HP 3455A - Page 40

Model
3455A
Section IV
b.
If the DVM reading
is out
of
tolerance by a per-
centage that is greater
than
the
maximum allowable error of
the standard, the
DVM
is
dermitcly outside of its
specifica-
tion.
c.
If the
DVM
reading
is in
or
out of tolerance by a per-
centage that is
less than the
maximum allowable
error
of
the
standard, it is in one of the
ambiguous regions (shaded
areas)
shown in Figure
4-1.
The DVM may or may not be
within its specification and the only way to tell for sure is
to
use
a
more accurate standard.
4-24.
As the accuracy
specifications of the standard
approach the specifications of the
DVM
to be tested, the
ambiguous regions
sliown
in
Figure
4-1
become wider
and
the uncertainty contributions of the standard become
increasingly significant. If the standard is less than three or
four times more accurate than the
DVM.
the performance
test is not practical
because
the
ambiguous regions cover
most of
the DVM’s error range. From a practical stand-
point, the dc standard should be at
least five times
more
accurate
than the
34S5 A
specifications
to
be tested. If such
a standard is nut
available,
an
alternative approach is
to
use
a
calibrated
standard that is extremely stable and (pre-
ferably) two to
four
times more
accurate than
the 3455A.
When this is done, the correction factors
given
on the
dc standard’s calibration chart must be algebraically added
to the 34SSA test readings. Test
validity
depends on the
calibration
uncertainties
and the
short-term
stability of
the
standard.
4-25.
The
Reference Divider recommended in the follow-
ing
DC Voltmeter Accuracy Test is, according to its pub-
lished specifications, accurate enough
to
test all but the
1-
volt and
10-
volt full-scale 24-hour specifications. The
1-
volt and
10-
volt full-scale specifications can be tested using
the DC Transfer Standard also recommended in the pro-
cedure.
4-26. OPERATIONAL VERIFICATION
TESTS.
4-27.
DC OPERATIONAL
ACCURACY TEST.
4-28.
The DC Transfer
Standard required for
the
following test must be
calibrated
to
a
1.017 V
to
1.019 V
standard cel) that has been
calibrated by the
National
Bureau of Standards
(NBS). If the 345SA is to be
tested
for its
24-hour accuracy
specifications, the Transfer
Standard must be adjusted for
optimum
1-volt and
10-volt output accuracy using NBS-calibrated stan-
dards. It is recommended that the Transfer Standard be
calibrated and adjusted just prior to use. After calibra-
tion, it
should
be left on and, if possible, kept
in
a con-
trolled
environment where the ambient temperature is
within one or two degrees
of the
temperature
in
which it
was calibrated. The following procedure should be per-
formed in that same environment.
4-29.
If the recommended DC Transfer Standard or its
equivalent
is not
available,
an NBS-calibrated standard
cell (1.017
V
to
1.019 V)
can be
substituted. If
this
is
done, check the full-scale accuracy of the 345SA 1
V and
10
V
ranges using the
Reference Divider recommended
in the procedure.
4-30.
Tatt Procwlura.
Equipment Required:
Reference
Divider
(Fluke Model 7S0A)
DC Transfer Standard (Fluke Model 731A)
DC Standard
(Systron
Donner Model M106A)
DC Null
Voltmeter
(-hp- Model 419A)
a.
Set the 34SSA controls as
follows:
FUNCTION DCV
RANGE 1 V
HIGH RESOLUTION ON
AUTO CAL ON
GUARD ON
TRIGGER
INTERNAL
b. Set the DC
Transfer
Standard
for an output of 1
V. Connect the output of the transfer standard to the
3455A INPUT.
c. The 34S3A reading
should
be
within
the test
limits
listed in Table
4-1
,
verifying its 1-volt full-scale accuracy
with
High Resolution on.
d. Set
the 3455A RANGE to 10 V. The 3455A
reading should be
within
the test limits listed in
Table
4-3, verifying
its
10-volt tenth scale accuracy with High
Resolution on.
e. Set the
Transfer
Standard for
an output of 10 V.
The 345SA reading
should
be
within the test limits listed
in Table
4-1
verifying
its
10-volt full scale accuracy with
High
Resolution
on.
Table
4-1.
DC
Accuracy Tast
(1 V.
10 V Full Scala; High
Ratolutioa On).
Lflvei Range
24 Houi
Te$( Llmiit
90 Day
Test Limits
1
V
10
V
1 V
10 V
0 999966
to
1 .000034
9.99977 to 10.00023
0.999936
to
1.000064
9.99947
to 10.00063
f. Set the
3455A HIGH RESOLUTION
to
OFF. The
34SSA reading should be
within
the test limits listed in
4-3