外文翻译
题目Programmable Logic Controller
目录
Programmable Logic Controller (PLC) (1)
1. About Programmable Logic Controller (PLC) (1)
2. INTRODUCTION (2)
3. OPERATION SEQUENCE (4)
3 .1 The Input and Output Scans (5)
3.2 The Logic Scan (5)
4 PLC STATUS (6)
5. MEMORY TYPES (7)
6. SOFTWARE BASED PLCS (8)controller翻译中文
7. SUMMARY (8)
8. PRACTICE PROBLEMS (8)
9. PRACTICE PROBLEM SOLUTIONS (9)
中文翻译 (11)
1. PLC介绍 (11)
2．指令 (12)
3．运行顺序 (13)
3.1 输入输出扫描 (14)
3．2 逻辑扫描 (14)
4．PLC状态显示 (15)
5．存储器类型 (16)
6．基于软件的PLC系统 (16)
7．概要 (17)
8．实际问题 (17)
9．实际问题解答 (17)
Programmable Logic Controller (PLC)
1. About Programmable Logic Controller (PLC)
PLC (programmable logic controllers) is the control hubs for a wide variety of automated systems and processes. They contain multiple inputs and outputs that use transistors and other circuitry to simulate switches and relays to control equipment. They are programmable via software interfaced via standard computer interfaces and proprietary languages and network options.
Programmable logic controllers I/O channel specifications include total number of points, number of in
puts and outputs, ability to expand, and maximum number of channels.  Number of points is the sum of the inputs and the outputs. PLC may be specified by any possible combination of these values.  Expandable units may be stacked or linked together to increase total control capacity.  Maximum number of channels refers to the maximum total number of input and output channels in an expanded system. PLC system specifications to consider include scan time, number of instructions, data memory, and program memory.  Scan time is the time required by the PLC to check the states of its inputs and outputs. Instructions are standard operations (such as math functions) available to PLC software. Data memory is the capacity for data storage. Program memory is the capacity for control software.
Available inputs for programmable logic controllers include DC, AC, analog, thermocouple, RTD, frequency or pulse, transistor, and interrupt inputs. Outputs for PLC include DC, AC, relay, analog, frequency or pulse, transistor and triac. Programming options for PLC include front panel, hand held and computer.
Programmable logic controllers use a variety of software programming languages for control. These include IEC 61131-3, sequential function chart (SFC), function block diagram (FBD), ladder diagram (LD),structured text (ST), instruction list (IL), relay ladder logic (RLL), flow chart, C, and Basic. The IEC
61131-3 programming environment provides support for five languages specified by the global standard: Sequential Function Chart, Function Block Diagram, Ladder Diagram, Structured Text, and Instruction List. This allows for multi-vendor compatibility and multi-language programming. SFC is a graphical language that provides coordination of program sequences, supporting alternative sequence selections and parallel
sequences. FBD uses a broad function library to build complex procedures in a graphical format. Standard math and logic functions may be coordinated with customizable communication and interface functions. LD is a graphic language for discrete control and interlocking logic. It is completely compatible with FBD for discrete function control. ST is a text language used for complex mathematical procedures and calculations less well suited to graphical languages. IL is a low-level language similar to assembly code. It is used in relatively simple logic instructions.  Relay Ladder Logic (RLL), or ladder diagrams, is the primary programming language for programmable logic controllers (PLC). Ladder logic programming is a graphical representation of the program designed to look like relay logic.  Flow Chart is a graphical language that describes sequential operations in a controller sequence or application. It is used to build modular, reusable function libraries. C is a high level programming language suited to handle the most complex computation, sequential, and data log
ging tasks. It is typically developed and debugged on a PC.  BASIC is a high level language used to handle mathematical, sequential, data capturing and interface functions. Programmable logic controllers can also be specified with a number of computer interface options, network specifications and features.  PLC power options, mounting options and environmental operating conditions are all also important to consider.
2. INTRODUCTION
For simple programming the relay model of the PLC is sufficient. As more complex functions are used the more complex V onNeuman model of the PLC must be used. A V onNeuman computer processes one instruction at a time. Most computers operate this way, although they appear to be doing many things at once. Consider the computer components shown in Figure 1.
Figure 1 Simplified Personal Computer Architecture
Input is obtained from the keyboard and mouse, output is sent to the screen, and the disk and memory are used for both input and output for storage. (Note: the directions of these arrows are very important to engineers, always pay attention to indicate where information is flowing.) This figure can be redrawn as in Figure 2 to clarify the role of inputs and outputs.
Figure 2 An Input-Output Oriented Architecture
In this figure the data enters the left side through the inputs. (Note: most engineering diagrams have in
puts on the left and outputs on the right.) It travels through buffering circuits before it enters the CPU. The CPU outputs data through other circuits. Memory and disks are used for storage of data that is not destined for output. If we look at a personal computer as a controller, it is controlling the user by outputting stimuli on the screen, and inputting responses from the mouse and the keyboard.
A PLC is also a computer controlling a process. When fully integrated into an application the analogies become;
Inputs - the keyboard is analogous to a proximity switch
Input -circuits - the serial input chip is like a 24Vdc input card
Computer - the 686 CPU is like a PLC CPU unit
Output - circuits - a graphics card is like a triac output card
Outputs - a monitor is like a light
Storage - memory in PLC is similar to memories in personal computers
It is also possible to implement a PLC using a normal Personal Computer, although this is not advisable. In the case of a PLC the inputs and outputs are designed to be more reliable and rugged for harsh production environments.

版权声明：本站内容均来自互联网，仅供演示用，请勿用于商业和其他非法用途。如果侵犯了您的权益请与我们联系QQ:729038198，我们将在24小时内删除。