Campbell 21X Operator's Manual page 122

ON
11.
OUTPUT PROCESSING INSTRUCTIONS
wind vector
flirection over an output interual.
Two
differer* calculations
of
wind
vector
direction (and standard deviation of wind vector
direction)
arg available, one
of
which
is
weighted
foqwind speed.
When used fvith polar sensors, the instruction
does
a mod{rlo divide by 360 on wind direction,
which
allow{ the wind direction (in degrees) to
be 0
to
360,l0 to 540, less than 0, or greater
than
540. Tfe
ability
to handle a negative
reading is u$eful in
an example where a difficult
to reach wind vane is improperly oriented
and
outputs 0 dQgrees at a
true reading of 340
outputs 0 dQgrees at a
true reading of 340
degrees.
Tl'fe
simplest solution is to enter an
offset of
-20
in
the instruction measuring the
wind vane, vfhich results
in
the correct output
following
When
a
speed
sample is
0,
the instruction
uses 0 to
scalar or resultant vector
wind speed hnd standard deviation, but the
sample is
n(t
used in
the computation of wind
direction.
user may not want
a
sample less
than
the threshold used
in
the standard
deviation.
lff
this is the case instruction 89 can
be used to
wind speed, and if less than
the
Instruction 30 can set the input
to
0.
Standard deiviation
can be processed one of
two
ways:
1) using every sample
taken during
by
from
s
for
2).
Aveqaging sub-interval
standard
ions minimizes the effects of
69
WIND VECTOR
*'*
FUNCTION
Instruction
6p processes the primary variables
and direction from
either polar
(wind speedland direction) or orthogonal (fixed
East and
propellers) sensors. lt
uses
the
raw data to
mean wind
the mean wind speed, the
Standard deviation
of horizontal wind
fluctuations from sub-intervals is
calculated as
follows:
o(o)=[((oo1
)2+(c@2)2
...+1 oo*)2)/MJ1/2
where o(@) is
the standard deviation over the
output interual, and oO.t ...o@u are sub-interval
standard deviations.
PARAM.
DATA
NUMBER
TYPE
DESCRIPTION
2
Repetitions
4
Samples per sub-interval
(number
of scans)
2
Sensor/Output 2 digits:
AB
A
Sensortype:
0 = Speed and
Direction
1
= East and North
B
Output option:
0
S,
@1,
o(@1)
1
S,01
2
S, U,
@u,
o(Ou)
04: 4
First wind speed input
location
no.
(East wind speed)
05: 4
First wind direction input
location
no.
(North wind speed)
Outputs Generated: 2-4 (depending on output
option) for each repetition
A sub-interval is specified as a number of scans.
The number of scans for a sub-interval is given
by:
Desired
sub-interval (secs) / scan rate (secs)
In
an example where the
scan rate is
1
second
and the
Output Flag is set every 60 minutes, the
standard
deviation
is
calculated from
all3600
scans when the sub-interval is
0.
With a sub-
interval of 900
scans (15 minutes) the standard
deviation
is
the average
of
the
four sub-interval
standard
deviations. The last sub-interval
is
weighted if
it
does not contain the specified
number of scans.
magnitude, and
the mean
standard deviations processed
sub-intervals
of
the output period
01:
02:
03:
meander under light wind conditions, and
it
provides
mQre
complete information for periods
of
transition'
.
'
EPA
On-site Meteorological Program
Guidance
fdr Regulatory Modeling Applications.
1
1-1