Specifications

20
Important Oscilloscope Performance Properties (continued)
Update rate and oscilloscope connectivity
Update rate
Update rate refers to the rate
at which an oscilloscope can
acquire and update the display of
a waveform. While it may appear
to the human eye that the scope
is displaying a “live” waveform,
it is because the updates are
occurring so fast that the human
eye cannot detect the changes.
In actuality, there is some dead-
time in between acquisitions of
the waveform (Figure 28). During
this dead-time, a portion of the
waveform is not displayed on the
oscilloscope. As a result, if some
infrequent event or glitch occurs
during one of these moments, you
will not see it.
It is easy to see why having a fast
update rate is important. Faster
update rates mean shorter dead-
times, which means a higher
probability of catching infrequent
events or glitches.
Display
Window
Display
Window
“Effective”
dead-time
Acquisition
time
Acquisition
time
“Real”
dead-time
Figure 28. Visual depiction of dead-time. The circles highlight two infrequent events that
would not be displayed
Say for example you are
displaying a signal that has a
glitch which occurs once every
50,000 cycles. If your oscilloscope
has an update rate of 100,000
waveforms per second, then you
will capture this glitch twice per
second on average. If, however,
your oscilloscope has an update
rate of 800 waveforms per
second, then it would take you
one minute on average. This is a
long time to be watching.
Update rate specifications need
to be read with care. Some
manufacturers require special
acquisition modes to attain the
banner specification update rates.
These acquisition modes can
severely limit the performance
of the oscilloscope in areas such
as memory depth, sample rate,
and waveform reconstruction.
Therefore, it is wise to check the
performance of the oscilloscope
when it is displaying waveforms
with this maximum update rate.
Oscilloscope connectivity
Oscilloscopes come with a wide
range of connectivity features.
Some are equipped with USB
ports, DVD-RW drives, external
hard drives, external monitor
ports, and much more. All of
these features make it easier
to use your oscilloscope and
transfer data. Some oscilloscopes
also come equipped with
operating systems that allow
your oscilloscope to behave like
a personal computer. With an
external monitor, a mouse, and
a keyboard, you can view your
oscilloscope’s display and control
your oscilloscope as if it were
embedded in your PC’s tower.
You can also transfer data from
an oscilloscope to a PC via a
USB or LAN connection in many
instances.
Good connectivity features can
save you a great deal of time
and make completing your job
easier. For instance, it can allow
you to quickly and seamlessly
transfer data to your laptop or
share data with geographically
dispersed colleagues. It can also
allow you to remotely control
your oscilloscope from your PC.
In a world where the efficient
transfer of data is a requirement
in many situations, purchasing
an oscilloscope with quality
connectivity features is a very
good investment.
Oscilloscope Fundamentals