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(Shaded
areas
show
forbidden
calibration
zones)
Voltage
Ranges;
10V
and
LF
below
Errors
E
kHz
10 OkHz
100V
LF
HF
3.3kHz
301
kHz
100V
LF
Error
3
HFI
HF2
3.3
*HF1/HI
Frequen
HFI
is
a
Range.
HF2iso
100kHz
(Note
for
All
Current
Rang
kHz
10kHz
F2 cross-overs are
cy-
Range
dependent:
vailable
up
to
33kHz
on
tt
niy
available
above
30kH:
Range.
700V HF2
SET
rrxxJe
m
les:
>e
1
0kHz
i
on
the
ust
be
used)
3
Error
3
HF
1kHz
3kHz
SET
Calibration
If
Calibration
is
to
be
carried
out with sources
which
are not
exactly
at
Full
Range,
then the
SET
preselection
key
allows
the
4708
to
be
prepared
for calibration
at
other than
its
full
range
values. In
this
way
the
4708
can be
calibrated
between
20%
and
200%
of
full
range, except
for
lOOOV Range (20%
to
110%
-
max.
IIOOV).
Set
can
also
be used
as
a
means
of
compensating
for
known
errors
in
the
Measurement
System.
SPOT
Calibration
For each Output Range, a
user
may
select five
frequencies
for
SPOT
calibration.
The 4708
stores
frequencies
and
their
ampli-
tude
corrections,
in
memories which
are separate
from
those
used
for
wideband
corrections.
Enhanced
accuracy
is
obtained
at
these
spots,
as
any
flatness errors
in
the
wideband
correction
are eliminated.
Procedural
Notes
When
SPOT
is
pressed
the
4708 assumes
that the
spot
fre-
quency
is
to
be
changed,
and
so
defaults
frequency
to
IkHz.
When
used with
SET,
SPOT
calibration
can
be
carried
out
within
10%
of
full
range,
but
when
SPOT
is
used without
SET,
the
4708 assumes
that
the calibration
is
to
be
at
Full
Range.
Spot
achieves best
specification
if
used
at the
calibrated value.
Accuracy
tables are
given
in
Section
6,
with
an example show-
ing
Spot
linearity
on page
6-5.
For
Recall procedures see
Section
4,
4-10.
AC
Calibration
Sequence
INTRODUCTION
Because most
users
will calibrate
the
4708
via
thermal
transfer
standards, the calibration
procedures
assume
that this
method
will
be employed.
However,
details
of
setting
up
a thermal
transfer
standard
are
not included, as
there are several
different
models, each with
its
own
methods
of connection
and
proce-
dures.
Instead
it
is
assumed
that
users
will
be
able
to
operate
their
own
equipment
correctly,
according
to
the
manufacturer's
instruc-
tions.
The
procedures
which
follow
therefore concentrate
on
the
operation
of
the
4708
during
calibration,
accepting
that
the
required thermal
transfer will
be
set
up
to
a
DC
source of
suitable
accuracy.
GENERAL PROCEDURE
WARNING!
During Performance
checks
and
calibration
the Full
Range
voltage
is
preset at the
Thermal
Transfer
Standard
input
terminals.
On
lOOOV
checks
this
voltage
is
potentially
lethal,
so
EXTREME
CAUTION
must
be
ob-
served
when
adjusting the
Thermal
Transfer Standard
sensitivity.
Voltage
Calibration
using a
Thermal
Transfer
Select
AC
and
the desired
frequency
(or
Spot
frequency),
set
the
4708
OUTPUT
display
to
the Calibration
Standard
value,
and
switch the
4708
OUTPUT
ON.
If
calibrating
a non-nominal
voltage value,
SET
needs
to
be
selected.
Adjust
the
4708
output
to
obtain a
null at the
Calibration
Standard
value,
and
press the
Cal key
to
execute
the
calibration.
LF
Millivolt
Calibration
Because
'Hatness' data
is
passed
on
to
the millivolt
ranges
from
the
1
V
Range
calibration,
the
1
V
Range
must be
calibrated
first
A
DVM
is
then standardized
at
the required millivolt
value
and
frequency, using
the calibrated
IV
Range
and
an
Inductive
Voltage Divider (IVD).
The
desired
frequency
(or
Spot
fre-
quency)
is
selected, the
OUTPUT
display
set to
Full range,
and
incremented
or
decremented
to
give
the required
value
on
the
DVM.
If
calibrating at
a non-nominal
value
SET
must be
selected.
The
CAL
key
is
pressed
to
execute
the
calibration.
HF
Millivolt
Calibration
From
the
lOVRangea 10%
Range
correction
is
calculated.
This
is
applied
at
lOOmV
on
the
IV Range
to
standardize a
DVM,
which
is
subsequently used
to calibrate
the
lOOmV
Full
Range.
The
process
is
extended
to calibrate
the
10m
V
Range
from
10%
of
the
lOOmV
Range, and
ImV
Range
from
10%
of
the
10m
V
Range.
Current
Calibration
(Using
Thermal
Transfer Standard Current Shunts)
The method employs
a
DC
Current Standard, so
that
the shunt
8-11
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