The basic principle of the waveform display is known from the principle of the oscilloscope tube. When a DC voltage is applied to a pair of deflection plates, the spot will produce a fixed displacement on the screen, and the magnitude of the displacement is proportional to the applied DC voltage. If the two DC voltages are simultaneously applied to the vertical and horizontal two pairs of deflection plates, the position of the light spot on the phosphor screen is determined by the displacement in both directions. If a sinusoidal AC voltage is applied to a pair of deflection plates, the spot will move with the voltage across the screen. Referring to Figure 5-4, when a sinusoidal AC voltage is applied to the vertical deflection board, the voltage is Vo (zero) at the instant t=0, and the light spot on the phosphor screen is at the coordinate zero point 0 at time t. At the instant of =1, the voltage is V1 (positive value). The light spot on the screen is at 1 above the zero point of the coordinate. The displacement is proportional to voltage V1; at time t=2, the voltage is V2 (maximum positive value). ), the light spot on the screen is at 2 o'clock above the zero point of the origin of the coordinate, the displacement distance is proportional to the voltage V2; and so on, at the instants t=3, t=4,...,t=8, the screen The spots of light spots are 3, 4, ..., and 8 points respectively. The first cycle will be repeated in the second cycle of the AC voltage, the third cycle...

If the frequency of the sinusoidal AC voltage applied to the vertical deflection plate at this time is very low, only 1 Hz to 2 Hz, then a light spot moving up and down will be seen on the screen. The instantaneous deflection value of this spot from the origin of the coordinate 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 board is above 10Hz~20Hz, the phosphor screen persistence phenomenon and the persistence phenomenon of the human eye, the phosphor screen does not see a point moving up and down, but a Vertical bright line. The length of the bright line is determined by the peak value of the sinusoidal AC voltage peak when the oscilloscope's vertical amplification gain 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 voltage, is applied to a pair of deflection plates, how does the light spot move on the screen? See Figure 5-5. When there is sawtooth voltage on the horizontal deflection board, the voltage is Vo (the maximum negative value) at the moment of time t=0, and the starting point of the light spot on the left side of the coordinate point on the screen (zero point). ), the displacement distance is proportional to the voltage Vo; at time t=1, the voltage is V1 (negative value), the light spot on the screen is at the left point of the coordinate origin, and the displacement distance is proportional to the voltage V1; Analogy, at time t=2, t=3,. . . For each instant of t=8, the corresponding position of the light spot on the screen is 2, 3,..., 8 points. At the moment t=8, the sawtooth voltage jumps from the maximum positive value V8 to the maximum negative value Vo, and then the light spot on the screen moves from the 8 o'clock position to the left. If the sawtooth wave voltage is periodic, the first cycle will be repeated for the second cycle, the third cycle,... Of the sawtooth wave voltage. If the frequency of the sawtooth wave applied to the horizontal deflection plate is very low at this time, only 1Hz to 2Hz, the light spot will be seen on the screen from the left zero position to the right 8 points at a uniform speed, and then the light spot From the right 8 o'clock, move to the left zero starting position very quickly. This process is called scanning. When a periodic sawtooth voltage is applied to the horizontal axis, the scan will continue on and off.

The instantaneous value of zero from the start point of the light spot 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 board is above 10Hz~20Hz, a horizontal bright line will be seen due to the persistence phenomenon of the fluorescent screen and the persistence phenomenon of the human eye. The length of the horizontal bright line is on the oscilloscope. The horizontal amplification gain is determined by the sawtooth voltage value. The sawtooth voltage value is proportional to the time. The displacement of the light spot on the screen is proportional to the voltage value. Therefore, the horizontal bright line on the fluorescent screen can be Represents the timeline. Any equal line segment on this bright line represents an equal period of time. If the signal voltage to be measured is applied to the vertical deflection board, the sawtooth wave scanning voltage is applied to the horizontal deflection board, and the frequency of the measured signal voltage is equal to the frequency of the sawtooth wave scanning voltage, and a cycle of the measured value will be displayed on the fluorescent screen. The waveform of signal voltage changes with time (as shown in Figure 5-6). As can be seen from Figure 5-6, at the instant t=0, the signal voltage is Vo (zero value) and the sawtooth voltage is V0' (negative value). The light spot on the screen is to the left of the origin of the coordinate, and the displacement distance is proportional to the distance. At voltage V0', at time t=1, the AC voltage is V1 (positive value), the sawtooth voltage is V1' (negative value), and the light spot on the screen is in the IIth quadrant of the coordinates. Similarly, at the instant of time t=2, t=3,...,t=8, the light spots on the screen are located at 2, 3,..., 8 points respectively. At time t=8, the sawtooth voltage jumps from the maximum positive value V8′ to the maximum negative value V0′, so that the light spot on the screen also moves from 8 o'clock to the left of the starting position 0 point extremely quickly. Later, in the case where the first cycle is repeated for the second period, the third period, and the second period of the signal to be measured, the trajectories traced by the light spots on the fluorescent screen are also overlapped on the trajectory described for the first time. Therefore, the measured signal voltage displayed on the fluorescent screen is a stable waveform curve that changes over time.

If the frequency of the measured signal voltage is equal to the integral multiple of the sawtooth wave voltage frequency, the waveform will show the stable waveform of the measured signal with an integer period. When the frequency of the measured signal voltage and the frequency of the sawtooth voltage are not integral multiples, a stable waveform cannot be obtained on the fluorescent screen, as shown in Figure 5-7. In Figure 5-7, on the first scan, the waveform on the screen is 0~1; on the second scan, the waveform on the screen shows 1~2; during the third scan, the screen The waveform curve between 2 and 3 is displayed on the screen.... It can be seen that the waveforms displayed on each screen are different, so the graph is unstable. It can be seen from the above that in order to stabilize the pattern on the fluorescent screen, the frequency of the signal voltage to be measured should maintain the integer ratio of the frequency of the sawtooth wave voltage, ie, the synchronization relationship. In order to achieve this, it is required that the frequency of the sawtooth wave voltage be continuously adjustable so as to be suitable for observing periodic signals of various frequencies. Secondly, due to the relative instability of the frequency of the measured signal and the frequency of the sawtooth oscillation signal, even if the frequency of the sawtooth wave is temporarily adjusted to an integral multiple of the frequency of the measured signal, the graph cannot be kept stable. Therefore, oscilloscopes are equipped with synchronizing devices. That is, a synchronization signal is added to a part of the sawtooth wave circuit to promote the synchronization of the scanning, and a simple oscilloscope (such as a domestic SB-10 type oscilloscope) can be used to generate a continuous scan (that is, generate a continuous sawtooth wave). For example), it is necessary to input a synchronization signal related to the frequency of the observed signal on its scanning circuit. When the frequency of the synchronization signal applied is close to the autonomous oscillation frequency of the sawtooth frequency (or close to an integer multiple thereof), it can be seen as sawtooth. The wave frequency "pulls in sync" or "locks." For oscilloscopes that have the function of waiting for scanning (that is, no sawtooth wave is generated at ordinary times, a sawtooth wave is generated when the signal is detected to perform a scan) (such as domestic ST-16 type oscilloscope, SBT-5 type synchronous oscilloscope, SR-8 In the case of double trace oscilloscopes, etc.), it is necessary to input a trigger signal related to the measured signal on its scanning circuit so that the scanning process closely cooperates with the measured signal. In this way, as long as the appropriate synchronization signal or trigger signal is selected as required, any process to be studied can be synchronized with the sawtooth wave scanning frequency.

Two-wire oscilloscope display principle In the electronic practice technology process, it is often necessary to simultaneously observe the time-varying process of two (or more) signals. The electrical parameters of these different signals are tested and compared. In order to achieve this goal, based on the principle of using ordinary oscilloscopes, people use the following two methods to simultaneously display multiple waveforms: one is a dual-line (or multi-line) oscillometric method; the other is double-track (or More traces of the oscillometric method. Oscilloscopes that are manufactured using these two methods are called dual-line (or multi-line) oscilloscopes and dual-trace (or multi-track) oscilloscopes, respectively. Dual-line (or multi-line) oscilloscopes are implemented using dual-gun (or multi-gun) oscilloscopes. The following is a simple description of a double-gun oscilloscope. The double-gun oscilloscope has two independent electron guns to produce two electrons. There are two groups of independent deflection systems that each control a bunch of electrons for movement up and down and left and right. The screens are common, so that two different electrical signal waveforms can be displayed on the screen at the same time. Two-wire oscilloscopes can also be implemented using single-shot two-wire oscilloscopes. This kind of oscilloscope only has one electron gun. In operation, it depends on special electrodes to divide electrons into two beams. Then, the two independent deflection systems in the tube control the two electrons up and down and left and right movements, respectively. The screens are common and can display two different electrical signal waveforms at the same time. Due to the high manufacturing process requirements and high cost of the two-wire oscilloscope, the application is not very common.