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MAINTENANCE
7.4.2 Module
Recognition
Programming
Normally,
a module is factory programmed
to be proper-
ly recognized by the unit when it is first turned on. In rare
instances, however, a problem with one of the NVRAMs
on the module may occur, with the result that the module
will not be properly
recognized.
Use the following
pro-
cedure to program the instrument
for the module install-
ed. The same procedure can be used to program the chan-
nel 1 A/D module should a similar NVRAM
problem oc-
cur with that module in the future.
NOTE
If A/D
module
recognition
programming
is
necessarv. calibration
accuracv of the instrument
,l
,
is suspect because calibration
constants are also
stored in NVRAM.
The performance
verification
procedures
in Section 5 should be performed
to
check instrument
accuracy. Instrument
configura-
tions defined
by the setup mode may also be
altered if an NVRAM
fault occurs.
1. Turn on the power to the instrument,
and verify that
the unit goes through
its usual power up cycle. If a
recognition
fault occurs, the instrument
will notify you
of that fact with the following
message:
CAN'T IDENTIFY
3
Note that the channel number that cannot be identified
is displayed
along with this message.
2. Use the Uprange or Downrange button to scroll through
module types, as displayed
on the front panel. For a
Model
1944 installed
in the channel
1 location,
the
display message is:
lMHZ
A/D IN 1
With an A/D module installed as channel 2, the message
is:
I~MHZ AID IN 2
The lMHz
frequency
indicates the maximum
conver-
sion rate of the installed
A/D module.
3. When the type of module installed
in the correspon-
ding location is shown on the display, press the ENTER
key to complete programming.
4. Cycle power
and verify
that the instrument
goes
through its normal power up cycle without
displaying
a module recognition
error. If the problem still exists,
one of the NVRAMs on the corresponding
module may
be faulty. Refer to the troubleshooting
procedures
in
paragraph
7.8 for further
information.
5. If A/D module recognition
was programmed,
refer to
Section 5 for procedures to verify module accuracy. If
those procedures
show that the NVRAM
fault has
degraded accuracy, the module should be calibrated by
using the procedures
in paragraph 7.5 of this section,
7.5 CALIBRATION
An advanced feature of the Model 194 is its digital calibra-
tion capabilities.
Instead of the more conventional
time-
consuming
method
of adjusting
numerous
calibration
potentiometers,
the technician
need only apply an ap-
propriate calibration voltage and then digitally calibrate the
instrument,
either
from the front panel,
or over the
IEEE-488 bus.
Calibration
should be performed
every 12 months, or if
the performance verification
procedures located in Section
5 show the instrument
is operating
outside its stated
specifications
(Model 194 specifications
are located at the
front of this manual). If the calibration
procedure cannot
be performed properly, refer to the troubleshooting
infor-
mation in this section.
WARNING
Certain
steps
in the calibration
procedure
re-
quire
the use of hazardous
voltage.
Be careful
not to contact
these
voltages
to ensure
per-
sonal
safety.
7.5.1 Recommended
Calibration
Equipment
Recommended calibration equipment
is listed in Table 7.3.
Other equipment
may be substituted
as long as accuracy
specifications
are at least as good as those given in the
table. In general, calibration
equipment
accuracy should
be at least five times better than equivalent
Model
194
specifications.
NOTE
Use a calibrator with low noise or the instrument
may not calibrate properly.
7.5.2 Environmental
Conditions
Calibration
should be performed under laboratory condi-
tions having an ambient temperature
of 23 i3'C
and a
relative humidity
of less than 70%. If the instrument
has
be subjected to a temperature
outside this range, or to
higher humidity,
allow at least one additional
hour for the
instrument
to stabilize before beginning
the calibration
procedure.
7-6
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