Campbell 21X Manual do Operador descarregar pdf (Página 161)

SECTION

14. INSTALLATION

AND MAINTENANCE

damage

the datalogger.

Campbell

Scientific's

DC112

phone

modem has spark

gaps

on the

phone

lines.

A 12

AWG wire should

run

from

the

modem

ground

terminalto earth

ground.

laboratory

applications, locating

stable

earth

ground

is not

always obvious. In

older

buildings,

new

cover

plates

on old

AC sockets

may indicate

that

a safety

ground

exists when

fact

the socket

is not

grounded.

a safety

ground

does

exist, it is

good

practice

to verify

that it

carries no

current. lf the integrity

of the

power

ground

cannot

verified,

it is better

ground

the system

to a massive metalobject

such

as a steelwater

pipe.

In the field,

an earth

ground

may

be created

through

grounding

rod. A

AWG

larger

wire

should be run

between the 21X

terminal

and

the eafth

ground.

Campbell

Scientific's

CM10

and CM6 Tripods

come complete with

ground

and lightning

rods,

grounding

wires,

and

appropriate

ground

wire

clamps.

14.8.2

EFFECT

OF GROUNDING ON

MEASUREMENTS:

COMMON

MODE RANGE

The common

mode range is the voltage

range,

relative

to the 21X

ground,

within

which

both

inputs

a differential measurement must

lie in

order for

the differential

measurement to be

made.

Common mode

range

for

the 21X is

IS.OV.

For example,

if the high side of

differential

input is

at 4V and the

low

side is

3V relative

to 21X

ground,

measurement

made

on the +5.0V range

would

indicate

signal of 1V. However,

if the

high

input

changed

to 6V,

the common

mode

range is

exceeded

and

the measurement cannot be

made.

Common

mode range

may be exceeded when

the 21X is

measuring

the output

from

a sensor

which

has its

own

grounded

power

supply

and

the low

side of the

signal is referenced

power

ground.

the 21X

ground

and

the

sensor

ground

are at sufficiently

different

potentials,

the

signalwillexceed

the

common

mode range.

solve this

problem,

the sensor

power

ground

and

the 21X

ground

should

connected,

creating

one

ground

for

the system.

a laboratory

application,

where

than

one AC

socket

may be

used to

power

various

sensors,

it is not

always

safe to

assume

that the

14-6-

power

grounds

are at the same

potential.

safe, the

ground

of allthe AC sockets in use

should

be tied together with a 12 AWG wire.

14.9

MAINTENANCE

The 21X requires

a minimum of routine

rnaintenance.

A few

preventative

maintenance

steps willoptimize

battery life and decrease

the

chances

of datalogger failure.

The

21X alkaline

supply should

not drop

below

9.6V betore replacement.

When not in use,

remove

the eight

cells to eliminate

potential

corrosion of contact

points

and

store in a cool

dry

place.

When not in

use, the 21XL lead acid battery

should

be stored in a cool, dry environment with

the AC

charging circuit activated.

Discharging

the 21XL lead

acid batteries

below 11.76V

causes

permanent

damage,

or at least

drastically diminishes

the batteries'

normal life

expectancy.

When connecting

an external

battery to the

21X, use care

to avoid shorting

the +12V and

ground

from

the battery.

Four

packets

of active desiccant are

provided

with

each

21X.

Two

packets

are

located in

the

battery

base and two spare

packets

are sealed

plastic

bag. Used desiccant

may

reactivated

by oven drying for about 16 hours at

120oC. Routine

desiccant replacement is

required for reliable

datalogger service.

14.10

CALIBRATION

PROCEDURES

The 21X requires

little maintenance or

calibration. Measurements

are

made in such a

way

that small errors in the calibration are

automatically removed.

Measurements can be

made

to determine whether

the

accuracy of the

21X is within

the specifications

given

at the

this

manual.

lf needed,

the

calibration

procedures

described

this section

can

pedormed

by an experienced technician having

the suggested equipment.

NOTE: The

precision

the

21X

exceeds

that of most standard

electronic

equipment.

These

procedures

require that the

test

equipment have a

precision

and accuracy

equal to or better

than the 21X.

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