Unit23 The Introduction to Process Control①
Key Words and Terms
1.process n.过程(这里指工业生产过程)
2.instrumentation n.仪表装置
3.objective n.目标
4.block diagram 方框图
5.manipulated    a.（可）操纵的，manipulated variable 操纵量（指
自动控制系统中可以根据需要改变的变量）
6.batch    a.分批的，间歇（式）的
7.actuator n.执行器、执行机构
8.tune vt.调节、调整
9.pose vt.形成、造成、提出、陈述
10.r esidence time 驻留时间
11.c atalyst n.催化剂、刺激（促进）因素
12.f ail-safe vi. n.失效保护
13.v alve stem 阀芯
14.f eed forward 前馈
15.s et-point 设置点
16.a lgorithm n.算法
Notations and Translation
The goal of this chapter is to provide a motivation for, and an
introduction to, process control and instrumentation. After studying this chapter, the reader, given a pro
cess, should be able to do the following: •Determine possible control objectives, input variables (manipulated and disturbance) and output variables (measured and unmeasured), and constraints (hard or soft), as well as classify the process as continuous, batch, or semi-continuous
•Assess the importance of process control from safety, environmental, and economic points of view
assess v. 估定，评定
从安全、环境及经济的角度评估过程控制的重要性。
reactor pressure vessel•Sketch a process instrumentation and control diagram
•Draw a simplified control block diagram
•Understand the basic idea of feedback control
•Understand basic sensors (measurement devices) and actuators (manipulated inputs)
•Begin to develop intuition about characteristic timescales of dynamic behavior
Develop v. 产生
Intuition n. 直觉，直觉的知识
Process engineers are often responsible for the operation of chemical processes. As these processes become larger scale and /or more complex, the role of process automation becomes more and more important. The
objective of this textbook is to teach process engineers how to design and tune feedback controllers for the automated operation of chemical processes.
A conceptual process block diagram for a chemical process is shown in Figure 1. Notice that the inputs are classified as either manipulated or disturbance variables and the outputs are classified as measured or unmeasured in Figure 1. To automate the operation of a process, it is important to use measured of process outputs or disturbance input to make decisions about the proper values of manipulated inputs. This is the purpose of the controller shown in Figure 2; the measurement and control signals are shown as dashed lines. These initial concepts probably seem very vague or abstract to you at this point. Do not worry, because we present a number of examples in this chapter to clarify these ideas. The development of a control strategy consists of formulating or identifying the following.
为了使过程自动地运行，重要的是，测量过程的输出或者干扰输入以确定输入操纵量的合适值。
控制策略的形成包括，阐述并确定如下事项。
1. Control objective(s).
2. Input variables—classify these as (a) manipulated or (b) disturbance variables; inputs may change continuously, or at discrete intervals of time.
3. Output variables —classify these as (a) measured or (b) unmeasured variables; measurements may be made continuously, or at discrete intervals of time.
4. Constraints —classify these as (a) hard or (b) soft.
5. Operating characteristics —classify these as (a) continuous, (b) batch, or (c) semi-continuous (or semi-batch).
6. Safety, environmental, and economic considerations.
7. Control structure —the controllers can be feedback or feed forward in nature.
Here we discuss each of the steps in formulating a control problem in more detail.
1. The first step of developing a control strategy is to formulate the
control objective(s)②. A chemical-process operating unit often consists of several unit operations. The control of an operating unit is generally reduced to considering the control of each unit operation separately. Even so, each unit operation may have multiple, sometimes conflicting objectives, so the development of control objectives is not a trivial problem.
一个工作装置的控制通常可以简化为考虑每个单元操作的控制。2.Input variables can be classified as manipulated or disturbance
variables. A manipulated input is one that can be adjusted by the control system (or process operator). A disturbance input is a variable that affects the process outputs but that cannot be adjusted by the control system. Inputs may change continuously or at discrete intervals of time.
3.Output variables can be classified as measured or unmeasured
variables. Measurements may be made continuously or at discrete intervals of time.
4.Any process has certain operating constraints③, which are classified as
hard or soft. An example of a hard constraint is a minimum or maximum flow rate—a valve operates between the extremes of fully closed or fully open. An example of soft constrain is a product composition—it may be desirable to specify a composition between certain values to sell a product, but it is possible to violate this
specification without posing a safety or environmental hazard.
在销售产品时，通常希望某成分位于某个范围，但该指标的超标不会对安全及环境产生危害。
5.Operating characteristics are usually classified as continuous, batch, or
semi-continuous(semi-batch). Continuous processes operate for long periods of time under relatively constant operating conditions before being “shut down”for cleaning, catalyst regeneration, and so forth.
For example, some processes in the oil-refining industry operate for
18 months between shutdowns. Batch processes are dynamic in
nature—that is, they generally operate for a short period of time and the operating conditions may vary quite a bit during that period of time. Example batch processes include beer and wine fermentation, as well as many specialty chemical processes. For a batch reactor, an initial charge④is made to the reactor, and conditions (temperature, pressure) are varied to produce a desired product at the end of the batch time. A typical semi-batch process may have an initial charge to the reactor, but feed components may be added to the reactor during the course of the batch run.
Another important consideration is the dominant timescale⑤of a process. For continuous process this is very often related to the residence time of vessel. For example, a vessel with a liquid volume of 100 liters and a flow rate of 10 liters/minute would have a residence

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