Continuous Arming; Front Panel Arming; External Arming; Alarm Conditions - Keithley 775A Instruction Manual

4.
Press the
GATE/DELAY
button.
^rb.e
GATH/DELAY
indi-
cator turns
off
and
the
GATE
light
turns on,
5.
Connect
the signal to
be counted
to
the
Channel
A
in-
put
terminal.
The Model
775A
will
begin accumulating
counts.
2.7
ARMING
Arming
alloy's
a
measurement
to
be
triggered
by
the in-
put signal
The Model
775
may
be
armed
to
take readings
in
four ways:
1.
Continuously
armed
in the normal,
mode.
2, Witl-\
the front
panel
RESET
button
when
the
instmment
i.s
in
hold mode.
3.
Through an arming
pulse
applied
to
the rear
panel
EXT
ARMING
k
GATE/DELAY
input
when
the
instrument
is
in
the hold
mode.
4,
With
commands
giv^n over the
IEEE-488 bus
as des-
cribed in Section
3.
This section covers iront panel
and
external
arming
in detail.
2.7.1
Continuous Arming
When
the instrument
is
not
in the
hold
mode and
there
is
no
signal
present
at
the input terminals, the
instrument
will stay in the
idle state
and
the
GATE
light will
not
flash.
An
input signal
with
the
correct
dmirric
range
and
cor-
rect
input control setting will
initiate,
a .measurement
cy-
cle
and
the
GATE
light
will flash
every time the
internal
gate
opens.
2 J.2 Front
PansI
Arming
Front pane]
arming
is
done
with the
RESET
button, This
arming
mode
is
very useful
in
burst
measurements where
a
signai
is
present onlv temporarily To use
front
panel
ar-
ming perform the following
steps.
1,
Enter the
hold
mode
by
pressing the
MODE
button,
The
HOLD
light will
turn
on and
the
GATE
light will cease
flashing; indicating
the in.strument
is
in
the one-shot
ar-
ming mode. Tne
display
will
zero
and
n,o
new^
readings
are
processed
until
an arming stimulus
is
applied.
2, To.
trigger a single
reading, press
and
release the
RESET
brrtlon!
Tne instrument
will
be ready
to take
and
pro-
cess the next reading.
3,
To
arm
the
instrument
for
a
new
mea,surement, press
the
RESET
button, the display will zero,
4,
To
remove
the
instrument from the one-shot
arming
mi
ie,
press
the
MODE
button, until the
.HOLD
light
turns
off.
External arming operates
much
like
front
panel
arming
ex-
cept
for
the
arming stimulus
itself.
In this case the
arm-
ing stim,uiu.s
is
applied
to
the
rear
panel
EXT
ARMING
&
GATE/DELAY
lerminal
(see
Fi^ore
2-2),
The
Input arm-
ing
pulse
must conform
to
TTL
levels.
To
use
extemai
ar-
ming, proceed
as follows:
1.
Place the instrument
in
the hold
mode
by press.mg the
MODE
button,
(refer to
paragraph
2.7.2).
Note
that the
GATE
light
will
not
flash, indicating that the
instrument
is
i.n
one-shot
mode. The
instrument
will
cease process-
ing readings
while
it
is
waiting
for
the
arming
signal,
2.
Connect
the external
arming source
to the rear
panel
EXT ARF4ING
&
GATE/DELAY
connector,
The
first
posith'e
going pulse
at
the input terminal
wiB.
cause
the
Model
775
to
take
and
process the next
available signal
Note
that after
each positive
going
transition
of the
ar-
m.ing signal,
the
numeric
dtepiay will
be
set to
read zero
until the
next data
is
processed and
displayed,
3.
To return the instrument
to
the continuous mode, press
and
release
the
MODE
button
until
the
HOLD
light
turns
off.
2 J.4
Alarm Conditions
labk
2-2
lists
the front
panel conditions
that wtil
cause
the
instrument
to
sound an audible alarm.
Some
of these
conditions
are errors,
while others provide
irsfonnation
to
the
user,
Table
2-2.
Alarm Conditions
Item D«scription
i
i
1
1
Pressing
two buttons other than those
specific'd as legal.
:
2
Pressing the
GATE/DELAY TTMH A
or
|
button w'hen high
or
low
limits are
reached.
3
Pressing the
LEVEL
A
or
f
button u hen
upper
or
lower
limits are
reached.
4 After selecting
the
number
of digits
to
be
diaplayed, pressing the
LEVEL
A
or
'W
but-
ton
after
the
limits
are
reached,
-
-
1
2.8
AFFUCATIONS
Applications
for
the
Model
775
are
many and
varied and
will
depend on
the
user's need.s.
Figure 2-3 contains
a.n
application
concerning
fall
time
measurements;
while
Figure 2-4 contains an
application
using delay
to
measure
contact d.weli time.
For application information
on
hugh
fre-
quency
multiplexed
measurements,
refer to
Figure
2-5.