Calibration Constants; Calibration Constants; Hp 8340B/41B; Instrument Access - HP 8340B Manual

HP
8340B/41B
Assembly-Level Service
Calibration Constants
Three sets of calibration constants containing
calibration data, serial number, option, HP-IB
address,
and checksum information, are
maintained by the
instrument:
•
Working Data
This data contains the calibration
information that is
required for optimum instrument perfor¬
mance. This
is
the only set of calibration constants accessed
during normal operation. Working
data
is
stored
in
RAM
on
the
A60
processor assembly, and is
maintained by
a
battery with enough
energy to support RAM
for three
full
years when the instrument
is
disconnected from ac mains.
•
Protected Data
This data resides in
EEPROM
and
contains calibration information that
is essentially the
same as
in
the working data. (PEAK and
SHIFT PEAK auto tracking functions change
noncritical calibration
constants
in
working data to optimize performance. This
is
the one area where working and
protected data can normally differ.) If
any unacceptable difference occurs
between
working and
protected data, the instrument copies the protected data values into working data
RAM memory.
You can view or update
this data.
•
Default Data
This data resides in UVEPROM, and differs
from the working and protected data. ROM-based
default data
has immunity to
improper value changes. The data, however is
not for a
specific
instrument, rather,
it is
data representing
the typical instrument.
When using default calibration
constants,
instrument performance
is good, but not optimized for peak performance. To
return
the instrument to
peak performance, manually enter into protected and working
memory
the
instrument-optimized calibration constants from the printed copy of calibration constants shipped
with your instruments (see
HOW TO
RESTORE FACTORY-OPTIMIZED CALIBRATION CON¬
STANTS, in
this
section).
The instrument only selects default data if
a
problem exists in both working and protected data.
If
this occurs, the
CAL DEFAULTED message appears
in the
ENTRY DISPLAY
and the
FAULT
indicator
lights.
INSTRUMENT ACCESS
During
normal operation, the instrument accesses working data to obtain the calibration information
required for optimum operation. In addition, the instrument accesses working data after
an instrument
preset,
but only to verify that
the
CHECKSUM
(cat constant
#99)
is accurate (see Figure A-2).
When
you press
[INSTR PRESET],
the working data cal
constants
1
through
98 are summed
and then
complemented.
The
result
is
compared
with the
CHECKSUM.
If
the
two numbers agree, the instru¬
ment continues normal operation.
If not,
protected data is written into the working data memory
location and the
CHECKSUM test
is
repeated.
If
the checksum test passes, the data
in
protected data
is
stored as working data.
CALIBRATION RESTORED
appears
in
the ENTRY DISPLAY.
If
the
CHECKSUMS
do not
agree, default data
is written to the working data. Working data now
contains the default values, the front panel
FAULT light
lights,
and CAL DEFAULTED
is
displayed.
Press
[SHIFT] [MANUAL]
to
display the FAULT diagnostics
in the
ENTRY
DISPLAY;
the
CAL light
flashes (note that the protected data
was
not changed. For troubleshooting, this
data can be written
into the
working data and viewed
—
see USER
ACCESS).
HP 8340B/41B
Assembly-Level Service Calibration Constants
A-ll