inductor phase

[electrolust]

After watching w2aew #55 I tried to measure a series LC circuit for resonance.  I found that the resonance point was where I expected, but I could not get the total signal (across both L+C) to 0V or even close.  After some head scratching I realized that it's because the inductor phase was not 90° to the input signal.  Am I doing something wrong?

Here are traces of the capacitor and inductor alone, with a 50r current sense resistor (annotated "load") to measure the input signal.  The inductor is 7m2 with DCR 83r at the test frequency of 5300Hz.  Inductor SRF is 1.4MHz.  I guess I should test at the SRF but I haven't come across any information that the frequency affects the phase.

In the cap trace, the phase is -91.x and this is within the phase error of the 2 probes.

For 20 traces, I found that the probes themselves are out of phase an average of 0° but a max of about 2°.  That seems pretty damn noisy to me, is my expectation out of wack?  I'm measuring across ch. 2 and ch. 3 which are on different "banks" of the scope, would I get better results if I used ch. 1 and ch. 2 instead?  Even if that corrected it or I otherwise solved that issue, note that the inductor phase error is 13° by itself, and that in the LC circuit the phase error L and C is 20°.  So the probe error is small compared to inductor "error".

[electrolust]

Ah.

I see now, it is because I'm not near enough to the SRF of the inductor.



source: https://meettechniek.info/passive/parasitic.html