Application Note

2 Fluke Corporation Troubleshooting made simple with Fluke’s 190 Series II ScopeMeter
®
Catching signal
transients with capture
and replay
If you’re looking for a voltage
spike on the mains, for example,
the instrument should be set
to trigger on positive- or nega-
tive-going voltage pulses with
amplitude slightly larger than
mains voltage. This method can’t
be used, however, to capture
glitches that do not have voltage
levels higher than the signal
level. The solution then is to use
pulse-width triggering set to
capture, for example, negative-
going pulses with duration less
than a specified time. With the
200 MHz version (190 Series
II ScopeMeter), which has rise
and fall times of 1.7 ns, pulses
as narrow as 3 ns can easily
be captured using pulse-width
triggering. Setting the trigger to
capture negative-going pulses
that last longer than 20 ms can
also capture missing cycles on
the mains.
To see how often the event
occurs, just leave the ScopeMe-
ter connected to the circuit for as
long as you like then press the
Replay key to see and analyze
the captured events.
Looking for sags and
swells with TrendPlot™
The 190 Series II ScopeMeter’s
TrendPlot feature is used spe-
cifically for occasions in which
relatively long-term monitor-
ing is needed. Operating in the
ScopeMeter’s digital multimeter
mode, TrendPlot offers the ideal
way to locate causes of intermit-
tent problems that occur perhaps
only once an hour or once a
week. Besides ambient tempera-
ture fluctuations, voltage sags or
swells on the mains or a failing
power supply are other intermit-
tent problems that can be traced
with TrendPlot. In this mode,
the ScopeMeter acts in effect as
a paperless recorder, plotting for
more than 22 days the average,
minimum, and maximum values
of any selected scope or meter
measurement. Using this feature,
long-term irregularities can
easily be spotted. TrendPlot also
offers the important advantage
of accurate time stamping with
a resolution down to 0.2 sec-
onds to show exactly when an
irregularity occurs. This can be
displayed as either time-of-day
or elapsed time, depending on
the nature of the change you’re
trying to monitor.
While TrendPlot is running,
the ScopeMeter operates unat-
tended, continuously recording
the required data while
dynamically setting the vertical
ampli-tude scale to display the
maximum and minimum values,
and automatically compressing
the time scale to show the com-
plete trend from the start.
Analyzing fast, complex
electrical processes
Here’s where the 190 Series II
ScopeRecord mode comes in
handy. This is a continuous-
sampling mode in which the
scope records points (consist-
ing of minimum and maximum
values) at a rate of 125 MS/s.
With a 30,000-point deep
memory, the ScopeMeter can
record continuously in this
mode for up to 48 hours, captur-
ing glitches as short as 15 ns.
What’s more, a 100x zoom func-
tion makes the smallest details
visible, such as the shape of an
individual power cycle.
The figure shows what hap-
pens when an UPS switches
over from the inverter to mains
supply. Although the switcho-
ver would not be visible with a
normal display of say 200 ms/
div, captured with ScopeRecord;
the switchover is clearly visible
using a 100x zoom factor. In this
case, the display clearly shows
that no interruption in supply
has occurred, with the mains
voltage connected and in phase
within just a few milliseconds.
Setting the ScopeMeter to trigger on negative-going pulses longer
than 20 ms will detect missing cycles on the mains.
Plotting long-term irregularities with ScopeMeter’s TrendPlot
feature
ScopeRecord shows a voltage irregularity when switching off a UPS