Tektronix 2221 - Page 41

Controls , Connectors , and Indicators - 2221 Operators
O
In the absence of an adequate trigger signal , the
sweep (
or acquisition
) free
- runs . The
instrument
otherwise behaves as in P - P AUTO .
1
П
П
П
ต
In STORE mode , the last acquired waveform is
held on display between triggering events . The
pretrigger portion of the acquisition memory is
continually acquiring new pretrigger data until a
trigger event occurs . How the waveform display is
updated after the trigger occurs , depends on the
SEC / DIV setting . SCAN mode is selected from
5 s per division to 0.1 s per division .
SGL
SWP_Arms the
trigger circuit for
a single
sweep in NON - STORE or a single acquisition in
STORE . Triggering requirements are the same as
in NORM
Trigger Mode .
After the
completion of a
triggered NON
- STORE
sweep
or
STORE
SGL
SWP acquisition , pressing in the SGL SWP but
ton rearms the trigger circuitry to accept the next
triggering
event
start the
next
storage
acquisition .
or
From 5 s per division to 0.1 s per division , the
pretrigger portion
of the
displayed
waveform is
updated by the pretrigger data in the acquisition
memory , then the posttrigger data points are
placed in the display as they are acquired . For
faster sweep speeds , the posttrigger data points
are
acquired in
the
acquisition
memory prior to
completely updating the waveform display , using
the newly
acquired data .
In STORE mode , when the SGL SWP is armed ,
the acquisition cycle begins but the READY LED
does not come
on until the
pretrigger portion of
the acquisition memory is filled . At the time the
READY LED
comes on , the
acquisition
system
is
ready to accept a trigger . When a trigger event
occurs , the
posttrigger
waveform
data
is stored
to complete the single - sweep acquisition . After
the acquisition completes , the READY LED goes
out , and the Single Sweep can be rearmed .
P - P AUTO - TV
LINE — in the
NON -
STORE mode ,
triggering occurs on trigger signals having ade
quate amplitude and a repetition rate of about
20 Hz
or
faster . In
the
absence of a
proper
trigger
signal , an autotrigger is generated , and the sweep
free
runs .
П
n
an
In
STORE
mode , for
SEC
/ DIV
settings of 5 s
per
division to 0.1 s per division , the P - P AUTO
Trigger mode is disabled , ROLL mode is selected ,
and the acquisition is free running . At faster
SEC / DIV settings , triggering occurs under the
same conditions as NON - STORE mode P - P
AUTO
triggering
,
and
acquisitions are
auto
trig
gered if proper triggering signal conditions are not
met . The
manner in which
the display is
filled and
updated is the
same
as
for
NORM
triggering .
The SEC / DIV switch setting and the STORE
mode determine how the display is updated . For
settings of 5 s per division to 0.1 s per division , a
storage
process
known as
Triggered Roll
is used
.
The last acquired waveform is erased when SGL
SWP is armed . In Triggered Roll the display rolls
from right to left until the trigger is received .
Then , the display continues rolling until the post
trigger
acquisition record is
filled , and then
the
display
freezes .
When in ROLL mode , triggers are disabled and
the
signals signals are continuously
acquired and
displayed . The waveform display scrolls from right
to left
across
the
crt with
the
latest
samples
appearing at the right edge of the crt .
n
ย
For SEC / DIV settings of 50 ms to 5 us ( RECORD
store mode ) , the display is updated as a full
record . The previously displayed waveform
remains on the crt
until the
posttrigger
portion
of
the acquisition memory is filled . The waveform
display is then
updated with
the newly
acquired
data in its
entirety
. For
SEC / DIV
settings
of 2 us
to 0.05 us ( REPETITIVE store mode ) , a partial
record is acquired each time the SGL SWP but
ton is
RESET
,
overlaying the
samples
accumu
lated
from
past
acquisitions .
For either
NON -
STORE or
STORE mode , the
range of the TRIGGER LEVEL control is automat
ically restricted to the peak - to - peak limits of the
trigger signal for ease in obtaining triggered
displays and acquisitions . P - P AUTO is the usual
Trigger Mode selection for obtaining stable
displays of TV Line information .
TV
FIELD-
Permits stable
triggering on a
televi
sion field ( vertical sync ) signal when the P - P
AUTO and the
NORM
Trigger
buttons
are
pressed in together ( see VAR HOLDOFF Control ) .
24 ) READY - TRIG'D Indicator - A dual - function LED indi
cator
. In
P - P
AUTO
and
NORM Trigger
modes , the
LED is
turned
on
when
triggering
occurs
.
In SGL
SWP Trigger mode , the LED turns on when the
trigger circuit is armed
,
awaiting a
triggering event ,
and
turns off
again
after the
single
sweep ( or
acquisition
)
completes .
O
П
n
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