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I
f
SECTION
8
ROUTINE AUTOCALIBRATION
Users
requiring
to verify
the
specification
without
adjustment
to
the Instrument's
calibration
status
refer
to
Section
7.
For
full
Information
on
calibration
of the
4708
refer to
the Calibration
and
Servicing
Handbook,
Section
1.
The
activation
procedure
is
illustrated
below:
The
4708
Autocal Feature
Using
the
standard 'Autocal'
feature,
the
4708
is
calibrated
entirely
from
the front
panel
(or
remotely
via the
IEEE
488
Interface).
Because
it
is
not necessary
to
remove
the covers,
thermal disturbance
is
avoided
and
the
4708
can
be
put
back
into
service
immediately
after calibration.
Users wishing
to
maintain
the
highest
specification
(24
Hours)
can
recalibrate daily,
on
a
regular
basis,
if
desired.
The
procedures contained
in this
Section provide
the essential
infor-
mation
for
setting
up
such
routines.
It is
not necessary
to
update
all
ranges, as
it
is
possible
to
calibrate
one
output
range.
During
the
Autocal
process, the
microprocessor
adjusts correc-
tion factors
which
are already stored
in
non-volatile
memories.
After adjustment, the
updated
factors are
continuously applied
to
correct the
4708
output amplitude.
Special
keys
are
used
in
the
Autocal
mode.
They
are
illustrated
below:
+h'm
-lim
%
ppm
HHI
Guard Sense Spec
Error Offset
,Test
.
STD
^
SET
/
±0
\
CAL
The
threee
keys
labelled
STD, SET, and
±0
preselect
alternative calibration
modes. To
finally
implement any
calibration,
the
CAL
key
must be
pressed.
STD, SET, and ±0 have
press
on/off action.
These keys
are activated
by
a
simple
procedure.
On
the rear
panel
there are
two
switches: the
IEEE
address switch,
and
a
security
key
switch labeled
RUN/CAL
ENABLE. By
setting
the
address switch
to
31
(ADD
1 1 1 1
1)
for
Front Panel
calibra-
tion
and
the
key
switch
to
CAL
ENABLE,
four of
the front
panel
MODE
keys
are reassigned
to
calibration functions,
permitting
access
to
the correction
memories.
IEEE
488 Address
Set
to:
ADD
11111
(Address
31)
5
4
3
2
1
Security
keyswitch
Set
to:
(on the rear panel)
CAL ENABLE
Thus
the four calibration
keys
(labelled
in
red) are
acti-
vated,
and
the
cal
legend appears
on
the
MODE
display.
Once
the
keys
are activated,
up
to
four
modes
of
calibrating the
4708
become
available.
The
meanings
of
the
modes
differ
slightly for
DC
and
AC
Calibration.
The
meanings
of
the
names,
and
the detailed
procedures
for
using
the
modes,
are
described
overleaf.
8-1
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