Oscilloscopes are very complex instruments. The “front end” is all about being able to capture a huge range of signals at a huge rate of speeds. This is what lets you hook up the same probe to AC mains one day, and pick up millivolt signals another day, and to collect many minutes of data on a single screen vs displaying the shape of a multi-MHz wave. This isn’t just about capture, at least as important is the triggering part: how to decide what to pick up for display on the screen.
With the Xminilab presented recently, a lot of this has been solved in software, supporting a pretty impressive range of options, even for triggering. The Xminilab is particularly interesting because the full source code is available.
But for serious work, you’ll need an Owon or Rigol scope. These can sample at up to 1 Gsa/s, i.e. one billion samples per second. Truly, truly capable front-ends, able to handle very wide voltage and acquisition speed ranges.
The Hameg HMO2024 is more expensive, and many of its specs are not much better than the Owon (worse even, in some cases: a smaller display size and less sample memory).
The devil is in the details. Here’s a recent screen from the HMO2024 (borders cropped):
And here’s my first cut at acquiring the same info on the Owon (click for full size):
Let me add that I now have lots of experience with the Hameg, and only just started using the Owon, so there might be relevant features I’ve failed to set up in an optimal fashion.
A couple of quick observations:
- This is not a “typical” measurement setup: a very slow, low-amplitude signal is nothing like the usual measurements one would come across, with higher signal levels, and faster sampling rates. Then again, that’s part of the whole point of an oscilloscope: it’s so versatile that you end up using it in lots of situations!
- As you can see, the Owon has a lot more pixels to display a signal on, so I was able to increase the voltage sensitivity one notch to get more detail, and capture a bit longer.
- Some differences are obvious but not that important: the Owon provides less information on-screen about the current settings, and it does not use anti-aliasing for the traces (i.e. intensity variations to produce a fake “sharpening” effect of steep lines).
The two major differences are that: 1) the Hameg lets me apply additional digital signal processing to effectively reduce the random variations and smooth out the signal (this is done after capture, but before drawing things on-screen, i.e. all in software/firmware), and 2) the Hameg includes support for a “reference trace”, i.e. storing a previous trace in its built-in memory, and displaying it in white next to a new capture – to compare power consumption with and without WiFi, in this case.
Note that the Owon capture depth was set to 1,000 samples instead of the maximum 10 Msa, otherwise the screen would have shown a very wide red trace, almost completely swamping out the signal shown on screen. With this reduced setting, the current consumption is still fairly easy to estimate, despite the lack of low-pass filtering.
Is this a show-stopper for the Owon? Not really. It still gives a pretty good impression of the current consumption pattern during starup of the Carambola 2. If you really wanted to improve on this, you could insert an analog filter (a trivial RC filter with just 2 passive components would do). With a bit of extra work, I’m sure you can get at least as good a current consumption graph on the Owon.
The trade-off is (recurring) convenience and setup time vs. (up-front) equipment cost.
PS. The Rigol DS1052E does have a low-pass filter – every scope has different trade-offs!