电气专业英语课文翻译(9)

人可以被添加到系统中从而达到维持炉温在期望值的目的。图所示通过观察炉里的温度计人可以改变控制开关的位置从而更接近的获得需要温度。特别强调的是，人的参与提供了一种输出量反馈到输入并与期望值相比较的方法。实际控制加热元件依靠期望温度和实际温度之间的差异。指挥中通过任何必要的改变来减少误差。例如，如果温度降低，加热电流就要增加来提供更多的热量。

Systems in which the output has an effect upon the input are called closed-loop control systems or, more commonly, feedback controls systems. The feedback capture of the system in Fig.8.2 may be seen by tracing the closed-loop. The function of comparing the actual temperature with the desired value is performed in the mind of the operator, and the command is executed by the response of his muscles. Even though close-loop control of the oven is established by the operator, the results may be less then satisfactory. The temperature will cycle above and blew the desired value as the operator adjusts the switch even though the excursions would tend to decrease with operator experience. A change in the level of the power source or in the ambient temperature surrounding the oven would adversely affect the system‘s output. In addition, watching a thermometer and operating a switch would be a dull and time-consuming task. This arrangement could be described as a manual closed-loop control system.

输出对输入有影响的系统称之为闭环控制系统，或者更通俗的称为反馈控制系统。图中，通过跟踪闭环系统可以看到反馈的本质。比较实际温度和期望温度的功能是在操作者的大脑中完成的，命令通过他的肌肉执行。即使炉的闭环控制系统由人建立，结果可能并不理想，操作者调整开关即使偏差会趋于减小随着操作者的经验，温度仍然会在期望值上下浮动。电源电平的改变或是炉周围环境温度的改变，会不利的影响系统的输出，另外观察温度计和控制开关是一种枯燥又费时的任务，这个方案可以称为手动闭环控制系统。

To further improve performance and obtain more precise control, the human may be replaced by a mechanical, electrical, or other form of comparisons and control unit. Fig 8.3 shows, on the automatic basic, that is, without human intervention. The temperature is now measured by a thermocouple, a device that generates an electrical voltage proportional to temperature. This voltage is fed back and compared with a reference voltage that represents the desired temperature. The difference between the two voltages is amplified electronically and controls the current to the heating element. Since the voltage feedback is subtracted from the reference voltage, it is known as a negative-feedback signal.

为了更加提高性能并且获得更加精确地控制，人可以被机械的、电气的或者其他形式比较和控制单元代替。图所示在自动的基础上即没有人的参与，温度由温度计测量，这个设备产生与温度成比例的电压，这个电压反馈到代表期望温度的参考电压并与之比较。这两个电压之差被电气放大，并且控制加热元件的电流由于电压反馈是从参考电压中减去的，它被称为是负反馈信号。

The example has illustrated how automatic closed-loop control is employed to perform a task more rapidly and consistently than can be accomplished by a human being. The use of negative feedback in a closed-loop control system tends to maintain a desired value of a quantity or condition by measuring the existing value, comparing it to the desired value, and using the difference as a means of initiating action to reduce the difference. The negative-feedback concept has become the foundation for automatic-control-system design.

这个例子说明了自动闭环控制可以比人参与完成的控制更快更稳定的完成一个任务。闭环控制系统中负反馈的应用趋向于维持一个量在期望值或是这样一个状态：通过测量实际值并与期望值相比较，然后用差别作为启动动作来减小差别。负反馈概念已经成为自动控制设计的基础。