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How can I see in this picture that the signals are AC coupled? Does not AC coupled means that the DC offset is 0 and the sine is centered to the origin? Both signals have an offset from what I can see here.

enter image description here

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    \$\begingroup\$ Those are not "just" sine waves. They appear asymmetric to me, and the contribution from the noise can not be ignored. Their average (dc) value may not be exactly half way between the peaks. Maybe you should tell us more about the signals and how you captured them. \$\endgroup\$ – Elliot Alderson Sep 11 at 17:20
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    \$\begingroup\$ You have noise and to me it looks like your positive and negative periods seem to have different width. So it could be AC coupled ... or not. \$\endgroup\$ – Oldfart Sep 11 at 17:20
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    \$\begingroup\$ Zoom out with the screen shot and let's see the 'scope settings. \$\endgroup\$ – Transistor Sep 11 at 17:30
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How can I see in this picture that the signals are AC coupled?

You can't. We can see that both signals have zero mean, but we can't tell why that might be. AC coupling could explain it.

Does not AC coupled means that the DC offset is 0 and the sine is centered to the origin?

Yes, the peaks of a sine wave would be centered on the origin.

Both signals have an offset from what I can see here.

These are obviously not sine waves. But they do appear to be exact complements of each other, and they cross each other exactly at zero on the vertical axis. Therefore, there is no common-mode signal. This means either of two things:

  • Neither signal has a DC offset. (the simplest case)
  • Both signals have a DC offset, and the offsets exactly cancel each other. (unlikely)
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