Lately I've been trying to wrap my mind around the idea of phase-shift between current and voltage in reactive circuits.
I figure that I can understand it better if I can get pictures of what I'm working with. So I tried the following:
- Ran 120VAC through a couple of series inductors. They're the biggest transformers I have, but their magnetizing load was still pitiful, something like 0.025A.
- Put a current clamp probe around the hot wire feeding the inductors. Hooked the ground and test leads of an oscilloscope to each lead of the clamp probe. This gave me a waveform on my scope that showed the current draw to the inductors.
- Hooked the second probe of my 'scope between the hot and neutral wires supplying the inductors. This gave me a voltage waveform.
- Triggered both waveforms from a single input. I figured that if each the current and voltage waveforms were actually 90 degrees of out phase that this would cause them to be displayed that way.
That's not what happened. I each waveform to display amplitude accurately, and they were ever-so-slightly out of step, but definitely not 90 degrees. And adding or subtracting inductance from the circuit did not change phase shift (if that's what it was).
I was thinking maybe I needed to make all my grounds common? Scope probe grounds + power neutral + current clamp grounds? But I'm really weary about grounding out my current-clamp, it's the only one I have and with an output resolution of 1mV it seems sensitive enough to be damaged if I put even a couple of volts across the output leads.
Any ideas from electronic gurus?
-John
