Gill Instruments Ltd
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MaxiMet
Page 8
Issue 1
Doc. No. 1957-PS-000x
March 2015
Derived Parameters selectable using MetSet Software (see page 5 for applicability).
AH
Absolute Humidity.
The humidity of the atmosphere, usually expressed as the number of grams of water
contained in 1 cubic metre of air.
(Note Relative Humidity also output, expressed as a percent, measures the current absolute
humidity relative to the maximum for that temperature).
Absolute humidity shall be computed as:- H = C · P
w
/T.
Where:-
H = absolute humidity
C = Constant 2.16679 gK/J
Pw = Vapour pressure in Pa
T = Temperature in K
Result e.g. 08.14 g/m
3
.
AVGSPEED
Average Speed.
Outputs the World Meteorological Organisation (WMO) Average Wind Speed reading based on
AVG short and AVG long settings (see page 36).
Result e.g. 001.45 (Metres/second default).
AVGDIR
Average Direction.
Outputs WMO Average Direction Wind reading based on AVG short and AVG long settings (see
page 36).
Result e.g. 145 (degrees).
AVGCDIR
Average Corrected Direction
Outputs WMO average Compass Corrected Direction wind reading based on AVG short
and AVG long settings (see page 36).
Result e.g. 131 (degrees).
CDIR
Corrected Direction
Corrected Wind Direction shall be computed as the Apparent Wind Direction using the
compass heading reading.
Result e.g. 116 (degrees).
DEWPOINT
Dewpoint.
Output calculated Dewpoint from Temperature and Humidity readings.
T
d
= T
n
/ (Y-1)
where
T
d
= Dewpoint temperature
Y = m/log
10
(Pw/A)
T
n
=Triple point temperature (in K)
Pw = Pws . RH / 100 (hPa)
Pws = water vapour saturation pressure (hPa)
Result e.g. 45.1 (%).