Quote from: TinselKoala on April 30, 2017, 07:28:56 AM
Repeating the above calculations and taking the scope's reported RMS values and phase shift as "exact", along with a more precise measurement of the DC coil resistance as 10.4 ohms, I get

Total Input Power = 0.011846 W or 11.85 mW.
Total dissipated power in R1+R2+Rcoil = 0.01178 W or 11.78 mW.

Rounding to three significant digits we have 11.8 mW in = 11.8 mW out.

So your coils are dissipating all the energy they receive?
Quite odd for an inductor-dont you think?.

Is this at it's resonant frequency?,or have you tried a range of frequencies?.


Brad

Quote from: tinman on April 30, 2017, 07:57:38 AM
So your coils are dissipating all the energy they receive?
Quite odd for an inductor-dont you think?.

Is this at it's resonant frequency?,or have you tried a range of frequencies?.


Brad

No, it's not at resonant frequency, I have tried a range of frequencies and these shots are done where I can get a display that looks somewhat like yours in terms of phase shift.

The coils are acting like a combined resistance + inductance. They are dissipating essentially no power in the inductance and are dissipating power in the resistance. Perhaps they are radiating a little power in RF but that is really negligible. As you can see the calculations come out very balanced as to "input" vs. total dissipation in the resistive elements, both for your coil (assuming very small resistance of your coil) and for mine (using its measured 10.40 ohms DC resistance). No, it's not odd for an inductor, it is behaving just as expected, I think, where it is dissipating power only in its DC resistance.

I finally got a set of measurements including the Average Power that are consistent. I think the Rigol's measurements are very sensitive to how many cycles of waveforms are on-screen and how much screen height they take up.

So now the Average Power in this scopeshot, calculated manually from Vrms x Irms x (cos phaseshift) reported values,  is equal to the scope's automatically calculated Average Power on the Math trace.

Quote from: TinselKoala on April 30, 2017, 09:08:17 AM
I finally got a set of measurements including the Average Power that are consistent. I think the Rigol's measurements are very sensitive to how many cycles of waveforms are on-screen and how much screen height they take up.

So now the Average Power in this scopeshot, calculated manually from Vrms x Irms x (cos phaseshift) reported values,  is equal to the scope's automatically calculated Average Power on the Math trace.

TK,

Yes you are correct regarding the number of cycles taken in the overall measurement as they must be complete cycles for the greatest accuracy.  At present all the math is being calculated from screen edge to screen edge.  Does your scope or TM's have the ability to take measurements between vertical cursors?

PM

Quote from: partzman on April 30, 2017, 09:29:22 AM
TK,

Yes you are correct regarding the number of cycles taken in the overall measurement as they must be complete cycles for the greatest accuracy.  At present all the math is being calculated from screen edge to screen edge.  Does your scope or TM's have the ability to take measurements between vertical cursors?

PM

Yes, the Rigol has vertical and horizontal cursors, but they only report raw voltage, delta-voltage and time and delta-time values. So phase shift would still have to be manually calculated from the delta-t between zero crossings of the waveforms, I guess. There is also an automatic cursor mode that "tracks" what the "quick measurements" show, in other words, the cursors will snap to the portions of the waveform(s) that correspond to what the Measurements are showing. But the cursor readouts themselves only have voltage and time values.

TM's scope also has cursors but I don't know what they can show. I'll have to check the Atten manual.