Campbell 21X Manuale dell'Operatore Scaricare il pdf (Pagina 113)

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

1 2 ... 108 109 110 111 112 113 114 115 116 117 118 ... 190 191

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