Campbell 21X Operator's Manual page 90

SECTION
8.
PROCESSING
AND PROGRAM CONTROL EXAMPLES
Beginning of
Loop
Delay
Loop Count
Do
Set high Flag 0 (output)
Resolution
High Resolution
Sample
Rep
Loc
End
Do
Set high Flag
1
End
Table
1
Mode
10
Memory Allocation
lnput Locations
lntermediate Locations
8.8.2 EXAMPLE WITH BIN AVERAGING
The 21X
was used to generate data simulating
wave data
from an ocean buoy with four
superimposed sine wave signals, 0.1, 0.125,
0.14,
and O.2Hz. The 2048 generated samples
simulate a
sampling rate
of
0.5 Hz or a2.O
second scan
rate.
Figure 8.8-3 shows
a plot of
part of
the simulated
signal. A
FFT
with 8
bin
averaging
was performed
on the
data. A
multiplier of 0.1
was used to keep the FFT
results
smaller than the +6999 upper limit of low
resolution Final
Storage. The
results
of
the FFT
are shown Table 8.8-4 and are illustrated
in
Figure 8.8-4.
In
the example program, a multiplier of 0.1
is
used in
the FFT lnstruction. By reducing the
FFT results by
a
factor of
10,
the Low
Resolution output format can be used,
thus
maximizing
the Final Storage capacity. A Low
Resolution
data point requires 2 bytes of Final
Storage memory,
while a High Resolution data
point requires
4 bytes. When memory is
a
limiting factor, the data should be scaled to be
less
than 6999, so the Low Resolution format
can
be used.
SINULATED OCEAN
WAVE
BUOY
DATA
feo/fL .t/tr. .rb/?. .\./6, .2/.
o 6 12 16 2.
JO
)6 42 4! 5. 60 66 72 76 O. 90 96 to2r6ll'
Iffi
N 5ECAOs
FIGURE
8.8-3. Simulated Ocean
Buoy
Wave
Data
SII1ULATED
OCEAN WAVE BUOY
FFT
RESULTS
areo/
Et
.r
/
1
r.
-123/9.
.1
1/6, .2/.
o-@r95 0.0)12
0-ru.5
0.697 0.rro95
0.t.t2
0.17t.5 0.267
0
2595
trr ftwrcrEs
(o-oot95-o.2.7c5 tu)
FIGURE
8.8-4. Simulated Ocean Buoy
FFT
Results
13:
P87
01:
0
Q2:
512
14:
P86
01:
10
15:
P78
01:
1
16:
P7O
01:
1
O2:
1-
17:
P95
18:
PBo
01:
11
19:
,t
'A
01:1030
02:
260
o.9
o.a
0.7
o.6
o.5
o-a
o.J
o.2
o.r
&14