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8502A
2.
Hie
minimum
voltage applicable to
the
externa!
reference terminals
is
the greater
of
either
±
1
00
u V,
ora
value
found
with
the following formula:
Vmin
=
±
i
Vjn
I
10
^
3.
The
resistance
between
either
EXT REF
terminal
and
INPUT
LO
should be
less
than 20
Kohms.
Normally,
EXT REF LO
will
be
tied to
INPUT
LO.
2-48.
REMOTE
249.
If
an optional
remote
interface
is
installed,
the
REMOTE
switch
may
be used
to toggle into or
out of
remote
control.
With
the
IEEE
(Option
—05)
Interface
installed,
only toggUng
out
of
remote
control
is
permitted
from
the front panel.
When
in
remote
control,
only
the
remote
switch
and
the
power
switch
will
have
any
effect
on
the instrument's operation.
A
reset
caused
by power
inter-
ruption
will
return the
instrument
to
local
control.
2-50.
Remote
control
does
not
affect
analog
inputs
on
the
High
Quality Bus.
With Rear
Input (Option
-17)
or
Switchable
Front
-
Rear
Inputs
(Option -16),
separate
Sense Hi
and
Lo, Source Hi
and
Lo,
Guard,
Ohms
Guard,
and
External Reference
connections
must
be
made
remotely.
2-51.
Memory
2-52.
The
8502A
provides considerable
versatility in
measurement
manipulations through
both
front
panel
and
remote programming.
Displayed
numbers
are
computed
from
measured
data
according to
the
following general
equation, where:
y
=
the
displayed
number
m
=
the scaling factor or external reference
X
=
the actual
input (averaged samples)
b
=
the offset factor
(subtracted)
2-53.
Either displayed values or
numeric
sequences
may
be
stored
as
memory
factors.
NOTE
Storing
a
value
in
memory
does not
select
a
mathematical
operation.
The
operation
must
be
selected separately
before or
after the value
is
stored.
2-54.
LIMITS
2-55.
Any
currently displayed value
may
be stored
as a
limit value.
Withsuch
values stored
as
references,
the
8502A
(toggled into the limits
mode)
will
yield
a
display
of;
1.
HI
if
the reading
is
greater
than
the
high
limit.
2.
PASS
if
the reading
is
less
than
or
equal
to the
high
limit
and
greater
than
or
equal
to the
low
limit.
3.
LO
if
the
reading
is
less
than the
low
limit,
NOTE
HI,
LO, and
PASS
describe the
normally
dis-
played
reading,
with
all
math
operations
com-
pleted,
relative
to the
limit values.
2-56.
Only
one
set
of
limits
may
be
stored
at
a time.
A
function
change
will exit
the
Limits
mode
but
retain stored
values.
2-57.
PEAK
2-58.
Highest
and
lowest
values displayed
in
any
series
of
measurements
may
be
stored
when
in
the
Peak mode.
Toggle
in
and
out of
this
mode
by
depressing the
PEAK
switch.
Peak
values
will
be
retained
after
the
mode
is
deact-
ivated
but
lost
should
the instrument be
reset
or the
mode
re
selected.
2-59.
CALIBRATION
MODE
2^60.
The
CAL
switch
will
be
found on
the
front panel
behind
a small
plastic
cover
which
pulls
out
and
hinges
down.
Sliding the
switch
down
places the
8502A
in
the
Calibration
mode.
This
mode
is
designed primarily
to
be
used with
the Calibration
Memory
(Option —04).
When
this
module
is
installed
and
the
instrument
is
in the Cal-
ibration
mode,
correction factors can
be
stored
at
the
decade point
for
each
range
and
function.
Refer
to
Section 6
of
this
manual
for
complete
Calibration
Memory
procedures.
2-61.
If
the
Calibration
Memory
is
installed,
inadvertent
use
of
the
STORE
switch
will
store the
last
reading
as
a
cal-
ibration factor
and
erase calibration factors for
the
function
and
range
in
use
at
the time.
To
correct
this
possible
mistake
without
a
calibration
standard, disconnect the input, short
the
input
terminals,
and
press
STORE
again.
2-62.
Whether
or
not
the Calibration
Memory
module
is
installed,
entry
into
the
Calibration
mode
(CAL
LED
flashes) necessitates
consideration
of
the
following
alter-
ations to
the
8502A's
display:
2-7
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