# Why do I get the wrong phase shift?

I am trying to compare theory vs simulation values and it seems to be that there are differences. I am using Multisim to simulate a RLC circuit, the LC are in parallel and in series to the resistor.

The circuit is given, In the practical I used a function generator with an amplitude of $$\10 V_{\text{pp}}\$$ (5V to -5V). Now that I am working on the theory part, I used the maximum value as the magnitude to get the correct voltage, however I keep getting wrong phase shifts.

The parallel components impedance is $$\Z=218j\$$

Applying the voltage divider rule... $$\V_{R_{1}}=\frac{R_{1}}{Z_{1}+R_{1}}V_{in}\$$

$$\V_{R_{1}} = (0.75\angle-41^{\circ})(5\angle0)= 3.76\angle-41^{\circ} \text{V}\$$

The oscilloscope show's a different angle,

This shows that VR1 lags Vin.

$$\\theta = (2.66\cdot10^{-3}\cdot50\cdot360^{\circ}) = 48^{\circ}\$$

When is the magnitude of input voltage phasor 10Vpp and when is it just the maximum 5Vp? Why am I getting big difference in phase shifts (48 compared to -41)? Thank you for taking the time.

• Have you considered that your inductor might not be that accurate; it could be maybe 20% different to what is marked on the component. You clearly are not using the precise peak tops of the waveforms. More care needed is my impression. Oct 10, 2022 at 17:21
• The inductor will also probably have significant series resistance; 650 mH is quite a lot. That will throw things off as well (though not by too much). I recommend also using the zero crossings instead of the peaks, if you must use the cursors manually instead of a measurement function, as those are less difficult to line up your cursors on. Oct 10, 2022 at 19:37
• When the green wave is too late versus red, phase is not "negative"? Oct 10, 2022 at 20:50

The oscilloscope show's a different angle,

Check this Maple sheet and picture.

When the sine is "too late" versus the generator, the phase is negative.
Is it?

As pointed out by @Hearth

With your data, the serial resistance of the inductor should be ~ 117 Ohm.
Calculate 20*log10(3.753/4.960)= -4.88 db.
Do AC analysis (parameter rr, serial resistor). At 50 Hz, just read this value and rr.

If you make a larger analysis, you should have this (guess: min @ 200 Hz).