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1、6.Variable Name（变量名称）（变量名称）The controlled variable(C)is the process output variable that is to controlled.In a process control system,the controlled variable is usually an output variable that s a good measure of the quality of the product.The most common controlled variables are position,velocity,t
2、emperature,pressure level and flow rate.控制变量（C）是过程的输出变量，用来控制。在过程控制系统中,控制变量通常是一个输出变量,它能很好地衡量产品的质量。最常见的控制变量有位置、速度、温度、压力和流量水平。The set point(SP)is the desired value of the controlled variable.设定点（SP）是控制变量的期望值。The measured variable(Cm)is the measured value of the controlled variable.It is the output of t
3、he measuring means and usually differs from the actual of the controlled variable by a small amount.测量变量（CM）是衡量价值的控制变量。这是输出的测量手段和通常不同于实际的控制变量的一小部分。The error(E)is the difference between the setpoint and the measured value of the controlled variable.It is computed according to the equation E=SP-.错误（E）
4、的设定值与控制变量的测量值之间的差异。它是根据方程计算E=SP-。The controller output(V)is the control action intended to drive the measured value of the controlled variable toward the setpoint value,The control action depends on the error signal(E)and on the control modes used in the controller.控制器的输出（V）是用于驱动控制动作的控制变量设定值的实测值，控制作
5、用取决于误差信号（e）和用于控制器的控制方式。The manipulated variable(M)is the variable regulated by the final controlling element to achieve the desired value of the controlled variable.Obviously,the manipulated variable must be capable of effecting a change in the controlled variable.The manipulated variable is one of
6、the input variables of the process.Changes in the load on the process necessitate changes in the manipulated.Variable to maintain a balanced condition.For this reason,the value of the manipulated variable is used as a measure of the load on the process.操纵变量（M）通过控制元件的调节来实现所需的受控变量的值，达到可变。显然，操纵变量必须能够影响
7、控制变量的变化。操纵变量是一个过程的输入变量。负载变化的过程需要改变操作变化。变量来维持一个平衡的状态。出于这个原因，操纵变量的值作为对过程测量的负荷。The disturbance variables(D)are process input variables that affect the controlled variable but are not controlled by the control system.Disturbance variables are capable of changing the load on the process and are the main
8、reason for using a closed-loop control system.干扰变量（D）是过程输入变量，它受控制变量的影响，但不受控制系统的影响。干扰变量能够改变负载的过程，主要的原因是使用闭环控制系统。The primary advantage of closed-loop control is the potential for more accurate control of the process.There are two disadvantages of closed-loop control:(1)closed-loop control is more expe
9、nsive than open-loop control,and(2)the feedback feature of a closed-loop control system makes it possible for the system to become unstable.An unstable system produces an oscillation of the controlled variable,often with a very large amplitude.闭环控制的主要优点是对过程的控制有更精确的潜力。闭环控制有两个缺点：(1)闭环控制比开环控制更昂贵；（2）一个闭环控制系统的反馈功能使系统变得不稳定。一个不稳定的系统产生的控制变量的振荡，通常是一个非常大的振幅。Selected from“Introduction to Control System technology,4th Ed.,by Robert N.Bateson,Macmillan Publishing Co.,1933”.选自“控制系统技术，第四版的介绍，罗伯特N.贝特森，麦克米兰出版有限公司，1933。