HP 3455A - Page 42

Model 3455A
Section )V
voltage
and
vernier
controls for a zero
reading
on the
null meter.
r.
Downrange
the Null Meter and adjust
the
Reference
Divider’s
course
and fine controls for a null is
obtained on the 3
microvolt
range.
s. Set the
Reference Divider's Standard Cell switch to
Open.
Allow ten minutes for the Reference
Divider
to
warm-up and stablize.
t. Set the
Reference Divider’s Standard Cell
switch
to
Momentary and, if necessary, readjust the fine control
for a null indication. Release the Standard Cell
switch.
u.
The 34S5A reading should be
within
the Test
Limits
given
in Table
4-3.
(1000
V,
1
kV
range),
verify-
ing the full-scale accuracy at
-f
1000
V with High
Resolution on.
NOTE
AUTO-CAL may have to be turned
off
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.
Table
4-2.
DC Accuracy Tact {High
Raaolution Off).
Level
3455A
Range
74 Hour
Teet Limits
90 Day
Test Limits
0-1 V
10
V
1
0.1 V
10 V
.
.099992 to 1 00008
9.9997
to
10.0003
.099989 to
.100011
9.9994 to 10.0006
NOTE
Each lime 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.
cautionJ
Always downrange the Reference
Divider
before
downranging
the 34S5A.
When
upranging,
always uprange lhe34S5A
before
upranging the Reference
Divider.
Table
4-3.
DC Accuracy Teat
(High Resolution On).
Divider
Output
3455A
Rinoe
74 Hour
Test Limits
90 Day
Test
Limits
1000
V
100
V
5 V
1
V
1000 V
100
V
10 V
10 V
999
957
to
1000.043
99.9957
to
100.0043
4.99987 to 5.00013
0.99995 to
1.00005
999.927 to 1000.073
99.9927 to 100.0073
4.99972
to 5.00028
0.99992 to
1.00008
'For
positive readings
onlV-
Oo not apply
negatiiA voltages greater
than
•
500 V de.
v.
Set
the Reference
Divider’s
Output
Voltage and
345SA RANGE to each setting (100
V and below) listed
in Tables
4-2
and
4-3
with High Resolution on or off as
indicated. At each setting,
the 34SSA reading should be
within
the
Test Limits given in the table. (Be sure to
maintain
null when
the
Reference Divider's output
is
changed.)
ynrvmmrrrrv^
|CAUTION4
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.
w. 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. Turn the dc
standard’s output back on.
Verify
the
negative
dc
accuracy for all settings 100
V and
lower. Again, do not apply more than
-500 V dc to the
3455A
INPUT.
4-31. AC
Operational Accuracy Tact
4-32.
The
3455A
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
74SA/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
74SA output is
0.047t high at 1
V, 50 kHz, set the 74SA error measure-
ment
control
to
-t- 0.047o 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
74SA/746A Operating and
Service Manuals. Calibra-
tion
charts for these instruments
are normally
valid
for
at
least 30 days.
4-33.
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
345SA 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
±
0.254'» 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 4-3) can be used.
4-34.
Test Procaduru.
Equipment Required:
AC Calibrator (-hp-
Model 745 A/746A)
Test
Oscillator (-hp- Model 652A)
4-5