While doing some Can-Bus work (yes the No-Gear Bull), we noticed that the 2 scopes we have gave remarkably different results, in terms of noise!
Up until doing these screen shots, I thought it was just noise, and to that extent the 2 captures (and screen shots) are taken directly using the same leads, same USB2 cable, same laptop, with least wiggle during swap over possible. All 4 channels were earthed for both in the same place (as we have different earth needs for the 2 scopes - so needed to rule that out) ... As near identical as we could manage.
However, sample settings did change between swapping of scope, although only noticed this now doing the screen shots! ...
We have had this noise issue before (well noticed it), both from using Pico Templates and our own templates/existing captures, but also from scratch set up when switching devices during tests.
In this scenario we started with the 3243 and swapped over to the 4425 (manual reconnected and device selection needed as the auto connected can't swap device upon USB unplug - replug ... can this be fixed, even with a warning of device type swap?, so we don't loose the settings?
So, now I do have some possible logic as to the noise levels being differnet (a 20fold higher sampling rate), so the 3series is just missing the extreme peaks, although surely there would be a 1 in 20 chance of catching the peaks at the higher level?
The 3423 is using 200ns Sample interval, 5MS/s sample rate = sample size of 10,000, while the 4425 then uses (based on same starting template) Sample interval 10ns, Rate 100MS/s = Sample size 200,000) ?!
This all came about as we were concerned at noise levels leading to corrupt messages (as we still have one ECU being problematic in this regard), but based on the Diagnostics all talking to each ECU and otainign valid payload data, without errors or DTC, then the noise was finally rule out (or at least not primary to our issue - although certainly wasted a couple of man days chasing it
So a few questions:
- Why does the sample rates change between device changes, as we started with the 3 series (the less capable), surely the lower setting could be used on the 4 series, why would they change?
- Why does the 3series never pick up the extreme's if it only about 20times better sampling surely the peaks are still peaks and once in a while we'd see them (and we don't)?
- Is the noise a factor? Should we be concerned?
Ok, I know very few users have a 3series and 4 series, but swapping devices and device side by side comparisions should be a little better.
I still have an alergic reaction tot he usb cable discconection loosing all the data that's unsaved (please fix this, just disable the start/record button, as viewing and setting up should be possible without the scope plugged in)
Keen to hear other observations and learn a little more