I have a not-cheap Keysight scope which had the same problem. They replaced the analog front end board under warranty.
Have you Quick Cal engaged ? It's in the Utilities menu and runs in the background while you use the scope.Yes, there is. If I disconnect the probe (nothing connected to the BNC input), there's an offset too. If I set the time base to something like 10 or 20 ms (that's already pretty slow), there's still a non-zero mean value.
I updated firmware and did a self callibration successfully. Still, the offset is there.
Could it be a fault? Sometimes is larger, sometimes is lower (same setup).
Today, while working on a real circuit, I got zero offset for a couple of minutes. Then, the offset came back (same circuit, same probe, same attenuation, etc.)
Tried one period, one and a half, two, three, three and quarter, and many others. Same result.Just a thought, but does the amount of offset vary with the frequency of the sine wave?
Some screenshots for your study, all using RMS and Statistics, first Peak Detect, 2nd 16 Averages and 3rd 3 bits ERES all of which can be selected from the Acquire menu.
SDS1104X-E, 1x probe grabber and reference lead connected to ground, 2mV/div
I used a 220 nF PET capacitor.Out if interest, what size capacitor did you use in the external circuit ?
you still have the times 10 engaged, so I am guessing your using the 10:1 probe, can you connect directly , with the capacitor, and send us a picture of the setup .
Maybe. That's why I'm asking for advice, as I have no expensive scope at hand to compare the performance against.it could be that you are expecting to much from the scope,
Averaging doesn't solve the problem. Anyway it wouldn't be a solution for me, as I'm interested in single events and noise measurements too, which cannot be averaged.And with the averaging switched on?
The noise might come from the signal generator. It is not a great piece of equipment, and the signal is quite low. For larger signal the noise is almost invisible (it powers from a linear supply).I also note your sine wave looks terrible, there is an amazing amount of noise on it.
This too.I'd like to see a picture taken of the setup, as you say this is low voltages, so setup is very critical.
I tried with a borrowed Tektronix scope. It is a 12 years scope, not recently callibrated, but I get the same behaviour (even worse sometimes).I would also not be surprised if there is not a low frequency on the sine wave as well,
is the mean value constant, or does it vary when your using the external capacitor ,
I'd like to see a picture taken of the setup, as you say this is low voltages, so setup is very critical.
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