Rigol DHO804 Test and Compare Thread

[Fungus]

Thanks! Thinking about it, you probably hardly use the encoders for "discrete" selections -- menu entries or virtual keyboards -- at all,

I just tried it and you CAN use them in drop-down selections. You can even push them to confirm the choice.

I'd never even noticed that before. 

[Martin72]

Just tested the XY mode with the batronix demo board.
It looks really good and I would like to have this split screen with my other scopes as well.
Nice effect:
Ch1 yellow, Ch2 blue, what is the conclusion?
Right, green for the XY representation...

[ebastler]

That looks nice and clean!
But can you play Asteroids on it? 

Actually, the resolution looks like it might be good enough for Asteroids' 10-bit X/Y DACs. And the DHO manual states you can even map a Z (blanking) input to one of the remaining analog channels! So maybe the answer is "yes". 

Edit: Does it support intensity grading in XY mode?

[Martin72]

Edit: Does it support intensity grading in XY mode?

Will check this tomorrow..

[mawyatt]

Well we've been able to hang on to this 824 longer than expected (client has much more pressing issues to resolve, so doesn't need any distractions at this time), and decided to try and give the XY mode a whirl.

Here's a couple characteristic curve 2N3904 plots utilizing XY mode with an external AWG (OMG we utilized the forbidden "S" brand AWG!!!).

For those not familiar with silicon bipolar transistors, these are plots created by sweeping the collector emitter voltage Vce, while stepping the base current and plotting collector current.

The 2N3904_CTR0 curve shows the NPN bipolar operating in reverse (backwards, or upside down) mode as it's often called, where the collector and emitter are effectively interchanged by allow a negative Vce for the NPN type (also shows the forward direction, centered around 0 volts). Note the lower Beta (current gain) and breakdown (steeper collector current slope) in the reverse direction wrt to the forward normal operation mode. This reverse mode was often utilized way back due to the very low Vcesat voltage at low to modest currents.

Anyway, seems the little 824 can produce some nice XY plots!!

Best,

[blargg]

Not sure which Rigol thread to post this in. Just unboxed my DHO804 and trying a basic task, triggering off clocked data. I've got it in Normal trigger mode, on the clock line. Data comes in a burst, then nothing for a couple of seconds. I'd expect the scope to keep triggering on clocks until they stop, showing the last capture on trigger. Instead of overlays several captures on screen. In Gear->Display->Persistence I've got it set on Min (there's no Off). Is there no way to have it just show the most recent capture?

EDIT: I tried the same on my 1054Z and it worked as I expected, always showing only a single capture on screen at any given moment (there Persistence was also set to min., which is apparently off on that model).

[Fungus]

Not sure which Rigol thread to post this in. Just unboxed my DHO804 and trying a basic task, triggering off clocked data. I've got it in Normal trigger mode, on the clock line. Data comes in a burst, then nothing for a couple of seconds. I'd expect the scope to keep triggering on clocks until they stop, showing the last capture on trigger. Instead of overlays several captures on screen. In Gear->Display->Persistence I've got it set on Min (there's no Off). Is there no way to have it just show the most recent capture?

EDIT: I tried the same on my 1054Z and it worked as I expected, always showing only a single capture on screen at any given moment (there Persistence was also set to min., which is apparently off on that model).

Do you press "STOP"?

Maybe you want the "freeze" setting at the bottom of the display settings.

[blargg]

Not sure which Rigol thread to post this in. Just unboxed my DHO804 and trying a basic task, triggering off clocked data. I've got it in Normal trigger mode, on the clock line. Data comes in a burst, then nothing for a couple of seconds. I'd expect the scope to keep triggering on clocks until they stop, showing the last capture on trigger. Instead of overlays several captures on screen. In Gear->Display->Persistence I've got it set on Min (there's no Off). Is there no way to have it just show the most recent capture?

EDIT: I tried the same on my 1054Z and it worked as I expected, always showing only a single capture on screen at any given moment (there Persistence was also set to min., which is apparently off on that model).

Do you press "STOP"?

Maybe you want the "freeze" setting at the bottom of the display settings.

Freeze only affects the display when it's stopped. In Run mode it still overlays multiple traces; the freeze switch has no effect there. I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

[ebastler]

Freeze only affects the display when it's stopped. In Run mode it still overlays multiple traces; the freeze switch has no effect there. I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

Thanks for the video. The DHO800 captures all look strange to me, including the initial Single capture. What happened to the intensity grading?? 

[blargg]

Freeze only affects the display when it's stopped. In Run mode it still overlays multiple traces; the freeze switch has no effect there. I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

Thanks for the video. The DHO800 captures all look strange to me, including the initial Single capture. What happened to the intensity grading?? 

It's there, there just isn't much overlap. Screenshot attached.

[Fungus]

What happened to the intensity grading?? 

You mean like this?

[ebastler]

What happened to the intensity grading?? 

It's there, there just isn't much overlap. Screenshot attached.

Thanks, the still screenshot looks better. In the video it appeared like all pixels were on at full intensity on the DHO800, while the DS1054Z showed dim lines at the fast vertical edges vs. brighter lines for the high and low states. Probably just a camera exposure artefact, with the DHO traces set to a higher brightness than on the DS1054Z?

Still, the contrast between the edges and the steady logic states is not very pronounced at all on the DHO screenshot. But the root cause of the overlaid traces doesn't seem to be in a persistence or saturation setting or something along those lines.

@Fungus -- sure, I know that the DHO scope can do intensity grading. I just couldn't see any of it happening in the video.

[Fungus]

Freeze only affects the display when it's stopped. In Run mode it still overlays multiple traces; the freeze switch has no effect there. I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

Maybe it's just that the capture rate is much higher on the DHO. Try setting set trigger holdoff so it triggers less often...

Technically speaking: The DHO is showing something closer to what you'd see on an analog 'scope. "Min" persistance doesn't mean there's no persistence.

[Martin72]

It's there, there just isn't much overlap. Screenshot attached.

Regardless of everything, I would choose Auto memory, you still have 10k fixed as a setting(according to the screenshot)

[ebastler]

[I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

I have one more question -- although it is probably unrelated to the effect under discussion: In the video, what are you doing to set the DHO to Single and Run mode, respectively? I see your hand operating the DS1054Z, and the status indicators on the DHO just seem to follow along "magically". What am I missing there?

[Fungus]

[I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

I have one more question -- although it is probably unrelated to the effect under discussion: In the video, what are you doing to set the DHO to Single and Run mode, respectively? I see your hand operating the DS1054Z, and the status indicators on the DHO just seem to follow along "magically". What am I missing there?

I think he's pressing a "send some data" button somewhere off-camera.

[ebastler]

I think he's pressing a "send some data" button somewhere off-camera.

Yes, that obviously is happening too, to actually start the triggering and sweep. But how does the "Single" LED on the DHO light up at 0:07 in the video, and how does the "Run/Stop" LED turn green at 0:12?

[blargg]

Freeze only affects the display when it's stopped. In Run mode it still overlays multiple traces; the freeze switch has no effect there. I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

Maybe it's just that the capture rate is much higher on the DHO. Try setting set trigger holdoff so it triggers less often...

Technically speaking: The DHO is showing something closer to what you'd see on an analog 'scope. "Min" persistance doesn't mean there's no persistence.

Fair point. The DHO is freezing what the analog scope would have last shown (before it fades out during the couple of seconds of no activity for the test signal in the video).

I looked around and enabled UltraAcquire mode and for it gives what I wanted (and what the 1054Z does), but that's a new can of worms because it seems like this should not work and I can't figure out why it's not making multiple captures stacked/in perspective etc. as this mode should (I played around for a while and couldn't get consistent results, will have to dig into this another day).

[I made a short video demonstrating. https://files.catbox.moe/jzlpc0.mp4

I have one more question -- although it is probably unrelated to the effect under discussion: In the video, what are you doing to set the DHO to Single and Run mode, respectively? I see your hand operating the DS1054Z, and the status indicators on the DHO just seem to follow along "magically". What am I missing there?

Sorry about that, was just off the top of the camera. For the first test I hit Single on the '804, then hit Run (same buttons I press on DS1054Z except the latter also requires setting the mode to Normal as it switches to Auto).

The test signal has a bunch of pulses for about 4ms, then nothing for a couple of seconds.

[ebastler]

Actually, I still like the intensity grading of the DS1000Z series better, not to speak of the higher models of this heritage...

I just revisited the older posts on DHO intensity grading, prompted by the observed difference to the DS1054Z in blargg's video. There were some earlier comments that the DHO's grading does not look as convincing as on other scopes, including Rigol scopes.

It looks to me like the DHO800/900 varies the pixel intensity only based on how often a pixel was redrawn. In contrast, the DS1054Z (and many other scopes) also take into account how fast the "beam" was moving when drawing the trace. I.e. if there is a lower density of actual acquisition points, say on the fast edge of a signal, the interpolated line is rendered dimmer on the DS1054Z, but not on the DHO.

Visible in TurboTom's photo (re-attached here) along the envelope of the modulated signal, which is brighter only on the DS1054Z. (Because the carrier frequency "takes a slow turn" at its peaks.) And visible in blarrg's video, a few posts above, where the DS1054Z shows a marked contrast between the fast edges vs. the high/low logic states of the signal, but the DHO does not. (Except for the low state in some areas, which occurs more often.)

Does this make sense? Maybe a DHO owner can specifically confirm or refute this theory by looking at suitable test signals?

[ebastler]

I've got it in Normal trigger mode, on the clock line. Data comes in a burst, then nothing for a couple of seconds. I'd expect the scope to keep triggering on clocks until they stop, showing the last capture on trigger. Instead of overlays several captures on screen. In Gear->Display->Persistence I've got it set on Min (there's no Off). Is there no way to have it just show the most recent capture?

EDIT: I tried the same on my 1054Z and it worked as I expected, always showing only a single capture on screen at any given moment (there Persistence was also set to min., which is apparently off on that model).

I just tried this on the DS1054Z (with a different signal and timing), and can get the same qualitative effect. I used a modulated signal from a function generator which comprises a sequence of different bursts; the Single capture in the first picture gives an idea. When I set the scope to Run mode with Normal trigger, let it aquire for a moment and then switch the generator output off, the DS1054Z also shows an overlay of multiple sweeps, see the second picture. Persistence is at "minimum" here as well.

So the behavior you observed is not unique to the DHO. I think Fungus is right: The fact that the DS1054Z only shows a single sweep in your setting, while the DHO shows multiple, is due to a higher waveform update rate on the DHO. If one deliberately wants to isolate a single sweep, a trigger holdoff time is requred.

[2N3055]

This little persistence bug  is not a show stopper but just one of  the little quirks that Rigol is known to do sometimes.

Just a note.

While it seems you guys figured out what is happening, that is still not really correct behavior.
It should show only data from last trigger event, if persistence is disabled.

Looking for workarounds is wrong approach. File a bug report.
Fact that DS1000Z also did it wrong is not excuse  for anything.

[ebastler]

This little persistence bug  is not a show stopper but just one of  the little quirks that Rigol is known to do sometimes.

Turns out that this has been discussed four years ago with respect to the DS1000Z: https://www.eevblog.com/forum/testgear/rigol-ds1054z-persistance-in-stopwait-mode/

I would argue that the real limitation (or bug if you want) is that the persistence time can't really be set to 0, but only to "minimum". According to a comment by PeDre in the linked thread, that seems to mean 20 ms for the D1000Z -- not sure whether that number applies independent of the selected time base.

Pressing Stop or no longer providing triggers (in Normal triggering mode) will just freeze the last display, which is what I would expect from a DSO. But since there is always a bit of persistence "happening" while in Run mode, that last display will show multiple sweeps overlaid, if the sweep time is less than the persistence time.

Hence, if we submit a bug report, it should be "persistence time cannot be set to zero" in my understanding.

I have no idea what the DHO800's "Waveform Freeze" option does in this mix. Does it somehow override the persistence setting and force it to zero -- but only when entering Stop mode?

[Fungus]

I have no idea what the DHO800's "Waveform Freeze" option does in this mix. Does it somehow override the persistence setting and force it to zero -- but only when entering Stop mode?

Yes.

[ebastler]

I have no idea what the DHO800's "Waveform Freeze" option does in this mix. Does it somehow override the persistence setting and force it to zero -- but only when entering Stop mode?

Yes.

So, when the scope is waiting for a trigger in RUN mode, and showing the most recently acquired set of persistent traces on the screen -- can you press STOP, and it redraws the screen content from the acquisition buffer, showing just a single trace?

That would be another workaround for the "can't have zero persistence" limitation. But it seems that allowing a "persistence: none" setting would be the cleaner way from a UI perspective. I wonder whether there is some deep division-by-zero type limitation in the rendering engine for the intensity-graded display which does not allow this?

[Fungus]

So, when the scope is waiting for a trigger in RUN mode, and showing the most recently acquired set of persistent traces on the screen -- can you press STOP, and it redraws the screen content from the acquisition buffer, showing just a single trace?

Yes.

That would be another workaround for the "can't have zero persistence" limitation. But it seems that allowing a "persistence: none" setting would be the cleaner way from a UI perspective. I wonder whether there is some deep division-by-zero type limitation in the rendering engine for the intensity-graded display which does not allow this?

It simply doesn't make sense on a fast 'scope.

Imagine it's updating a byte of random serial data 60 times a second on screen. All the bits are going to be flickering between 0 and 1 at full frame rate. How does "persistence=0" help with that? All it does is move the persistence to your eyes.

Now imagine they're not completely random. Maybe they're 25% zeros. A bit of little bit of persistence will help you see the bias more clearly..


Where the DHO destroys the DS1054Z is in segmented memory mode. In this mode you can record all the bytes and play them back with "persistence=0".