[vox-tech] Re: [vox] [ot] Oscilloscope recommendations?

[Jeff Newmiller]

This is rather technical, Mark, so I have moved to vox-tech...

On Thu, 20 Dec 2001, Mark K. Kim wrote:

> Hello, all EE people...
> 
> I've been asked to recommend an oscilloscope for my work, but I don't know
> what to get.  Can someone recommend something in a few price ranges?  I
> don't know the max price my boss is willing to spend...

I don't know what is good on the market right now, but there are some
general tips for selecting digital oscilloscopes...

Digital is usually good, but not always.  Many slower DSOs assume the
signal is periodic, and overlay offset samples near the advertised limits.  
Think of trying to get 100 cycles on a 10MHz sine wave.  A slow DSO may
watch for the trigger (rising zero crossing, for example), and sample
every 1microsecond starting on the trigger on the first pass, but after
ten samples stop and watch for another trigger, and wait 0.1 microseconds
before starting another 10 sample series.  By repeating this ten times,
and overlaying the data, you get what looks like a nice sine wave, without
the high sample rate requirement on the analog-to-digital converter.

Unfortunately, if you are trying to debug a microprocessor system and need
to trigger on a transient digital output on the x channel and watch
another line on the y channel, you need the full advertised sampling rate
for transient signals.  This is just a characteristic of certain DSOs that
you want to watch out for so you won't be surprised.  Sometimes full-rate
transient analysis is not as important as cost, so there is no right or
wrong answer.  Analog or combined analog/digital might be an option for
cheaper transient recording, but I don't know what the state of the art is
there anymore.

Another thing to be careful to do is get a few probes... and learn how to
adjust them if you are working with signals near the instrument limits so
you don't get probe artifacts (overshoot or damping) in the traces.

---------------------------------------------------------------------------
Jeff Newmiller                        The     .....       .....  Go Live...
DCN:<jdnewmil@dcn.davis.ca.us>        Basics: ##.#.       ##.#.  Live Go...
                                      Live:   OO#.. Dead: OO#..  Playing
Research Engineer (Solar/Batteries            O.O#.       #.O#.  with
/Software/Embedded Controllers)               .OO#.       .OO#.  rocks...2k
---------------------------------------------------------------------------