What is the concept of dual amplitude?

It is actually a concept relative to single amplitude: double amplitude refers to peak-to-peak (P-P), which is the displacement. What the human eye sees is the displacement of the object. When calculating frequency, amplitude, and acceleration, the amplitude at this point is the single peak value (0-P). Be careful to note the difference between the two. Double amplitude, that is, peak-to-peak (P-P) = 2 times the single peak value (0-P)

Reply to 1# 888flash: Amplitude can be described in two ways – as single amplitude or double amplitude – and they mean the same thing. If the double amplitude is 10, then the single amplitude is 5; both values are referenced to the position of the entire machine in its free state when it is at rest. Vibrating upward to the peak (assuming the stroke is 5) constitutes one single amplitude, while vibrating downward to the lowest point (also assuming the stroke is 5) constitutes the other single amplitude. Adding these two together gives the double amplitude of 10. Your amplitude gauge is used to observe the vibration direction and amplitude. Those angled lines are used to view the vibration angle. The black circle is used to indicate the amplitude intensity. After the vibration settles down upon startup, that straight line becomes the clearest; the angle (an acute angle) it forms with the horizontal line is the vibration direction angle. The diameter of each black circle is different; take a close look. When one of those circles vibrates to the point where it is almost in tangent contact, its amplitude is roughly that value. If two 8mm circles are tangent to each other, the amplitude will be 8. The value shown here is the value of the dual amplitude. When checking the direction of vibration, remember to draw a horizontal line alongside the diagonal line on the paper you’re using; then use a level to check it before sticking it in place. It cannot be placed randomly, otherwise the direction will be incorrect. The amplitude isn’t affected by this direction – it can be determined by looking at the circles.