Campbell 21X Manual do Operador descarregar pdf (Página 162)

The

procedures

are

for

calibrating the 3.

voltage and the clock.

Other

factors

such as r

offset in

CAO

voltage require that the 21X

be

returned to

the factory

obtain

14.10.1

VOLTAGE REFERENCE

CALIBRATION

PROCEDURE

SUGGESTED

INSTRUMENTS

Five

and one

half digit digitalvolt

meter

(DVM)

with

10 micrQvolt resolution.

The accuracy of

the

DVM

neQds

to be

equalto that

of the

21X

which

is +1 niV at 5 V DC.

I

I

PROCEDURE

1.

Remove

lthe

21X battery

base

and unplug

the

battefy from the

21X. Remove

the tour

screws

hblding the aluminum

cover

plate

and

remQve the cover

plate.

Lay the

21X,

panel

dolrvn,

on a

padded

flat surface

with

the circuft cards

up and exposed

as shown

in Figure

14.6-1 . Plug the battery

back

into

the

21X. Turn on the

21X.

2.

Set the

QAC

to output 0.000

volts

DC by

programfning

the

21X

as

follows:

01:

01:

01:

02:

03:

o4:

05:

06:

Table 1 Programs

Sec. Execution

Interval

Excite,

Delay,Volt(SE)

Rep

5000

mV slow

Range

lN Chan

Excite all reps

dEXchan

1

Delay

(units.01sec)

mV Excitation

as

instructed

Loc

[:MEAS.

mV

]

Mult

Offset

ratios, DAC non-linearity,

and

the switched

excitation

or the

repair. Please callthe

factory

to

:ation before sending

in

the unit.

SECTION 14.

INSTALLATION

AND MAINTENANCE

Monitor the

Digital to Analog Conveder

(DAC)

output by connecting the

positive

lead

of

the

DVM to the DAC OUTPUT

TEST

POINT which is the

left

side

of

the

3.3

K

resistor

shown

in Figure 14.10-1.

Connect

the

negative lead of the DVM

to

any

ground

on the

front

panel.

Set the

DVM

to

read on

its most

sensitive

DC

Volt scale.

Adjust

the

DAC

OFFSET

POTENTIOMETER

(see

Figure 14.10-1)

for

a DVM

reading of 0.0000

V +0.0001.

Change

the 21X's

program,

so that

lnstruction

4,

parameter

6

reads 4000 to

change

the

DAC

output

to 4 V. Set up

the

DVM

to read

4 V DC.

6. Adjust

the

VOLTAGE REFERENCE

GAIN

POTENTIOMETER

(see

Figure 1 4.1 0-1

)

untila

DVM reading of

4.0000 V +0.0001

is

obtalned.

7.

Change

the 21X's

program,

step

2,

so

that

Instruction

4,

parameter

6

reads

-4000

to

change

the DAC output to

-4

V.

8. A DVM

reading of

-4.000

V +0.0025 verifies

the

linearity.

lf

this

reading is off, the

21X

needs

to be sent in for

repair.

9. Lock

both

potentiometers

into

position

with

a dab

of finger nail

polish.

14.10.2 CLOCK

CALIBRATION

PROCEDURE

The clock

circuitry resides on the CPU

card

(the

card

farthest

from the front

panel).

The

frequency

of the clock crystal

exhibits a

parabolic

response to temperature.

The

frequency

maximum occurs at

room

temperature

and drops off slowly at

hotter

or

colder temperatures.

When the 21X leaves

the

factory it is

calibrated to be

20

ppm

fast. lf

the

21X is

placed

in a

controlled

environment

with

the temperature

close to

room

temperature,

it

would be

better to set the

crystalfrequency

exactly on.

SUGGESTED

INSTRUMENTS

Digital f requency

counter

PROCEDURE

4.

5.

1

1

07:

08:

09:

P4

1

5

1

1

900

0000

Changp

1

1

0

14-7

1 2 ... 157 158 159 160 161 162 163 164 165 166 167 ... 190 191

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