Products > Test Equipment

Bode Plot Torture Test

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Someone:

--- Quote from: mawyatt on November 08, 2022, 02:14:01 pm ---
--- Quote from: Someone on November 07, 2022, 10:49:45 pm ---The built in bode/FRA/sweep functions are effectively "toys" for the educational market. As black boxes of mystery its not possible to practically compare the different implementations without a huge amount of reverse engineering (over to you lot if you really want to do that rather than just the apples to grapes to bricks comparisons that usually end up). When you know what the noise/aggressor/non-ideal components that need to be avoided are then you select/design-in a suitable capture and processing method to minimise those effects, but that needs the flexibility of scripting/programming.

100dB of displayed dynamic range is easy when exploiting the front end attenuation and a benign DUT. But 100dB of dynamic range below the noise? that need some effort but is still possible. That level of interference/noise in the plot from mawyatt's first post would be "very poor"/low-effort from my experience.

--- End quote ---

Won't discount the Educational value, but we've found this feature quite useful in our home lab. Sure, would prefer a "Proper" lower frequency Network Analyzer, which would have normally been available in our labs before retiring (can't recall the model tho), but now with a limited out-of-pocket budget and less funded work to support such equipment we'll have to do with what's available.

Like someone said the "The Best Equipment is what you have!!".

100dB below the noise environment is quite difficult indeed, altho the Miles Signal Processor (MSP) and the GPS "Deep Fade Algorithm" did such many decades ago.

Anyway, for now quite happy with the Bode capability of the SDS2000X+, altho wish as mentioned the processing speed could be altered by means of user selectable features, and the "Black Box" was opened to let us "see" what's inside ;)
--- End quote ---
Without controls to adjust the trade-offs it is great if it does what you want, and useless if not. It is a toy as you have so few controls over it, people dont decide if their scope is good or not from what is shown when you press the "autoscale" button. The bode plot is like that, few controls, and it only puts up a pretty picture if the system is well behaved/normal. You claim how it works great on your torture test, but that can easily be chosen to show off the particular implementation (ignoring that implementations downsides, slow speed as in the other thread).

Why push people to consider if the built in "toy" is good or bad, when they can use the scope with more flexibility and power by automation? All the scopes can do that, quickly and easily. Other people complain the sweep speed of the Siglent is too slow, which is required for your demonstration of suppressing noise. I say the built in bode/FRA/sweeps are not worth wasting time on, particularly when your demands get more specific.

What would be interesting to find out is how much filtering and what filtering types are being employed by the different implementations, so that people can recreate them and consider what is best for their application. But so far this thread is more promotion than testing, the configurations and signals arent reproducible:
how much bandwidth did your noise source have for its 1Vrms level?
what was its distribution?
how long did the scope take to complete the whole sweep?

change up any of those parameters and the result is radically different (so much so its impossible to reproduce anything comparable) then nctnico goes add more of the same pretty pictures with no context/information:
what were the relative amplitudes and noise signals? they dont even look the same as the first post.

pdenisowski:

--- Quote from: nctnico on November 08, 2022, 02:37:47 pm ---I wouldn't be so quick to label features as 'toys' or 'educational'. For example: having digital inputs on DSOs (=MSO) has helped to kill the market for logic analysers even though an MSO is a far cry from a real logic analyser
--- End quote ---

That's putting it mildly :)  The T&M instrument company I previously worked for sold lots of very large and very expensive logic analyzers back in the day, and the stand-along logic analyzer market seems to have almost completely disappeared. 

nctnico:
@Someone: feel free to pitch ideas on what you think would be a valid test.

mawyatt:

--- Quote from: Someone on November 09, 2022, 03:16:57 am ---The built in bode/FRA/sweep functions are effectively "toys" for the educational market. As black boxes of mystery its not possible to practically compare the different implementations without a huge amount of reverse engineering (over to you lot if you really want to do that rather than just the apples to grapes to bricks comparisons that usually end up). When you know what the noise/aggressor/non-ideal components that need to be avoided are then you select/design-in a suitable capture and processing method to minimise those effects, but that needs the flexibility of scripting/programming.

100dB of displayed dynamic range is easy when exploiting the front end attenuation and a benign DUT. But 100dB of dynamic range below the noise? that need some effort but is still possible. That level of interference/noise in the plot from mawyatt's first post would be "very poor"/low-effort from my experience.


Without controls to adjust the trade-offs it is great if it does what you want, and useless if not. It is a toy as you have so few controls over it, people dont decide if their scope is good or not from what is shown when you press the "autoscale" button. The bode plot is like that, few controls, and it only puts up a pretty picture if the system is well behaved/normal. You claim how it works great on your torture test, but that can easily be chosen to show off the particular implementation (ignoring that implementations downsides, slow speed as in the other thread).

Why push people to consider if the built in "toy" is good or bad, when they can use the scope with more flexibility and power by automation? All the scopes can do that, quickly and easily. Other people complain the sweep speed of the Siglent is too slow, which is required for your demonstration of suppressing noise. I say the built in bode/FRA/sweeps are not worth wasting time on, particularly when your demands get more specific.


--- End quote ---

You "think" these are "toys" within your capability and of limited value, however in the capable hands of others they can be quite useful "toys". As shown on other threads plotting the Closed Loop Characteristics of a Feedback System, an Oscillator, a SMPS, or the Injection Locking Characteristics of an Oscillator, might be quite useful to those with an understanding/need of such! However, these might be "pretty plots" to someone else which is fine, but doesn't deter the fundamental inherent value to others!!

Why would someone want to program code and use a computer to create and display a Bode Plot which is "Built-in" the stand alone DSO, and then have to do this over and over for different measurements, setups and DUT? Sure the DSO Built-In Bode Function is limited in user tailoring, but certainly simpler than the coding/computer route even with the slow performance!! Often one can adjust setup/DUT to work around the Bode limitations, which we did with the "pretty plots" of the Injection Locking Peltz Oscillator. BTW we've never seen this type of Bode use for creating Injection Locking plots, would have been useful in our distant past work!!

https://www.eevblog.com/forum/projects/injection-locked-peltz-oscillator-with-bode-analysis/

rf-loop has cleverly shown how to "extract" the effective BW utilized within the "Black Box" Bode function, we've confirmed this result.

So maybe Siglent is "listening" and will open the "Black Box" and/or allow more user parameter adjustments!!

Anyway, YMMV as to the Bode Plot Functionality, and we'll keep using our "Toy"  ;)

Best,

mawyatt:

--- Quote from: pdenisowski on November 09, 2022, 11:07:05 am ---
--- Quote from: nctnico on November 08, 2022, 02:37:47 pm ---I wouldn't be so quick to label features as 'toys' or 'educational'. For example: having digital inputs on DSOs (=MSO) has helped to kill the market for logic analysers even though an MSO is a far cry from a real logic analyser
--- End quote ---

That's putting it mildly :)  The T&M instrument company I previously worked for sold lots of very large and very expensive logic analyzers back in the day, and the stand-along logic analyzer market seems to have almost completely disappeared.

--- End quote ---

We also found this built-in MSO LA feature quite useful recently when debugging a 128 Independent Channel +-100V 16 bit AWG for use with a new Phased Array Technology. We needed to "See" the relative timing between digital and analog channels and the built-in LA proved highly useful.

Best,

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