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SECTION
10.
PROCESSING INSTRUCTIONS
PAR. DATA
NO. TYPE
DESCRIPTION
01: 4
Input location no. of atmospheric
pressure in kilopascals
IPRESSURE]
02: 4
Input location no. of dry-bulb temp.
IDB
rEMP.l
03: 4
lnput location no.
of
wet-bulb
temp.
IWB
TEMP.]
04: 4
Dest. input location for
vapor
pressure
Input locations
altered:
1
[VP or Z]
*** 58
LOW PASS
FILTER
***
FUNCTION
Apply
a numerical approximation to an analog
resistor
capacitor (RC) low pass (LP) filter using
the following algorithm.
F(X;)
=
W*X;+
F(X;_1). (1-W)
Where,
X =
inputsample,
W =
user entered weighting function,
o<w<1
lf
W=O, F(X|)=X1;
if
W=1
, F(X|)=X,
F(Xi-1)
=
output calculated
for previous sample.
The equivalent
RC
time
constant
is
given by
TAIV,
where
T
is
the sampling time in seconds.
For
values
of
W less than 0.25, the analogous
"cut off"
frequency
(the
frequency where the
ratio of output
to input is .707)
is
accurately
represented by
W/(2IIT).
For larger values of
W,
this "analog" estimate
of
the cutoff
frequency
becomes less representative.
On the
first execution after compiling, F(x) is set
equalto
X.
PAR. DATA
NO. TYPE
DESCRIPTION
*** 59
BRIDGE
TRANSFORM
'**
FUNCTION
This instruction is used to aid
in
the conversion
of
a ratiometric Bridge measurement by
obtaining the value
for R. which
is
equivalent to
Rf[)V(1-X)], where X
is
the value derived
by
the
standard
21X Bridge Measurement Programs
(with appropriate multiplier and otfset, Section
13.5) and
R1
represents
the MULTIPLIER value
The result of Instruction 59 is stored
in
the
same location that
X
was.
PAR. DATA
NO. TYPE
DESCRIPTION
Repetitions
Starting input location and
01:
2
02:
4
destination
03: FP
Multiplier
(Rf)
tx
IMULT.
01:
2
o2'.
4
03:
4
data
Repetitions
[REPS]
First input location for input data
txl
Dest. input location for filtered
lnput locations
altered:
1
for
each repetition
***
60
FAST FOURIER TRANSFORM
***
THEORY
Instruction
60 performs a Fast Fourier
Transform (FFT) on a set of data contained
in
contiguous locations
in Input
Storage. The
FFT
is used to
obtain information
on
the relative
magnitudes and phases of the various
f
components in
a
time
varying
signal.
FFT
requires that the signal be sampled at
a
frequency
that is at least two times faster than
the highest frequency component
in
the signal.
For
example, a
signal representing ocean
with a maximum frequency of
0.125
Hz
would
need
to be sampled at a rate of 0.25 Hz or
greater. The
measurements must be made at
the appropriate sampling rate and stored
in
contiguous input locations before
the FFT can
be
applied. The
measured data
stored
in
sequential input locations
is
also referred
to
as
the "originaltime series data".
The results
of
the FFT can be expressed as:
1)
the
realand
imaginary components,
2)
the
magnitude and phase components, or
3)
the
power
spectra. The
real and imaginary results
are analogous to the orthogonal (east and
representation of
a
wind
vector. The
magnitude
and phase results are analogous to
the polar
(speed and
direction) representation of
a
wind
vector. The
power
spectra results indicate the
[F(X) or
z]
04: FP
Weighting function,
W
IWI
lnput locations
altered:
1
for each repetition
10-6
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