Table of Contents
Advertisement
Operating
Instructions — Type
3A74
2. Specific Information
This
information
is provided
as
an
operational
guide
concerning
the
use
of chopped
and
alternate
modes
of
operation.
(a) Displaying
non-repetitive
signals.
To
compare
time
and
phase
relationships
of
non-repetitive
signals,
use
chopped-mode
operation.
The
suggested
fastest
sweep
rate that you can use and still obtain good resolution is
summarized
in Table 2-2.
TABLE
2-2
Chopped-Mode
Resolution
Number
of
Recommended
Approx.
Number of
Channels
in
Maximum
Segments
in Each
Use
Sweep
Rate
Trace
2
10 psec/div.
25
3
20 psec/div.
35
4
20 psec/div.
25
If sweep
rates faster than those shown
in Table 2-2 are
used,
resolution
decreases
and
you
may
prefer
to use
single-trace
operation.
(b) Displaying
repetitive signals. The most likely dividing
point between the use of chopped-mode operation at low
sweep
rates and
alternate-mode
operation
at high sweep
rates is 0.2 millisec/div. At this sweep
rate, or when
using
higher
sweep
rates,
alternate-mode
operation
produces
an uninterrupted display when
viewing
repetitive signals
500 cps or higher. That
is, the alternate-mode
switching
cycle is sufficiently fast to produce an apparently steady
display.
If the lower sweep
rates are used for viewing signals
500
cps
or
lower,
the
alternate-mode
switching
cycle
becomes
more
noticeable
and
you
may
prefer
to use
the
chopped-mode
of
operation
to
produce
steadier
displays.
Multi-Trace
Triggering
1. Comparing
time-related
signals.
To
obtain
a
stable
display and
to see true time or phase
relationship
between
signals which
bear
a fixed
time relationship
to each
other,
apply the reference signal to channel 1. Use the channel
1
controls in a conventional manner. Pull the TRIGGER switch
outward and the time base will internally trigger on channel
1 only. Apply the signals to be compared
to the other chan-
nels. Set the CHOP.-ALT.
switch
to a position
best suited
for your application.
With the TRIGGER switch in its outward position, trigger-
ing
on
channel
1 only
is independent
of the
channel
1
MODE
switch setting. That is, you can set channel 1 MODE
switch
to
OFF
anytime
you
want
to
remove
channel
1
waveform from the screen and exclude it from the switching
cycle.
Triggering
will
not
be affected.
Signals
in the
re-
maining
channels will continue to be displayed
unaffected
and
referenced
to
channel
1],
regardless
of
the
MODE
switch
setting.
2. Displaying
signals
unrelated
in time.
It is often
pos-
sible
to obtain
a
stable
display
of signals
unrelated
in
time.
This
is
accomplished
by
setting
the
CHOP.-ALT.
2-6
switch
to ALT., pushing
the TRIGGER
switch to its inward
position,
and
using
ac-coupled
internal
triggering
of the
time
base.
Then,
with
a proper
setting
of the time-base
Triggering
Level
control, the time base can trigger on the
signal
in each
channel
to assure proper electronic switch-
ing of the channels.
If you
should
experience
some
difficulty
in finding
a
proper
setting
for
the
Triggering
Level
control,
consider
these
factors
which
affect
triggering:
the
setting
of the
Type 3A74 POSITION
controls; the ac-coupled setting (AC,
AC
Slow, AC
Fast, AUTO.—depending
on which
positions
are available) of the time-base Triggering Coupling switch.
The
Type
3A74
POSITION
controls
affect the de com-
ponent
of the
composite
trigger
from
channel
to
channel,
and
the different ac-coupled
settings of the time-base Trig-
gering Coupling switch affect the waveshape of the trigger
as
it is ac-coupled
into the
time-base
triggering
circuits.
Consequently,
in addition to adjusting the Triggering Level
control, you
should
also try vertically positioning
the dis-
played
waveforms
to
different
points
on
the
ert
and
try
the different ac-coupled settings of the Triggering Coupling
switch to find the best triggering conditions.
Calibrated
Gain
Adjustment
Any
time you
move
the Type 3A74
from one oscilloscope
plug-in
opening
to another
you
must
adjust the common
gain
of the
unit to compensate
for differences
in crt de-
flection sensitivities.
1. Set the front-panel controls of the Type 3A74 to these
settings:
AC-GND-DC
(channel 1)
DC
VOLTS/DIV.
(channel 1)
02
VAR. GAIN
(channel 1)
CAL.
POSITION
(channel
1)
Centered
MODE
(channel
1)
NORM.
MODE
(channel
2, 3 and 4}
OFF
TRIGGER
Either position
CHOP.-ALT.
2. Set the time-base
sweep
rate and
triggering
controls
for a 0.1-millisec/div.
free-running
sweep.
Either position
3. Apply
a
0.1-volt
signal
from
the
oscilloscope
Cali-
brator
to
the
channel
1
connector.
(Use
a short
test
lead
through
a suitable
connector
adapter
to make
the direct
connection.
Use
a 0.05-volt
Calibrator
signal
if you
are
using
a Type
567
Oscilloscope.)
4. Adjust
the
CALIB.
control
to obtain
a deflection
of
exactly five major divisions. (2.5 major divisions if you are
using a Type 567 Oscilloscope.)
NOTE
If
the
CALIB.
control
does
not
have
sufficient
range,
set
channel
1
GAIN
ADJ.
near
midrange.
(A setting
a few
degrees
on either side of mid-
range
will give the CALIB.
control
enough
range.}
Then
set the CALIB.
control
as described
in step
4 of this procedure.
Next,
proceed
to the Channel
Gain
Adjustments
procedure
and
set
the
GAIN
ADJ.
for
channels
2,
3,
and
4.
Advertisement
Table of Contents
Need help?
Do you have a question about the 3A74 and is the answer not in the manual?