Author Topic: Rigol DHO800 memory depth / bandwidth upgrades and noise level!  (Read 18033 times)

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Offline Fungus

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #50 on: November 06, 2023, 09:56:17 pm »
Could you also measure the residual offset voltage (V_avg) on each channel? It will enter the V_rms calculation and might have a non-negligible effect. Some of the traces do not look perfectly centered to their respective 0V arrows.

Oh, yeah, I haven't done self-cal for a while. I have no idea what the bandwidth configuration was last time I did it.  :-DD

AC RMS shouldn't be affected by offset though.
« Last Edit: November 06, 2023, 10:05:00 pm by Fungus »
 

Offline 2N3055

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #51 on: November 06, 2023, 09:58:20 pm »
Try average for acquisition...

I set 32768 averages and it went down into the nV range. Rigol FTW!
Well it is logical...

Noise is going to average to zero AC. What is left is DC offset..
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Offline 2N3055

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #52 on: November 06, 2023, 10:00:03 pm »
Could you also measure the residual offset voltage (V_avg) on each channel? It will enter the V_rms calculation and might have a non-negligible effect. Some of the traces do not look perfectly centered to their respective 0V arrows.

Oh, yeah, I haven't done self-cal for a while.

AC RMS shouldn't be affected by offset though.
Auto cal should compensate zero offset but also vertical gain..
But these differences in channels are within normal spread. We are talking microvolts here...
"Just hard work is not enough - it must be applied sensibly."
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Offline Fungus

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #53 on: November 06, 2023, 10:01:34 pm »
Noise is going to average to zero AC. What is left is DC offset..

In AC RMS mode?
 
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Online Martin72

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #54 on: November 06, 2023, 10:03:47 pm »
Watch the diagram in the vertical menu and think about again...

Online ebastler

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #55 on: November 06, 2023, 10:16:10 pm »
@Fungus -- a quick check for offset contributions in the non-averaged noise measurements is still relevant, I think. Either re-calibrate and do the V.rms measurements again, or measure V.avg in addition to V.rms and calculate V.noise = srqt (V.rms² - V.avg²).

I would actually prefer the latter approach, which works even if the auto-calibration leaves some residual offset. As it does in my DS1054Z -- which comes in at approx. 400µV noise with the same 1ms/div, 1mV/div settings,  by the way, in case anyone is still looking for a reason to upgrade.  ;)
 

Offline Fungus

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #56 on: November 06, 2023, 10:16:33 pm »
One more before bed time...

I did a self-cal and measured Vavg as well as AC-RMS. There's only 3 channels because that's all that fits in the visible area (you guys can't scroll tables up/down like I can):

 

Online Martin72

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #57 on: November 06, 2023, 10:26:50 pm »
These are pretty good values.
One more thing about ac "mode" and dc-offset:
When switching to ac coupling, a cap will be switched between signal input and the following stages in the frontend.
This will have nearly no effect to the offset.
AC coupling will block the dc offset of the signal.

Offline Fungus

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #58 on: November 06, 2023, 10:28:12 pm »
These are pretty good values.

$399 Rigol FTW!
 

Offline 2N3055

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #59 on: November 06, 2023, 10:29:51 pm »
@Fungus -- a quick check for offset contributions in the non-averaged noise measurements is still relevant, I think. Either re-calibrate and do the V.rms measurements again, or measure V.avg in addition to V.rms and calculate V.noise = srqt (V.rms² - V.avg²).

I would actually prefer the latter approach, which works even if the auto-calibration leaves some residual offset. As it does in my DS1054Z -- which comes in at approx. 400µV noise with the same 1ms/div, 1mV/div settings,  by the way, in case anyone is still looking for a reason to upgrade.  ;)

AC RMS (Stdev) excludes DC offset by definition. There is separate RMS measurement that is AC+DC RMS
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
 
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Online ebastler

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #60 on: November 06, 2023, 10:34:32 pm »
@Fungus -- a quick check for offset contributions in the non-averaged noise measurements is still relevant, I think. Either re-calibrate and do the V.rms measurements again, or measure V.avg in addition to V.rms and calculate V.noise = srqt (V.rms² - V.avg²).

I would actually prefer the latter approach, which works even if the auto-calibration leaves some residual offset. As it does in my DS1054Z -- which comes in at approx. 400µV noise with the same 1ms/div, 1mV/div settings,  by the way, in case anyone is still looking for a reason to upgrade.  ;)

AC RMS (Stdev) excludes DC offset by definition. There is separate RMS measurement that is AC+DC RMS

Ah, thanks -- I had totally overlooked the AC.RMS bit.  :palm:
Just spent several minutes wondering how V.avg could possibly be larger than V.rms...
I guess this means it's bedtime for me!
 

Offline 2N3055

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #61 on: November 06, 2023, 10:34:43 pm »
These are pretty good values.

$399 Rigol FTW!

Actually 100-120µV of offset is not so good as it could be . You should run self cal.
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
 

Offline Fungus

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #62 on: November 06, 2023, 11:03:16 pm »
Actually 100-120µV of offset is not so good as it could be . You should run self cal.

I just did!

What was the spec of the vertical offset amplifiers again?

I'm happy with 100uV.  :popcorn:

 

Offline 2N3055

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #63 on: November 06, 2023, 11:09:06 pm »
Actually 100-120µV of offset is not so good as it could be . You should run self cal.

I just did!

What was the spec of the vertical offset amplifiers again?

I'm happy with 100uV.  :popcorn:

It is not bad.  Just trying to see where is the baseline...
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
 

Online ebastler

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #64 on: November 06, 2023, 11:10:09 pm »
What was the spec of the vertical offset amplifiers again?
I'm happy with 100uV.  :popcorn:

I don't think Rigol specifies the allowable residual offset after self-cal. But it seems they know it's not perfect -- that's why the bias adjustment allows you to compensate for small offsets and drifts manually, right? (Section 5.10 of the manual.)
 

Online bdunham7

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #65 on: November 07, 2023, 01:12:39 am »
Now people can compare to other scopes with same settings..

Here you go:



« Last Edit: November 07, 2023, 01:14:43 am by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline Bob773Topic starter

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Re: Rigol DHO800 memory depth / bandwidth upgrades and noise level!
« Reply #66 on: November 07, 2023, 03:34:04 am »
Thanks to all for the information regarding memory depth.  BTW I changed the title since this took a bit of a turn… let me know if it needs changed again, I am here to please  ;D
 
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Offline Fungus

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #67 on: November 07, 2023, 06:16:37 am »
Now people can compare to other scopes with same settings..

Here you go:



Is that a 1104X-E?

Why is it worse with the bandwidth limit on?
 

Offline tautech

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #68 on: November 07, 2023, 06:26:41 am »
Now people can compare to other scopes with same settings..

Here you go:



Is that a 1104X-E?

Why is it worse with the bandwidth limit on?

One of the X-E's.
Only std dev on std dev is worse.
Look at the Current value column.  ;)
Avid Rabid Hobbyist.
Some stuff seen @ Siglent HQ cannot be shared.
 

Online iMo

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Re: Rigol DHO800 memory depth / bandwidth upgrades and noise level!
« Reply #69 on: November 07, 2023, 08:28:07 am »
On the above Siglent picture the aprox 80uVrms noise is aprox 500uVp-p seen on the screen which basically matches the theory. The standard deviation of 2.44uV is the STD for the set of measurements (the 51 measurements of that 80uVrms), not to mix it with the "rms".

On the DHO804 picture the aprox 65uVrms is rather high, imho, that should lead to aprox 400uVp-p seen on the screen, so basically the "same level" as the Siglent.
« Last Edit: November 07, 2023, 08:36:15 am by iMo »
Readers discretion is advised..
 

Online ebastler

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Re: Rigol DHO800 memory depth / bandwidth upgrades and noise level!
« Reply #70 on: November 07, 2023, 08:35:09 am »
The standard deviation of 2.44uV is the STD for the set of measurements (the 51 measurements of that 80uVrms), not to mix it with the "rms".

It does get a bit confusing though, since the measured property is not called "rms" here, but also "StdDev". So there is a measured StdDev, and it is measured with a certain StdDev. All correct, and the table layout does make it clear what's what; but it does invite mis-reading it at a quick glance.
 

Online iMo

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Re: Rigol DHO800 memory depth / bandwidth upgrades and noise level!
« Reply #71 on: November 07, 2023, 08:46:32 am »
Yep, there is AC.rms, AV+DC.rms, Vpp (or Vpk-pk), and STD.
Btw., the noise levels of that Siglent and Rigol as depicted above are "almost the same" (20% diff in the noise is negligible). Thus the question is how the 8bit vs 12bit comparison would apply here..
Readers discretion is advised..
 

Offline 2N3055

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Re: Rigol DHO800 memory depth / bandwidth upgrades and noise level!
« Reply #72 on: November 07, 2023, 09:33:41 am »
Yep, there is AC.rms, AV+DC.rms, Vpp (or Vpk-pk), and STD.
Btw., the noise levels of that Siglent and Rigol as depicted above are "almost the same" (20% diff in the noise is negligible). Thus the question is how the 8bit vs 12bit comparison would apply here..

It depends. Since SDS1104X-E has 500µV/div real range, for small signal it would be pretty much the same.
SDS2000X+ shown above has much less noise than DHO800, despite being 8 bit. At 50Ω it would be even better (but so would DHO800 with external terminator).

So like I said many times before, it is not that simple.

All in all, Rigol finally made an inexpensive scope with quite competitive noise levels. It is not as good as good 12 bit scopes, and not even as good as best 8bit ones, but good nevertheless. Noise is no longer a problem. Especially for the price bracket.

It would be interesting to see how well DHO4000 fares.
"Just hard work is not enough - it must be applied sensibly."
Dr. Richard W. Hamming
 

Offline Serg65536

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Re: Rigol DHO800 memory depth is a deal breaker
« Reply #73 on: November 07, 2023, 10:29:34 am »
Oh, yeah, I haven't done self-cal for a while. I have no idea what the bandwidth configuration was last time I did it.  :-DD

Please, share your experience:

1) What is the DC accuracy of your DHO804 scope with DHO924 firmware?
     The good way to measure it is to test some precisely known voltage around 8V on 100mV/div range with offset.

2) You use vendor.bin upgrade or whole 924 firmware image?

My 804 has worst accuracy of 1.6% with 924 firmware image, when zero offset is calibrated.
 

Online ebastler

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Re: Rigol DHO800 memory depth / bandwidth upgrades and noise level!
« Reply #74 on: November 07, 2023, 11:38:55 am »
Btw., the noise levels of that Siglent and Rigol as depicted above are "almost the same" (20% diff in the noise is negligible). Thus the question is how the 8bit vs 12bit comparison would apply here..

I would expect that at the very low end of the range (high amplification), noise levels are dominated by the analog front end. ADC resolution comes into play when you look at the dynamic range. So an 8-bit scope with a carefully designed front end can fare pretty well in this test.

The Siglent SDS2000X plus in 10-bit mode has the lowest RMS noise in the measurements above. That makes sense to me, since the oversampling & averaging it performs in that mode should also help to reduce the (digitized) front-end noise.
 


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