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8505A
value
and
display the
ratio.
An
offset
value can be
subtracted
from
the
measured
value
to
display only the
deviation.
Scaling (or External Reference)
and
Offset
can
be used
in
combination
to
display
percentage
variation.
Examples
of
such operations
are
given
under
Applications
later in this section.
2-88.
Use
of
mathematic
operations
is
expressed
in
the
following formula:
MEASURED
VALUE
DISPLAY
=
OFFSET
SCALING
(OR
EXTERNAL
REFERENCE)
Measured
value
in this
formula
refers
to
the
measurement
as
influenced
by
all
selected
measurement
parameters.
This value
is
subject to the following
function-dependent
considerations.
1
.
V
DC
function:
measured
value
is
the
measured
voltage
less
V
DC
Zero
when
the
Zero
mode
is
used.
2.
OHMS
function:
measured
value
is
obtained
after
any
applicable
OHMS
Zero
is
applied.
2-89.
SCALING
2-90.
The
Scaling
mode
divides the
measured
value
(after
application
of
V
DC
or
OHMS
zero)
by a
known
amount
and
displays the quotient. Ratios,
percentage
deviations, or input/
output
relationships
can thereby be
displayed.
The
scaling divisor
may
be a
previously
displayed
and
stored value, or
any non-zero numeric
entry
from
+10
9
to
+10'
9
and from
-10
9
to -10'
9
.
When
compared
to
External Reference, Scaling
offers
a
much
wider
range.
Only one
scaling factor
may
be
stored
at
a
time.
2-91.
Storing the displayed value
as
a scaling factor
warrants
a
word
of caution:
insure that
the displayed
value
is
the true original display
by
first
toggling
out of
Scaling
and
Offset
modes
(respective
annunciators
off).
No
stored scaling
or
offset
value
is
lost in this
manner.
To
store the desired display,
push
STORE
SCALING.
NOTE
If the
multimeter
is
in
both Scaling
and
Offset
modes,
the scaling value
is
applied before
the
offset value.
2-92.
EXTERNAL REFERENCE
2-93.
Scaling
and
External Reference
modes
are
mutually
exclusive: selection of either
mode
automatically disables the
other.
The
external reference
value (always
measured
as a
dc
voltage)
is
applied
as
an
unswitched
input
through
the
rear
input connector.
2-94.
Immediately
after
a power-up
or
reset,
RECALL
EXT REF
can be used
to
verify
the
software version
number.
The
first
subsequent
use of
EXT REF
to activate
External Reference
mode
disables
this
software
identification feature.
When
toggling
into the
mode,
the
reference voltage
is
displayed
as
iong
as
the
EXT REF
button
is
depressed.
The
EXT
annunciator
is
lighted
when
the
mode
is
enabled.
2-95.
The
applied External
Reference
voltage
may
be a
maximum
of
±20V
dc
on
either
high
or
low
input
with
respect to
VOLTS INPUT
LO. The
voltage
between
External Reference high
and low
may
not
exceed
40V
dc.
The
minimum
acceptable External Reference voltage
is
the greater
of
±
1
00 u
V
or a value
found
with
the following
formula:
±
Vin
Vmin
=
-Jq^-
2-96.
Normally,
the
External Reference
low
terminal
is
tied
to
VOLTS INPUT
LO.
In
any
event, the resistance
between
either
External Reference terminal
and
VOLTS
INPUT LO
should be
less
than 20 kilohms.
A
reading
rate
of
eight
samples-per-reading
and
filter
bypass
are
specified for
each External Reference
input.
2-97.
OFFSET
2-98.
In Offset
mode,
the display represents
only
the
deviation
from
a
stored
offset
value.
Measurements
of
stability
of analog
variation are
thereby
possible.
The
multimeter automatically
subtracts a
programmed
numeric
(or
previously stored display
value)
from
the
measurement and
displays the
result.
No
increase
in
resolution
is
displayed while
in
the Offset
mode.
One
value
(whether
a
numeric
or a previous
display)
may
be
stored
at
a
time.
Programmed
numerics
may
range
from
+10
9
to
-10
9
(excluding
0).
The
stored
offset
value
may
be
recalled at
any
time.
2-99.
Special
Operations
2-100.
PEAK
2-101.
The
highest
and
lowest deviations
in
the
displayed value
may
be
recorded
in
the
Peak mode.
Measurement
stability
may
thereby be checked over a
period
of time.
The
PEAK
push
button
toggles into/
out
of
the
Peak mode. High and low Peak
values
may
be
recalled
any
time without
exiting the
Peak
mode
or
interrupting further
peak
recording.
The
following
sequence
is
used:
RECALL
HI
PEAK
RECALL LO PEAK
The
high or
low peak
value
is
latched
in
the display
as
long
as
the
PEAK
button
is
held depressed.
2-102.
Exiting the
Peak
mode
(toggle
PEAK
once)
halts
further
peak
recording,
but does not
erase
previously
recorded high
and low
values.
A
multimeter function
change
disables
Peak
mode
and
retains
peak
values.
At
any
time, reentry into the
Peak
mode
(toggle
Peak
again)
2-23
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