What is waveform display?

According to the principle of oscilloscope tube, when a DC voltage is applied to a pair of deflection plates, the light spot will have a fixed displacement on the screen, which is proportional to the applied DC voltage. If two DC voltages are applied to the 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 alternating voltage is applied to a pair of deflection plates, the light spot will move on the screen with the change of voltage. When sine AC voltage is applied to the vertical deflection plate, at time t=0, the voltage is Vo (zero value), the position of the light spot on the fluorescent screen is at coordinate origin 0, at time t= 1, the voltage is V 1 (positive value), and the light spot on the fluorescent screen is above coordinate origin 0 1, and the displacement and voltage are v/kloc-. At the instant of time t=2, the voltage is V2 (very positive), the light spot on the fluorescent screen is two points above the coordinate origin 0, and the displacement distance is proportional to the voltage V2; By analogy, at the moments of t=3, t=4, …, t=8, the positions of light spots on the fluorescent screen are 3, 4, …, 8 respectively. The first cycle will be repeated in the second and third cycles of AC voltage. If the frequency of sinusoidal AC voltage applied to the vertical deflection plate at this time is very low, only lHz ~ 2Hz, then a light spot moving up and down will be seen on the screen. The instantaneous deflection value of this light spot from the coordinate origin will be proportional to the instantaneous voltage applied to the vertical deflection plate. If the frequency of AC voltage applied to the vertical deflection plate is above 10 Hz ~ 20 Hz, what you see on the screen is not a point moving up and down, but a vertical bright line due to the afterglow phenomenon of the screen and the persistence phenomenon of human vision. When the vertical amplification gain of oscilloscope is fixed, the length of bright line depends on the peak value of sinusoidal AC voltage. 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 varies linearly with time (such as sawtooth voltage) is applied to a pair of deflection plates, how will the light spot move on the screen? When there is a sawtooth voltage on the horizontal deflection plate, at the instant of time t=0, the voltage is Vo (very negative), the starting position (zero point) of the light spot on the screen on the left side of the coordinate origin, and the displacement distance is proportional to the voltage VO; At the instant of time t= 1, the voltage is V 1 (negative value), the light spot on the fluorescent screen is on the left side of the coordinate origin 1, and the displacement distance is proportional to the voltage V 1; By analogy, at times t=2, t=3, ... t=8, the corresponding positions of the light spots on the screen are 2, 3, ... 8. At the moment of t=8, the sawtooth voltage jumps from a very positive value V8 to a very negative value Vo, and the light spot on the screen moves from the 8 o'clock position to the zero point of the initial position very quickly. If the sawtooth wave voltage is periodic, the first period will be in the second period and the third period ... If the voltage frequency of sawtooth wave applied to the horizontal deflection plate is very low at this time, only 1Hz ~2Hz ~ 2 Hz, you will see the light spot move from the left starting position zero to the right eight, and then move from the right eight to the left starting position zero very quickly. This process is called scanning. When the periodic sawtooth voltage is applied to the horizontal axis, the scanning will be repeated. The instantaneous value of the light spot starting 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 voltage frequency of sawtooth wave applied to the deflection plate is above 10Hz~20Hz ~ 20Hz, a horizontal bright line will be seen due to the afterglow phenomenon of the fluorescent screen and the persistence phenomenon of human vision. The length of this horizontal bright line depends on the sawtooth voltage value of the oscilloscope under a certain horizontal amplification gain, which 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 represent the time axis. Any equal segment on this bright line represents equal time periods. If the measured signal voltage is applied to the vertical deflection plate and the sawtooth wave scanning voltage is applied to the horizontal deflection plate, and the frequency of the measured signal voltage is equal to the frequency of the sawtooth wave scanning voltage, the periodic waveform curve of the measured signal voltage changing with time will be displayed on the fluorescent screen. When the second cycle and the third cycle of the measured periodic signal both repeat the first cycle, the trajectory traced by the light spot on the fluorescent screen also overlaps with the trajectory traced for the first time. Therefore, the measurement signal voltage displayed on the fluorescent screen is a stable waveform curve that changes with time. In order to make the picture on the screen stable, the frequency of the measured signal voltage should keep an integer ratio relationship with the frequency of the sawtooth wave voltage, that is, a synchronous relationship. In order to realize this, it is required that the frequency of sawtooth voltage can be continuously adjusted to adapt to the observation of periodic signals with different frequencies. Secondly, due to the relative instability of the frequency of the measured signal and the frequency of the sawtooth wave oscillation signal, even if the frequency of the sawtooth wave voltage is temporarily adjusted to an integer multiple of the frequency of the measured signal, the mode cannot always be stable. So there is a synchronization device in the oscilloscope. That is, a synchronization signal is added to a certain part of the sawtooth wave circuit to promote the synchronization of scanning. For simple oscilloscopes (such as domestic SB- 10 oscilloscopes) that can only produce continuous scanning (i.e. continuous sawtooth wave), it is necessary to input a synchronous signal related to the frequency of the observed signal into their scanning circuits. When the frequency of the added synchronous signal is close to the self-oscillation frequency of the sawtooth wave frequency (or close to its integer multiple), oscilloscopes (such as domestic ST- 16 oscilloscopes, SBT-5 synchronous oscilloscopes, SR-8 dual-trace oscilloscopes, etc.) have the function of waiting for scanning (that is, they do not generate sawtooth wave at ordinary times, but only generate a sawtooth wave when the measured signal arrives), so it is necessary to input an AND into their scanning circuits. In this way, as long as the appropriate synchronization signal or trigger signal is selected according to the needs, any process to be studied can be synchronized with the sawtooth wave scanning frequency. In the process of electronic practice technology, it is often necessary to observe the process of two (or more) signals changing with time at the same time. And test and compare these different signals. In order to achieve this goal, on the basis of applying the principle of ordinary oscilloscope, people use the following two methods to display multiple waveforms at the same time: one is the double-line (or multi-line) oscillometric method; The other is the double trace (or multi-trace) oscillometric method. The oscilloscopes manufactured by these two methods are called double-wire (or multi-wire) oscilloscopes and double-trace (or multi-trace) oscilloscopes respectively. Double-wire (or multi-wire) oscilloscope is realized by double-gun (or multi-gun) oscilloscope. Let's take a double gun oscilloscope tube as an example to briefly explain it. The double gun oscilloscope tube has two independent electron guns to generate two electron beams. There are also two independent deflection systems, each of which controls a beam of electrons to move up and down, left and right. The fluorescent screen is used for * *, so two different electric signal waveforms can be displayed on the screen at the same time, and a single-gun double-line oscilloscope can also be used to realize the double-line oscilloscope. This oscilloscope tube has only one electron gun, and it works by means of special electrodes to split electrons into two beams. Then, two independent deflection systems in the tube control the two electron beams to move up and down and left and right respectively. The fluorescent screen used for * * can display two different electric signal waveforms at the same time. Because of the high requirements of manufacturing process and high cost, the application of double-wire oscilloscope tube is not very common. Double-trace oscilloscope, double-trace oscilloscope (or multi-trace oscilloscope) is based on the single-line oscilloscope, adding a special electronic switch to realize the separate display of two (or more) waveforms. Because the dual-trace (or multi-trace) oscilloscope is easier to realize than the dual-trace (or multi-trace) oscilloscope, there is no need to use the "double-cavity" or "multi-cavity" oscilloscope with complex structure and expensive price, so the dual-trace (or multi-trace) oscilloscope has been widely used. In order to keep the two signal waveforms displayed on the fluorescent screen stable, it is required that the frequency of the measured signal, the frequency of the scanning signal and the switching frequency of the electronic switch must meet a certain relationship. First of all, there should be an integer ratio between the frequency of the two measured signals and the frequency of the scanning signal, that is, "synchronization". This principle is the same as that of a single-wire oscilloscope, except that there are two signals to be measured, one scanning voltage. In practical application, the two signals that need to be observed and compared often have internal relations, so the above synchronization requirements are generally easy to meet. In order to make the waveforms of the two measured signals displayed on the fluorescent screen stable, in addition to meeting the above requirements, the switching frequency of the electronic switch must be reasonably selected to make the number of waveforms displayed on the oscilloscope suitable for observation. First of all, the working mode of the electronic switch is related to the switching frequency of the electronic switch. There are two working modes of electronic switch: "alternating" conversion and "intermittent" conversion. The waveform displayed by alternating conversion method is very similar to that displayed by double-line oscillometric method, and they have no discontinuity. However, because the waveforms of the measured signals UA and UB appear alternately on the screen in turn, if the alternate gap time exceeds the visual duration of human eyes and the afterglow time of the screen, the waveforms seen on the screen will flicker. In order to avoid this situation, electronic switches are required to have a sufficiently high switching frequency. That is to say, when the frequency of the measured signal is low, the alternating conversion mode should not be adopted, but the intermittent conversion mode should be adopted. When the electronic switch works in intermittent switching mode, in each process of X-axis scanning, the electronic switch samples each displayed measurement signal several times at a sufficiently high switching frequency. In this way, even if the frequency of the measurement signal is low, the flicker phenomenon of the waveform can be avoided. Dual-trace oscilloscope mainly consists of two channels: Y-axis preamplifier circuit, gate circuit, electronic switch, hybrid circuit, delay circuit, Y-axis postamplifier circuit, trigger circuit, scanning circuit, X-axis amplifier circuit, Z-axis amplifier circuit, calibration signal circuit, oscilloscope tube and high and low voltage power supply circuit. When the display mode switch is placed in the alternate position, the electronic switch is a bistable circuit. It is controlled by the gate signal from the scanning circuit, so that the two front channels of the Y axis work alternately with the change of the gate signal of the scanning circuit. The number of alternate conversions per second is related to the repetition frequency of the scanning signal generated by the scanning circuit. Alternating working state is suitable for the measured signal whose observation frequency is not too low. In order to observe the waveform of the measured signal changing with time, a linear scanning voltage (sawtooth voltage) must be added to the horizontal deflection plate of the oscilloscope tube. The scanning voltage is generated by the scanning circuit. When the trigger signal is added to the trigger circuit, the scanning circuit is triggered, and the scanning circuit generates corresponding scanning signals; When no trigger signal is applied, the scanning circuit does not generate a scanning signal. There are two kinds of triggers: internal trigger and external trigger, which are selected by the trigger selection switch. When the switch is placed in the internal position, the trigger signal comes from the measurement signal sent through the Y-axis channel. When the switch is placed in the external position, the trigger signal is sent from the outside. The signal should be an integer ratio to the frequency of the measured signal. In the use of oscilloscopes, most of them use internal trigger mode. The low voltage in the high and low voltage power supply circuit is used to supply the low voltage power supply required by oscilloscopes at all levels, and the high voltage is used to supply the power supply of the oscilloscope display system. For more information, please consult Beijing Oriental Zhongke Integrated Technology Co., Ltd., thank you!