How much noise floor and other things matter in oscilloscope usability

[Fungus]

Ripple same settings on both oscilloscope
AC, normal mode, 1x probe

I disagree that there's a huge difference in useful information. Sure, the Siglent line is thinner but The Rigol is showing the ripple just fine.

You should also be able to change the displayed part of the signal (the red bit) by twisting the selection knob on the Rigol (ie. intensity setting).

And again: What does averaging mode do if you turn it on in this situation? Why is this being avoided?

[Fungus]

This is even worse than I expected ( ). I don't care about the open / shorted inputs at the most sensitive V/div (Rigol does digital zoom there so it is not an apples for apples comparison) but I do care about the display of an actual signal. On the Siglent you can clearly see spikes on the signal which are completely obscured on the Rigol.

I dunno what those "spikes" are but they're not ripple. To me it seems liek the Rigol is perfectly capable of showing the ripple from that power supply. Is there anybody here who can't see the ripple in this image or thinks that the 14.003mV displayed value is somehow massively different than the 14.048mV displayed by the Siglent?


(and this is without averaging, apparently, averaging can only improve this)

Is the Siglent display or the number displayed by the Siglent worth 400 Euros more? I dunno. It's all relative, but I could buy all sorts of useful stuff for 400 Euros.

However you look at it: You'll have a hard time convincing me that the Rigol is a disaster. Sure the Siglent's line is thinner but the Rigol is perfectly capable of showing the ripple on screen and measuring it. That's what really counts, and is the subject of this thread.

[nctnico]

Just stop trying to make right what is clearly wrong. The small spikes that the trace shows on the Siglent (or any other modern DSO other than Rigol mentioned in this thread) can point to other problems. An FFT will tell more but again, on the Rigol the HF component riding on the lower frequency ripple likely gets drowned in the noise. The Rigol MSO5000 is outright horrible. Claiming anything else is delusional. Edit: pay close attention to the excellent example G0HZU posted below. It may save your bacon one day trying to find an illusive problem in a circuit.

At some point cheap doesn't make up for poor performance. In the end you'll need to buy an extra instrument to make the measurement cheaper gear can't do. Been there, done that and wasted enough money on cheap gear which in the end didn't deliver.

[G0HZU]

And again: What does averaging mode do if you turn it on in this situation? Why is this being avoided?

OK I'll bite...If you want to see the effects of averaging then see the example below.

I've just set up a couple of function generators and summed the waveforms into my old HP Infinium scope. I've set the scope to 50R input and done everything in x1.

The scope is set to 1mV/div and I've turned on the 30MHz bandwidth limit. Waveform 1 is a triangle wave at about 500Hz and it is about 5mV pkpk. Waveform 2 is a series of narrow positive pulses each of amplitude 1mV and they occur every 768us. The plots below show the low noise performance of this old scope and also show how averaging can cause information to be lost.

See below for a single shot capture and see also for what happens with averaging. The information about the pulses is totally lost in the averaged screenshot because the period of the triangle wave and the pulses is different. I hope this helps?

[bdunham7]

However you look at it: You'll have a hard time convincing me that the Rigol is a disaster. Sure the Siglent's line is thinner but the Rigol is perfectly capable of showing the ripple on screen and measuring it. That's what really counts, and is the subject of this thread.

What are you going to do when the ripple is even smaller?  For example, here is a ~150uV_rms 10MHz signal being clearly triggered and displayed.  This signal was displayable--triggerable and above the noise threshold on a Tek 2465B (shown), a Tek 2221A (digital and analog) and the Siglent 1104X-E (although just barely and not as reliably).  I was able to do the same thing with a 1MHz and 100Hz signal of approximately the same amplitude.  What would it look like on the Rigol? 

You can't average your way out of this when you are looking for noise--possibly non-periodic--in the first place.  On the Tek 2221A and the Sig 1104X-E, averaging made the signal look nicer but I'm not convinced that means better. 

[bdunham7]

There is a huge difference between this two scopes.
The Rigol has a faster update of the image, almost double... and the quality of the rappresentation, i mean the graphics, of the signal is a lot better than the Siglent. It seem like the Siglent had a lower resolution. There is not a huge difference in the speed of the user interface and also the Rigol appear to have a better quality of the material of the scope. But the front end noise is a lot different.
Judge by your self from the photos attached.

Could you try the ripple and maybe no probe (like the first photos) with the Siglent in the 10-bit acquisition mode?

[Fiorenzo]

Normal mode
Probe connected 1x and grounded

Shorting the probe tip can be tricky.  For lowest noise it is not sufficient to simply clip the probe's ground lead to the probe's tip because the loop will pick up ambient noise.  Best is to short the tip out with a coaxial probe tip to BNC adapter plugged into a BNC short or 50 ohm termination, but winding wire around the probe tip also works.

Yes I have put the wire of the probe in the less noisy position

[Fiorenzo]

So i did a lot of photos.
First two comparison: no probe, 1mv/div, 20mhz BW limit.

Irrelevant. Only real signals count.

4x avarage no probe

Averaging only works when there's a periodic signal.

Ripple same settings on both oscilloscope
AC, normal mode, 1x probe

No averaging?

That's the only thing that counts - if averaging mode can better show the underlying signal or not.

Normal mode
Probe connected 1x and grounded

Shorting the probe tip can be tricky.  For lowest noise it is not sufficient to simply clip the probe's ground lead to the probe's tip because the loop will pick up ambient noise.

Yep. Connecting the ground clip to the probe actually creates an antenna.

I know but i put the probes in the same manner with the lowest noise captured, i also did the photos with avarage on the signal of the ripple i didn't had the time to upload

[Fiorenzo]

There is a huge difference between this two scopes.
The Rigol has a faster update of the image, almost double... and the quality of the rappresentation, i mean the graphics, of the signal is a lot better than the Siglent. It seem like the Siglent had a lower resolution. There is not a huge difference in the speed of the user interface and also the Rigol appear to have a better quality of the material of the scope. But the front end noise is a lot different.
Judge by your self from the photos attached.

Could you try the ripple and maybe no probe (like the first photos) with the Siglent in the 10-bit acquisition mode?

Yes i will do. The 10 bit more reduce the noise as i checked yesterday evening. I will post some photos.
In regard of the Rigol It Is in my opinion a very good scope but It has the problem of the noisy front end

[Fiorenzo]

Ripple same settings on both oscilloscope
AC, normal mode, 1x probe

I disagree that there's a huge difference in useful information. Sure, the Siglent line is thinner but The Rigol is showing the ripple just fine.

You should also be able to change the displayed part of the signal (the red bit) by twisting the selection knob on the Rigol (ie. intensity setting).

And again: What does averaging mode do if you turn it on in this situation? Why is this being avoided?

The spikes you can clearly see in the Siglent i think are switching noise  coming from the next stage of this psu. I am going to do some test about It to check if the front end noise of the Rigol is covering such interference

[Fiorenzo]

As asked some photos with the avarage mode

4x average

In my opinion the avarage, even if It conserve almost the shape of the signal, destroys "the low intensity" informations

[Fungus]

The spikes you can clearly see in the Siglent i think are switching noise  coming from the next stage of this psu. I am going to do some test about It to check if the front end noise of the Rigol is covering such interference

Thanks for the photos! This is all very useful information.

The one remaining test is to see the effect of turning up the display intensity on the Rigol to see if it reveals those spikes better (without averaging).

[2N3055]

I 'm reading some of these posts and 

It is obvious MSO5000 has much more noise, and that it is a problem, unless you only look at digital signals and just want to look at general shape and some timing information.
It is shame, really, because new Rigol scopes are much more powerful processing wise than the old ones, and generally held great promise but analog front end/ADC noise performance is not very good.

Scope with low noise is always going to be better instrument than the one with high noise. Why is that even a discussion?
Is this some audiofool discussion how this huge noise is pleasant to look at because it's pretty? 

I don't use bandwidth limiting, averaging or any "signal cleanup" features when I'm looking into a signal I want to understand. You would want to look at this switcher signal with a full 1GHz bandwidth and with as low noise scope you can.
To really see what is there... Switching ripple is most of the time least interesting part of switching PSU. We expect it to be there, and most of the time it will be roughly what we calculated. Other, higher frequency stuff (those little hairs on top) is much more problematic and most of the time those will give you headaches.. Nanovolts of those will already be seen on any EMI test...

You filter, limit and "cleanup" signal in circumstances where you understand your signal and you want to ignore noise and other parts of signal on purpose. If your signal is buried inside the noise, you average.
But is that noise part of signal you're measuring or your scope is not irrelevant. If it comes from DUT I want to know that. I want to see it..
Only way to do that is to have low noise scope.

Of course, like OP correctly asked, there is a point of diminishing returns..
Is scope with 5 uV of RMS noise so much better than one with 50uV RMS noise for measuring this switcher signal from this example? Probably not.
It would be definitely better but probably not usefully so in this case. But one with 50uV of RMS noise is definitely better than one which has trace that is whooping 20 mV wide... On a signal that is 60mV P-P...
On this test I would call MSO5000 from Rigol useless for this measurement. And averaging this not autocorrelated signal ( it doesn't repeat cleanly and doesn't retrace it's waveform exactly but varies slightly all the time) will not extract more detail but will hide even more information about signal..

OTOH Siglent shows pretty much perfect representation of the signal, big peaks, ripple AND little hairs. That is your switcher output. That is useful information..

Little Micsig STO1104C/E, or Siglent SDS1104X-E could do equally good job here.

Sad part is that little Rigol DS1054Z would be much better for this signal than MSO5000.. DS2000A had excellent low noise front end .. But new series of Rigol scopes is very powerful in processing power but analog performance is worse than older series. Shame really, otherwise they are very nice scopes.



 

[Fiorenzo]

The spikes you can clearly see in the Siglent i think are switching noise  coming from the next stage of this psu. I am going to do some test about It to check if the front end noise of the Rigol is covering such interference

Thanks for the photos! This is all very useful information.

The one remaining test is to see the effect of turning up the display intensity on the Rigol to see if it reveals those spikes better (without averaging).

Sorry fungus i have been very busy. I have more photos. Check in the next messages

[Fiorenzo]

16x average

[Fiorenzo]

Max average possibile

[Fiorenzo]

Fungus actually i think in my modest opinion that the Rigol is a greate scope, for sure i will miss it due to its graphics and fast acquisition, comparing both the scope you see the difference a lot. But It has also a lot more noise.... I have an idea to show you how much the signal degrade due to this problem.

[tautech]

Fungus actually i think in my modest opinion that the Rigol is a greate scope, for sure i will miss it due to its graphics and fast acquisition, comparing both the scope you see the difference a lot. But It has also a lot more noise.... I have an idea to show you how much the signal degrade due to this problem.

Study the screenshots you've just posted to see just how fast it actually is with averaging engaged.

Which initiates another question; what would the MSO5000 sampling drop to if one more channel was activated ?

[Fungus]

Just stop trying to make right what is clearly wrong. The small spikes that the trace shows on the Siglent (or any other modern DSO other than Rigol mentioned in this thread) can point to other problems.

I'm not trying to make anything "right", I'm just trying to see if the Rigol would prevent somebody from doing their job with this signal.

Questions:
(1) Can the Rigol display/measure the ripple? It clearly can.


(2) Can the Rigol see the high frequency spikes? Maybe not as well as the Siglent but they're clearly visible.


(and the jury is out until we know the effect of turning the intensity up/down to enhance them - just like you had to do on old Analog 'scopes to see artifacts like that)

Bottom line: The Rigol can see what's going on in that signal.

What are you going to do when the ripple is even smaller?

Get an amplifier? 

Does ripple/noise/electronics magically stop at 1mV? There's plenty of signals that the Siglent can't see either...

[Fungus]

Which initiates another question; what would the MSO5000 sampling drop to if one more channel was activated ?

It's not difficult: With two channels you get 4GHz/channel, with three or four channels you get 2GHz/channel.

At no point is it less than the Siglent with just a single channel.

[Fungus]

But It has also a lot more noise.... I have an idea to show you how much the signal degrade due to this problem.

All 'scopes degrade the signal, none are perfect.

The real problem with this Rigol vs. Siglent comparison is that you're comparing two devices side by side where one of them happens to work better at 1mV then the other one does.

ie. When you turn the Siglent's vertical control to "max" then it makes the Rigol look bad at that level. If you were comparing 1V signals or 5V signals in your screenshots then you wouldn't see the same difference between them.

Guess what? Electronics doesn't magically stop at the exact place where the Siglent's vertical control does. There's plenty of signals below 1mV. You'll need an amplifier to see them and the exact same same amplifier would work with a Rigol, too.

Plus: You originally said you do digital stuff, so... 

[tautech]

Which initiates another question; what would the MSO5000 sampling drop to if one more channel was activated ?

It's not difficult: With two channels you get 4GHz/channel, with three or four channels you get 2GHz/channel.

At no point is it less than the Siglent with just a single channel.

It is when you overlook the full picture of each scopes acquisition system.

With channels 1 and 3 of each scope activated a very different picture may emerge at some timebase settings.

[2N3055]

I'm not trying to make anything "right", I'm just trying to see if the Rigol would prevent somebody from doing their job with this signal.


Get an amplifier? 

Does ripple/noise/electronics magically stop at 1mV? There's plenty of signals that the Siglent can't see either...

This not a stupid debate club where we debate whether it is more appropriate to say "apply the law" or "apply the letter of law"..
This is physics and measurements and math. There is no negotiation with these guys.
You are wrong and stop being a spoiled child. You. Are. Wrong. Take it as an adult.

Worse is worse, and if you can chose, chose better. Why on Earth would you take worse device and then spend years "figuring out" how to deal with fundamental shortcomings (that you really can't fix because of it's nature) than simply take something that actually works much better.

Nothing does anything magically. Usually more than good enough is when we know scope contributes less than few percent of the error. That also coincides with what can be easily seen with naked eye and 8 bits of a scope.
When scope shows 20 mV noise on top of 65mv P-P signal that is definitely bad. Unusable for that measurement. Fact that it shows something is not that useful. It needs to show it accurate enough so person looking into scope can make something with it..

Also you keep repeating about some magical amplifiers. Amplifiers that have DC-100 Mhz bandwith and less noise as even a little Micsig or Siglent SDS1104X-E cost as much as a good scope from Keysight. There are amplifiers for audio frequency range that can be used for low noise measurements. Those are useless for measuring a things mentioned here.. So no, some mythical preamps are not a solution.

[Fungus]

With channels 1 and 3 of each scope activated a very different picture may emerge at some timebase settings.

Yes, because if you enable to adjacent channels the Siglent only has 1GS/sec to look at 350Mhz signals, ie. it's getting uncomfortably close to Nyquist.

Turning a channel off can bump the sample rate to 2GS/sec and give a different picture.

The Rigol MSO5000 series is one of the few oscilloscopes which can maintain a comfortable Nyquist margin with any combination of channels.

[Fungus]

Also you keep repeating about some magical amplifiers. Amplifiers that have DC-100 Mhz bandwith and less noise as even a little Micsig or Siglent SDS1104X-E cost as much as a good scope from Keysight.

Yes, but amplifiers from DC to 1MHz are incredibly cheap (ie. a $2 OP-amp plus power supply) and would be perfectly adequate for audio work and looking at power supply ripple.

Amplifiers from 10kHz to 2GHz are also incredibly cheap.