Phase measurement with an oscilloscope

Phase measurement. The measurement of the phase difference between two signals can be performed using the dual-trace display function of the instrument. Figure 2.21 shows an example of two leading and lagging sine wave signals with the same frequency displayed using a dual-trace square wave display. At this time, the "trigger source" switch must be set to the channel connected to the leading signal, and the "Time/DIV" switch must be set to make the displayed sine wave waveform larger than 1 cycle.

As shown in Figure 2.21, one cycle occupies 6 grids, and 1 grid scale represents the waveform phase 60. Therefore, the phase difference Acp is

Observe the Lissajous diagram and press the "XY" button. The signal input from the "CH1" port is the X-axis signal, and its deflection sensitivity is still read according to the vertical deflection factor switch indication value of the channel. Input the Y-axis signal from the "CH2" port, and the oscilloscope will work in XY display mode.

When the oscilloscope's X-axis and Y-axis simultaneously input sinusoidal signals, the movement of the light spot is the synthesis of two mutually perpendicular resonant vibrations. If the ratio of their frequencies is an integer, the synthetic trajectory is a closed figure, called a Lissajous figure. The figure of the Lissajous figure is related to the frequency ratio and the phase difference of the two signals, but the Lissajous figure has a simple relationship with the frequency ratio of the two signals:

The formula contains the number of tangency points of the circumscribed horizontal lines and the number of tangency points of the circumscribed vertical lines of the Lissajous diagram, as shown in Figure 2.22.