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DC
Calibration
STD
key
STD
calibration
is
carried
out
on
the
IV
or 10
V
range,
and
differs
from
the
"SET'
procedure only
in
the
use of
the
STD
key
instead
of
the
SET
key.
It
changes
the
DC
gain
of
all
voltage
and
current
ranges
in
the
same
ratio,
and
thus
performs
the
same
function as
trimming
the internal
Master
Reference
voltage.
The
facility
can
be
used
to
avoid a
full
recalibration
of
the
4708
when
Labo-
ratory
References have been
re-standardized
(or
for instance
when
a
4708
has
been
moved
from
one
country
to
another). In
DC
mode
it
does not
affect
AC
or
Ohms.
SET
key
The
SET
key
allows
calibration
to
any
value
in
the selected
Range
(e.g.
at
a standard
cell volt-
age):
SET
key
Before
selecting
SET,
the
1
4^
keys
are
operated
to
place
the Calibration
Standard value
on
the
OUTPUT
display
and
set
the
4708
output
level.
Pressing
SET
then
informs
the
4708
that calibra-
tion
is
to
be
carried
out
at this
value.
The
instrument
acknowledges
by
duplicating the
value
on
the
MODE
display.
Next
the
1
4^
keys
are
manipulated
to
null the
4708
output
against the Calibration
Standard
(the
OUTPUT
display
changes
during
this
adjust-
ment).
Pressing
the
CAL
key
executes
the
calibration.
The 4708
memorizes
the difference
between
the
two
display values
and
exits
from
SET
mode.
This
is
shown
by
transfer
of
the
Standard value
from
the
MODE
display
to the
OUTPUT
display.
The
instrument uses
the difference
to
modify
stored constants,
which
in
"RUN"
mode
correct
both
positive
and
negative outputs
on
the
cali-
brated
range
only.
If
the Calibration
Standard value
is
below
2%
of
Full
Range,
the
4708 assumes
a request
for
"Offset"
correction;
but
if
at
2%
or above,
"Gain"
correction
is
assumed.
±0 key
The ±0
key
is
used
to align the
ON-h and
ON-
zeros
of
all
voltage
and
current
ranges
by
a 2-part
calibration
on
the
lOV
range.
The±0
Alignment
Routine
on Page
8-6
is
necessary only
when
the
ON+
and
ON-
zeros
on
the
lOV
range
do
not co-
incide
at
the
same
null.
CAL
Key
The
CAL
key
executes
the preselected
Autocal
facility,
as
described
in
"SET"
above.
Alterna-
tively,
it
can
be
used without
first
pressing
SET,
±0
or
STD
to calibrate
Voltage
or
Current
ranges,
but only
at
2^ro
or
Nominal
Full
Range
values:
Before
selecting
CAL,
the
Zero
or Full
Range
key
is
pressed
to set
the
4708
output
level.
Next
the
1
4-
keys
are
manipulated
to null
the
4708
output
against the Calibration
Standard
(the
OUTPUT
display
changes during
this
adjust-
ment).
Pressing
CAL
commands
the
4708
to calibrate.
The
instrument decides
on
"Zero
Offset" or "Full
Range
Gain" from
the
OUTPUT
display value
(defined
by
the
same
limits
as for
"SET"), and
executes
the
calibration.
The
difference
between
the
OUTPUT
display
value
and
the
value
chosen
by
the
4708
is
used
to
modify
the stored constants
mentioned
in
"SET"
above.
Autocal
Availability
As
the
Autocal keys perform
specific
DC
tasks,
they
are available
only
as defined
by
Table
8.
1
.
The
message "Error
3"
appears
on
the
MODE
display
for
any
attempt
to
select
an
inappropriate
mode.
Table
8.1
Autocal
availability
for
DC
Calibration
DC
Voltage
DC
Current
Reeletanoe
(O)
(DC)
<0
Local
Sense
(2-wlre)
Remote
Sertee
(4-wlre)
SET
Zero
offset for
range
at
User's selected value
tOOmV-
1000V
Ranges
only
All
CAL
Gain
for
range
at
User's
standard value
lOOmV-
1000V
Ranges
only
Ranges
±0
and
CAL
Alignment
of internal
ON+
and
ON-
zeros
10V
Range
only
STD
and
CAL
Internal
Reference
gain
at
User's
Standard
value
IV and 10V
Range
only
CAL
Zero
offset for
range
All
Ranges
All
10Q-1MQ
Only
Gain
for
range
at Full
Range
Value
lOmV-
1000V
Ranges
only
Ranges
Ranges
only
All
Ranges
8-2
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