# How to find phase shift from oscilloscope?

In university we are tasked to input a 10Vpp 50Hz signal, in a series RLC circuit. I’m having trouble understanding the difference between a positive and negative edge phase shifts on Agilent Oscilloscope DSO1012A.

On the oscilloscope the values seem to be different for each the positive and negative edge phase shifts while usually it seemed a phase shift had only one angle relative to a reference waveform. There were no other phase shift options in the time menu.

How can I find the phase shift and magnitude?

Voltage across the capacitor waveform (GREEN), supply (YELLOW):

• It may look different because your zero points for channel 1 and channel 2 aren't the same. Try setting them both to the middle of the scale. Oct 5, 2022 at 13:45
• @Hearth Just AC-couple both channels? Oct 5, 2022 at 13:50
• @winny I suppose that would work. I was thinking of using the vertical position control. Oct 5, 2022 at 13:57
• @Hearth Vertical position control and setting trigger to 0V helped me measure it using the grid. Is there a reason as to why they measure differently if the frequency is the same and the waveform is stable? In a case I got Pha_R1-2=-79 and Pha_F1-2=282 across resistor on the same circuit. I was able to measure the phase shift manually and it was correct. I don't understand what these two values are for. Oct 10, 2022 at 17:05
• @Arcadius Is this a current-voltage measurement? Have you deskewed the current probe? Oct 10, 2022 at 19:14

A good thing to do would be to calculate these expressions by hand instead of relying on the scope to do the work (it becomes important to double check equipment)

Magnitude is simply the height of the signal. There are several ways to express it, Peak to Peak (or Vpp, which is the height from top to bottom of the whole signal)

Phase Shift is the angle between the sine waves, this assumes that they are the same frequency and they need to be centered around zero.

The first thing to do would be to align the centers and then calculate the delay between sine waves, you could convert this to angle

Phase angle φ = time delay (in seconds) × frequency f * 360 (in degrees)

• When do we set the magnitude as the peak to peak and when is it just the maximum value? Oct 10, 2022 at 16:57