CoDeSys引导：实践IEC 61131-3编程语言在PLC中的差异与应用

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《可编程逻辑控制器：基于IEC 61131-3的CoDeSys实用方法》是一本由John R. Hackworth和Frederick D. Hackworth Jr.合著的实用指南，着重于介绍PLC（Programmable Logic Controller）编程方法及其应用。自PLC市场出现竞争以来，不同品牌间的编程语言差异日益显著，尽管早期的标准如指令列表（Instruction Lists, IL）和梯形图（Ladder Diagram, LD）被广泛应用，但每个制造商都对这些基础语言进行了自家的扩展，形成了各自的“方言”。该书内容广泛，共分为12章，旨在提供一个全面的学习平台，而非局限于单一制造商的产品。第1章介绍了梯形图基础，这是PLC编程中最基本的概念，用于描述设备的工作流程。接着，作者探讨了PLC的基本概念，包括其在工业自动化中的角色和功能。第3章深入到PLC的实际编程技巧，讲解如何利用各种编程语言如结构文本（Structured Text, ST）、功能块图（Function Block Diagram, FBD）等，这些是根据IEC 61131-3国际标准制定的五种标准编程语言之一。CoDeSys是一个跨平台的工具集，允许用户使用这些标准化的语言在多种PLC上进行编程，从而提高了兼容性和效率。随着章节的推进，书中涵盖了高级编程技术，如助记符编程代码（Mnemonic Programming Code），这有助于程序员更高效地编写程序；第6章讨论了接线技术，强调了实际安装和布线在控制系统设计中的重要性；第7章和后续章节分别关注模拟输入/输出、离散位置传感器、编码器、变送器等，以及高级传感器的应用。第10章和11章深入到闭环控制和电机控制的实现，包括PID（Proportional-Integral-Derivative）控制，这是工业自动化中常见的控制策略。最后，第12章着重于系统的完整性和安全性，探讨了如何确保PLC系统在复杂工业环境中的稳定运行和防护措施。《Programmable Logic Controllers: A Practical Approach to IEC 61131-3 Using CoDeSys》是一本实用的教材，不仅教授基础知识，还帮助读者理解和掌握多种编程方法，以适应不同厂商的PLC产品，并熟悉国际标准IEC 61131-3。通过本书，学习者不仅能学会特定设备的编程，还能提升跨平台工作的能力，对于从事PLC编程或工业自动化领域的专业人士来说，具有很高的参考价值。

Chapter 1 - Ladder Diagram Fundamentals

1-13

Figure 1-19 - Wire Marker

or white wire (do not use green - it is reserved for safety ground wiring). Notice that in

Figure 1-18 the wire connecting T1 to F1 is not numbered. This is because in our design

we will be using a transformer with the fuse block included. Therefore, this will be a

permanent metal strap on the transformer and will not be a wire.

The wire generally used within the controls circuitry

is AWG14 or AWG16 stranded copper, type MTW or THHN.

MTW is an abbreviation for “machine tool wire” and THHN

indicates thermoplastic heat-resistant nylon-coated. MTW

has a single PVC insulation jacket and is used in

applications where the wire will not be exposed to gas or oil.

It is less expensive, more flexible, and easier to route,

bundle, and pull through conduits. THHN is used in areas

where the wire may be exposed to gas or oil (such as

hydraulically operated machines). It has a transparent, oil-

resistant nylon coating on the outside of the insulation. The drawback to THHN is that it

is more expensive, is more difficult to route around corners, and because of its larger

diameter, reduces the maximum number of conductors that can be pulled into tight places

(such as inside conduits). Since most control components use low currents, AWG14 or

AWG16 wire is much larger than is needed. However, it is generally accepted for panel

and controls wiring because the larger wire is tough, more flexible, easier to install, and can

better withstand the constant vibration created by heavy machinery.

Reference Designators

For all electrical diagrams, every component is given a reference designator. This

is a label assigned to the component so that it can be easily located. The reference

designator for each component appears on the schematic diagram, the mechanical layout

diagram, the parts list, and sometimes is even stamped on the actual component itself.

The reference designator consists of an alphabetical prefix followed by a number. The

prefix identifies what kind of part it is (control relay, transformer, limit switch, etc.), and the

number indicates which particular part it is. Some of the most commonly used reference

designator prefixes are as follows:

T transformer

CR control relay

Rresistor

C capacitor

LS limit switch

PB pushbutton

S switch

SS selector switch

Chapter 1 - Ladder Diagram Fundamentals

1-14

SWITCH1 SWITCH2

LAMP1

Figure 1-20 - AND Lamp Circuit

TDR or TR time delay relay

M motor, or motor relay

L indicator lamp or line phase

Ffuse

CB circuit breaker

OL overload switch or overload contact

The number of the reference designator is assigned by the designer beginning with the

number 1. For example, control relays are numbered CR1, CR2, etc, fuses are F1, F2, etc.

and so on. It is generally a courtesy of the designer to state on the electrical drawing the

“Last Used Reference Designators”. This is done so that anyone who is assigned the job

of later modifying the machine will know where to “pick up” in the numbering scheme for

any added components. For example, if the drawing stated “Last Used Reference

Designators: CR15, T2, F3", then in a modification which adds a control relay, the added

relay would be assigned the next sequential reference designator, CR16. This eliminates

the possibility of skipping a number or having duplicate numbers. Also, if components are

deleted as part of a modification, it is a courtesy to add a line of text to the drawing stating

“Unused Reference Designators:” This prevents someone who is reading the drawing from

wasting time searching for a component that no longer exists.

Some automation equipment and machine tool manufacturers use a reversed

component numbering scheme that starts with the number and ends with the alphabetical

designator. For example, instead of CR15, T2, and F3, the reference designators 15CR,

2T, and 3F are used.

The components in our diagram example shown in Figure 1-18 are numbered with

reference designators. The transformer is T1 and the fuse is F1. Other components will

be assigned reference designators as they are added to the diagram.

Boolean Logic and Relay Logic

Since the relays in a machine perform some type of control operation, it can be said

that they perform a logical function. As with all logical functions, these control circuits must

consist of the fundamental AND, OR, and INVERT logical operations. Relay coils, N/C

contacts, and N/O contacts can be wired to perform

these same fundamental logical functions. By properly

wiring relay contacts and coils together, we can create

any logical function desired.

AND

Generally when introducing a class to logical

operations, an instructor uses the analogy of a series

Chapter 1 - Ladder Diagram Fundamentals

1-16

Lamp Switch Switch

21 2

()( )

(1-2)

SWITCH1

SWITCH2

LAMP2

Figure 1-23 - OR Lamp Circuit

SWITCH1

SWITCH2

LAMP2

Figure 1-24 - OR Circuit

There are a few important details that have been added along with the switches and

lamp. Note that the added wires have been assigned the wire numbers 3 and 4 and the

added components have been assigned the reference designators PB1, PB2, and L1. Also

note that the switches are on the left and the lamp is on the right. This is a standard

convention when designing and drawing machine circuits. The controlling devices (in this

case the switches) are always positioned on the left side of the rung, and the controlled

devices (in this case the lamp) are always positioned on the right side of the rung. This

wiring scheme is also done for safety reasons. Assume for example that we put the lamp

on the left side and the switches on the right. Should there develop a short to ground in the

wire from the lamp to the switches, the lamp would light without either of the switches being

pressed. For a lamp to inadvertently light is not a serious problem, but assume that instead

of a lamp, we had the coil of a relay that started the machine. This would mean that a short

circuit would start the machine without any warning. By properly wiring the controlled

device (called the load) on the right side, a short in the circuit will cause the fuse to blow

when the rung is activated, thus de-energizing the machine controls and shutting down the

machine.

The same approach may be taken for the OR

function. The circuit shown in Figure 1-23 illustrates two

switches wired as an OR function controlling a lamp,

LAMP2. As can be seen from the circuit, the lamp will

illuminate if SWITCH 1 OR SWITCH 2 is closed; that is,

depressing either of the switches will cause the lamp

LAMP2 to illuminate. The Boolean expression for this

circuit is

For those more familiar with logic diagramming, the OR gate representation of the OR

circuit in Figure 1-23 and Equation 1-2 is shown in Figure 1-24. Again, when drawing

machine controls diagrams, we do not use this schematic representation.

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CoDeSys引导：实践IEC 61131-3编程语言在PLC中的差异与应用

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