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实验 2 示波器的原理和应用

Laboratory 2: The Principle and Applications of Oscilloscope

An oscilloscope is a type of electronic test instrument for the observation of constantly varying signal voltages and other parameters, such as period and frequency. It can also be used to view and measure the change of the most electrical quantities that can be converted into voltage over time. The frequency response of a modern digital oscilloscope has a range of values from to . Many Oscilloscopes can also capture, store and repeat the waveform of an electrical signal for a specified time interval, which have been widely used in the sciences, medicine, engineering, and telecommunications industry.
示波器是一种电子测试仪器,用于观察不断变化的信号电压和其他参数,例如周期和频率。它还可用于查看和测量随时间可转换为电压的大多数电量的变化。现代数字示波器的频率响应范围 。许多示波器还可以在指定的时间间隔内捕获、存储和重复电信号的波形,这些波形已广泛应用于科学、医学、工程和电信行业。

1 实验任务 Objectives 1 实验任务 Goalss

(1) Understand the basic working concepts of the oscilloscope and types of measurement that can be made with it.
(1) 了解示波器的基本工作原理和可以用它进行的测量类型。
(2) Use the oscilloscope to observe the waveform, amplitude and frequency of voltage signal.
(3) Use the oscilloscope to plot the Lissajous pattern.
(3) 使用示波器绘制 Lissajous 模式。

2 实验原理 Background 2 实验原理

(1) The basic constituent of an oscilloscope is the cathode ray tube (CRT) as shown in Figure1. This highly evacuated tube contains an electron gun, two sets of deflection plates ( -plates, -plates), and a fluorescent screen at the enlarged end: The purpose of the gun is to produce an electron beam by evaporating electrons off the cathode and focusing them into a narrow stream. The electrons are accelerated to a high velocity and strike the fluorescent screen, leaving a bright spot where they hit. The electron beam traces out a pattern on the screen - depending on the potential difference across the plates. This same principle is used in producing a pattem on a screen!
(1) 示波器的基本成分是阴极射线管 (CRT),如图 1 所示。这个高度真空的管子包含一个电子枪、两组偏转板( -板、 -板)和放大端的荧光屏:枪的目的是通过蒸发阴极上的电子并将它们聚焦成狭窄的流来产生电子束。电子被加速到高速并撞击荧光屏,在它们撞击的地方留下一个亮点。电子束在屏幕上描绘出图案 - 取决于板上的电位差。同样的原理也用于在 屏幕上制作 pattem!
The oscilloscope has connections which permit potential differences (voltages) to be applied across the -plates and -plates. If a voltage is applied across the plates, it produces an electric field which deflects the electron beam (recall ). The amount of deflection is directly proportional to the amplitude of the applied voltage. If is applied to the -plates and is applied to the -plates, the electron beam plots a graph of " versus " on the screen. Although the scope will graphically display
示波器具有允许在 板和 板之间施加电位差(电压)的连接。如果在极板上施加电压 ,它会产生一个电场 ,使电子束偏转(回想 一下)。挠度与施加电压的幅度成正比。如果 应用于 -plates 并 应用于 -plates,则电子束会在屏幕上绘制 “ vs ” 的图形。尽管示波器将以图形方式显示
two voltages " versus ", the most common application is that of displaying a time-varying voltage as a function of time . The time-axis is produced by the scope's HORIZONTAL SWEEP circuit which generates a linear voltage (ie. ) across the -plates. This feature enables the oscilloscope to plot very quickly variations in the instantaneous voltage. On the other hand, a voltmeter only provides an "average" value of the voltage and cannot measure instantaneous voltage.
两个电压“ ”,最常见的应用是显示时变电压 作为时间 的函数。时间轴由示波器的水平扫描电路产生,该电路产生线性电压(即。 ) 跨 -plates。此功能使示波器能够非常快速地绘制瞬时电压的变化图。另一方面,电压表只能提供电压的“平均”值,不能测量瞬时电压。
(2) Deflection of electron beam
As shown in Fig 2, if a voltage is applied to the vertical deflection plates, the electron beam will experience a force in the direction opposite of the electric field and thus make deflection. The vertical displacement of the electron beam spot:
如图2所示,如果对垂直偏转板施加电压 ,电子束将承受与电场相反方向的力,从而产生偏转。电子束光斑 的垂直位移:
Figure 2: Electron Deflection
图 2:电子偏转
For a given oscilloscope tube, remains constant. Therefore, the value of potential across the plates is proportional to the displacement of the electron beam spot: ,
对于给定的示波器管, 保持恒定。因此,两板上的电位 值与电子束光斑 的位移成正比:
(3) Waveform generation (3) 波形生成
According to fluorescent materials on the screen will not disappear immediately after the hit by the electrons, if the frequency of voltage signal applied to the horizontal or vertical deflection plates is high enough, the time interval between two adjacent electrons hit is shorter than that of fluorescence missing, then a straight horizontal or vertical line will be displayed on the screen.
If the signal to be studied is applied to the vertical deflection plates to deflect the beam vertically and at the same time a voltage that increases linearly with time is applied to the horizontal (deflection) plates thus causing the beam to be deflected horizontally at a uniform constant rate, the combination of these two deflections allows the beam to reach any portion of the fluorescent screen: the vertical displacement of the beam spot , the horizontal displacement . Therefore, the signal applied to the vertical plates is displayed on the screen as a function of time.
如果将要研究的信号施加到垂直偏转板上以垂直偏转光束,同时将对水平(偏转)板施加随时间线性增加的电压,从而使光束以均匀的恒定速率水平偏转,这两种偏转的组合允许光束到达荧光屏的任何部分: 光斑 的垂直位移,水平位移 。因此,施加在垂直板上的信号作为时间的函数显示在屏幕上。
Figure 3: Diagram of wave generation
图 3:波浪生成图
Since the electron beam is deflected in the horizontal direction, the displacement . Therefore, if the value of is given, then the period of the signal to be studied can be obtained by: .
由于电子束在水平方向上偏转,因此位移 .因此,如果给出 的 值,则待研究信号的周期可以通过以下方式获得:
(4) Synchronization and flip-flop
(4) 同步和触发器
In order to obtain steady traces on the tube face, an internal number of cycles of the unknown signal that is applied to the vertical plates must be associated with each cycle of the sweep generator. Thus, with such a matching of synchronization of the two deflections, the pattern on the tube face repeats itself and hence appears to remain stationary. To synchronize the horizontal deflection the vertical input, such that the horizontal deflection starts at the same point of the input vertical signal each time it sweeps, a triggering circuit is used. Sweep must remain at rest unless adequate trigger signal arriving.

3 实验器材 Apparatus 3 实验器材

Oscilloscope; function generator; coaxial wires

4 实验内容 Procedure 4 实验内容

(1) Connect the Oscilloscope calibrated signal to , then observe the waveform and record the value of peak-to-peak voltage , frequency and period .
(1)将示波器校准信号接上 ,然后观察波形,记录峰峰值电压 、频率 和周期 值。
(2) Determine the voltage, period and frequency according to different sine waveforms.
The magnitude of the peak voltage displayed on the scope face is proportional to the displacement of the electron beam spot:
示波器面上显示的峰值电压大小与电子束光斑 的位移成正比:
The period is proportional to the horizontal distance :
周期 与水平距离 成正比:


As shown in Fig 5, if set the VOLTS/DIV to 2, the peak-to-peak voltage of the sine wave shown on the screen is represented by the vertical distance between the positive peaks to the negative peaks, then:
Peak Voltage:  峰值电压:
Root mean square (RMS) Voltage: .
均方根 (RMS) 电压: .
We can also get the period which is measured as the length of the segment joining the corresponding points of two adjacent waveform fragments.
我们还可以得到周期,该周期 被测量为连接两个相邻波形片段相应点的段的长度。
Figure 5: Determination of Voltage
(3) Plot Lissajous Patterns.
An Oscilloscopes' horizontal deflection is generally driven by the internal sawtooth signal from a "timebase" generator, but it also has some provision to deflect the beam with an external signal. When use two signal generators, one to the input and one to the input, then a more complex shape can be observed on the screen. If the two signals are sinusoidal, and their frequencies are in exactly integral ration, you will get stable, pretty figures called Lissajous Patterns.
示波器的水平偏转通常由来自“时基”发生器的内部锯齿信号驱动,但它也有一些规定,可以通过外部信号偏转光束。当使用两个信号发生器时,一个用于 输入,一个用于 输入,然后在屏幕上观察到更复杂的形状。如果两个信号是正弦的,并且它们的频率正好是积分比,你会得到稳定、漂亮的数字,称为 Lissajous 模式。
Lissajous Patterns are the superposition of two sinusoidal ( simple harmonic) motions at right angles to each other. The pattern you observed in Fig 6 is a simple lissajous pattern for horizontal-to-vertical frequency ratios of and the trajectory of particle undergoing the simple harmonic motion is described by the numbers. Note that even the two sine waves have the same frequency, the patterns shown on the screen will vary according to various phase differences.
Lissajous 模式是两个正弦(简单谐波)运动的叠加,彼此成直角。您在图 6 中观察到的模式是水平与垂直频率比的 简单 lissajous 模式,并且经历简单谐波运动的粒子的轨迹用数字描述。请注意,即使两个正弦波具有相同的频率,屏幕上显示的模式也会根据各种相位差而有所不同。
Figure 6: Producing Lissajous Patterns
图 6:生成 Lissajous 图案
The Lissajous Patterns can be used for direct comparison of frequencies of two signals, you can then use it to measure unknown frequency.
Lissajous 模式可用于直接比较两个信号的频率,然后您可以使用它来测量未知频率。
As shown in Fig 6, if a horizontal line and a vertical line are drawn across the pattern, the ratio of points that touch these lines equals the frequency ratio of vertical and horizontal signals:
如图 6 所示,如果在图案上绘制一条水平线和一条垂直线,则接触这些线的点之比等于垂直和水平信号的频率比:
Points of tangency to a horizontal line
: Points of tangency to a vertical line

5 注意事项 Warning

  1. Be careful when using electrical appliances.
  2. Turn off all sources of electricity before you leave the laboratory.

实验数据分析 Data Analysis

(1) Measure the voltage, period and frequency of the oscilloscope internal calibration signal:
(2) Determine the voltage, period and frequency according to different sine waveforms:
AC Signal Vp-p Vp V T
(3) Observe and plot Lissajous Patterns corresponding to each ratio of frequency:
(3) 观察并绘制与每个频率比相对应的 Lissajous 模式:

7 思考题 Questions

(1) What does a basic oscilloscope consist of? How does an oscilloscope work?
(1) 基本示波器由哪些部分组成?示波器是如何工作的?
(2) How does an oscilloscope display an voltage or current waveform on its screen?
(2) 示波器如何在屏幕上显示 电压或电流波形?
(3) How to use the oscilloscope to measure the voltage, period and frequency of an unknown signal?
(4) How to make lissajous patterns on an oscilloscope?
(4) 如何在示波器上制作 lissajous 图案?