Autonerdz forums

i posted these on iatn awhile back while asking for help.  what i did not know is that the modis would alias the capture at higher timebases.  the glitches you see are not actually there.  when scoped at a 10ms timebase all was well. 
i got myself into trouble on that forum by mentioning my desire for a pico because i wanted to see more on the screen while the scope was actually capturing the waveform.  no one seemed to understand that i did not want to have to stop the scope to "zoom out" like the modis requires you to do.  i will be buying a pico as soon as i possibly can.

Crackerclicker,

What you show there is a sample rate issue.  It's also an operator error issue.  You are not alone coming to grips with the way the Modis operates.  It's not exactly intuitive and backward from most other scopes.

As you can see from the attached chart, your selected 200ms sweep is really a 52.4 second capture time.  At that time base, the scope is only sampling at 2500Hz.  That means that there are 400 microseconds between each sample point which is not fast enough to capture some of your CKP pulses at that RPM.

A Pico 4423 would be able to sample every 3 microseconds at a 50 second capture time.  That's 133x faster.

OK, so that is the scope limitation.  The operator error part is that you simply used too much capture time and pushed the beyond its limits.  Very easy to do...

This is the single most common error I see with Modis users.  You think you are looking at the capture time when the scope is running but you are not.  Fact is, it is impossible to see what you are capturing when the scope is running.  In order to see the capture time, you must stop the scope and zoom all the way out.  The modis runs fully zoomed in and you can only see a small part of what is being captured.  Once you get used to this operation, you can use it much more effectively and stay within bounds.  All scopes have limits, some more than others.   

I must say here that we are only comparing the scope part of the Modis and its much more than a scope.  The Modis scope is the most powerful native hand held four channel automotive scope available.  Just takes some getting used to.

Back to the Verus for a moment....Very nice looking unit

The Verus is well marketed. It is also very expensive. The
PC platform it uses is a very limited one with minimal
resources. For example, it's not even capable of running a
PicoScope where a $400 PC from Office Depot is.

Consider the limitations of an aftermarket scan tool. Also
consider the scope, which is a very good one, but not nearly as
powerful as a PicoScope which is up to 200x faster.

Then consider the costs of a top of the line PC with some
good additions, like a PicoQuad Kit and a couple of factory
level scanners. You would be in a way better place for less
$$.

Then consider what happens if something goes terribly wrong
with the Verus and the down time to get it repaired. Compare
this to a 20 minute trip to the local PC store to get
another PC and load up your apps. You could be back up and
running within hours instead of weeks.


Fisher,

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Not easily.  The down time between captures would have to be calculated for those settings.  All I can tell you is that there may be injection events taking place during the down time between acquisitions you are not seeing.

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It is NOT sampling at 10MHz.  It would only be able to do that at the very fastest time bases.  True sample rate is a function of the record length (how many samples can it collect on one pass), max ADC speed, and capture time.

To illustrate, consider a one second capture time and your 256 point record length.  What is your sample rate?  It cannot be more than 256 samples per second.  Doesn't matter that the ADC can sample at 10MHz.  You only have 256 samples to work with.  To sample at 10MHz you would have to reduce your capture time to 25 microseconds.

We have a sample rate calculator that helps compare the performance of different scope if you have the max ADC speed and record length specs:

http://www.autonerdz.com/java/SampleRateCalculator.html

Crackerclicker,

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Nothing wrong with making a mistake, as long as we learn from them   

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That's all it takes.   

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You will find that it's much harder to push a Pico beyond its limits.  Plus you will be able to see the entire capture time when the scope is running.  You will also be able to zoom in way more than the Modis can.  Up to 3 million x magnification.    

You will also be able to trigger a full capture, which the Modis cannot.

And so much more...

We look forward to having you in the Autonerdz Picogroup.   

crackerckicker,

There is so much wrong with that article I don't even know where to begin....

It's misleading at best.  

Suffice it to say that there is no mention of one of the primary specs that allow a scope to maintain a good sample rate.  Record length.

Probably because UEI ADL 7103 that he offers only has an 800 point record length.  

This is only slightly better than an old Fluke 97/98.

The 25MHz max speed means little without the record length.

You can plug those specs into our sample rate calculator to see what it really does at different time bases:

http://www.autonerdz.com/java/SampleRateCalculator.html

You can start with either the current release or the beta.  Either one though will need the 4000 driver field fix applied after installation.

Call us if you need help with that.

Discussions on each of these builds in the Picogroup area with details on how to apply the patch.

Tom, I have been waiting for someone to clarify these arguments for me and the "buckets" analogy was great.  Also, as I was reading the article you are probably most likely referring to, specifically the one that showed an actual screen capture, I was thinking the same thing.  Why not increase the time on the screen, then zoom in if you find an issue, because the Pico has the ability not to miss near as much info when "zoomed" out during data capture right?  I feel like there is so much animosity between the two camps its ridiculous.  I've been researching scopes for almost a year now, and find that all of the top performers will do so much that any one would be great for auto use, it really just depends on personal preference.  I just don't get why so many guys out there love to bash on other scopes?  I feel like most of the people that feel very strongly one way or the other about there own scopes don't really know how to utilize them to there full extent, maybe I'm way off base, I don't know, I'm just chomping at the bit to use the shops tool budget money at the end of  the year!!!

If you want your Pico to operate like the Snap-on offerings with a continuous single scrolling buffer, the solution is very simple. In streaming mode, set a repeat trigger on the right edge of the screen at a voltage level that will never be met by the signal being tested or trigger off a channel that is not being used- done. Now use the space bar to stop the scope when the event occurs.

The data will draw left to right with old data falling off the left side into oblivion. The “Pico Gap” no longer exists.

This is where the superior sample rate and record depth of Pico really shows. In this example, I have two seconds on the screen sampling at 1MS/s. The Snap-on offerings with 2.6 seconds on the screen sample at 50KS/s.

The video below is a little jerky due to it being an animated gif.

Brian