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1、外文文献原稿和译文原 稿PID for process control ProfileA continuous process is one in which the output is a continuous flow. Examples are a chemical process, a refining process for gasoline, or a paper machine with continuous output of paper onto rolls. Process control for these continuous processes cannot be a
2、ccomplished fast enough by PLC on-off control. Furthermore, analog PLC control is also not effective or fast enough by PLC on-off control. Furthermore, analog PLC control is also not effective or fast enough.The control system most often used in continuous processes is PID (proportional-integral-der
3、ivative) control. PID control can be accomplished by mechanical, pneumatic, hydraulic, or electronic control systems as well as by PLCs. Many medium-size PLCs and all large PLCs have PID control functions, which are able to accomplish process control effectively. In this chapter, we discuss the basi
4、c principles of PID control. We then explain the effectiveness of PID control by using typical process response curves and show some typical loop control and PID functions. Loop and PID control are designations used interchangeably by different manufacturers. Actually, some loop controls are not str
5、ictly the PID type. However, assume they are the same.PID PrinciplesPID (proportional-integral-derivative) is an effective control system for continuous processes that performs two control tasks. First, PID control keeps the output at a set level even though varying process parameters may tend to ca
6、use the output to vary from the desired set point. Second, PID promptly and accurately changes the process level from one set point level to another set point level. For background, we briefly discuss the characteristics of each of the PID control components: proportional, integral, and derivative.P
7、roportional control, also known as ratio control, is a control system that corrects the deviation of a process from the set level back toward the set point. The correction is proportional to the amount of error. For example, suppose that we have a set point of 575 cubic feet per minute (CFM) in an a
8、irflow system. If the flow rises to 580 CFM, a corrective signal is applied to the controlling air vent damper to reduce the flow back to 575 CFM. If the flow somehow rises to 585 CFM, twice the deviation from set point, a corrective signal of four times the magnitude would be applied for correction
9、. The larger corrective signal theoretically gives a faster return to 575 CFM. In actuality, the fast correction is not precise. You return to a new set point at the end of the correction, for example, 576.5 CFM, not 575 CPM. Proportional control does not usually work effectively by itself, resultin
10、g in an offset error.To return the flow to the original set point, integral control, also known as reset control, is added. Note that integral control cannot be used by itself. Remember, with proportional control only, we had an output error from our original set point. We ended up at 576.5 CFM, not
11、 575 CFM. Integral control senses the product of the error, 1.5 CFM, and the time the error has persisted. A signal is developed from this product. Integral control then uses this product signal to return to the original set point. An integral control signal can be used in conjunction with the propo
12、rtional corrective signal. In the controller, the added integral signal reduces the error signal that caused the output deviation from the set point. Therefore, over a period of time, the process deviation from our original 575 CFM is reduced to minimum. However, this correction takes a relatively l
13、ong period of time.To speed up the return to the process control, point, derivative control is added to the proportional-integral system. Derivative control, also known as rate control, produces a corrective signal based on the rate of change of the signal. The faster the change from the set point,
14、the larger the corrective signal. The derivative signal is added to the proportional-integral system. This gives us faster action than the proportional-integral system signal alone. A typical PID control system is s is the commonly used parallel type.The controller output signal is utilized through
15、a control system to return the process variable to the set point.An illustration of a system using PID control is shown in figure 23-2. In this system, we need a precise oil output flow rate. The flow rate is controlled by pump motor speed. The pump motor speed is controlled through a control panel
16、consisting of a variable-speed drive. In turn, the drives speed control output is controlled by an electronic controller. The electronic controller output to the drive is determined by two factors. The first factor is the set point determined by a dial setting (or equivalent device). Second, a flow
17、sensor feeds back the actual output flow rate to the electronic controller. The controller compares the set point and the actual flow. If they differ for some reason, a corrective signal change is sent to the motor controller. The motor controller changes motor speed accordingly by changing the volt
18、age applied to the motor. For example, if the output oil flow rate goes below the set point, a signal to speed up the motor is sent. The controller then uses PID control to make the correction promptly and accurately to return to the set point flow. If the dial is changed to a new setting, the funct
19、ion of the PID system is to reach the new set point as quickly and accurately as possible.Hyd 河 I*I rnt心 j1JLi IFIGURE 23-2 General Control SystemDifigramHydraulic Pumpgg :际 I STP旨P PJogsEbta 祠g旧I W1 st rw motor Ntfor conroiPumc and rrfltaf； Lontial pgu* loaihtr bg尊aOil flor*i UqIo-Typical Continuou
20、s Process Control CurvesTo illustrate some of the possible system response curves for process control systems, we will use the electromechanical system shown in figure 23-3. By response curves, in this example, we mean output position versus time. The curves to be shown are for various types of cont
21、rol, including PID.Figure 23-3 shows a control system with a feedback loop, which can be PID. The dial is set to a position in degrees, and the output device is to take the position set on the dial. The output is to follow quickly and accurately any change from one dial setting to another.FIGURE 23-
22、3 Position Indicator with PID ControlPID ModulesPLCs often come equipped with PID modules, used to process data obtained by feedback circuitry. Most such modules contain their own microprocessor. Since the algorithms needed to generate the PID functions are rather complex, the PID microprocessor rel
23、ieves the CPU of having to carry out these time-consuming operations.To understand the PID module, refer to figure 23-7. The PLC sends a set-point signal to the PID module. The module is made up of three elements: the proportional, integral, and derivative circuits. The proportional circuit creates
24、an output signal proportional to the difference between the measurement taken and the setpoint entered in the PLC. The integral circuit produces an output proportional to the length and amount of time the error signal ispresent. The derivative circuit creates an output signal proportional to the rat
25、e of change of the error signal.The input transducer generates an output signal from the process being controlled and feeds the measured value to the PID module. The difference between the set point coming from the PLC and the measured value coming from the input transducer is the error signal.Some
26、sort of correcting device, such as a motor control, valve control, or amplifier, takesthe error signal and uses it to control the correction sent to the process being controlled.FIGURE 23-7 Block diagram of PID Module译文连续过程中的PID控制简介一个持续的过程是一个输出是一个持续不断的流动。例子是一个化学过程，精炼 过程的汽油，或纸机连续输出的纸张上卷。过程控制的这些持续不断的进
27、程不能足够 快的PLC开关控制。此外，模拟PLC控制也没有有效的或不够快用PLC开关控制。此 外，模拟PLC控制也没有有效的或不够快。控制系统最常用的是在持续不断的进程的 PID （比例积分微分）控制。PID控制可以通过机械，气动，液压，或电子控制系统 以及PLC的。许多中型PLC和所有大型PLC的PID控制的职能，能够有效地完成过程 控制。在本章中，我们讨论的基本原则的PID控制。然后，我们解释的效力，PID 控制用典型的过程响应曲线，并显示一些典型的闭环控制和PID功能PID控制原理PID （比例积分微分）是一种有效的控制系统的连续进程，执行两个控制任务。 首先，PID控制的输出保持在设定
28、的水平，即使不同的工艺参数可能会导致输出到不 同的理想设定值。其次，PID控制及时准确的工艺水平的变化从一个设定点，以另一 套点水平。为背景下，我们简要讨论的特点，每个PID控制部分组成：比例，积分和 导数。比例控制，也被称为比例控制，是一个控制系统，纠正偏差的一个进程的设定水 平回到对设定点。这次调整比例的金额错误。例如，假设我们有一个设定点五七五立 方英尺每分钟（立方英尺）在气流系统。如果流量上升到580立方英尺，纠正信号用 于控制气孔阻尼器，以减少流回到575立方英尺。如果不知流上升到585立方英尺的 两倍偏离设定点，纠正信号的4倍的规模将申请更正。较大的纠正信号理论上给出了 更快返回5
29、75立方英尺。事实上，快速纠正不准确的。回到你的一套新点结束时的修 正，例如，576.5立方英尺，而不是575千次展示费用。比例控制通常不能有效地开 展工作本身，从而抵消错误。返回到原来的流量设定点，积分控制，也被称为复位控制，是补充。请注意，积 分控制不能使用本身。请记住，只有与比例控制，我们有一个输出错误从我们原来的 设定值。我们结束了在576.5立方英尺，而不是575立方英尺。积分控制产品感官的 错误，1.5立方英尺，时间错误依然存在。信号开发此产品。积分控制然后使用此产品的信号，返回到原来的设定值。一个不可分割的控制信号可以用来配合比例纠正信 号。在控制器，额外的积分减少了错误信号，造
30、成信号输出偏离设定值。因此，在一 段时间内，这一进程偏离我们原来的575立方英尺的减少到最低限度。然而，这需要 纠正相当长的一段时间。为了加快恢复过程控制，点，导数控制添加到比例积分系统。导数的控制，也被 称为速率控制，生产出的基础上纠正信号的变化率的信号。快变化的设定点，较大的 纠正信号。衍生信号加到比例积分系统。这使我们更快地行动，比比例积分系统信号 的。一个典型的PID控制系统是常用的平行类型。该控制器的输出信号的数字是利用 通过控制系统返回的过程变量的设置点。说明系统采用PID控制是如图23-2。在这一体系中，我们需要一个确切的石油 产量流量。流量控制水泵电机的速度。水泵电机的速度控制
31、通过控制面板组成的变速 驱动器。反过来，驱动器的速度控制输出控制的电子控制器。电子控制器输出驱动器 是由两个因素。第一个因素是确定的设置点拨号设置（或同等器件）。第二，流量 传感器反馈的实际输出流量的电子控制器。该控制器的设定值比较，与实际流动。如 果他们有所不同的某些原因，纠正信号改变发送到电机控制器。电机调速控制器的变 化相应的改变电压适用于汽车。例如，如果石油输出流量低于设定点，一个信号，以 加快汽车发送。该控制器然后使用PID控制，使校正及时准确地返回到设定流量。如 果拨打被更改为一个新的设置，职能的PID控制系统，达到新的设定点尽快和尽可能 准确地。图23-2 一般控制系统图液压泵典
32、型的连续过程控制曲线为了说明一些可能的系统响应曲线的过程控制系统，我们将使用机电系统如图 23-3。的响应曲线，在这个例子中，我们的立场意味着输出随时间。该曲线显示为 不同类型的控制，包括PID控制。utpulPo$ili?n JndicatqrOutputOevittEreci/i&ai rndxahng inpvtPosrtionElect泊 I Power 代。|由自 Output Device图23-3显示了控制系统的反馈回路，可PID控制。拨号设置为位置度，和输出设 备是采取的立场上，确定了拨号。输出是按照快速，准确的任何变化从一个拨号设置 到另一个。Erecinci Sr丽凯Ind
33、icating inputPosition图23-3的位置与PID控制指标PID控制模块PLC的往往配备PID控制模块，用于处理获得的数据反馈电路。大多数这样的模 块包含自己的微处理器。由于算法需要生成的PID功能都相当复杂，缓解的PID微处 理器的CPU无需进行这些耗时的操作。理解的PID模块，参见图23-7。的PLC发出了一个设定点信号的PID控制模块。该 模块是由三个要素：比例，积分和微分电路。电路的比例创造了输出信号的比例之间 的差额而采取的测量和设定输入到PLC的。积分电路产生的输出比例的长度和大量的 时间错误的信号存在。衍生电路产生输出信号成比例的变化率的错误信号。传感器产生的输入输出信号的过程控制和饲料的测量值的PID控制模块。之间的 差额确定点来自PLC和测量值从输入传感器是错误的信号。某种纠正设备，如电机控 制，阀控制，或放大器，以错误的信号，并使用它来控制校正送交过程控制。
