Products > Test Equipment

Rigol DG800 (long) list of problems and the sad death of a FPGA

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MarkoAnte:
Hi,

so I bought a Rigol DG822 and o boy is it problematic.
The same problems were confirmed on DG832 and also on the DG1062Z. I suspect the same goes for higher end new models. But I think the supplier wanted to save face and didn't want to test all the way up to 2k model.

I am working on a phase measurement sistem so I need a square wave and a sin wave, of known phase and known frequency (nothing more). All the problems I found were form using it only this way so there are sure to be more problems. Here are the problems I got so far.

First the most important problem (that killed my FPGA). The DC offset is not set when the signal is turned on.
The signal is set for 0 to 3.3 V, 1 MHz square wave. The time base is set to 2ms/div, and then zoomed in to 500ns/div. You can see that the "averaging" on the 2ms/div shows how the signal ramps up as the DC offset kicks in.
This is how the turn on looks like:


Just to prove that this is not some oscilloscope trickery, here is a picture of the start with 200 ns/div time base.


This is what killed my FPGA (mid ranged kintex (150 euro + bga rework ) :'( ). The pin got -1.65 V, was clamped to -0.7 ish = -(1.65-0.7)V/50R = 20mA (max is 10mA). During testing I turned the function generator output off/on quickly and that killed the diode / the pin.  :palm:

Second the phase alignment is broken.
 Lets set the output frequency to 0.8 MHz and angle to 0 deg. Then lets change the frequency form 0.8 MHz to 1.3MHz in 0.1 MHz steps, pressing the align button every time, here are the results:
f[MHz] 0.8 0.9 1.01.11.21.3Angle[°] 10 12.2 15.81.74.6-0.4
From the data sheet: Range 0° to 360°, Waveform Phase Resolution 0.03°. Resolution 0.03°, accuracy 0.03° +/- 20°  :palm:

Third problem, communication with PC is broken.
When I tired to connect to the FG form the PC I got: 

--- Code: --- * Connected to: USB0::0x1AB1::0x0643::DG8A205203709::INSTR
-> *IDN?
<- (Return Count:55)
Rigol Technologies,DG822,DG8A205203709,00.01.08.00.01

 * Error!!!
VISA:  (Hex 0xBFFF0015) Timeout expired before operation completed.


--- End code ---

I didn't waste much time on this, it could be me, my pc or just my FG. But as for all these problems I got no solutions form both rigol and the seller.

Forth problem, general SW bugs.
List a few that I noticed:
- align does not work some times (even if we ignore the 2 problem),
- save presets saves some settings but not the others eg. It shows frequency coupling on, but it is not. You have to turn it off and then on and then its ON. So the function is basically usless,
- (more general) the touch screen is dodgey at best, as is the setting stuff with the wheel.

Fifth, more subjective one
The design: non stackable, edgy :D, with tini-tiny out of place power button that I feel like I will brake it every time. But this is  :horse: .

All the problems (except 4 and 5) were reported to the seller and promptly ignored. I then had to call them and they said that they could not repeat the problems. I had to go there 4 times to show how to set frequency and square wave form so they could "reproduce" the problems  :palm:. Mind you this is the official re seller, that only sells rigol and agilent. They even got a big "HP EXPERT" diploma hanging on the wall.    :-DD

They contacted Rigol and were ignored (it seams) then I contacted Rigol and were also promptly ignored. I got no solutions to try, all I got is they can replace the FG. What QC in Rigol is doing I don't know  :-//.  These are the problems you look for when testing new firmware eg. what happens on turn on.

So if you are looking for a function generator look for something else.


 
 


TurboTom:
Marko -

sorry to hear about these mishaps. I completely agree with you that this way of implementing the offset is a complete no-go. I can confirm the same behavior on my "improved" DG800.



Since the DG2000 series is basically the same hardware in a different coat, I'm sure this is also true for this sereies. But I'm surprised that the DG1000Z behaves similarly since this is a much more mature product.

FYI, I checked the offset switch-on behaviour of the DG4000 and the SDG6000X which both behave unproblematic (if you don't mind the inital voltage level half-way between maximum and minimum signal level).



Interestingly, the DG4000 offers a setting "DDS Hold" which can be toggled on/off and is hidden in the Utility/CHxSet/2nd Page/ menu and permits a more or less direct start of the output signal with a "proper" level. Yet, output relay bounce may now be an issue.



On the other hand, if "DDS Hold" is on, when changing other parameters, like frequency as shown here, the signal may get pretty much messed up momentarily.




There's another interesting parameter in the aforementioned menu page of the DG4000 -- "Range" which can be toggled between "Auto" (default) and "Hold": This will prevent switching the attenuation/amplification levels of the output amplifier of the corresponding channel, preventing relay bounce / glitches to appear when changing the output amplitude. Obviously, the amplitude range is then limited to what's possible within that locked attenuator setting. But I consider this an option that may be quite useful at times.

The DG4000 is the only AWG that I've got access to that has no issues with the phase relation between the output signals of the two channels. The DG800 produces a considerable phase step when crossing the 1MHz "border" as you mentioned. Seems like something gets reconfigured at that frequency internally.

But even the SDG6000X shows an (apparently constant) phase delay between the outputs of something like 56ns. It's not related to scope channels, signal cables or what not. Since "Phase Coupled" mode doesn't  permit to enter a constant delay (only relative or degrees) between the channels, there's no way to compensate for this (well, you could use different lengths of cables...). If running the instrument in phase mode "independent", such a compensation is possible by individual entry to the channel phase delays, but since the phase is no longer locked, it's not certain that no drift may occur (though I didn't observe any).





It's also worth to mention that all the generators produce glitches or momentarily pause the signal (for a few milliseconds) when parameters (frequency) are changed.

In case of square or pulse signals (or in general signals with a small number of discrete levels), there should be a menu setting of the "initial level" or "initial phase" that is present at the output while the output enable relay gets switched on. This way, there won't be the chance for any "invalid" signal level to appear at the output while enabling the signal. Simply outputting half-way between maximum and minimum signal level definitely isn't the proper way to do it.

Since I haven't got access to any recent "A-Brand" AWG, I cannot verify if the situation is better with one of these, but when going into detail, every single one of the "B-Brand" units that I've got access to, leaves quite a lot to wish for. Unfortunately, the firmware turn-around times are quite long and it's not sure if the manufacturer implements every "improvement" that gets carried on to him.

But I'm pretty sure that most "serious" B-Brand manufacturers are well informed of the discussions going on here on EEVBlog Forum concerning their products. I guess Rigol will at least "silently" take care of the faulty offset signal switch-on procedure in one of their next firmware updates...

MarkoAnte:
TurboTom ty for so much detail.

I'm pretty sure it was DG1000Z. I think I would prefer the non lethal option form DG4000 to the DG800 one.

But I think that these is a modern problem type of deal. I tested the FG integrated into MSO-X 3034A there is the result:

Better but still crap.

I then said fu to agilent/rigol and went to a tektronix dealer. He only had AFG1022 to show me. In that model we had difficulty setting a phase between a sin and a square wave. But also on start up there was a combination between the 3034A and your DG4000. It was mid scale then it started with a similar thing that the 3034A  does. I did not take a picture sadly - was not my lab/scope/time.

We also tested a old model afg3000 looking thing. Don't remember the exact number. Had only 1 channel. No longer on sale, obsolete ect. No problems. Square wave, started form 0 when to 3.3, first cycle was correct duty cycle.

Maybe I will go to some friends on university and nage them into letting me try some old FG. It would be interesting to see how many of the old FG do it correctly.

The most infuriating this is, that this is obviously bad SW design.

At the end I would be batter off just making my own FG :D FPGA, R2R for sin wave, pin for square wave and just dump the contents of RAM to R2R. Generate RAM contents form matlab and just re-flash the FPGA for different frequency/angle. I don't need any THD or stuff like that. Just a sin wave and a square wave of a same selectable frequency and angle.

thinkfat:
Talking about strange behavior, my SDG2042X doesn't hold phase between channels if one of them is at a very low frequency. When setting a 10MHz sine wave on one and a 1Hz PWM on the second channel, phase shifts by 90° every second.

worsthorse:

--- Quote from: MarkoAnte on January 20, 2020, 10:36:29 am ---Hi,


Third problem, communication with PC is broken.
When I tired to connect to the FG form the PC I got: 

--- Code: --- * Connected to: USB0::0x1AB1::0x0643::DG8A205203709::INSTR
-> *IDN?
<- (Return Count:55)
Rigol Technologies,DG822,DG8A205203709,00.01.08.00.01

 * Error!!!
VISA:  (Hex 0xBFFF0015) Timeout expired before operation completed.


--- End code ---

I didn't waste much time on this, it could be me, my pc or just my FG. But as for all these problems I got no solutions form both rigol and the seller.


--- End quote ---

Thanks for sharing this info.  On the communication problem, I've run into this, too. My DG832 USB communication is unreliable on older PCs. It also fails when the USB is going through a hub.  Direct connection to a more modern laptop seems to reliably work. 

The offset is a bigger issue. I use a lot of older equipment, so I am used to measurable delays between powering on and outputs being in a known state. I don't apply that to my modern gear and I guess I need to start doing so.

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