Datron 4708 User Handbook Manual page 84

DC
Current
Verification
(100|jA-
1
A
Full
Range
Values)
Summary
of Verification
Procedures
Full
Range
Current
(Using Preferred Standard Shunts)
The 4708
is
used
on
its
IV
range
to
standardize the
DMM
at
IV.
The 4708
is
then
set to
its
100|iA
range,
with
its
1+ and
I-
terminals connected across the lOkfl
shunt,
and
the
DMM
is
connected
to
measure
the voltage across
the shunt.
The 4708
output current
is
adjusted
until the
DMM
voltage
reading represents
nominal lOOjiA
full
range output into the
1
Okfl shunt.
At
this
setting the reading
on
the
4708
OUTPUT
Display
is
recorded.
The
accumulated
uncertainties are also
recorded,
and
the Validity Tolerance Limits
calculated.
The
4708
is
verified
if
the
OUTPUT
Display reading
is
within
the
tolerance
limits.
For
the
1mA,
10mA
and
100mA
ranges, the preferred shunts
also require the
DMM
to
be
standardized
at
1
V;
but
for the
1
A
range
the
0.
1
0
shunt
is
used
to
keep
the output
power
at
a
low
level,
so
the
DMM
is
standardized
at
lOOmV.
The
procedure
is
detailed
on
pages
7-10/11.
Interconnections
Interconnection
instructions in
this
section are necessarily
simple and
basic,
and
are
mainly
intended
to
show
connec-
tions
to
the
4708.
It is
recognized
that
they
may
need
to
be
adapted
to
meet an
individual
user's
requirements.
It is
assumed
that users will possess
knowledge
of the operation
and use of standards equipment such
as that
mentioned
above.
Equipment Requirements
•
A DC
Voltage Source,
calibrated to suitable accuracy
at
IV
and
lOOmV.
Example:
The
verified
DC
Voltage ranges
of the instrument under
test.
•
A
set
of
Calibrated Current Shunts of
suitable
accuracy.
•
A
DMM
of
sufficient resolution
and
stability to
measure
the voltage across the
set
of
shunts.
Example:
A
Datron
1281, 1081, 1071 or 1061
A
used
as
a transfer-measurement
device.
N
.
B
.
To
allow
the
same
value
to
be
set
on
the
DC
Voltage
Source
for the four
lower
ranges, the shunts
may
be of
four
decade values.
Then
the
same
DMM
sensitivity
can
be
used
on
each
range.
CAUTION
When
choosing a
set
of current shunts, ensure
that their
power
dissipation ratings are
sufficient to
avoid
permanent
degradation
from
the self-heating effects
of
the
current
being checked. This
applies particularly
to
the
1
Amp
shunt.
Preparation
Before attempting any
verification
ensure
that the
follow-
ing steps
have been
carried
out.
1
.
Turn on
the instrument
to
be checked and
allow
at least
2
hours
warm-up
in the specified
environment.
2
.
Cancel any
MODE
keys, ensure
OUTPUT
is
OFF
and
check
that
'cal' is
not present
on
the
MODE
display.
(If
'cal' is
present, turn the Calibration
Keyswitch on
the
Rear
Panel
to
its
RUN
position).
3.
Before connecting
and
operating
any
equipment,
consult
the
manufacturers' handbooks.
4
.
Self-Test: Press the Test'
key
to
carry out the
test
routine described
in
Section
4.
Terminate
the
test
routine.
5
.
If 'Spec'
Mode
is
required,
select either
24
hr,
90dy
or
lyr
on
the
Rear
Panel
CALIBRATION INTERVAL
Switch.
When
received
from
Datron,
90dy
is
the
relevant
selection.
The
report sheets hold figures for
this
interval.
7-8