Please note that the Rigol has known bugs in its RMS measurement calculations so I wouldn't trust those figures. I probably shouldn't have included them in the scopeshots, I should have put p-p values instead so that we humans could calculate the RMS values from them instead of relying on the scope's math for that.


Meanwhile, trusting TinMan's Atten scope's RMS measurements... I performed some calculations using the values from his three scopeshots above. I posted these on OUR but I'm repeating the post here for discussion.

___________________________________

Ok.... it would still be better if your scope could compute the phase shift itself. But in your First shot, if we take the rms current through R1 (CH2) as 0.0618V/10R = 0.0062 A_rms as the current being supplied to the system, and the voltage drop across the whole circuit (CH1), and estimate the phase shift as 72 degrees, we then calculate the total input average power as
P = V_rms x I_rms x cos (72 degrees)
P = 6.60 x 0.0062 x 0.309
P = 0.0126 W or 12.6 mW

And if we calculate the power dissipated in R1 as
P = V_rms²/R
P = 0.071²/10
P = 0.0005 W

And the power dissipated in R2 as
P = V_rms²/R
P = 0.348²/10
P = 0.0121 W

So we get the total power dissipated in the resistors as
0.0005 + 0.0121 = 0.0126 W or 12.6 mW.

Coincidence?

This result is very sensitive to the Phase Shift in part 1, so we really need a good measurement of that. 

Quote from: TinselKoala on April 30, 2017, 04:24:25 AM
Brad, I've done the same thing with my Tesla Bifilar solenoid coil, just because it's easier to work with than the pancake coil. Here are my three scopeshots that correspond to your three shots above. Using 10 ohm resistors just as you have done and connected to FG and scope exactly as you have done.

Note that the CH2 RMS measurement is practically the same for #1 and #2, as it should be since the probe and ground reference positions haven't changed. And also note that the phase shifts in #2 and #3 are also the same, as it should be since both half-coils have essentially the same inductance.

I don't much like using the fine-tuning controls on the V/div scales to make the traces the same height on the screen, but since you did that, so did I.

My scope, thankfully, will do Measurements on the Math trace so I've shown the Average value of the Math in all three cases. I'm too coffee-deficient at the moment to be able to tell if these are valid values or what they might mean, though.

So your total P/in is 6.99mW ?
dissipated power in R1&L1 is 4.27mW ?
And in R2& L2 it is 3.81mW ?
So P/in is 6.99mW
P/out is 8.08mW ?

Also,i think my scope is toasted,or has a hickup there some where.


Brad

Quote from: tinman on April 30, 2017, 06:41:27 AM
So your total P/in is 6.99mW ?
dissipated power in R1&L1 is 4.27mW ?
And in R2& L2 it is 3.81mW ?
So P/in is 6.99mW
P/out is 8.08mW ?

Also,i think my scope is toasted,or has a hickup there some where.


Brad

No, the scope isn't calculating the Math value correctly for some reason. And not trusting the Vrms values, I went ahead and did the P-P x 0.3535 to get RMS values of my own...and they are quite close to the RMS values reported by my scope so maybe the RMS bug has been fixed in the latest firmware revision which I loaded a few weeks ago. But the Math averages shown on the scope are definitely still wrong.

Repeating the same calculations on my values that I did for yours, here's what it looks like.

Total input power is V_rms x I_rms x Cos (82.7 degrees) = 4.86 x 0.0193 x 0.127 = 0.0119 W or 11.9 mW.
Power dissipated in R1 is P = I²R = 0.0193² x 10 = 0.003725 W
Power dissipated in R2 is P = I²R = 0.02187² x 10 = 0.004783 W
Total power dissipated in resistors is then 0.00851 W or 8.51 mW.
BUT... my coil has a lot of turns of fine wire and its DC resistance is 10.3 ohms total. So we have to include the power dissipated in that resistance as well.
Power dissipated in coil's DC resistance is P = I²R = 0.0193² x 10.3 = 0.003837 W or 3.84 mW.

And that brings our total dissipation to 0.01235 W or 12.35 mW  -- compared to our input calculation of 11.9 mW. This is within rounding and measurement error of being equal.  COP=1.04 is not significantly greater than 1.0 considering the measurement uncertainties and roundings.

Quote from: tinman on April 30, 2017, 06:41:27 AM

Also,i think my scope is toasted,or has a hickup there some where.


Brad

Try join to "church" , maybe you earn a new one, and your envy and of some fellows could become in happiness.


Nelson Rocha

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.