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Table
8.4
STEPS
IN
RESISTANCE CALIBRATION
(Internal
resistor
value
measurement and
storage)
a)
Remote Sense
(Internal 4-wlre,
connected as
Fig. 8.3a)
Calibration at Full
Range.
Resolution
7.5
digits,
Tolerance
±
199.9
ppm
(±1999
digits).
Step
Range
Measured
resistance value. Calibration
Limits
1
lOOMSi
99.980,01
to
100.019,99
Mn
2
lOMn
9.998,001
to
10.001,999
3
iMn
.9998,001
to
1.000,199,9
Ma
lOOkfl
iokn
1k£2
99.980,01
9.998,001
.9998,001
99.980,01
to
100.019,99
kn
to
10.001,999
kfi
to
1.000,199,9
k£2
to
100.019,99
b)
Local
Sense
(Internal 2-wire,
connect
as
Fig
8.3(b),
Remote Sense
OFF)
Calibration at Full
range
and
Zero.
Resolution
as
listed In Table.
Tolerances
-OO
+
1.9990.
on lOO
-
IMO
Ranges,
—OO
+ 0.9000
for
zero
on lOO -
1MO
Ranges.
Range
1MQ
100k^2
Resolution
(digits)
Resistance value
Limits
Zero
Limits
.000,000,0
to
.000.000,0
MC
0.000,00
to
0.000,90
kn
Step 5
value, -0
+1
999
digits
Step 6
value, -0
+1
999
digits
Step 7
value, -0
+1
999
digits
Step
8
value, -0
+1999
digits
AC
Calibration
'Wideband'
Calibration
When
CAL
is
pressed without
preselecting
SET,±0
or
STD;
the
4708 makes
the
assumption
that
each
OUTPUT
Range
is
to
be
calibrated at the
exact
Full
Range
value,
at
either
LF
or
HF,
or
both.
This allows
two
correction values
to
be
stored for
each output
range.
From
their
difference, the
microprocessor
calculates
a
compensation
factor,
which
affects the
corrections applied
at
all
subsequently-selected frequencies
on
that
output range.
In
this
way,
the
4708
can be
calibrated
to
meet
its
'Wideband'
specifi-
cation.
To
ensure
that
the selected
Low
and High
frequencies
have
sufficient
separation for the
compensation
to
be
effective
over
the
full
frequency
range,
calibration
is
automatically prohibited
in
an
'excluded'
band
of
frequencies
for
each
output
range.
Because
of
the
extended frequency range of lower Voltage
ranges,
and
the
Voltage/Frequency
constraints
on
higher
Volt-
age
ranges, the
exclusion
band
can
differ
from one
output range
to
another.
If
an excluded frequency
is
selected, the calibration
is
cancelled
and
Error 3
is
displayed.
The
following
diagram
illustrates
the
mid-frequency
exclusions:
8-10
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