Nassau Community College
Electronics and Telecommunications
Reference Sheet

Oscilloscope Phase Measurements


Performing Phase Measurements:

A common time measurement performed with the oscilloscope is a measurement of the phase angle between two waveforms. The traces on the oscilloscope must be properly set up. Then the phase angle may be determined using information from the display.


Setting Up The Waveform Display:

1. Begin by setting the vertical amplifier coupling switch (AC-GND-DC) to AC. This will block the DC on the signal, making it easier to center the trace.

2. Adjust the vertical amplifier VOLTS/DIV control to get the largest possible display on the screen. It may be necessary to adjust the vertical amplifier POSITION control to center the trace as you do this. Be sure the red CAL knob is in the detent position. This must be done for both channels.

3. Adjust the horizontal time base SEC/DIV to get about one cycle of the waveform on the display. You must have at least one complete cycle, but as few cycles as possible to maximize accuracy.

4. Set the vertical amplifier coupling switch (AC-GND-DC) to GND on each channel. This will result in a horizontal line for each channel
Horiz. 1

5. Using the vertical position control for each channel, position the two lines on the center graticule line.
Horiz. 2

6. Switch both vertical amplifier coupling switches (AC-GND-DC) to AC. This results in both traces being seen.
Traces 1

7. Use the horizontal position control to position one of the traces at an intersection of the graticule lines.
Traces 2


Measuring Phase:

The formula used to calculate phase angle is:
formula

1. Count the number of horizontal divisions from the where the trace crosses the intersection point to where the other waveform crosses the center graticule line. This is t
t measurement

2. Measure the period of one of the waves. This is T.
T measurement

3. The phase angle is:
formula

Be sure to record which wave is leading.