Mode - Datron 4708 User Handbook Manual

The 4708
output has
now
been compensated
for the gain
error
of
the
DMM.
All selected output values
wUl
be compensated
in the
same
ratio
on
this
range and
function
until either the ratio
is
changed
or Error
mode
is
selected.
The
Mode
display
presents the
compensation
ratio directly.
Note
that the
compen-
sation polarity
is
shown,
not
the error
polarity,
therefore the true
output
is
the
sum
of both displayed
values;
in this case
+10.000000V
-
lOOppm =
+9.999000V.
The
linearity of
the
DMM
may now
be checked by
directly
comparing
its
reading with
the
OUTPUT
display
settings,
e.g.
at
+5V
on
this
range, both 4708 and
DMM
read
+5.000000V,
although
the terminal
voltages are
+4.995000V.
Other
linearity
check
values could
be:
Nominal
Check
Point
4708
set
Value
DMM
Reading
Terminal
Voltages
-0.5V
+0.1V
+0.01V
-0.500000V
+0.100000V
+0.010000V
-0.500000V
+0.100000V
+0.010000V
-0.499950V
+0.099990V
+0.009999V
Full Scale
Limiting.
The
OUTPUT
display cannot
be
raised
to
a value which
sets
its
overrange
digit to greater than
1
,
and
the
Error
MODE
display
cannot
be
raised about ±9.9999%
(±999.9ppm).
Nevertheless,
a combination of
OUTPUT
display value
and
gain error could
result in an
off-scale value.
The 4708
prevents
this
by
rejecting any demand
for an
error-corrected
OuQmt
Voltage
in excess of fuU
scale.
The
user
is
informed
by Error
5 message on
the
MODE
display
with
no
change
to the
OUT-
PUT
display.
Deselection of Error Mode
Deselection
clears the
MODE
display, turns the
green Error
LED OFF
and
restores the 4708
gain
factor to
unity.
Normally
the
mode
is
deselected by
repressing the Error
key, but
it is
also
turned off by
changing
FUNCTION
or
RANGE.
'Offset'
Mode
(DC
Functions
only)
Offset key
A
device being checked
against the 4708
(say
a
DMM)
may
have
an
inherent zero
offset
error. Nevertheless,
a
user
may
wish
to
perform
other measurements
before removing
the
offset
error.
The 4708
'Offset'
Mode
is
used
for
this purpose.
N.B. The
MODE
1 4
keys have an automatic
action:
If
a key
is
held pressed,
the display will
increment or decrement
continuously
until the
key
is released.
The
value of output
at the
4708
terminals
is
now
the
sum
of
the
OUTPUT
display value
and
the
MODE
display
offset
value.
The
following
example
generates an
offset
of -lOOpV
on
the
lOV
range of a
DMM,
for
all set values (unless
the
4708 would
be
driven
off-scale).
Connect
the
DMM
to the 4708, both
set to
lOV
range, ensuring
that
4708 Error and
Offset
LEDs
are
UNLIT.
Note
that the negative
polarity
of
the Offset
value
shown
on
the
MODE
display indicates
that the
Output
voltage
is
more
nega-
tive than the value on
the
OUTPUT
display,
i.e.
the
4708
offset
polarity
is
displayed, not the polarity
of
the
DMM
offset
error.
Observe
(1)
DMM
is
offset
T
(-4l00nV)
DMM
4-14