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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