Sampling Rate Mystery

Ask any questions about using PicoScope Automotive software here.

Sampling Rate Mystery

Postby AlexMpico » Sun Jul 08, 2018 11:00 am

Hi all, help me please to understand how to get the best/highest sampling rate on my Pico. My scope tech sheet says it has a Bandwidth of 25Mhz and a Sampling Rate of 200MS/s.

However, when I'm tracing a Sec ig pulse from the primary side (with 1:20 attention dialled in) the best real rate I can get is as follows:
The Pico indicates it is tracing;
• 1 sample per 1.28us, at
• 781.3kS/s, delivering
• 7813 samples across the 10ms screen
I can manually request a higher rate, but it hits the wall and won't go higher.
What is limiting the actual rate?
Can I achieve a higher rate for a cleaner trace??

Really appreciate advise for the you more knowledgable folk. I'm a relative newbie here.
.psdata file attache as a eg.
thanks
alex
Attachments
180708 Idle Hyundai Prim Ig 1ms.psdata
(51.67 KiB) Downloaded 40 times
AlexMpico
Newbie
 
Posts: 5
Joined: Sun Jul 08, 2018 10:49 am

Re: Sampling Rate Mystery

Postby Martyn » Mon Jul 09, 2018 3:22 pm

You are using a 2205a, not designed for automotive use, which only has a 16kS memory, so that will be limiting factor. You will be able to get a bit more by setting the trigger to single at the bottom to capture just one event.
Martyn
Technical Support Manager
Martyn
Pico Staff Member
Pico Staff Member
 
Posts: 254
Joined: Thu Aug 11, 2011 9:43 am
Location: Cambridgeshire

Re: Sampling Rate Mystery

Postby AlexMpico » Wed Jul 11, 2018 11:57 pm

Thank you Martyn for takking a moment to reply
Yes the 2205 is my entry scope and I have my sights on the 4000 series when I can afford it.
I have to congratulate you guys cos I find the 2205 excellent for almost all functions, and I use 20:1 attenuators for extra protection and added V range
I don't find the memory/buffer an impediment at the moment, though it's always nice to have more.
What I am not clear on is why the memory length would limit the available/deliverable sample rate?
Can I increase available sample rate by dialling down number of buffer screens?
I assume your single shot suggestion would deliver all available sample to one screen, instead of across all buffer screens?? Or is the available sample rate delivered across 1S and just proportionately distributed to the screen according to time base??
Really appreciate your help as I learn and move towards the better scope.
thanks
Alex
AlexMpico
Newbie
 
Posts: 5
Joined: Sun Jul 08, 2018 10:49 am

Re: Sampling Rate Mystery

Postby Martyn » Thu Jul 12, 2018 8:05 am

The 2205 operates in a slightly different way to the deep memory scopes. With Deep Memory scopes the 32 of 32 (adjustable in preferences to higher values up to 10000) waveform buffer reflects actual segments in the on board memory and the raw data is stored on the device for each buffer. A subset of this data is downloaded to display on the screen, but the raw data remains until you stop the scope and save the data to file.

With the 2205 it is actually quicker to always download the data to the PC rather than storing on the device, so the on board memory is segmented into two and each time a buffer is collected it is downloaded to the PC. If you require the fastest sampling rates you have to select faster timebases, 5usec/div or quicker.

In reality you are getting much better performance out of the device than you would if it operated in exactly the same way as the higher memory scopes.
Martyn
Technical Support Manager
Martyn
Pico Staff Member
Pico Staff Member
 
Posts: 254
Joined: Thu Aug 11, 2011 9:43 am
Location: Cambridgeshire

Re: Sampling Rate Mystery

Postby AlexMpico » Thu Jul 12, 2018 12:00 pm

Fantastic Martyn. I appreciate the explanation and sharing the knowledge.
I'm really glad that a comp like Pico actually provides this option/level of quality scope that allows people like me to get into the craft of 'scoping with an amazing tool at an affordable price.
There's a lot of grunt in the 2205 ... only thing i would add is 12 bit resolution.

When you say it's better to "download to the PC" -- do you mean save as .psdata file?
If not can you elaborate if there's some way to integrate scope and pc memory?

thanks heaps.
Alex
AlexMpico
Newbie
 
Posts: 5
Joined: Sun Jul 08, 2018 10:49 am

Re: Sampling Rate Mystery

Postby Martyn » Thu Jul 12, 2018 1:43 pm

"download to the PC" means that it is more efficient for the software and driver to get the raw data from the scope over the USB bus, and process it on the PC rather than leaving it on the scope. The data will remain in the applications memory for use in viewing, or applying math channels, and will only be saved to a psdata file if you ask it to.
Martyn
Technical Support Manager
Martyn
Pico Staff Member
Pico Staff Member
 
Posts: 254
Joined: Thu Aug 11, 2011 9:43 am
Location: Cambridgeshire

Re: Sampling Rate Mystery

Postby AlexMpico » Fri Jul 13, 2018 11:15 am

I see, ok, so I thought this is happening anyway by default because the scope is hooked up Via the USB cable. No?
Is there a setting that governs this?
Alex
AlexMpico
Newbie
 
Posts: 5
Joined: Sun Jul 08, 2018 10:49 am

Re: Sampling Rate Mystery

Postby Martyn » Mon Jul 16, 2018 9:02 am

The deep memory scopes will transfer only the data that is needed for display purposes. As an example if you were collecting 1M Samples in each display buffer there is no point in transferring all of this to the PC and then drawing the trace on a screen that at most can support up to 4k pixels, you would need to selectively downsample to display anyway, performing this on the device is more efficient, and leads to a greater refresh rate between buffers.

With your 2205a, as it is a low memory device, and it is more efficient to download all the data for each buffer.

I wouldn't worry about the numbers too much, there are no settings you can change anyway, and you are getting the best possible performance out of your 2205a :D
Martyn
Technical Support Manager
Martyn
Pico Staff Member
Pico Staff Member
 
Posts: 254
Joined: Thu Aug 11, 2011 9:43 am
Location: Cambridgeshire

Re: Sampling Rate Mystery

Postby AlexMpico » Mon Jul 16, 2018 1:44 pm

Hey Martyn, thanks so much for taking the time to explain. In any case the 2205a is a great learning tool. Looking forward to eventually scaling up to the 4000 series.:-)
AlexMpico
Newbie
 
Posts: 5
Joined: Sun Jul 08, 2018 10:49 am


Return to PicoScope 6 Automotive software

Who is online

Users browsing this forum: No registered users and 2 guests