Frequency Response Analyzer with Bode Plots

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yosi
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Re: Frequency Response Analyzer with Bode Plots

Post by yosi »

Dear Aaron, Thanks a lot !

I could managed to fix.
When I installed PicoscopeSDK, I unselected Ps6000x devices.
That seems to be the reason of this problem.

First, I uninstall and re-install v0.7.3b of FRA4. -- nothing changed.
Next, signed in as different user, and try -- same, no change.

As to your suggestion '2)' , I could not figure out what you meant acturally,
because I 've never seen FRA4's splash screen at that time.
I thought you mean picotech's Picoscope application, and questioned why?
I have installed FRA4 into windows 7 environment, and knew FRA4 splash screen.

Then to make things clean, I reinstalled both FRA4 and SDK, that worked.
After mean time, I remember that I might disabled Ps6000a device.

Thanks again.

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer »

Thank you, yosi, for reporting back. Since this:
yosi wrote:
Sat Mar 27, 2021 5:29 am
When I installed PicoscopeSDK, I unselected Ps6000x devices.
seems like a completely reasonable thing to do, I'll see if I can replicate. If I can, I'll work on improving the application so it doesn't crash and offers a better diagnostic.

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer »

yosi wrote:
Sat Mar 27, 2021 5:29 am
Dear Aaron, Thanks a lot !

I could managed to fix.
When I installed PicoscopeSDK, I unselected Ps6000x devices.
That seems to be the reason of this problem.

First, I uninstall and re-install v0.7.3b of FRA4. -- nothing changed.
Next, signed in as different user, and try -- same, no change.

As to your suggestion '2)' , I could not figure out what you meant acturally,
because I 've never seen FRA4's splash screen at that time.
I thought you mean picotech's Picoscope application, and questioned why?
I have installed FRA4 into windows 7 environment, and knew FRA4 splash screen.

Then to make things clean, I reinstalled both FRA4 and SDK, that worked.
After mean time, I remember that I might disabled Ps6000a device.

Thanks again.
Well, I'm happy you got it working :), but I can't really tell what was going on. I tried re-installing the SDK without PS6000a and ps6000 support, but can't get it to crash. Only other thing I can think of that may be relevant is what version of the Picoscope app you had installed. The FRA app is setup to delay load the DLL files in order to implement a preference for the versions from SDK folders first. If it fails to load those, it can load DLLs from the Picoscope app. If there were some kind of incompatibiity there maybe it would cause an issue.

GJA14
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Re: Frequency Response Analyzer with Bode Plots

Post by GJA14 »

I'm looking to do loop gain and phase Bode plots on SMPS with switching frequency 100Khz or less. Are the 2204A and 2205A capable of doing adequate FRA plots for the above scenario or is it necessary to go up to higher models with higher sample rates, memory depth, and resolution and if so what are the minimum scope specifications needed for the above case?

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer »

GJA14 wrote:
Tue Apr 27, 2021 3:43 am
I'm looking to do loop gain and phase Bode plots on SMPS with switching frequency 100Khz or less. Are the 2204A and 2205A capable of doing adequate FRA plots for the above scenario or is it necessary to go up to higher models with higher sample rates, memory depth, and resolution and if so what are the minimum scope specifications needed for the above case?
Hello GJA14! Here's a good thread covering this topic: topic41113.html

Key takeaways:
  1. Due to the small buffer and 8-bit resolution, scopes like the 2204A and 2205A will likely have problems with SMPS FRA
  2. Both larger memories and higher resolution can help, but both may not be required
  3. One key factor is the amount of ripple (noise) you'll be recovering the small stimulus from
So, while I've not tested to confirm (all of) this, here is my opinion:
  1. The PS5000D scopes are probably best for this application due to huge buffer depth, high resolution and bandwidth limiter
  2. The PS4x24A scopes are probably a good choice because of their huge buffer depth and 12-bit resolution
  3. If you could guarantee very low ripple and get away with a relatively large stimulus, an 8-bit scope with large buffer (e.g. PS2208B) may work just fine

GJA14
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Re: Frequency Response Analyzer with Bode Plots

Post by GJA14 »

Thanks hexamer for your points and opinions.

I had previously read the thread you linked along with all of the links within it, however I wasn't sure what range of freq. was being attempted in that one. By the numbers it would seem that for 100Khz and below that the 2000 series should work with the exception of the very small buffer memory depth on the 2204A and 2205A, but after looking through the specifications on the 2000 series: https://www.picotech.com/oscilloscope/2 ... ifications --- I noticed that under the SDK/API section it calls out that the "Buffer Memory in USB Streaming Mode" is "Limited Only by PC". This would seem to make the very small buffer depth on the 2204A and 2205A a none issue if indeed the FRA software through the SDK/API was able to take advantage of that.

Can you confirm whether the FRA uses only the internal buffer memory (block mode) or if it uses or is able to use the USB streaming mode and the PC's memory for the buffer memory?

I know that the latest version of the FRA offers real time plotting so it makes me think that perhaps it is using the USB streaming mode.

hexamer
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Re: Frequency Response Analyzer with Bode Plots

Post by hexamer »

GJA14 wrote:
Thu Apr 29, 2021 6:38 am
Thanks hexamer for your points and opinions.

I had previously read the thread you linked along with all of the links within it, however I wasn't sure what range of freq. was being attempted in that one. By the numbers it would seem that for 100Khz and below that the 2000 series should work with the exception of the very small buffer memory depth on the 2204A and 2205A, but after looking through the specifications on the 2000 series: https://www.picotech.com/oscilloscope/2 ... ifications --- I noticed that under the SDK/API section it calls out that the "Buffer Memory in USB Streaming Mode" is "Limited Only by PC". This would seem to make the very small buffer depth on the 2204A and 2205A a none issue if indeed the FRA software through the SDK/API was able to take advantage of that.

Can you confirm whether the FRA uses only the internal buffer memory (block mode) or if it uses or is able to use the USB streaming mode and the PC's memory for the buffer memory?

I know that the latest version of the FRA offers real time plotting so it makes me think that perhaps it is using the USB streaming mode.
I appreciate you doing the research and thinking out of the box.

This seems like a nice idea, but unfortunately (1) I can confirm the current version only supports block capture/transfer and (2) even if it did support USB streaming mode, there would be limitations:

The 2204A and 2205A have a sampling rate limit of 1 MS/s in USB streaming mode. Why is that important? It means that signals above 500 kHz will be aliased into the measurement. In your SMPS example there are higher order harmonics of the 100 kHz switching frequency above 500kHz, and some switching transients well above that. Might you get lucky that these don't get aliased into the DFT/filter? Maybe, but hard to tell. For SMPS measurements it's best to set the sampling rate to at least 2x the scopes bandwidth limiter. For the PS5000D scopes, with a 20 MHz bandwidth limiter, the default "Noise reject" mode sampling frequency is 62.5 MS/s

As for others scopes that support faster USB streaming, well ... they also have much larger buffers. The 2206A with its 32 MS buffer may be workable in block mode. The narrowest bandwidth it could achieve in the DFT is about 30 Hz, which seems pretty decent. That may be workable for SMPS, but again, I have not tested it, and you need to consider takeaway 3 above.

I certainly don't want to discourage experimentation, but I am doubtful :(

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