Products > Test Equipment

About Picos' Sampling Rate

<< < (3/7) > >>

bdunham7:

--- Quote from: balnazzar on October 29, 2022, 11:03:51 am ---I'd like someone knowleadgeable about Picos to explain this.. I mean, what good will the 1 GSa/s do, if the signal is processed and displayed by the software, which has access to just 15-20 MSa/s??

Of course it can't function in such a way, so I basically don't understand how a USB scope actually work.

--- End quote ---

You may not understand how a DSO in general actually works, at least in practice.  The scope can acquire and store samples at its advertised rate up to the stated memory depth and that typically takes a very short time, memory depth divided by sample rate.  So for 10Mpoints and 1GSa/s, your acquisition time is 10ms.  After the acquisition, the scope gets to work processing and displaying the samples and depending on the mode that it is in, it typically won't do another acquisition until all that is done.  The time that it is busy like this is called 'blind time', and this is often very significant.  Lets say it take the scope 90ms to do all the processing, giving you a blind time of 90%.  You can see that the total throughput of samples is actually only 100MSa/s in the long run. 

So in the case of the PicoScope, it normally works the same way.  It takes a capture up to its internal memory depth then gets to work processing it.  In this case, the sample memory is transmitted over the USB cable to the PC for processing and the time it takes to do that is just added to the blind time.  Of course the faster processing in the PC and the ability of the PicoScope to retrigger right after the data has been sent may offset that  somewhat.

The continuous sample rate is much, much lower and this also has an analogue with regular DSOs.  They typically have a continuous sampling (roll mode) ability that will display a moving chart, but at a much lower maximum sample rate than the advertised maximum.  Some may also have a digitizing or data recording function that allows you to continuously export, but again always at a much lower sample rate.

The key here is real-time memory access.   In order for a scope to do 1GSa/s, it has to write at least 1Gb/s to memory in real time.  That just isn't going to happen over a USB cable or even internally in a PC without a hardware buffer.

jasonRF:

--- Quote from: balnazzar on October 29, 2022, 03:01:34 pm ---
--- Quote from: jasonRF on October 29, 2022, 02:51:36 pm ---If you are holding out for 4 channels then you will probably need to wait a long time, or be willing to spend a lot of money.  Are you keeping all of these devices you are buying, or returning some?   Because sds1104x-e + AD2 + 2205a = a hefty sum of money.   

By the way, I do not think Picoscopes support SCPI. 

I will post my project when it is in a little better shape.  I need to redo the hardware design and clean up the script.   It will probably take 4+ weeks, since my job is taking up most of my time at the moment.  I am making it truly bare-bones, for the purpose of sharing something simple that actually works.  The script uses standard Fourier analysis to extract just the frequency of interest, and also adjusts the vertical setting for each frequency to maximize dynamic range. Others that have more microcontroller and python experience can add bells and whistles (lcd front-panel on generator, GUI for software, etc).   This is my first project using either, and I am not actually doing anything with the arduino beyond using a few commands from a library I downloaded.    I may eventually pick up a cheap SCPI-compatible scope (maybe vds1022i) to see if I can make that work as well.  Just for fun.   :)

Jason

--- End quote ---

I'm returning both the Siggy and the AD2 (both of them = 1000 bucks). My budget is limited to that sum.
I'm returning the Siglent because I like the scope very much, but I just cannot concentrate with its acoustical noise. And I'm returning the AD2 because I like the software but the instrument itself is quite limited. Great for some specific stuff, not so for other tasks. So that leaves me with the VDS1022i that is surprisingly decent for the price (and has much more sensitivity than the ad2) but cannot bode plot.. Once I saw the post about bode plotting with an external generator, I thought to buy the 2205A for 200$ so to have a pro tempore cheap bode plot device until I find a decent scope for 1 grand maximum.  In your opinion, will its amount of memory be sufficient for doing FRA with an external generator?

Wasn't aware that Picos don't support SCPI  :( I'll do some experiments with the 1022i and let you know, though.

Thanks!

--- End quote ---

One thing that would be interesting for you to do is measure the channel-to-channel crosstalk on the vds1022i.  The specs are pretty poor at 40:1, compared to 200:1 for the Pico.  If it really is just 40:1 then that will limit the ability of the owon to do Bode plotting.  In practice I get much better than 200:1 on the 2204a although I have never measured it directly.  The owon might similarly exceed the spec. 

If the vds1022 has sufficiently low crosstalk, then if I were you I would try to get Bode plotting working on the vds1022i before buying a 2205a.   Especially since the scope hardware on the two models has similar capability in some ways.  The vds1022i has a little better sensitivity and the 2205a has a little more memory.   Of course the software is the big difference.   

I can post a draft of my script and the hardware by next weekend if you want to see if you can modify it to work with the vds1022i.   A quick and dirty approach might be to use the nice python API that florentbr wrote for the vds1022i. 

Jason

Anthocyanina:

--- Quote from: balnazzar on October 29, 2022, 03:01:34 pm ---
I'm returning both the Siggy and the AD2 (both of them = 1000 bucks)... And I'm returning the AD2 because I like the software but the instrument itself is quite limited. Great for some specific stuff, not so for other tasks...

--- End quote ---

I'm curious about this, what have you found you aren't able to do with the AD2? not from testing the limits of it but from daily use? I have a rigol 1104z, a keysight 1102g, an owon 1022i, and the AD2, and unless I need more bandwidth or more channels, I go to the AD2 for pretty much everything else

balnazzar:

--- Quote from: Anthocyanina on October 29, 2022, 05:16:54 pm ---
--- Quote from: balnazzar on October 29, 2022, 03:01:34 pm ---
I'm returning both the Siggy and the AD2 (both of them = 1000 bucks)... And I'm returning the AD2 because I like the software but the instrument itself is quite limited. Great for some specific stuff, not so for other tasks...

--- End quote ---

I'm curious about this, what have you found you aren't able to do with the AD2? not from testing the limits of it but from daily use? I have a rigol 1104z, a keysight 1102g, an owon 1022i, and the AD2, and unless I need more bandwidth or more channels, I go to the AD2 for pretty much everything else

--- End quote ---

See this: https://www.eevblog.com/forum/testgear/is-a-rigol-mso5000-overkill-for-a-hobbyist/300/

from post #311 onwards. Maybe a bit before that in order to get context.

Basically I'm unhappy with its two levels of sensitivity and doing everything else as digital zoom.

Im interested in your opinions & experiences about the use of AD2 with (relatively) low level signals.

balnazzar:

--- Quote from: jasonRF on October 29, 2022, 03:59:21 pm ---
--- Quote from: balnazzar on October 29, 2022, 03:01:34 pm ---
--- Quote from: jasonRF on October 29, 2022, 02:51:36 pm ---If you are holding out for 4 channels then you will probably need to wait a long time, or be willing to spend a lot of money.  Are you keeping all of these devices you are buying, or returning some?   Because sds1104x-e + AD2 + 2205a = a hefty sum of money.   

By the way, I do not think Picoscopes support SCPI. 

I will post my project when it is in a little better shape.  I need to redo the hardware design and clean up the script.   It will probably take 4+ weeks, since my job is taking up most of my time at the moment.  I am making it truly bare-bones, for the purpose of sharing something simple that actually works.  The script uses standard Fourier analysis to extract just the frequency of interest, and also adjusts the vertical setting for each frequency to maximize dynamic range. Others that have more microcontroller and python experience can add bells and whistles (lcd front-panel on generator, GUI for software, etc).   This is my first project using either, and I am not actually doing anything with the arduino beyond using a few commands from a library I downloaded.    I may eventually pick up a cheap SCPI-compatible scope (maybe vds1022i) to see if I can make that work as well.  Just for fun.   :)

Jason

--- End quote ---

I'm returning both the Siggy and the AD2 (both of them = 1000 bucks). My budget is limited to that sum.
I'm returning the Siglent because I like the scope very much, but I just cannot concentrate with its acoustical noise. And I'm returning the AD2 because I like the software but the instrument itself is quite limited. Great for some specific stuff, not so for other tasks. So that leaves me with the VDS1022i that is surprisingly decent for the price (and has much more sensitivity than the ad2) but cannot bode plot.. Once I saw the post about bode plotting with an external generator, I thought to buy the 2205A for 200$ so to have a pro tempore cheap bode plot device until I find a decent scope for 1 grand maximum.  In your opinion, will its amount of memory be sufficient for doing FRA with an external generator?

Wasn't aware that Picos don't support SCPI  :( I'll do some experiments with the 1022i and let you know, though.

Thanks!

--- End quote ---

One thing that would be interesting for you to do is measure the channel-to-channel crosstalk on the vds1022i.  The specs are pretty poor at 40:1, compared to 200:1 for the Pico.  If it really is just 40:1 then that will limit the ability of the owon to do Bode plotting.  In practice I get much better than 200:1 on the 2204a although I have never measured it directly.  The owon might similarly exceed the spec. 

If the vds1022 has sufficiently low crosstalk, then if I were you I would try to get Bode plotting working on the vds1022i before buying a 2205a.   Especially since the scope hardware on the two models has similar capability in some ways.  The vds1022i has a little better sensitivity and the 2205a has a little more memory.   Of course the software is the big difference.   

I can post a draft of my script and the hardware by next weekend if you want to see if you can modify it to work with the vds1022i.   A quick and dirty approach might be to use the nice python API that florentbr wrote for the vds1022i. 

Jason

--- End quote ---

yes, if you can post a draft, it would be great. Even if it's still rough, just to get the idea! Thanks.

Also, where can I find this florentbr's repository?

As a starting point (not specifically for FRA, but in general for Python/SCPI with Owon hardware), I thought about this: https://github.com/CircuitAnalysis/OWON

Made by this guy: for the 6000 series.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod