EE4life said:
I have made some changes to my setup and I am receiving better results. I will share my observations once I am ready.
Okay, here the grand finale.
An oscilloscope is not the best tool the measure phase. But here is the best setup using it
1. Measure current with a non inductive resistor (test the phase of it on an LCR meter!)
2. Measure total voltage and current using the same model voltage probe. This will help to eliminate any delay differences between the probes
3. Use a vernier scope (highly adjustable time base). Make sure to get exactly a whole number of cycles on the screen. Take the data to your computer. Minus CH1 from CH2 to get the voltage over the sample. CH2 is the current, in phase. Use FFT analyzer to get the phase at the frequency that you are driving at. Minus the phase of voltage and current to get the phase between them.
I also found that the level of the impedance you are measuring effects the phase measurment due to interaction with the probe impedance. Amplitude is very accurately measured, however, phase measurements are strongly perturbed by probe impedance interactions.
The fact about FFT part is critical. Among other reseasons, there is always sometype of bias on your waveform, even with AC coupling. It does not matter too much when the phase is low, but with a near 90 phase a small change in phase due to DC offset could mean negative power!
Also getting exactly getting a whole number of cycles on a screen, for it increases the phase resolution dramatically when you are talking about 100milidegrees resolution.
LabVIEW has good FFT analysis methods and I would reccomend using the "estimate main frequency component and phase" option, or its called something like that. Please post if there are questions. Sorry for being a little vague, but I hope it provide some good info.