The Romer-Lewin ring with inductors (part 5a: Measuring the current - effects of burden voltage)

Of the different ways to measure the current in this low impedance loop (with my low-cost hobbyist equipment), only the use of a low-value sensing resistor results in a decent accuracy.
Shown here are the computations and simulations of the ring with real inductors, when there is a 1 ohm sensing resistor and when an ammeter with an internal resistance of 10.5 ohm is inserted in the loop.
The UT210E clamp ammeter is of no use, since it can only measure AC current at frequency around the 50-60 Hz mark, and we're running at 4kHz.
The UT139E has a bandwidth of about 1 kHz, so its current measurements at 4 kHz would give a value that's considerably attenuated (not mentioning the problem due to its burden voltage.)
The UT61E has a much larger bandwidth and works fine at 4 kHz but we need to consider its burden voltage.
It turns out that inserting the UT61E as an ammeter on the mA range places an additional resistance of 10.5 ohms in a circuit whose total impedance has a magnitude of 16 ohms. This perturbation inevitably changes the current we want to measure from about 9.9 mA (rms) to 6.3 mA (rms), introducing an error of nearly 40%. (It's 37.3%, in case you are wondering). The burden voltage is about 64 mV (rms) and it hogs most of the EMF in the ring.
Using a 1 ohm sensing resistor and measuring the voltage it develops can help in getting an accurate measurement, reducing the error to 'just' 2.8%. Not exactly a negligible error, but a good step forward.
In the next video I will show the UT61E's burden voltage on the scope.