RC电路的过渡过程.doc

Experiment 4 Transient Process of RC Circuit
I Objectives
1. To Learn to use oscilloscope.
2. To study the square wave responses of first-order circuits.
II Apparatus and Equipments

Name
Spec.
Number
1
Two-channel oscilloscope
XJ4328
1
2
Function generator
EE1641D
1
3
Elements
R=510Ω, 1 kΩ, 2 kΩ, 3 kΩ, 10 kΩ
C=0.1μf, 0.3μf, 0.4μf, 1μf,3 μf, 10μf
1
III Preperations
1. The rectangular pulse responses of a RC circuit
Fig.4-1 and Fig.4-2 are the rectangular pulses and a RC circuit respectively.

Fig.4-1 Rectangular pulses Fig.4-2 RC circuit

Supply the signal of rectangular pulses to the RC circuit, we get the responses shown in Fig.4-3 if the initial value of uC is zero. Obviously, RC circuit charges and discharges continuously. It’s the essence of pulse responses of RC circuit.
2. Applications of a RC circuit
(1) Differential circuit in Fig.4-4——when the parameters R and C make the time constant τ<<tp (the width of rectangular pulses), we can get the impulse response μR shown in Fig.4-5.
(2) Integral circuit in Fig.4-6——when the parameters R and C make the time constant of the circuitτ>>tp, we can get the response uC shown in Fig.4-7. The output voltage uC is approximately the integration of the input voltage ui.

Fig.4-3

Fig.4-4 RC differential circuit Fig.4-5 Response of the circuit Fig.4-4

Fig.4-6 RC integral circuit Fig.4-7 Response of the circuit Fig.4-6

IV Lab Work
1. Measure the peak values and periods of sinusoids produced by a function generator.
2. Measure the magnitude, periods, and pulse width of square waves produced by a function generator.
3. Measure the phase difference of two sinusoids.
Supply the sinusoid ui (f=1kHz, Up-p=1V) to the circuit Fig.4-4, observe the voltage ui and uR with oscilloscope, measure the phase difference of them, and compare the magnitudes of them. The parameters are listed as follow:
(1) R=1kΩ, C=0.1μf;
(2) R=1kΩ, C=0.2μf;
(3) R=2kΩ, C=0.1μf;
(4) R=1kΩ, C=10μf.
4. Study the transient process of a RC circuit
Supply a square-wave signal (amplitude 4V, periods 4ms, and pulse width tw about 4ms) to the circuit Fig.4-6.
(1) Observe the waveforms of uR, uC, and ui in the caseτ=RC<;
(2) Observe the waveforms of ui and uC simultaneously in the caseτ=RC=(;
(3) Observe the waveforms of ui and uC simultaneously in the caseτ=RC>;
(4) Observe the waveforms of ui, uC, and uR simultaneously in the caseτ=RC>;
V Preparations
1. Reading and understanding the specification of two-channel oscilloscope XJ4328;
2. Preparing the circuit parameters for lab work 4.
VI Discussions
1. Give the data measured and draw the waveforms observed;
2. Analyze the effects of the circuit parameters on the square-wave responses in first-order circuits.

实验四 RC电路的过渡过程
一、实验目的
1．学习使用XJ4328示波器显示波形和测量幅度、频率、相位的方法。
2．研究一阶电路的方波响应。
二、实验仪器设备

名 称
规格，型号
数量
1
二踪示波器
XJ4328
1台
2
函数发生器
EE1641D型
1台
3
实验元件
R=510Ω, 1 kΩ, 2 kΩ, 3 kΩ, 10 kΩ
C=0.1μf, 0.3μf, 0.4μf, 1μf,3 μf, 10μf
1块
三、实验原理
RC串联电路是电子线路中经常用到的线路，对一个工程技术人员，熟悉它的性能是必要的。
1．RC电路的矩形脉冲响应
矩形脉冲序列波形如图4-1所示。

图4-1 矩阵脉冲序列波形图 图4-2 RC串联电路图

若将此矩形脉冲序列信号加在电容电压的初始值uC（0）=0的RC电路上，如图4-2所示，其响应曲线如图4-3所示。
显然，电路的脉冲响应实质是RC电路不断充放电的过程。
2．RC电路的应用
(1) RC微分电路
如图4-4所示的电路，选择适当的电路参数，使电路的时间常数τ<<tp (矩形脉冲宽度)，于是电阻两端电压u0为正负交替的尖脉冲，如图4-5所示。

图4-3

图4-4 RC微分电路 图4-5 微分电路的输入电压和输出电压波形
(2) RC积分电路
如果将RC电路的电容两端作为输出端，如图4-6所示，在电路参数满足τ>>tp时条件下，电路的输出电压近似地正比于输入电压对时间的积分。输入电压为矩形脉冲时，输出电压波形为三角波，如图4-7所示。
uc

图4-6 RC积分电路 图4-7 RC积分电路的输入输出电压波形

四、实验任务
1．利用示波器测量函数发生器输出正弦波的幅值和周期（自己调节）。
2．利用示波器测量函数发生器输出方波的幅值、周期和脉冲宽度。
3．利用示波器测量相位差。
按图4-4接线，AB间接函数发生器输出的正弦信号取f=1kHz, Up-p=1V。在示波器屏幕上同时观察ui和uR的波形，测量两个电压的相位差，并注意比较两个电压的幅值大小。电路参数分别为：
(1) R=1 kΩ, C=0.1μf;
(2) R=1 kΩ, C=0.2μf;
(3) R=2 kΩ, C=0.1μf;
(4) R=1 kΩ, C=10μf。
4．利用示波器研究RC电路的过渡过程
按图4-6接线，AB间接函数信号发生器输出的方波信号，方波幅值为4伏，周期为4毫秒，脉冲宽度tw约为2毫秒。
(1) 选用电路参数使τ=RC<，分别观察ui、uR、uC的波形。
(2) 选用电路参数使τ=RC=(，同时观察ui和uC的波形。
(3) 选用电路参数使τ=RC>，同时观察ui和uC的波形。
(4) 选用电路参数使τ=RC>，同时观察ui、uR、uC的波形。
五、预习要求
1．阅读XJ4328型二踪示波器简介
*2．观看“电子示波器原理”电视录像片
3．拟定任务4中的电路参数
六、总结讨论
1．在坐标纸上画出被观察的波形，算出被测数据。
2．分析一阶电路中电路参数对方波响应的影响。