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teslaalset · July 05, 2010, 04:54:30 PM

@ Omnibus,
I guess it depends on how you mount the current probe in the setup.
Below two possibilities.
The top one includes the current throught the voltage probe
The bottom one excludes the current through the voltage probe
It would be interesting to see the difference in current results.

B.t.w. I noticed a quite large offset in the input current. Did you check the offset having no input signal from the generator?

Omnibus · July 05, 2010, 06:02:45 PM

teslaalset,

That's a very reasonable suggestion but I'll have to try it at some other time. I just changed the setup with the one I used earlier in which I'm trying to eliminate the voltage probes. Do you remember the setup with the copper plated board, the BNC's and the two feet BNC cable? I just tried it and am getting efficiencies on the order of 0.05. Will have to work on this more. As for the current offset, that was due to the current probe not being set to zero. Doesn't seem to affect the result, though.

Omnibus · July 05, 2010, 07:23:34 PM

@teslaalset,

Here are the results with and without current through the 1X voltage probe. As you can see there's substantial difference. Nevertheless, the effect persists. Also, the current offset seems less or slightly in the opposite direction thi the direction it was at before zeroing the current probe.

Omnibus · July 05, 2010, 10:54:53 PM

Just did an experiment by attaching two, even three 1X passive voltage probes to the same point of measurement to see if the loading by the probe would have any effect on the signal. The signals were practically overlapping and i didn't see any distortion of the wave. Similar was the behavior of the 10X probes attached to the same point of measurement. Also, holding the probe lead, moving it around and even twisting it didn't show any effect on the signal. As far as I understand, although 10X probes have higher impedance, they are unsuitable for low level signals such as the studied here and probably that's the reason for the weird results (0.05 efficiency) when using such probes. The best test in this respect was the one suggested by @teslaalset which clearly demonstrated a shunting effect by the probe and yet the OU effect was still preserved, as the Excel spreadsheet above indicate. This question regarding the accuracy of measurement together with the ostensible problems in our case with the least squares line fitting have to be understood well.

teslaalset · July 06, 2010, 04:32:11 AM

Quote from: Omnibus on July 05, 2010, 07:23:34 PM
@teslaalset,

Here are the results with and without current through the 1X voltage probe. As you can see there's substantial difference. Nevertheless, the effect persists. Also, the current offset seems less or slightly in the opposite direction thi the direction it was at before zeroing the current probe.

I played around with these data files and encountered a significant effect on the 'plus current' data.
What you can see is that the 'plus current' data is not very reproducible, or instable or it shows a trend that is ongoing.
The 'minus current' data shows a good overlap of the X-Y graph, while the 'plus current' file doesn't.
Seems that measuring only one input sinus period is not good enough to do a reliable analysis.