most of today's benchtop oscilloscopes
can count captured pulses and some
scopes can also totalize events
using a real-time counter so what's the
difference between
counting captured pulses and totalizing
events
hi i'm johnny hancock product manager
for keysight's infiniivision
x-series oscilloscopes let's get started
and i'll show you the difference between
these different types of measurements
so i've got my oscilloscope set up to
capture
a burst of pulses it's going to be
thousands of pulses and i'm going to
count those pulses two different ways
i'm going to use the pulse count
measurement which i have set up
and the hardware totalizer so
from my generator over here i'm going to
go ahead and generate
the burst of pulses and they each
measure 6 000. now if i
generate the burst again
the pulse count still says 6 000. it
took the next acquisition
and and counted the number of pulses
again
the totalizer continues to count up so
now it's 12
000. 18 000
24 000 but for a single burst of pulses
they both gave the same answer but there
is a limitation
on the pulse count uh it can't count
more than about 30 000 pulses
across screen whereas the totalizer
is essentially unlimited now it's not
quite infinity but it's pretty darn
close
it's up there about 64 bits
now if i change my time-based setting
and let's clear
my readings and start from zero again
generate my six thousand pulses
the oscilloscope pulse count measurement
only measured one thousand because it
only measures
what's captured on screen whereas the
hardware totalizer
still measured six thousand because it
doesn't depend on what's digitized
it's counting the number of trigger
level crossings
just like a standalone counter would do
here's another example comparing pulse
count on the digitized waveform
versus the totalized capability using
the hardware counter
this is a digital clock signal and it
has a very
infrequent glitch out of one million
cycles of the clock
there's this very narrow glitch and
right now i have the totalizer running
and it's just counting up right now it's
up to
270 280 million
hits or crossings the pulse count just
simply says
17 because it sees 17 pulses
across screen what i would like to know
though
is the number of times
this very infrequent glitch occurs and
we can count that by changing
from just trigger level crossings on
channel one
to trigger qualified events now i have
to go scope set up
triggering on a narrow pulse and now you
can see it counting up
much more slowly we're up to about 30
40 and so it's counting the exact
number of glitches that occur real time
has nothing to do with the waveform you
see on screen
so far it looks like the hardware-based
real-time totalizer is winning this
battle between the
hardware-based totalizer and the pulse
count on the digitized data
i now want to show you a different
example where
the pulse count is going to win the
battle so here's an example
this is a serial bus signal it's called
usb
pd usb power delivery
and perhaps i want to know how many
pulses
occur in a particular burst or frame
so right now i'm doing a gated
measurement by cursors
and i'm zeroed in on just one burst of
pulses
and i want to know how many pulses are
in that burst
the pulse count says there's 211.
the totalizer is just giving me a
running total
of trigger level crossings and it's uh
it's
somewhat meaningless uh let's let's
measure this next burst here
so in this next burst there's 117 pulses
so this can be very handy if you if you
have serial
buses where there must be a certain
amount of pulses
per burst or per packet
you can very accurately accurately
measure it with the pulse count
if you think you might have learned
something in this short video to make
you more proficient
in performing oscilloscope measurements
i invite you to view our other
infiniivision
oscilloscope measurement tips videos
to learn more about keysight's
infiniivision x-series oscilloscopes
go to the url listed on your screen or
contact
one of keysight's authorized
distributors
thanks and semper fi