2018 - Keysight 1000X scope - product design FLAW at 50Hz measurements

[Kiriakos GR]

Product design flaw spotted from one owner of DSOX1102G and a video shown on YouTube.

Symptom: 24V regular transformer output this measured with significant error by switching from DC to AC coupling.
ACV-rms measurement shown more than 10 % error even in comparison with a rms multimeter.

Keysight justified this flaw by their R&D saying:
AC coupling is useful for view waveforms with large DC offsets. 
AC coupling places a 10 Hz high-pass filter in series with the input waveform and removes  DC offset voltage from the waveform.  Keep in mind that 10 Hz is the filter’s -3dB point (and still has some attenuation).
AC coupling should only be used on sine waves greater than 100 Hz and square waves greater than 200 Hz. DC coupling should be used on frequencies lower than that.
So, it's basically a filtering thing when using AC coupling.


ITTSB Blog ....
I did run identical test at my (GW Instek)  GDS-2000A and there is no such measuring unbalance.
7V RMS  at 50Hz  was produced by an AWG generator.
I did double Verification by using regular probe at times X1 & x10 and also by using  single high-performance 50 Ohms cable with BNC plugs.

I wanted to explore if impedance mismatch this can be held responsible in any way.

If you do using Keysight 1000X scope or 2000X or 3000X,  you better check how it performs, because caused error in electrical measurements this could be huge.
Keysight marketing team in past five years it does ignores professionally working electricians bloggers, therefore too bad for them.