
1+0.32 e/p
Where T = True temperature (Kelvin)
Ts = Sonic temperature
e = Vapour pressure of water in air
p = absolute pressure of water in air
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