Reactive power - Reactive Generator research from GotoLuc - discussion thread

[poynt99]

Weren't Luc's sample scopeshots showing both channels DC coupled? On Tek scopes I've used, there appears a little "sine wave" symbol next to the channel settings when the channel is AC-coupled, and nothing when the channel is DC coupled. Inversion is shown by the downward pointing arrow.

I don't know, I didn't check the screen on the video.

All I can say for sure right now is that Luc had both channels set to AC coupling in his last video, and I doubt he has ever changed that setting, at least not for a while. One could go look at the video and see if the little squiggle is there.

[poynt99]

Poynt, your test shows the effect of AC coupling of one trace on the resultant Math trace mean. But I have a question about the effect on the mean of the original trace itself. Should an AC-coupled signal produce a "mean" value of zero, for that trace itself, before entering into the multiplication math trace?

I'm not sure I fully understand all of your question.

A DC coupled trace will produce a zero MEAN if the area of excursions above and below the zero ref line are equal.

An AC coupled trace will always produce a zero MEAN I think because the zero ref line always settles to the average value of the wave form.

It is irrelevant if the voltage or current trace have a MEAN of zero, because the MEAN of the trace doesn't enter into the multiplication. We're only taking the MEAN of the product. Make sense?

[poynt99]

OK Luc.

Here is the link to that software for your scope. Hopefully the link works.

http://depositfiles.com/files/89djph9ky

Let me know when you have it, as I'll probably delete it afterwards.

.99

[TinselKoala]

I don't know, I didn't check the screen on the video.

All I can say for sure right now is that Luc had both channels set to AC coupling in his last video, and I doubt he has ever changed that setting, at least not for a while. One could go look at the video and see if the little squiggle is there.

OK, I checked the screen on the video and it does not indicate AC coupling by the usual squiggle. Very tricky; there doesn't seem to be any way to tell the channel coupling except by going into the setup menu, where we can see that Luc has AC coupling set on both channels. The coupling isn't indicated on the normal scopeshot apparently. That's a "gotcha" that means one needs to be very careful using that particular scope model. As we can see, your higher-end Tek scope indicates clearly the coupling with the sine wave squiggle.

The coupling issue has come up before. Many people seem to think that you need to use AC coupling to measure an AC signal, but as we now know, that's not what it's for at all. Looking at how the scope accomplishes the miracle of AC coupling might help one to understand just what it does and how it's used. AC coupling merely switches in a capacitor in series with the probe input lead, blocking the DC component of any input signal and only letting the AC component pass to the scope's input.

[poynt99]

Yeah, good to know that some Tek scopes don't have that squiggly indicating AC coupling.

Well, glad it got sorted though. Will be interesting to see if Luc's results change as dramatically as I showed.