Rigol DHO914S Bode plot

[moffy]

Personally, I'm not too worried about the issue yet as the basics are very good, noise floor, sampling seems good, display is excellent. I think and hope the other issues can be resolved by firmware updates.

[moffy]

The Bode Plot function appears broken. When I tried a simple low pass RC with 100Hz to 10kHz at 50 pts/decade, 1V amplitude,  it worked with the ripple TimFox mentions. When I increased the sample points to 100 pts/decade it changed CH2 resolution to 20mV/div and the top waveform display showed CH2 clipped and it hung until I turned off the Bode Plot window. I think at present a script and PC control might be a more effective way of Bode Plotting until a fix is provided. The on screen display for the Bode Plot function is awfull.

[TurboTom]

Moffy - you are 100% correct. But considering that the whole point of having a DHO900S is more or less the advertized Bode Plot function, what sense does it make to purchase this scope while you've still got to do the "heavy lifting" in a PC. Moreover, my findings with the instability of the inegrated AWG (bugs thread) won't make me feel any better regarding a PC-operated DHO900S. In this case, "any old scope" with phase difference and amplitude measurement and a digital AWG will do the trick. Or, as I mentioned somewhere before, one of these "analog workbench" gadgets will do a pretty good job at Bode Plotting / Network Analysis as well.

[moffy]

Thanks for the heads up TurboTom about the AWG I will check out your posts. In spite of the issues I am still reasonably happy with the 's' version as long as I can have sine/square/triangle.

[Cees]

The Bode Plot function appears broken. When I tried a simple low pass RC with 100Hz to 10kHz at 50 pts/decade, 1V amplitude,  it worked with the ripple TimFox mentions. When I increased the sample points to 100 pts/decade it changed CH2 resolution to 20mV/div and the top waveform display showed CH2 clipped and it hung until I turned off the Bode Plot window. I think at present a script and PC control might be a more effective way of Bode Plotting until a fix is provided. The on screen display for the Bode Plot function is awfull.

There is a solution that I do use now too but is it actually an error caused in the automatic gain setting. Before starting the measurement you can still manually set the gain of each channel. I then set the sensivity for each channel to 10 volts per devision.  When the plot is started the algorithm will have to amplify the gain first. The result is that the plot continues. If the gain is too sensitive at the start then the signal will clip in advance and the plot will not continue to the next frequency. The software should attenuate the gain until the signal falls below the clipping point. So based on the digital value coming out of the ADC you could decide to adjust the value downward so that the waveform fits in the window.

[Cees]

Herewith a comparison of two measurement signals, the AWG of the 924S with a signal from a professional 24 bit audio analyzer. I suspect that the 14 bit AWG is fundamentally much better but that the AWG picks up a lot of interference in the device itself. The red curve is the 24 bit analyzer and green concerns the 924S.  What is also noticeable is the huge jitter the 924S gives. In itself this is not such a problem for the Bode plot as long as the input channels use sharp bandpass filters.

[moffy]

The Bode Plot function appears broken. When I tried a simple low pass RC with 100Hz to 10kHz at 50 pts/decade, 1V amplitude,  it worked with the ripple TimFox mentions. When I increased the sample points to 100 pts/decade it changed CH2 resolution to 20mV/div and the top waveform display showed CH2 clipped and it hung until I turned off the Bode Plot window. I think at present a script and PC control might be a more effective way of Bode Plotting until a fix is provided. The on screen display for the Bode Plot function is awfull.

There is a solution that I do use now too but is it actually an error caused in the automatic gain setting. Before starting the measurement you can still manually set the gain of each channel. I then set the sensivity for each channel to 10 volts per devision.  When the plot is started the algorithm will have to amplify the gain first. The result is that the plot continues. If the gain is too sensitive at the start then the signal will clip in advance and the plot will not continue to the next frequency. The software should attenuate the gain until the signal falls below the clipping point. So based on the digital value coming out of the ADC you could decide to adjust the value downward so that the waveform fits in the window.

I tried it out and it worked.

[Cees]

The Bode Plot function appears broken. When I tried a simple low pass RC with 100Hz to 10kHz at 50 pts/decade, 1V amplitude,  it worked with the ripple TimFox mentions. When I increased the sample points to 100 pts/decade it changed CH2 resolution to 20mV/div and the top waveform display showed CH2 clipped and it hung until I turned off the Bode Plot window. I think at present a script and PC control might be a more effective way of Bode Plotting until a fix is provided. The on screen display for the Bode Plot function is awfull.

There is a solution that I do use now too but is it actually an error caused in the automatic gain setting. Before starting the measurement you can still manually set the gain of each channel. I then set the sensivity for each channel to 10 volts per devision.  When the plot is started the algorithm will have to amplify the gain first. The result is that the plot continues. If the gain is too sensitive at the start then the signal will clip in advance and the plot will not continue to the next frequency. The software should attenuate the gain until the signal falls below the clipping point. So based on the digital value coming out of the ADC you could decide to adjust the value downward so that the waveform fits in the window.

I tried it out and it worked.

Great!!

[TurboTom]

Can someone with a DHO900S please try to verify this finding: https://www.eevblog.com/forum/testgear/rigol-dho800900-oscilloscope-bug-reports-firmware/msg5106039/#msg5106039

I doubt that this problem is unique to the specimen that I've got here, but it may be possible. Thanks a lot!

[moffy]

Can someone with a DHO900S please try to verify this finding: https://www.eevblog.com/forum/testgear/rigol-dho800900-oscilloscope-bug-reports-firmware/msg5106039/#msg5106039

I doubt that this problem is unique to the specimen that I've got here, but it may be possible. Thanks a lot!

Yep, got exactly the same behavior going from 2.147kHz to 2.148kHz brought up 'open the app again'.

[Cees]

Bode plot problem is solved.  New firmware available.

https://supportcn.rigol.com/Public/Uploads/uploadfile/files/ftp/Firmware/DHO800_DHO900(Software)UpdateV00.01.01.zip

[ebastler]

Bode plot problem is solved.  New firmware available.

So you already checked out the Bode plot? That was quick! 

And a pleasant surprise from Rigol -- not only is there a first firmware update very soon, but it seems to fix more than what they announce in the release notes. There's hope... 

[Cees]

Bode plot problem is solved.  New firmware available.

So you already checked out the Bode plot? That was quick! 

And a pleasant surprise from Rigol -- not only is there a first firmware update very soon, but it seems to fix more than what they announce in the release notes. There's hope... 

The only thing left is the fixed vertical scales, amplitude and phase. Should be nice to have vertical auto ranging as well

[TimFox]

I have installed the upgrade:  now waiting for thorough warm-up before new self-calibration.

[KedasProbe]

Date from firmware 1.1 August 10, only 17 days after first firmware release.
I assume those firmware 1.0 DHOs were build in the first 17 days of production.

So what happened in the next 60 days for firmware updates? (3.5 times the same period)
edit: let assume they are working on new features....

[TurboTom]

They solved the Scope App crashing bug if frequency of the AWG is adjusted with encoder 1  .

Yet, regarding the Bode Plot, I couldn't find much of an improvement. But I've got to admit, I used the scope screen as the "window to the data" and not an external CSV visualization. Wiggles were still recognizable, anyway.

[TimFox]

So I installed the update, checked "about" to verify the new firmware rev level, re-did the self-calibration (with everything disconnected), re-connected the exact connections I had before, and there might be a very slight improvement.
Graphing the .csv file using the same settings on the graphing software, but adding points to the phase curve (heavier line) at the actual data points, I found a very similar result posted below.
One important clue might be that the "ripple" seems to have a period of roughly 6 or 7 points.
The manually-added cursor at -3 dB and -45 deg remained the same.

[ebastler]

Oh, sigh... I must have misunderstood Cees' post #60 then.

Here's hoping that Rigol do address this next time round. Getting one of the two selling points of the DHO 900 series wrong should be kind of important to them...

[Fungus]

Oh, sigh... I must have misunderstood Cees' post #60 then.

Here's hoping that Rigol do address this next time round. Getting one of the two selling points of the DHO 900 series wrong should be kind of important to them...

At least we know why it wasn't mentioned in the release notes.

Mystery solved!

[KedasProbe]

Anyone connected a second oscilloscope to ch1 when doing a bode plot to see what the input signal looks like?

They could (for speed reasons) like do 5 sin waves at the same time and sort them out with a FFT on both channels. (Amplitude and Phase are provided by an FFT)
but this will introduce errors that they may not take into account so maybe that is what we see.

Delivery of mine is delayed until next week (for now)

[TurboTom]

Not necessary - in the little upper window, the input signals of the corresponding two channels are displayed vs. time. They are proper sinewaves!

[KungFuJosh]

Graphing the .csv file using the same settings on the graphing software

What software are you using for graphing?

[TimFox]

I'm using "Grapher" from Golden Software.
It's a package I used at work before retiring, and it is a bit expensive since the package includes lots of stuff.
However, I purchased it for home since I really like to make professional-looking graphs.

[TimFox]

I just got off the phone with a useful guy at Rigol's North American office.
He's sending me an e-mail, to which I shall respond with my graphs and data for them to evaluate.

[KungFuJosh]

I'm using "Grapher" from Golden Software.

Yikes. That is a little pricey, especially as a subscription model. I guess I'll stick with Excel. The graphs definitely look nice though. Excel also makes nice graphs, but I was hoping for something with fewer steps.