Campbell 21X Instrukcja Operatora Pobierz pdf (Strona 64)

7.

MEASUREMENT

PROGRAMMING EXAMPLES

This section

some

examples

of

lnput

Programming

for

common

sensors

used with the

21X.

These

examples

only the connections,

lnput, Program Control,

and Processing

Instructions

necessary to

pertorm

and

store

the data in engineering

units in lnput Storage.

Output

Processing

lnstructions

pre

omitted.

lt is teft

for the

user

to

program

the necessary

instructions to obtain

the

final

data

in the

desired.

NO OUTPUT

TO FINAL

STORAGE WILL

TAKE

PLACE WITHOUT

ADDITIONAI-

PROGRAMMING.

The examplQs

given

in this

section

would likely be only

fragments of

larger

programs.

ln

general,

the

examples

atp

written with the

measurements

made by

the

lowest

numbered

channels,

the

instructions

lt

the beginning

of

the

program

table,

and

low

number

lnput Storage

locations

used to

store

the

dala.

lt is

unlikely

that

an application and

21X

configuration exactly

duplicates

that assumed

In an

THESE EXAMPLES

ARE NOT

MEANTTO BE USED

VERBATIM; SENSOR

AND INPLJT

LOCATIONS SELECTED

MUST

BE

ADJUSTED

FOR THE

ACTUAL

CALIBRA

UNLESS

OTHERWISE

NOTED,

ALL EXCITATION

CHANNELS

ARE

ANALOG OUTPUT.

7.1 DIFFERENTIAL

VOLTAGE

.

LI2OOS

SILICON PYRANOMETER

The silicon

pyranometer puts

out a

current which

is dependedt

upon the solar

radiation

incident

upon

the

sehsor.

The current

is measured as

the

voltage

across a

fixed

resistor. The

Campbell

Ll200S

uses a

100

ohm

resistor.

calibration

supplied

by Ll-COR,

the

int

. The calibration

in terms of

volts is

rers of the

pyranometer,

is

given

determined

py

multiplying

the

pA

calibration by

the

resistanbe

of the fixed

resistor.

The calibratfon

of the

pyranometer

used

in

this

example

is

{ssumed

to be

76.9pA/kW/m2,

which

when multillied

by 100 ohms

equals

7.69mV/kWfm2.

The

multiplier

used

to

convert

the

voltage

feading

to

kWm2

is

1 17 .69mV

lklv

/ m2

=

0.

1

3004.

Most

LI-COR

calibrations

run between

60 and

90uA/kWnl2,

which

correspond

to

calibrations

of

6.0 to

9.dmV/kWm2.

Above

the

earth's

atmospherd,

the

flux

density

through a

surface

normal

to

the solar beam

is 1.36kWm2;

radiation

on earth

will be

less than

this.

Thus,

the

1SmV

soale

provides

an

adequate

range

(g.omv/kwm2

x 1.36

kWm2

<

15mV).

CONNECTIONS

The

pyranqneter

output

is measured

with a

differential

{oltage

measurement

on channel

3.

The

low sidp

of signal

is

jumpered

to

datalogger

ground

to

hold the

signalwithin

common

mode

range

(Section

14.3-2).

FIGURE

7.1-1.

Wiring Diagram

for

Ll200S

PROGRAM

01:

P2

Volt

(DIFF)

01:

1

Rep

02:

2

15 mV slow

Range

03:

3

lN

Chan

04;

1

Loc

[:RAD

kWm2]

05:

.13004 Mult

06:

0

Offset

7.2 DATALOGGER

AND

SENSOR

WITH

A

COMMON

EXTERNAL

POWER

SUPPLY

Some sensors

either contain

or

require

active

signal conditioning

circuitry to

provide

an easily

measured

analog

voltage

output.

Generally, the

output is referenced

to

the

sensor

ground.

The

associated current

drain usually

requires a

power

source

external to

the

21X. A typical

connection

scheme

where AC

power

is not

available

and

both the 21X and

sensor

are

powered

by

an

external battery

is shown

in

WHITE OR CLEAR

7-1

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