Campbell Scientific CR10 CR10 Measurement and Control - Page 148

SECTION

10.

PROCESSING INSTRUCTIONS

Although the

algorithm

requires an air pressure

entry, the daily fluctuations are small enough

that

for

most applications

a

fixed

entry

of

the

standard pressure

at

the site elevation will

suffice.

lf

a pressure sensor is employed,

the

current pressure

can

be used.

PARAM.

DATA

NUMBER

TYPE

DESCRIPTION

01:

4

Input location of

atmospheric

pressure

in kilopascals

IPRESSURE]

O2;

4

Input location of dry-

bulb

temp.

[DB

TEMP.]

03:

4

Input location

of

wet-

bulb temp.

lwB

TEMP.I

04:.

4

Destination input

location for

vapor

pressure

[VP

or

Z]

Input locations

altered:

1

*'*

58

LOW PASS

FILTER

***

FUNCTION

Apply

a

numerical approximation to an analog

resistor

capacitor

(RC) low pass (LP)

filter

using

the following algorithm.

F(Xi)

=

W*Xi+

F(Xi-1)

.

(1-W)

Where X

=

input sample, W

=

usef

entered

weighting

function

(O<

W

<1).

lf W=O,

F(X|)=X.,;

if

W=1,

F(X|)=X

and

F(Xi-1)

=

output

calculated

for

previous sample

The equivalent

RC

time constant

is

given by

TAA/,

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

Wl(2nT).

For larger values

of

W,

this

"analog" estimate

of

the

cutotf frequency

becomes less representative.

On the

first

execution after

compiling,

F(X)

is

set

equalto

X.

PARAM.

DATA

NUMBER

TYPE

DESCRIPTION

2

Repetitions

First input location

for

input data

Dest. input location

for

first

filtered

resultlF(X)

or

Zl

Weighting

function,

W

twl

Input locations

altered:

1

for

each

repetition

***

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

Rr[)U(1-X)],

where X

is

the value derived by the

standard CR10 Bridge Measurement

Instructions (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.

PARAM.

DATA

NUMBER

TYPE

DESCRIPTION

2

Repetitions

[REPS]

Starting input location

& result

destination

[X]

03:

FP

Multiplier

(Rf)

[MULT]

Input locations

altered:

1

for

each

repetition

***

61

INDIRECT INDEXED

MOVE

***

FUNCTION

Moves input data

from

location

X

to

location

Y,

where X and/or Y are indirectly addressed

(X

and Y are stored

in

the

locations specified by

Parameters

1

and

2).

lf

a

location parameter

is

specified

as

"indexed" (xxxx--), then the actual

input location referenced

is

calculated by adding

the current index counter to the value

in

the

specified input

location. When

used outside

a

loop,

the

addressing

is

simply indirect

because'

the

index counter is zero.

03:

04:

FP

10-6

Campbell Scientific CR10 CR10 Measurement and Control - Page 148

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