Introduction to the method of measuring phase with an oscilloscope
It is of practical significance to use an oscilloscope to measure the phase difference between two sinusoidal voltages. A counter can measure frequency and time, but it cannot directly measure the phase relationship between sinusoidal voltages. There are many ways to measure phase with an oscilloscope. Below, only a few commonly used simple methods are introduced.
1. double trace method
The double trace method uses a double trace oscilloscope to directly compare the waveforms of the two measured voltages on the fluorescent screen to measure their phase relationship. During measurement, connect the phase-advanced signal to the YB channel and the other signal 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 ruler. In this way, the phase angle of 360° in one cycle is divided into 8 equal parts, and each 1 div is equivalent to 45°. Read the difference T between the leading wave and the lagging wave on the horizontal axis, and calculate the phase difference φ according to the following formula:
φ=45°/div×T(div)
If T==1.5div, then φ=45°/div×1.5div=67.5°
2. Phase measurement using Lissajous figure method
Place the X-axis selection of the oscilloscope at the X-axis input position, connect signal u1 to the Y-axis input end of the oscilloscope, and connect signal u2 to the X-axis input end of the oscilloscope. Appropriately adjust the relevant knobs on the oscilloscope panel so that an ellipse of appropriate size appears on the screen (in special cases, it may be a perfect circle or a diagonal line).
How does an oscilloscope calculate scan speed?
The scanning speed of the oscilloscope is displayed on the upper left, 10mS/div; the attenuation factor of channel 1 is 1V/div (the probe attenuation ratio must match the setting); I don't understand what the horizontal width is.
Analog oscilloscopes can calculate frequency, period, peak-to-peak voltage…
Period T = scanning speed (t/div) × the number of grids div occupied by the waveform in one repeating period in the horizontal direction (peak to peak, or valley to valley>;
Frequency f=1/T;
Peak-to-peak voltage Vpp = attenuation factor (V/div) × number of grids occupied by the waveform in the vertical direction;
In this digital oscilloscope, these can be found in the menu, so there is no need to calculate, which is relatively convenient.
