Oscilloscope display principle
According to the principle of the oscilloscope tube, when a DC voltage is applied to a pair of deflection plates, the light spot will produce a fixed displacement on the fluorescent screen, and the size of the displacement is proportional to the applied DC voltage. If two DC voltages are applied to two pairs of vertical and horizontal deflection plates at the same time, the position of the light spot on the fluorescent screen is determined by the displacement in both directions.
If a sinusoidal AC voltage is applied to a pair of deflection plates, the light spot on the fluorescent screen will move as the voltage changes. Referring to Figure 5-4, it can be seen that when a sinusoidal AC voltage is applied to the vertical deflection plate, at the instant of time t=0, the voltage is Vo (zero value), and the light spot position on the fluorescent screen is at the coordinate origin 0. At time t =1, the voltage is V1 (positive value), the light point on the fluorescent screen is at 1 above the coordinate origin 0, and the displacement is proportional to the voltage V1; at the moment t=2, the voltage is V2 (maximum positive value ), the light point on the fluorescent screen is at 2 points above the coordinate origin 0, and the displacement distance is proportional to the voltage V2; by analogy, at each instant of time t=3, t=4,..., t=8, the fluorescent screen The positions of the polishing points are 3, 4,..., 8 o'clock respectively. In the second cycle, the third cycle of the AC voltage... the situation of the first cycle will be repeated. If the frequency of the sinusoidal AC voltage applied to the vertical deflection plate at this time is very low, only 1Hz to 2Hz, then a light spot moving up and down will be seen on the fluorescent screen. The instantaneous deflection value of this light spot from the coordinate origin will be proportional to the instantaneous value of the voltage applied to the vertical deflection plate. If the frequency of the AC voltage applied to the vertical deflection plate is above 10Hz to 20Hz, due to the afterglow phenomenon of the fluorescent screen and the persistence of vision of the human eye, what you see on the fluorescent screen is not a point moving up and down, but a line. Vertical bright line. The length of the bright line is determined by the peak-to-peak value of the sinusoidal AC voltage when the vertical amplification gain of the oscilloscope is constant. If a sinusoidal AC voltage is applied to the horizontal deflection plate, a similar situation will occur, except that the light spot moves on the horizontal axis.
If a voltage that changes linearly with time (such as a sawtooth wave voltage) is applied to a pair of deflection plates, how will the light spot move on the fluorescent screen? Referring to Figure 5-5, it can be seen that when there is a sawtooth wave voltage on the horizontal deflection plate, at the instant of time t=0, the voltage is Vo (maximum negative value), and the light spot on the fluorescent screen is at the starting position to the left of the coordinate origin (on the zero point). ), the displacement distance is proportional to the voltage Vo; at the instant of time t=1, the voltage is V1 (negative value), the light point on the fluorescent screen is at 1 point to the left of the coordinate origin, and the displacement distance is proportional to the voltage V1; with this By analogy, at each instant of time t=2, t=3,...,t=8, the corresponding positions of the light points on the fluorescent screen are points 2, 3,..., 8. At the moment t=8, the sawtooth wave voltage jumps from the maximum positive value V8 to the maximum negative value Vo, and the light spot on the fluorescent screen moves from 8 o'clock to the left extremely quickly to the starting position zero point. If the sawtooth wave voltage is periodic, the situation of the first cycle will be repeated in the second cycle, third cycle, etc. of the sawtooth wave voltage. If the frequency of the sawtooth wave voltage applied to the horizontal deflection plate at this time is very low, only 1Hz to 2Hz, you will see the light point on the fluorescent screen moving from the starting position zero on the left to 8 o'clock on the right at a constant speed, and then the light point moves again Move extremely quickly from 8 o'clock on the right to the starting position of zero on the left. This process is called scanning. When a periodic sawtooth voltage is applied to the horizontal axis, scanning will continue over and over again. The instantaneous value of the light spot from the zero point of the starting position will be proportional to the instantaneous value of the voltage applied to the deflection plate. If the frequency of the sawtooth wave voltage applied to the deflection plate is above 10Hz to 20Hz, due to the afterglow phenomenon of the fluorescent screen and the persistence of vision of the human eye, a horizontal bright line will be seen. The length of the horizontal bright line will be measured on the oscilloscope. When the horizontal amplification gain is certain, it depends on the sawtooth wave voltage value. The sawtooth wave voltage value is proportional to the time change, and the displacement of the light spot on the fluorescent screen is proportional to the voltage value, so the horizontal bright line on the fluorescent screen can Represents the timeline. Any equal segments on this bright line represent equal periods of time.
