Campbell 21X Operator's Manual page 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