Power Measurement Basics

[gotoluc]

Gotoluc, no it is not an issue at all.  AC coupling does not invert phase.  AC coupling removes information from below the cut off frequency.  In this case the probe has a cut off frequency of about 350Hz and the oscilloscope has a cut off frequency of about 5Hz.  The source signal is a clean 10kHz sine wave and has virtually no energy below 10kHz.  If the signal had a DC offset in it, the AC coupling would have removed that offset, shifting the signal up or down towards an average voltage of zero.

Thanks MarkE,

still much to learn

I was doing all my AC power calculation with AC Coupling and was told I must use DC coupling to get accurate math data. I was also told to leave probes to DC coupling as I would most never need to use AC coupling.
I hope this is not another debate issue

Hope to get all this straight soon

Thanks

Luc

[poynt99]

Mark we are communicating fine. It appears however that you have missed an important part of the video.

I would suggest now that my video parts are compiled in the correct order, you go and watch them again.

You will see that in the beginning of the Part1b video, not only do I clearly state and show that the battery power is negative, but I show that I am multiplying the negative load voltages by a negative loop current of -2.7mA.

For example, I clearly state in the video: " -2.7mA times our -5.43V, gives us a positive 14.7mW".

For your quick reference, here is a screen shot of that part of the video, clearly showing the negative wattage on the battery, and the positive wattages on the 3 loads.

[gotoluc]

Luc,

The AC coupling shown there is no problem. Mark is using a real current probe. The P6021A is only good down to 120Hz, so it would not be suitable for your AC measurements.

Okay, I see.

Would be nice to see a demo of making a current probe out of a Hall sensor and how to correctly use it.

Maybe once you have your new videos you could start a new topic to keep it clean and use this topic for discussions.

Thanks

Luc

[poynt99]

Luc,

Most Hall sensor probes are not capable of high frequency measurements, which is why there are AC only current probes. When you find a very expensive probe that goes from DC to say 100MHz, it most likely is accomplishing this through a combination of AC probe and DC hall sensor.

The two videos are up now. Please review them and let me know your thoughts. See reply#26 above for the new links.

[MarkE]

Thanks MarkE,

still much to learn

I was doing all my AC power calculation with AC Coupling and was told I must use DC coupling to get accurate math data. I was also told to leave probes to DC coupling as I would most never need to use AC coupling.
I hope this is not another debate issue

Hope to get all this straight soon

Thanks

Luc

Gotoluc you are doing the right thing by doing what you can to learn the subject.  Many people make the bad assumption that because they use an pricey piece of equipment that the measurements must be accurate when there are many ways to misapply even the best equipment and get terribly wrong answers.  If you pay attention to people like Poynt99 and tinselkoala you will do well.