Pico 2200-Series USB streaming constraints

Post any questions you may have about our current range of oscilloscopes
Mark_O
Advanced
Posts: 0
Joined: Fri Oct 03, 2014 5:58 am

Pico 2200-Series USB streaming constraints

Post by Mark_O » Sat Jun 30, 2018 11:57 pm

The official Specs for the 2204A and 2205A list this as only 1 MS/sec.

Moving to the 2405A (adding 2 extra channels to the 2205A) bumps it to 5 MS/sec. Hmm. Once you hit the 2206,2207,2208B and 2406,2407,2408B, this jumps to the expected 31 MB/sec that a USB2 bus would impose.

I'm curious what it is that constrains the lower models to 1 and 5 MS/sec, respectively. Thanks.

Martyn
Site Admin
Site Admin
Posts: 3532
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Pico 2200-Series USB streaming constraints

Post by Martyn » Mon Jul 02, 2018 5:31 am

The limit is due to the lower on board memory of these particular devices. This memory acts as a FIFO buffer providing a backup for when the USB bus is not accessible by our drivers to transfer the data. These restrictions are present so that we do not end up with data loss when streaming.
Martyn
Technical Support Manager

AlexMpico
Newbie
Posts: 0
Joined: Sun Jul 01, 2018 7:20 am

Re: Pico 2200-Series USB streaming constraints

Post by AlexMpico » Fri Aug 03, 2018 11:10 am

Is this IMS/s limit only relevant to Streaming Mode for the 2205A?

I still am struggling to understand how this Scope is capable of 200MS/s but nothing like that rate can be achieved in the ms/div range?? Best achieved is in the KS/s range??

Just my ignorance, I'm sure ... but trying to get the most out of my scope.

Martyn
Site Admin
Site Admin
Posts: 3532
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Pico 2200-Series USB streaming constraints

Post by Martyn » Tue Aug 07, 2018 10:47 am

1MS/s is related to streaming where data is sent across the USB bus.

200MS/s is the fastest rate the A/D in the device can sample at, but this can only be supported when saving to on board memory. When using PicoScope 6 you set the time across the display (timebase) as the fixed parameter, you can then request the number of samples that you would like to collect, and finally the software will then calculate exactly what can be achieved within the limits of the devices memory.

Memory / SamplingRate = CollectionTime

for a 2205a this would be

(16kS) / (200MS/s) = 80usecs

It is not possible to run at the fast speeds for collection times in the msecs, there is not enough memory
Martyn
Technical Support Manager

AlexMpico
Newbie
Posts: 0
Joined: Sun Jul 01, 2018 7:20 am

Re: Pico 2200-Series USB streaming constraints

Post by AlexMpico » Sat Aug 11, 2018 1:48 am

Martyn
I'm starting to understand the relationship between the buffer and the limits on sample rate.
Sorry I'm so slow, and appreciate your patience.
I take it the scope dials down the sample rate to spread samples across the timebase and number of screens set.
Say, for example, the time base (obviously in 'us' range) allows a given sample rate across 16 selected screens.
It seems to me that by halving the number of screens in the buffer capture to 8, it should allow the scope to (theoretically) double its sample rate?? (assuming the doubling is within it's max sample capacity, and within the pixel capacity of the screen monitor).
Does it work that way??

Martyn
Site Admin
Site Admin
Posts: 3532
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Pico 2200-Series USB streaming constraints

Post by Martyn » Wed Aug 15, 2018 1:42 pm

The primary factor is the time for a single screen, the second factor is the number of samples you would like on that screen, and it is these two factors that will define the sample rate that is chosen. How many buffers you will be able to collect will then depend upon how much memory the device has, so even if you have 32 set in preferences, you may only be able to record 5 because that is the number that drops out of the maths within the limits of the devices memory.

The slight curve ball with the 2205a is that when the sample rate that falls out of the maths is less than 1MS/s the software will decide to ignore the on board memory and just stream the data directly to the PC, it is more efficient to do this. So you can actually end up with many more buffers than you would expect to get with the limiting factor being the 100MSamples of the software not the 16kSample device memory.

It is confusing, so there are no problems with taking time to understand this.
Martyn
Technical Support Manager

AlexMpico
Newbie
Posts: 0
Joined: Sun Jul 01, 2018 7:20 am

Re: Pico 2200-Series USB streaming constraints

Post by AlexMpico » Sat Aug 25, 2018 4:07 am

So Martyn
Just following on from your very instructive comments.
As I understand it then, the 2205a in streaming mode is limited to 1MS/s or less and can capture 100MS max.
I'm tyring to understand better how the scope spits out the display within its constraints and how I can take it to the limits of its possibilites
(Poor little 2205a is taking a beating; probably doesn't deserve this!)
I've added some .psdata files, which might help you see and relay what I'm not understanding.

You will see in one file that I have a streaming capture at 1ms/div (10ms/screen) that is delivering:,
sample interval @ 1.28us. Rate @ 781.3 kS/s over 32 screens.
This means it has pumped out 250,000 samples across 32 screens.
What would/could I do to drive this closer or up to 1MS/s? Limit the number of screens?

You will see another streaming capture at 200ms/div (2s/screen), delivering:
Sample interval @ 3us. Rate @ 333.3kS/s over 1 screen.
It has pumped out 666,667 samples across the screen!

Again, why could I not, in this circumstance, drive the scope to stream a higher sample rate (up to 1MS/s)?
(note that I had the screen buffer here set to 1 screen, rather than using the a single shot mode. Forgot to try this but perhaps this would make a difference?)

Hope I'm not over-pressing my welcome, but your advice and instruction is proving very helpful.
cheers
Alex
Attachments
180708 Idle Hyundai Crank Prim Ig 200ms.psdata
(344.9 KiB) Downloaded 89 times
180708 Idle Hyundai Prim Ig 1ms 1.psdata
(51.67 KiB) Downloaded 75 times

Martyn
Site Admin
Site Admin
Posts: 3532
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Pico 2200-Series USB streaming constraints

Post by Martyn » Thu Aug 30, 2018 9:04 am

For the 200ms/div file where you have 700kS in the top tool bar, change this to 2MS. 2MSamples across a 2 second screen time, giving 1MS/s sample interval.

For the 1ms/div file set this to 20kS, which will give 1.56MS/s as the sampling interval.
Martyn
Technical Support Manager

terrypin
Newbie
Posts: 0
Joined: Mon Jun 16, 2014 4:23 pm

Re: Pico 2200-Series USB streaming constraints

Post by terrypin » Sat Sep 22, 2018 5:27 pm

Just found this thread and finding it very instructive. Like Alex, I too am trying to understand how to get the best out of my 2205A. I find the interaction of the various parameters rather difficult to grasp. And as described in my recent posts I have an additional obstacle in the slow speed of my USB ports.

Would it be possible to republish those PSDATA files Alex provided please?

Another difference is that I'm working with pulses from a device in my house over the long wires to my shed. So I want to use 20s per division or more, yet still be able to examine detail. I'm typically setting up the program, walking to the house, using the device (an IR remote control gadget) to create a pulse, then going back to the shed to examine it.

I haven't yet decided to undertake the replacement of my shed XP PC by a faster XP PC from my office (itself now replaced by a high end Win 10 PC). A key factor will be to properly understand the limitations that are due to the 2205A itself rather than my USB ports.

Terry, East Grinstead, UK

terrypin
Newbie
Posts: 0
Joined: Mon Jun 16, 2014 4:23 pm

Re: Pico 2200-Series USB streaming constraints

Post by terrypin » Tue Oct 02, 2018 8:12 am

"Would it be possible to republish those PSDATA files Alex provided please?"

??

Terry, East Grinstead, UK

Martyn
Site Admin
Site Admin
Posts: 3532
Joined: Fri Jun 10, 2011 8:15 am
Location: St. Neots

Re: Pico 2200-Series USB streaming constraints

Post by Martyn » Tue Oct 02, 2018 10:42 am

Not sure what you mean by republish, you can access them from the links.

If you mean use them elsewhere then you would need to contact AlexMpico regarding this.
Martyn
Technical Support Manager

terrypin
Newbie
Posts: 0
Joined: Mon Jun 16, 2014 4:23 pm

Re: Pico 2200-Series USB streaming constraints

Post by terrypin » Tue Oct 02, 2018 9:49 pm

Thanks Martyn. Those links were not displayed when I raised my request.

They are now, but present a message that a new version of the software is necessary for me to access them, as shown in attached.
(I'm still awaiting an answer to my question as to whether the 'Insert image ' tool is broken? IOW, is the Attachments method the only way to include an image in a post?)

Terry, East Grinstead, UK
Attachments
NewVersionNeeded.jpg

bennog
Advanced User
Advanced User
Posts: 42
Joined: Mon Nov 26, 2012 9:16 am
Location: Netherlands

Re: Pico 2200-Series USB streaming constraints

Post by bennog » Wed Oct 03, 2018 5:35 am

You can download the latest version of picoscope from https://www.picotech.com/downloads

Benno

terrypin
Newbie
Posts: 0
Joined: Mon Jun 16, 2014 4:23 pm

Re: Pico 2200-Series USB streaming constraints

Post by terrypin » Wed Oct 03, 2018 7:44 am

Thanks Benno, but I’m told by Pico Support that the version I am using is the last one supporting XP.

Terry, East Grinstead, UK

bennog
Advanced User
Advanced User
Posts: 42
Joined: Mon Nov 26, 2012 9:16 am
Location: Netherlands

Re: Pico 2200-Series USB streaming constraints

Post by bennog » Wed Oct 03, 2018 8:55 am

A ok then you have a problem.
As far as I know psdata files created with newer version of the software are not readable with older versions.
And there is also no backward conversion tool.

You can use the newest software on your in home windows 10 system (without scope)
Then you can view the psdata files

Benno

Post Reply