Digital
oscilloscopes
have
settings
that let
you
control
how the
acquisition
system
processes
a
signal.
Look
over the
acquisition
options
on your
digital
oscilloscope
while
you read
this
description.
Following
figure
shows
you an
example
of an
acquisition
menu.
Example
of an
Acquisition
Menu
Acquisition
Modes
Acquisition
modes
control
how
waveform
points
are
produced
from
sample
points.
Recall
from the
first
section
that
sample
points
are the
digital
values
that
come
directly
out of
the
Analog-to-Digital-Converter
(ADC).
The time
between
sample
points
is
called
the
sample
interval.
Waveform
points
are the
digital
values
that are
stored
in
memory
and
displayed
to form
the
waveform.
The time
value
difference
between
waveform
points
is
called
the
waveform
interval.
The
sample
interval
and the
waveform
interval
may be
but need
not be
the
same.
This
fact
leads to
the
existence
of
several
different
acquisition
modes in
which
one
waveform
point is
made up
from
several
sequentially
acquired
sample
points.
Additionally,
waveform
points
can be
created
from a
composite
of
sample
points
taken
from
multiple
acquisitions,
which
leads to
another
set of
acquisition
modes. A
description
of the
most
commonly
used
acquisition
modes
follows.
Sample
Mode:
This
is
the
simplest
acquisition
mode.
The
oscilloscope
creates
a
waveform
point
by
saving
one
sample
point
during
each
waveform
interval.
Peak
Detect
Mode:
The
oscilloscope
saves
the
minimum
and
maximum
value
sample
points
taken
during
two
waveform
intervals
and
uses
these
samples
as
the
two
corresponding
waveform
points.
Digital
oscilloscopes
with
peak
detect
mode
run
the
ADC
at a
fast
sample
rate,
even
at
very
slow
time
base
settings
(long
waveform
interval),
and
are
able
to
capture
fast
signal
changes
that
would
occur
between
the
waveform
points
if
in
sample
mode.
Peak
detect
mode
is
particularly
useful
for
seeing
narrow
pulses
spaced
far
apart
in
time.
Hi
Res
Mode:
Like
peak
detect,
hi
res
mode
is a
way
of
getting
more
information
in
cases
when
the
ADC
can
sample
faster
than
the
time
base
setting
requires.
In
this
case,
multiple
samples
taken
within
one
waveform
interval
are
averaged
together
to
produce
one
waveform
point.
The
result
is a
decrease
in
noise
and
an
improvement
in
resolution
for
low
speed
signals.
Envelope
Mode:
Envelope
mode
is
similar
to
peak
detect
mode.
However,
in
envelope
mode,
the
minimum
and
maximum
waveform
points
from
multiple
acquisitions
are
combined
to
form
a
waveform
that
shows
min/max
changes
over
time.
Peak
detect
mode
is
usually
used
to
acquire
the
records
that
are
combined
to
form
the
envelope
waveform.
Average
Mode:
In
average
mode,
the
oscilloscope
saves
one
sample
point
during
each
waveform
interval
as
in
sample
mode.
However,
waveform
points
from
consecutive
acquisitions
are
then
averaged
together
to
produce
the
final
displayed
waveform.
Average
mode
reduces
noise
without
loss
of
bandwidth
but
requires
a
repeating
signal.
Stopping
and
Starting
the
Acquisition
System
One of
the
greatest
advantages
of
digital
oscilloscopes
is their
ability
to store
waveforms
for
later
viewing.
To this
end,
there
are
usually
one or
more
buttons
on the
front
panel
that
allow
you to
stop and
start
the
acquisition
system
so you
can
analyze
waveforms
at your
leisure.
Additionally,
you may
want the
oscilloscope
to
automatically
stop
acquiring
after
one
acquisition
is
complete
or after
one set
of
records
has been
turned
into an
envelope
or
average
waveform.
This
feature
is
commonly
called
single
sweep or
single
sequence
and its
controls
are
usually
found
either
with the
other
acquisition
controls
or with
the
trigger
controls.
Sampling
Methods
In
digital
oscilloscopes
that can
use
either
real-time
sampling
or
equivalent-time
sampling
as
described
earlier,
the
acquisition
controls
will
allow
you to
choose
which
one to
use for
acquiring
signals.
Note
that
this
choice
makes no
difference
for slow
time
base
settings
and only
has an
effect
when the
ADC
cannot
sample
fast
enough
to fill
the
record
with
waveform
points
in one
pass.
