自动化专业英语看图写话-精选.pdf

图1-1A-3 含有R 、L 和C 的串联电路
Consider the circuit shown in Fig. 1-1A-3a,which consists of an inductor and resistor connected in series to a voltage source e. Assuming a loop current i, the voltage drops summed around the loop are The input voltage is summed negatively since ,in the direction of assumed current,it represents an increase in voltage. The drop across each passive element is positive since the current is in the direction of the develop votage.
Using the equations for the voltage drops in a resistor and inductor,we have
Eq. (1-1A -6) is the differential equation for the current in the circuit.
Fig. 1-1A-3b shows a series circuit containing a resistor ,inductor ,and capacitor. Following the Mesh-analysis method outlined above,the circuit equation is
Recalling that current i=dq/dt, a substitution of this variable may be made to eliminate the integral from the equation .the result is the second-order differential equation
开环和闭环系统（如图2-1A-1）：开环控制系统是控制行为与输出无关的系统。

而闭环
系统，其被控对象的输入在某种程度上依赖于实际的输出。

因为输出以由反馈元件决定的一种函数形式反馈回来，然后被输入减去。

闭环系统通常是指负反馈系统或简称为反馈系统。

Open-loop and closed-loop control systems(see Fig.2-1A-1).An open-loop system is one in
whice the control action is independent of the output, A closed-loop system,however,the input of
the plant is somehow dependent on the actual output.Since the output is fed back in a functional form determined by the nature of the feedback elements and then subtracted from the input ,a closed-loop system is often referred to as a negative feedback system or simply as a feedback system.
e u C
+ R
e i R
u R + + L +
C
a) b)
u L i
u R + + L + u L
L R u u e e
Ri t i
L d d e
t i C Ri t i
L d 1
d d e
C q t q
R t q
L d d d d 22
连续和离散系统：所有变量都是时间的连续函数的系统称做连续变量或模拟系统，描述的方程是微分方程。

离散变量或数字系统有一个或多个只是在特殊时刻可知的变量，如图
2-1A-2b，描述方程是差分方程。

如果时间间隔是可控的，系统被称做数据采样系统。

离散
变量随机地产生，例如：为只能接受离散数据的数字计算机提供一个输入。

显然，当采样间隔减小时，离散变量就接近一个连续变量。

Continuous and discrete systems: the system that all its variables are continuous function of time is called continuous-variable or analog system;the describing equations are differential equations. A discrete-variables or digital system has one or more variables known only at particular instants of time, as shown in Fig. 2-1-2 b, the equations are difference equations. If the time intervals are controlled, the system is termed a sampled-data system. Discrete variables naturally, as from a scanning radar that obtains position data once per scan or a data channel that transmits many pieces of information in turn . A discrete variable will obviously approach a continuous variable as the sampling interval is decreased.。