Magnapack

[MileHigh]

Tinman:

Note the impedance of the inductors will go up with frequency but I am only interested in the DC resistance measurements for the two coils that form the bifilar.  Also, the bifilar coil is a 1:1 transformer in this circuit and that means it actually looks like a resistive load because the secondary of the transformer is connected to a resistive load.  So it's probably fair to say that any possible high frequency inductance effects would be only due to the parasitic inductance associated with the lengths of the wires in the overall setup and the geometry and not due to the bifilar coil itself.

So it would be something like this: (first circuit)

1.  Measure the values of R1 and R2.
2.  Measure the DC resistance of each complete loop.
3.  Connect the signal generator and run the setup.
4.  Measure the RMS voltages across R1 and R2 to derive the RMS currents in each loop.
5.  Crunch the numbers and get the power dissipated in each loop to find the total power dissipated by the circuit.

I didn't think about the skin effect and it may also come into play.  It would lower the RMS currents, and you are measuring the RMS currents so you are at least accounting for the skin effect in the current measurement.  However, the effective DC resistance of the circuit would also increase because of the skin effect and you can't directly account for that.  Let's not go there because it will get too complicated and I may already be talking too much.

If you are interested in the measurements you could try to do the whole thing at a much lower frequency, like 500 Hz or 1 KHz.  Chances are the possible inductive effects of the wiring and any possible skin effects will become negligible.  In other words, bite off only so much at a time.

A similar issue applies for measuring the RMS voltages across the two resistors when the frequency is 690 kHz.  I don't know if your multimeter will make that measurement properly.  If you are not sure yourself here you have the advantage of being able to check the multimeter measurement against the scope measurement.  You absolutely must have the reference and signal contacts for both probes on exactly the same contact points at the same time.  Again, you can also compare the two measurements at 500 or 1 kHz with the expectation that they will be very close.  When you compare the two measurements at 690 kHz, there is a possibility that the multimeter would show a lower RMS voltage than the scope because of a high frequency roll-off effect.

You may laugh but I would not use the RMS voltage display on your scope until I knew your scope and knew that I could trust it.  I would divide the peak voltage of the AC waveform as read off of the display with my eyeballs by the square root of two to get the RMS voltage.  If your built-in scope RMS measurement was consistently in agreement with my "read the scope display by yourself and crunch" method then I would come to trust it.

If you do this, and then after the fact measure the DC resistance of all of the resistive elements in the circuit then you will be able to crunch the power dissipated in every component in the circuit.   That includes the individual windings of the bifilar coil.

MileHigh

[TinselKoala]

Grr. You are operating at two thirds of a megahertz. The DC resistance alone of the coils is almost irrelevant, would only become relevant if you were doing a DC control heating run. For the purposes of input and output power measurements, and for the scope shots to make any sense you need to know the total AC impedance of the coil and of the resistors. And even the interconnecting wiring. So you really need the inductance values of the coils and the wiring. You can calculate the inductance of the wiring from the dimensions, and you should be able to measure the inductance of the coils using any of a number of methods I and others have detailed, even without an inductance meter. Once you know the total AC impedance of the system then the power measurements will start to be interpretable. You may find that the left side and right side impedances are more different than you think, and this will of course affect your interpretation of the scope's voltage readings.

I have no problem with using a 0.1 ohm inline resistor for a current viewing resistor, and you should be able to monitor the voltage across the FG leads directly, so on the input you have Two traces that you can take a snapshot of, then laboriously hand-multiply some points together to get the instantaneous power function for the input. Then you can swap the probes over to the output 0.1 ohm resistor, and across the output transformer total load, and then do the same manual calculation for the output side. Using this method you don't need to worry about the impedances or phase relationships at all (yet...), all you need to do is compare areas of the resulting input and output instantaneous power functions.
On an analog scope or a 2-ch DSO that can't do math, it's a tedious process, but if you do it patiently you can arrive at answers that are within 5 percent of those you get using real 4ch topline DSOs with full on internal math. I know because I've tried it... several times.
It might take you four hours to get a good power function for the input, and another four to get the same for the output. Is overunity really worth all that work?

[MileHigh]

TK:

Are you sure you are not complicating things even more than me?  lol  My comments assume that Tinman is using a wonderful simple sine wave output from his signal generator.  That's what we see in the scope shots.  So all that you need is to work with sine wave excitation is RMS values and phase angles.  There is no need to become a human DSO with built-in math!

MileHigh

[tinman]

Well i now am starting to see why it's hard to learn how to measure things correctly.

Quote MH: but I am only interested in the DC resistance measurements for the two coils that form the bifilar.

Quote TK: Grr. You are operating at two thirds of a megahertz. The DC resistance alone of the coils is almost irrelevant, would only become relevant if you were doing a DC control heating run.

So two great minds telling me two different thing's?

Anyway,below is a scope shot of the input current and voltage .
CH1 is across the coil,and CH2 is across the .1 ohm resistor. Both grounds of the scope on the common conection ofcourse. Now with some more adjusting,i can get the current 180* out of phase with the voltage. Also i found it interesting that by adjusting the offset on the SG,only the current trace changed-the voltage trace remaind as is. From a 2 dimentional point of view,i can raise or lower the current trace through the voltage trace.

[MileHigh]

Tinman:

Myself and TK are not necessarily in disagreement.  We might have different reasons for what we are saying.  I am interested in the resistance of the coils, it's for the power dissipation measurements.

I suspect that TK made a reflex call but he can clarify that if he wants to.  He is making reference to the AC impedance of a coil of the bifilar at 690 kHz being much higher than the DC resistance of the coil.  I also stated that it's not a coil, it's a transformer, and on the far side of the transformer (the secondary) there is a resistive load.  So the primary "coil" of the bifilar transformer will have the characteristics of a resistor and the AC impedance at "conventional" high frequencies will not come into play.

Big disclaimer:  I note that I am saying this sight unseen and I am assuming that your bifilar coil/transformer is a typical "fist sized" coil.  I don't really know how your bifilar coil will respond when acting as a transformer at 690 kHz.  I would have to sweep it on the bench to find out.  TK and others have much better "feel" for these things and can make better preliminary estimates than me because they have the hands-on experience that I don't have.  You have to understand the context - people that work as engineers and technicians on the bench don't normally do these kinds of tests at all.  I never had any reason to do a bandwidth sweep of a hand-made bifilar transformer to see how it would work at 700 kHz.

MileHigh