Campbell Scientific CR10 CR10 Measurement and Control - Page 85

SECTION

7.

MEASUREMENT PROGRAMMING EXAMPLES

This

section

gives

some

examples

of lnput

Programming for common

sensors used

with the

CR|0.

These

examples detail

only

the

connections,

lnput,

Program Control, and

Processing lnstructions

necessaty

to

pertorm

measurements and store the data in

engineering

units

in lnput

Storage.

Output

Processing lnstructions

are

omitted

(see

Section

I

for some

processing

and

program controlexamples).

It

is

teft

to the user

to

program

the

necessary instructions to obtain the final data

in

the form desired. No

output

to

final

storage willtake place

without additional programming.

The examptes given

in

this

section

would likely be only fragments of larger

programs.

ln

general, the

examples

are

wriften with the measurements made

by

the lowest numbered

channels, the

instructions

at

the beginning of

the

prbgram

table, and low

number lnput

Storage

Locations

used

to

store

the

data.

lt

is

untikely that an application

and

CRl0

configuration exactly duplicates that assumed in

an

example.

These examples are not meant

to

be

used

verbatim;

sensor calibration, input channels, and

input

locations

must

be adjusted for the

actual circumstances.

Unless

otherwise noted, all excitation

channels

are switched analog output.

7.1

SINGLE'ENDED VOLTAGE

-

LI2OOS

SILICON PYRANOMETER

The silicon pyranometer outputs

a

current which

is

dependent

upon

the solar

radiation incident

upon

the

sensor.

The current

is measured as

the

voltage drop

across a

fixed

resistor.

The

Campbell

Scientific Ll200S

uses

a

100 ohm

resistor. The

calibration supplied by LI-COR,

the

manufacturers

of

the

pyranometer, is given

in

pA/kWm2.

To convert calibration values to

volts multiply

the

pA

calibration by

the

resistance

of

the

fixed

resistor.

The calibration

of

the

pyranometer used

in

this

example

is

76.9 pA/kWm2,

which when

multiplied

by

100 ohms equals

7.69mV/kWm2.

The

multiplier used to convert the voltage

reading

to

kWm2

is 17.69mV/kWlm2

-

o.13oo4 kWm2/mV.

Most LI-COR

calibrations

run between

60

and 90

pA/kWm2,

which correspond to calibrations of

6.0

to

9.0mV/kWm2.

Above the

eafth's

atmosphere, the flux density through

a

surface

normal to

the solar beam is 1.36kWm2;

radiation

at

the

surface

of

the

earth

will be

less than this.

Thus,

the 25mV

scale

provides

an

adequate

range

(9.0mV/kWm2

x

1.36

kWm2

<

25mV).

CONNECTIONS

The

pyranometer output

can be

measured with a

single-ended

voltage

measurement on channel

5.

There

are

twice as

many single-ended

channels as differential channels and

they

are

numbered

accordingly:

Single-ended channel

5

is

the

high side of differential channel

3

(3H);the

low side (3L) is single-ended channel

6.

01:

Pl

01:

1

02:

23

PROGRAM

Volt (SE)

Rep

03:

5

04:

1

05:

.13004

06:

0

25

mV

60

Hz rejection

Range

lN

Chan

Loc

[:RAD

kWm2]

Mult

Offset

/\T)4

r-\

UKIU

3H

AT\

A\,

^

Lt200s

BLACK

WHITE

OR

CLEAR

FIGURE

7.1-1. Wiring

Diagram

for

Ll200S

7-1

Campbell Scientific CR10 CR10 Measurement and Control - Page 85

Measurement Programming Examples

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