HP 3455A - Page 49

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 3455A.
When
upranging,
always
uprange the 3455A 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 3455A 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