目标值

目标值（target）也称为设定值（setpoint，简称SP）或参考值（reference），是模控学及控制理论中的名词，是指系统想要达到的状态^[1]，常用来描述系统标准的组态^[2]。变数相对其目标值的偏离量是以误差为准的控制系统的基础^[3]，会利用回授的方式使系统回到其稳态。例如一个锅炉有其温度设定值，也就是锅炉控制系统希望锅炉维持的温度。

在控制系统中，目标值是受控程序变数（PV）的目标值，系统会持续的将实际程序变数和目标值比较，系统会将目标值和实际程序变数相减，所得的即为误差讯号。若以数学表示，其误差讯号如下：

e(t)=SP-PV(t),

$e(t)$ 是特定时间 $t$ 的误差， $SP$ 是目标值， $PV(t)$ 是特定时间 $t$ 的程序变数。

控制器会利用误差讯号来调整控制输出，使程序变数尽量接近目标值，同时维持系统的稳定，并且让过冲降到最低。

参考资料

^ An 'essential variable' is defined as "a variable that has to be kept within assigned limits to achieve a particular goal": Jan Achterbergh, Dirk Vriens. §2.3 Cybernetics: Effective methods for the control of complex systems. Organizations: Social Systems Conducting Experiment. Springer Science & Business Media. 2010: 47. ISBN 9783642143168.
^ B. Wayne Bequette. Process Control: Modeling, Design, and Simulation. Prentice Hall Professional. 2003: 5. ISBN 9780133536409.
^ W. Ross Ashby. Chapter 12: The error-controlled regulator. Introduction to cybernetics (PDF). Chapman & Hall Ltd.; Internet (1999). 1957: 219–243 [2015-01-08]. （原始内容存档 (PDF)于2018-02-19）.

[Achterbergh-1] An 'essential variable' is defined as "a variable that has to be kept within assigned limits to achieve a particular goal": Jan Achterbergh, Dirk Vriens. §2.3 Cybernetics: Effective methods for the control of complex systems. Organizations: Social Systems Conducting Experiment. Springer Science & Business Media. 2010: 47. ISBN 9783642143168.

[Bequette-2] B. Wayne Bequette. Process Control: Modeling, Design, and Simulation. Prentice Hall Professional. 2003: 5. ISBN 9780133536409.

[Ashby-3] W. Ross Ashby. Chapter 12: The error-controlled regulator. Introduction to cybernetics (PDF). Chapman & Hall Ltd.; Internet (1999). 1957: 219–243 [2015-01-08]. （原始内容存档 (PDF)于2018-02-19）.

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参考资料