Post-capture waveform analysis: 8-channel Pico and ATS eScope -- try it yourself
In a recent thread it was asked how 8-channel scopes differ when it comes to sharing and analysing waveforms after they are captured. Ideally, to test that we would need to hook up a few different scopes to the same car, collect as many signals as possible and then take a look. May be at some point such an experiment will be carried out, but, meanwhile, I have done the following: I fetched the Picoscope waveform for a quad-cam engine collected by Matthew S.:
and exported the data as an array of floating point numbers, preceded by the sampling interval, the sample length, and the number of channels used. This is the most simple format possible for storing channel data, but, surprisingly or not, such file can be opened by the eScope:
A few notes about the conversion:
- the Picoscope waveform is collected at 2MS/s, while for eScopes the data has to be decimated to 125kS/s (the maximum sample rate for this scope when 5-8 channels are in use). Despite using an anti-aliasing filter, the decimation results in visible aliasing for some traces, for example, for the ignition trace (uneven height of the firing line); it is what it is, I tried my best.
- the Picoscope file format saves trace positions, scales, filters, cursor positions, and the zoomed-in region. Matthew nicely scaled and separated the traces, and they will be restored this way each time the file is opened. I don't know if it's possible to save trace settings in the eScope, so the data for the eScope will be loaded "as is" each time the file is opened.
- the Picoscope format supports conversion of transducer output voltage into custom units such as Amps. For the eScope I presented the amp-clamp output at 1V=10A scale (Channel 7).
- if you believe any step in such conversion is flawed, please let me know, and I will try to fix it.
So, here are the files and links to the software to open them:
Pico file from Matthew S.: diag.net/file/f3gc8r1px…
Exported file for eScope: diag.net/file/f32bg64eh…
Software for Picoscope: picoauto.com/downloads
Software for eScope PRO: automotivetestsolutions.com/software-updat…
(Download, enable Demo mode, switch to Deep Rec tab, then Load Deep Rec)
Here are sample exercises for the two waveform files:
- Zoom into two engine revolutions around second 3. Put phase rulers on the ignition sync. How many degrees away from the firing line is the CKP gap?
- What is the length, in microseconds, of each low pulse in the CKP trace?
- What is the maximum primary current in the ignition coil for the whole waveform?
- Scale and shift a trace up and down.
- Plot frequency of the CKP trace.
- What is the system voltage of this car?
Thanks for the fun exercise Dmitriy, I am very familiar with Pico and done quickly, I am working to get quicker with ATS Escope. I appreciate you doing this "try it your self".
Id and it was easy in pico. Not use to the escope . Have been playing with it for about six months but this was a good test
You are very welcome, Brian. Any chance to see you and your students go through this exercise in one of your webinars?
I may be able to work in your files. As we progress though the class that I do we go though the things measurements using the rulers and also suing the measurement functions, I share about 20 files with the students, mostly with 1 or 2 channel captures to keep confusion low as many times we have a wide range of experience levels attending. That said we make sure that every one is familiar doing…
Yeah, it is not the easiest example to go over, so people should already know the basics. I don’t mind anyone using the BIN file, but the source data comes from Matthew (many thanks to him), shared with DiagNet members. So... we might need Scott’s guidance on this one. The most straightforward way is for the students to sign up on DiagNet and fetch it right here, though. Cheers, Dmitriy.
Dmitriy, Here's a couple captures of data manipulation on the escope. And I answered some of the questions. I'm not sure exactly what you meant by maximum primary current "for the whole waveform" but here goes. - CKP gap from firing line = 11.3 deg - CKP low pulse = 41 micro sec - Primary current = 1.27a - CKP frequency = 750 hz - System voltage = 14.6v Zoomed in and channels shifted 1…
Bob, those screenshots look very nice indeed! About the current: the maximum for the whole waveform would be the highest point of the highest peak. Heights of the peaks are not exactly equal in this waveform, so how to find the highest? Also, wouldn’t 1.27A be too low for a known good peak primary ignition current? (Hint: I mentioned the scale for that channel in the description)
You're right about the amps, I missed that. I'll read through your information again and information again and then double-check the current.
I'm going to say the highest peak is 1.3V so at 1V=10A that should be 13A