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Section
IV
Model
3455A
when making measurements on
the
100
V
and
1000
V
ranges.
This
is
only necessary
when
using
a
DC
Standard
sensitive to
a
changing load impedance.
u.
The 345SA
reading
should be
within the Test
Limits given
in
Table
4-1!
(1000
V,
1
kV
range), verify-
ing the
full-scale
accuracy
at
+
1000
V
with
High
Resolution
off.
V.
With
the
3455A on
the
1
kV
range,
set
the
HIGH
RESOLUTION
to
ON.
w.
The 34SSA
reading
should be
within
the
Test
Limits given
in
Table
4-12 (1000 V,
1
kV
range),
verify-
ing the
full
scale
accuracy
at
+
1000
V
with
High
Resolution on.
NOTE
Each
time
the
Reference Divider
Output
Voltage
setting
is
changed, check
for
null
and,
if
necessary,
readjust the
Reference
Divider's fine control to obtain
a
null indica-
tion.
Always downrange
the
Reference Divider
before
downranging
the
3455 A.
When
upranging,
always uprange
the
3455
A
before
upranging
the
Reference
Divider.
X.
Set the
DC
Standard
for
an output of
+
500
V.
y.
Set the
Reference
Dividers
Input Voltage switch
to
SOO
V
and
center
the course
and
fine
adjustment con-
trols.
Set
the
Reference
Dividers
Output
Voltage
switch
to
500
V.
z.
Adjust
the
DC
Standard
and
Reference
divider as
outlined
in
Steps
q
through
t.
aa. Set
the
Reference
Divider's
Output
Voltage
and
3455A
RANGE
to
each
setting
(500
V
and
below)
listed
in
Table
4-12.
At
each
setting,
the
34S5A
reading
should
be
within the Test Limits given
in
the
table.
(Be
sure to
maintain
null
when
the
Reference
Divider's
output
is
changed.)
bb. Set the
3455A
RANGE
to
1
kV
and
set
HIGH
RESOLUTION
to
OFF.
cc.
Set
the
Reference
Divider's
Output
Voltage
and
3455A
RANGE
to
each
setting
(500
V
and
below)
listed
in
Table
4-1
1 .
At
each
setting,
the
3455
A
reading should
be
within the Test Limits given
in
the
table.
(Be
sure to
maintain
null
when
the
Reference
Dividers output
is
changed.)
fcMmONl
In the
following
tests
for
negative
readings,
the input
to
the
3455
A
must
not exceed -500
V
dc due
to
the
±
500
V
guard
to chassis
limitation.
dd.
Downrange
the
dc standard
to
1
V
output
and
turn off the
dc
standard's output. Reverse the
polarity
of
the
3455A
INPUT
connection
to
obtain negative
readings.
ee.
Set the
3455A
RANGE
to
1
kV
and
HIGH
RESOLUTION
to
ON.
Set the
Reference Divider Out-
put Voltage switch
to
500
V,
turn the
dc
standard's out-
put
back
on,
and uprange
to
SOO
V.
ff.
Repeat
Steps aa
through
cc to
verify the
negative
dc accuracy
for
all
settings
500
V
and
lower.
Again,
do
not apply
more
than -500
V
dc
to the
3455A
INPUT.
4-44.
AC
Voltmitar
Accuracy TasL
4-45.
The 34S5A
ac voltmeter accuracy
can be
verified
for
frequencies
up
to 100
kHz
on
all
voltage ranges
us-
ing
an
AC
Calibrator
such
as
the
-hp-
Model
745A/746A.
To
minimize
measurement
uncertainties
for
frequencies
below SO
Hz
and above
20 kHz,
the
AC
Calibrator
should be
calibrated
and
its
error
measure-
ment
control
should be used
to
adjust out the errors
in-
dicated
on
the calibration
chart.
For example,
if
the
calibration
chart
indicates
that
the
745A
output
is
0.04Vo high
at
1
V,
50 kHz,
set
the
745A
error
measure-
ment
control to
+
0.04i%
to
obtain a
precise
1
V
output.
The 745A/746A
can be
calibrated
during a
routine
per-
formance
test
using the
procedures
outlined
in
the
745A/746A
Operating
and
Service
Manuals.
Calibra-
tion charts for these
instruments are
normally
valid for
at least
30
days.
4-46.
A
Test
Oscillator
such
as the -hp-
Model 652A
can
be used
to
verify
the ac voltmeter
accuracy of
the
3455A
for frequencies
above
100
kHz
(specified for
1
V
and
10
V
ranges
only).
The
required
accuracy can be obtained
by
adjusting the Test
Oscillator
output
so
that
the
3455A
reading
at
10
kHz
is
the
same
as
the reading
ob-
tained
with
the highly accurate
AC
Calibrator.
This
reference
level
can
then be maintained
to
within
±
0.25<7t
over
the
100
kHz
to
1
MHz
range
using the
expanded-scale meter
on
the Test
Oscillator.
If
higher
accuracy
is
desired,
an
ac-to-dc
thermal
transfer techni-
que
(Figure
4-5)
can
be
used.
4-47.
Test Procedure.
Equipment
Required:
AC
Calibrator
(-hp-
Model 745A/746A)
Test Oscillator (-hp-
Model
652A)
4-12
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