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SECTION
7
SPECIFICATION VERIFICATION
Introduction
The
factory calibration
of
the
4708
ensures
traceable
accu-
racy
to
national standards.
Figures of
performance
are
quoted
in
the specifications
of
Section
6,
related
to
time
since
calibration.
This
section deals
with
usct- verification
of
the
4708
perform-
ance
to specification,
describing a
recommended method
of
verifying
each of
the
parameters
listed
below.
Supplemen-
tary
information
is
given
in
Appendices
to
the
section.
Choice
of Verification
Method
The
wide dynamic
range of
the
4708 makes
it
necessary
to
employ
different verification
methods
for different
groups of
output
and
frequency
ranges.
Naturally, the range,
accuracy
and
traceability
of
users'
standards
affects
the
manner
in
which
the
performance of any
new
equipment can be
verified.
Parameters
to
be
Verified,
with
Recommended
Methods
1.
DC
Voltage
Ranges
(100|xV to
lOOOV).
a. Full
Range
values are
verified against
a
DC
Voltage
Standard, using
a
precision divider
when
necessary.
b
.
DC
Linearity
is
verified
against the specification
on
the
lOV
range
at
±0V,
±1 V,
±10V
and
±19V,
using
the
same
method.
2.
DC
Current
Ranges
(100[xA to 1A).
Full
Range
values are
checked
using standard
shunts,
against
a
DMM
which
is
initially
standardized
to
the
instrument's
DC
Voltage
accuracy.
3.
AC
Voltage
Ranges
(IV
to
1000V).
a. Full
Range
values are
verified
at
LF
and
HF
by
direct
thermal
transfer
against
a
DC
Voltage
Standard.
b.
AC
Linearity
is
verified
at
IV,
lOV
and
19V
on
the
lOV
range
at
LF,
using
the
same
method.
4.
AC
Millivolt
Ranges (ImV
to
lOOmV).
Full
Range
values
are verified as follows:
a.
At LF:
Commercially
available
Inductive
Voltage
Divider,
and
standardized
DVM
transfer.
(Such
"IVD"s
are
normally only
suitable for
LF
verification,
up
to
about 5kHz).
b.
At
HF:
A
100%-to-10%
of
Range
Transfer
method,
after
verifying
lOV
range
HF
linearity
and
1
V HF
Full
Range
value.
A
DMM
is
standardized
and
corrected
for linearity error,
then
used
as
a
transfer standard.
An
alternative
method
is
described
at
Appendix 4
using a
Wideband
(to
lOOkHz)
Inductive
Voltage Divider
(WIVD).
5.
AC
Current
Ranges (1mA
to
1A).
a.
10mA,
100mA
and
1
A
Full
Range
values are
checked
using a
Thermal
Transfer Standard
fitted
with standard
shunts
at
LF
and HF,
against
a
DC
Current Standard.
b
.
The
1mA
Full
Range
value
can be checked
using
the
same
method, provided
that
low-current shunts
for the
thermal
transfer
standard are
available.
Alternatively,
if
calibrated
AC
current shunts are
available,
the
lOOpA-
lA
ACCurrentRanges
can
be
verifiedby voltage
measurement,
using a standardized
AC DMM,
as
described
in
Appendix
5,
6.
Resistance Values (10Q
to
100MQ).
Resistors are
checked
against
their
4-wire displayed
values,
and
resistors
plus
internal
wiring
(2-
wire) are
checked
against
limits
above
the
measured
4-wire
values;
using a
precision
DMM
or other accurate ratiometric resistance-measuring
equipment.
User's
Uncertainty
Calculations
Users
will
need
to
evaluate
the effects
of
their
own
Standards'
uncertainties,
so
calculations for
total
tolerance
limits
(Valid-
ity
Tolerance)
are
given
in
Appendix
2.
7-1
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