Measurement Of Oscilloscope Phase

Using an oscilloscope to measure the phase difference between two sinusoidal voltages has practical significance. Using a counter can measure frequency and time, but it cannot directly measure the phase relationship between sinusoidal voltages. There are many methods for measuring phase using an oscilloscope. Below, only a few commonly used simple methods are described.
1. Double trace method
The dual trace method uses a dual trace oscilloscope to directly compare the waveforms of two measured voltages on a fluorescent screen to measure their phase relationship. During measurement, the phase leading signal is connected to the YB channel, and the other signal is connected to the YA channel. Select YB trigger. Adjust the "t/div" switch so that one cycle of the measured waveform accurately occupies 8 div on the horizontal scale, so that the phase angle of a cycle of 360 ° is divided equally by 8, and each 1 div is equivalent to 45 °. Read the difference T between the forward wave and the backward wave on the horizontal axis, and calculate the phase difference using the following formula φ：
φ= 45°/div × T（div）
If T==1.5div, then φ= 45°/div × 1.5div=67.5°
2. Pattern method for phase measurement
Place the X-axis selection of the oscilloscope at the X-axis input position, connect the signal u1 to the Y-axis input terminal of the oscilloscope, and connect the signal u2 to the X-axis input terminal of the oscilloscope. Properly adjust the relevant knobs on the oscilloscope panel to make a suitably sized ellipse appear on the fluorescent screen (in special cases, it may be a circle or a diagonal line).
Let the signal u1 on the Y-axis deflection plate precede the signal u21/8 cycle on the X-axis deflection plate, and let the initial phase of u2 be zero φ 2=0, so when u2 is zero, u1 is a larger value. As shown in the figure at the "0" point. At this time, the light spot on the fluorescent screen is also correspondingly located at the "0" point. As time changes, u1 rises and u2 also rises, and the light spots on the fluorescent screen move to the right and up. After 1/8 cycles, u1 and u2 respectively reach the "1" point. At this time, u1 reaches the maximum value, and u2 is a larger value. The light spot on the fluorescent screen is located at the corresponding "1". If this continues, the light dot on the fluorescent screen will draw a clockwise rotating ellipse. If u1 lags behind u2, it forms an ellipse that rotates counterclockwise. Of course, this only occurs when the signal frequency is very low (such as a few Hertz), and on a short afterglow fluorescent screen, the phenomenon of clockwise or counterclockwise rotation of the light spots on the fluorescent screen can be clearly seen. As can be seen from the above, the shape of the ellipse varies with the phase difference between the two sinusoidal signal voltages u1 and u2. Therefore, the phase difference between two sinusoidal signals can be determined based on the shape of the ellipse Δφ。 Let A be the ordinate of the intersection of the ellipse and the Y axis, and B be the maximum coordinate of each point on the ellipse. As can be seen from the figure, A is the instantaneous voltage corresponding to u1 when t=0