THE Fluke ScopeMeter 190 series is a family of handheld test tools that combines the functions of digital multimeter with digital storage oscilloscope in bandwidths up to 200MHz and with up to 2.5GS/s real-time sampling per channel.
The Scope continuously records the last 100 screens in a FIFO memory. As soon as an anomaly is spotted on the scope or something suspect occurs that may have been missed on a first pass, the Replay button can be pressed to freeze the last 100 screens and allow them to be played over.
The feature, in fact, allows two sets of 100 screens with individual time stamps to be stored for later recall or download to a PC for more detailed analysis.
If looking for a voltage spike on the mains, for example, the instrument should be set to trigger on positive or negative-going voltage pulses with amplitude slightly larger than main voltage.
This method cannot be used to capture glitches that do not have voltage levels higher than the signal level. The solution for this scenario is to use pulse-width triggering set to capture (for instance) negative-going pulses with duration less than a specified time.
With the 200MHz version (ScopeMeter 199), which has rise and fall times of 1.7ns, pulses as narrow as 3ns can easily be captured using pulse-width triggering.
Setting the trigger to capture negative-going pulses that last longer than 20ms can also capture missing cycles on the mains.
To see how often the event occurs, just leave the ScopeMeter connected to the circuit for as long as you like then pressing the Replay key to see and analyse the captured events.
The ScopeMeter 190's TrendPlot feature was introduced specifically for occasions in which relatively long-term monitoring is needed.
Operating in the ScopeMeter's digital multimeter mode, TrendPlot offers the ideal way to locate causes of intermittent problems that occur perhaps only once an hour, or once a week.
Besides ambient temperature fluctuations, voltage sags or swells on the mains or a failing power supply are other intermittent problems that can be traced with TrendPlot.
TrendPlot also offers the advantage of accurate time stamping with a resolution down to one minute to show exactly when an irregularity occurs.
With the modern trend toward ever faster, more complex electronic control systems, the need for sophisticated test tools can only increase.
While advanced bench-top instruments may offer an impressive array of trouble-shooting features, their price and lack of portability generally preclude their use by mobile service engineers.
They need an instrument they can easily carry around and, since they never know what to expect on a call out, preferably one with the widest range of trouble-shooting features. Fluke's ScopeMeter 190 series fulfils these needs.