Rigol DS2072 DC offset

[leafi]

Hey

Is anyone else Rigol DS2072 have a DC offset on their traces? I ran self calibration and it gets rid of most of it but when I turn the power off and back on the offset comes back.

Thanks

[PA0PBZ]

I can test if you want, how exactly are you testing and what do you see?

[leafi]

Hi thank you.

I am setting both traces to 5mV / div @10X (500uV @ 1X) and set the averaging on in the acquire and set it to lets say 1024 samples. This will average out the noise and show the DC level. After the auto reboot from the self cal the traces are ok maybe +/- 1-3 mV. When I turn the power off on the scope and power it back on they come back as several divisions ~15mV and they change each time the scope is booted up.

Im trying to compare it right now with the scope I need to return. The one I need to return is not unlocked and the level too does jump around after boot up but not 3 divisions. It seems to hold the calibration better and is like +/- 1 mV after reboot but they do move around a bit.

[leafi]

It looks like a warm up time. Maybe I need to let it run for 1 hour then self test and then leave it alone. It is settling at about 500 - 600 uV but it changes each boot up. It started at like 10mV and has come down.

[PA0PBZ]

I did the same, see attachments. The first one was before running selfcal, in fact it was still on the factory self cal, I only have it for a few days.
The second one is after self cal, and it stays the same when switched off and on again. So it is just a minor offset, although on CH1 it seems still a bit more. BTW, this is also a 'converted' DS2072 

[leafi]

Thank you for the images. Im just trying to make sure this new scope is good. I already have to send 1 back :-(

However this has provided me the opportunity to try to compare them which is partly why Im having questions. One major difference is noise considering one is 200Mhz and one is still 70Mhz.

I have another question for you all, one scope came with the RP3300 and the other came with the RP3300A. The 3300A are fixed 10X and the 3300 are 1X/10X. The 3300A have lower input capacitance but are rated for lower bandwidth 300Mhz (RP3300A) vs 350Mhz (RP3300). Do you think I should keep the 3300 or 3300A and why?

[PA0PBZ]

Well, if it is as simple as 350MHz and 1x/10x versus 300MHz and only 10x I'd say keep the 3300. Mine came with the 3300A and I am ok with that. Mine is also hardware version 2.0 with an extra switchable 50 Ohm input, but it is not (yet) supported by the firmware. See the pictures here: https://www.eevblog.com/forum/testgear/rigol-ds2000-hardware-version-2-0/

[leafi]

So yours does not need a warm up time 

Mine needs like 10 minutes and the average comes down. 

Ill call Rigol but I dont know what they will say. The other unit I have is not so far off on power up but it too drifts with time. (kind of expected really). I just do not know if this is a symptom or another problem.

[Carrington]

I did the same too:
  - Before running selfcal, and after ~30 minutes I get a offset of ~800uV.
  - After selfcal see attachement.

[leafi]

after self cal mine is good. However if I turn it off for lets say 10 min and power it back on there its a 3 division offset which has to settle out and it takes several minutes. Do yours do that or is it 800 uV right away?

[Carrington]

In "cold" the offset is around 800 uV, and after ~30 minutes of "warm up" it returns to the same values than after a selfcal.
Do not worry, because this is normal. 

[leafi]

You are saying yours is 800uV at cold? Mine will get down good after some time ~10 min. :-/

 I talked with Rigol and they said the unit is speced with a 30 min warm up time. The unit I returned also did not immediately center at zero and had an exponential decay but the offset was less to start with. I guess as long as it gets there it will be ok.

Maybe I should get one of the 4 channel scopes. 4000 series.... well once they can unlock them fully too. Then I can have 4 channel scope on the bench where I need it and 2 channel at my desk.