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Question of the Month: Verus Vs Pico (Read 113,234 times)
Tom Roberts
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Question of the Month: Verus Vs Pico
Feb 3rd, 2010 at 1:15pm
 

We field a LOT of questions over the email and phone.  Every once in a while, we find one that just begs to be shared.  So here is the question of the month:

Quote:
I was trying to compare Snap-On Verus to a Pico, quite confusing.  If you get a chance, could you give me an example of a 1ms sweep for these units.   Thanks!


Confusing is right!  You are not the only one having trouble sorting that out.  First of all, the Verus scope is a Modis scope.  Specs are the same.

Modis/Verus is confusing because a Modis screen (sweep) is only a small part of the total capture time.  You cannot see the total capture time when the scope is running.  A Pico screen IS the total capture time which would be equivalent to the total of all Modis screens....(262 to 1747).

There has been much disinformation based on the misunderstanding of fundamental scope operational concepts.   One of these confusions has been termed the 'Pico Gap'  It's based on the claim that the Modis has no gaps between the screens and Pico does.  That is at best, misleading.  Modis has no gaps between its screens and it's capture time is seamless.  Pico also has no gaps during its capture time.  The difference is only in how that capture time is displayed.  Modis breaks that capture time up into tiny fragments, Pico does not.  Both record their capture times seamlessly.

So....what are the multiple Pico screens that do have gaps between them?  They are each a full buffer seamless capture record.  The big difference here is that Modis can only capture one full buffer record.  Pico can collect up to 1000.  Therefore the whole 'Pico Gap' argument is nonsense.  The additional screens that Pico can capture is something the Modis cannot do at all.

OK, so here is how you would compare apples to apples using the sample rate charts for a 1ms Modis sweep to a Pico:

First you cannot compare exactly the same capture times but you can get close.

Modis 1ms sweep is a 262ms total capture time sampling at 500Khz.  It does not matter if you are using one or four channels because they are always active and using resources even if you have turned them off.

Pico's closest capture time is 200ms.  At this capture time, Pico 4423 will sample at 20MHz running four channels and 80Mhz running one.  This is because the scope resources are devoted only to channels in use and not wasted.

So the sample rate comparison between the two shows that when running all four channels, the Pico is 40 times faster.  :-o

Now, when you get into the longer time bases, the Pico becomes hundreds of times faster than the Modis/Verus.

For example, comparing a Modis 100ms sweep which is a 26.2.second capture time to the closest Pico matching capture time of 20 seconds, the Pico will sample 200 times faster running four channels.

So....The real 'Pico Gap' is the difference in performance between the Pico and the Modis/Verus.  Pico would be the AA fueled dragster and the Modis would be the VW bug.  The 'Pico Gap' would the the space between them on a quarter mile run.   Smiley

Any questions?
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Re: Question of the Month: Verus Vs Pico
Reply #1 - Feb 3rd, 2010 at 6:25pm
 
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.
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Re: Question of the Month: Verus Vs Pico
Reply #2 - Feb 4th, 2010 at 7:40am
 
I have a question that is fit for this discussion. I have several older labscopes that all have probably 256 samples per screen; never any more than that. I know I cant see trends with that like with the Wrangler from hell.
  While I am looking at , say, an injector while running, although I cant see it happen, the screen is refreshed every... so often.
   I mean if I set my trigger to normal and set it for a falling signal at seven volts for example, I will see a classic pattern on the screen (at idle in good running condition). How do I know how often that pattern has changed? If it samples at 10 million samples per second, that doesn't mean I have seen all 10 million samples, no?
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Re: Question of the Month: Verus Vs Pico
Reply #3 - Feb 4th, 2010 at 9:15am
 

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.   Wink

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. Wink


Fisher,

Quote:
How do I know how often that pattern has changed?


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.

Quote:
If it samples at 10 million samples per second, that doesn't mean I have seen all 10 million samples, no?


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

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Re: Question of the Month: Verus Vs Pico
Reply #4 - Feb 4th, 2010 at 2:48pm
 
yes, i forgot to mention that everyone on iatn was kind enough to tell me it was operator error:)
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Re: Question of the Month: Verus Vs Pico
Reply #5 - Feb 4th, 2010 at 4:14pm
 

Crackerclicker,

Quote:
yes, i forgot to mention that everyone on iatn was kind enough to tell me it was operator error:)


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

Quote:
i got myself into trouble on that forum by mentioning my desire for a pico


That's all it takes.   Smiley

Quote:
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.


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.   Shocked 

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.   Wink


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Re: Question of the Month: Verus Vs Pico
Reply #6 - Feb 18th, 2010 at 11:48pm
 
got this in an email today.  thought it might be interesting to some and figured this would be as good a place for it as any. 
http://diagnosticnews.com/featured/automotive-labscope-specifications/
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Re: Question of the Month: Verus Vs Pico
Reply #7 - Feb 19th, 2010 at 8:58am
 
crackerckicker,

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

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.   Sad

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

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Re: Question of the Month: Verus Vs Pico
Reply #8 - Feb 19th, 2010 at 9:35am
 
yeah, while i was reading it i kept trying to compare what was written vs. what i've read about pico.  it seems the article was trying to tell us what the bare minimum should be for auto applications.  i don't want the bare minimum!! 
btw, got the pico yesterday.  only question right now is if i need to install the beta version first or separately from the other version?
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Re: Question of the Month: Verus Vs Pico
Reply #9 - Feb 19th, 2010 at 9:42am
 
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.
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Re: Question of the Month: Verus Vs Pico
Reply #10 - Nov 29th, 2010 at 3:58pm
 
Since this thread has been referenced on another discussion board along with some disinformation, I thought I would bring it forward and add a few points that might address the issues brought up there.....for those interested in the facts regarding Snappy vs Pico.

One is that, the Snappy scopes don't pause when the buffer is full and continuously collect data.  This is true.....But you are losing data constantly as soon as the buffer is full.  The old data falls away into the infinite abyss…gone forever.  If you don’t manually stop the scope in time, then the data you wanted is just gone.  

With PicoScope, you can at least have a good chance that it will not fall into the gap between buffers when the buffer gets full and it starts another.  With Snappy…the gap is infinite.  If the event falls outside of the buffer time it’s gone into oblivion.  There is no other bucket to catch the data.  PicoScope has up to 1000 buckets (buffers) Snappy scopes only one bucket.

Think of the Snappy scope buffer as a bucket with a big hole in it.  When it gets full, the contents leak out as fast as they are refilled.

Think of PicoScope as a series of MUCH LARGER individual buckets that don't leak.  As you fill one, you spill some on the floor as you move to the next bucket and so on.

In either case, what spills on the floor is data that is not saved.

One of the problems with having a single continuously filling and leaking bucket, is the Snappy triggering issues.  Snappy cannot trigger the full capture.  Therefore you cannot capture an intermittent with the scope unattended.  It requires a babysitter.  PicoScope does not.

One of the contributors there showed a PicoScope capture where the glitch was lost between the buffers (buckets).  This was due to less than optimal PicoScope use and strategy.   The capture time of 200ms/div was not well chosen.  When set up this way, the buckets are smaller and so what is lost between them is a larger percentage of what is captured.  Using larger buckets reduces this percentage.

For example, if a 20s/div capture was used, then better than 97% of all data would be in the buckets and less than 3% on the floor (This varies a little with the PC capability to write to the hard drive).  Now it is very unlikely that whatever happens would be outside of the buckets.  Each bucket would have 3 minutes and 20 seconds of data.  

With a PicoScope 4423, the huge buckets are possible.  Not so much with the Snappy scopes because they cannot maintain enough sample rate to do it.

Sure, you could do this with the Snappy at that time base of 2.6 seconds (10ms sweep) but you better be quick on the draw and be able to stop the scope in two seconds, or the glitch would be out of the bucket anyway.

Different strokes for different folks, but everyone needs the facts.



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Re: Question of the Month: Verus Vs Pico
Reply #11 - Dec 13th, 2010 at 6:47am
 
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!!!
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Re: Question of the Month: Verus Vs Pico
Reply #12 - Dec 13th, 2010 at 9:35am
 
Hi Kyle,

Quote:
for me and the "buckets" analogy was great.


I was hoping that would help illustrate.  I should have called the Pico ones barrels though since they can be up to 200x larger   Wink

Quote:
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 assume you mean by 'zoomed out' selecting a longer time base.  (actual zoom controls have no effect on the data captured).  If so, you are correct.  The longer the capture time, the less spills on the floor as a percentage of total time of all buckets.  How far you can go with this depends on the model PicoScope you are using and the type of signals you are acquiring.  You can go a LOT further with this if using a 4000 series scope as opposed to a 3000 series. Or..if the signals you are observing do not require higher sample rates.  

From 2 to 20 second capture times, a Pico 4423 can sample at 1mHz real time per channel with 1 or 4 channels active.  After that, the sample rate will gradually fall off.

The 4000 series scopes can also utilize something called rapid trigger at the faster time bases (1ms/div and faster) which reduces the time between buckets.  For example, you can view a single cylinder event and the engine would come apart before you reached an RPM where you would miss a single event.

Quote:
I just don't get why so many guys out there love to bash on other scopes?


I don't either.  Although I am obviously in the Pico camp, I am pleased when a tech starts using any good scope.  While we only make money when someone purchases a scope from us, we would rather see them get a scope they are comfortable with.  PicoScope isn't for everyone.  We do our best to make sure new PicoScope users are ready for it and it is the best choice for them.  This is one of the many reasons we have happy users world wide.  The last thing we want to do is sell someone a scope that isn't for them and have them be unhappy with it.

I try to keep subjective opinions and preferences out of the discussion and present only the facts.  You can argue opinions and preferences all day long, but facts are different.  The factual information is empowering and enables you to make an informed choice that fits you.  While some call this discussion a train wreck, I think there is an obvious reason why they have not come forward to disagree and add to the discussion in the light of day here.

All scopes have limitations, some more than others.  There are a lot of scope offerings out there that are not really very useful on todays cars.  The Snap-On offering are not in this category.  I have always said that in the native hand held scope category, you cannot do better than a Modis or V-pro.


Quote:
I'm just chomping at the bit to use the shops tool budget money at the end of  the year!!!


That's the desired effect   Wink  

We look forward to having you in 'The Cult'.   Grin
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Re: Question of the Month: Verus Vs Pico
Reply #13 - Jan 26th, 2011 at 10:03am
 
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
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« Last Edit: Jan 26th, 2011 at 1:35pm by Brian Haley »  

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Re: Question of the Month: Verus Vs Pico
Reply #14 - Jan 29th, 2011 at 10:20am
 
Hi Brian,

Great Tip!!

Matt Fanslow showed that to some of us a couple years ago. He also demonstrated that last year at the Vision conference.

Where you in that class? 

Is that where you saw it?

Paul
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