1、青岛理工大学外文翻译题目 ProgrammableLogicController学生姓名： 郭军义指导教师： 田艳兵自动化工程学院 电气工程及其自动化 专业 082 班2012 年 6月 12日目 录Programmable Logic Controller (PLC)11. About Programmable Logic Controller (PLC)12. INTRODUCTION23. OPERATION SEQUENCE43 .1 The Input and Output Scans53.2 The Logic Scan54 PLC STATUS65. MEMORY TYPES76
2、. SOFTWARE BASED PLCS87. SUMMARY88. PRACTICE PROBLEMS89. PRACTICE PROBLEM SOLUTIONS9中文翻译111. PLC 介绍112指令123. 运行顺序133.1 输入输出扫描143.2 逻辑扫描144. PLC 状态显示155. 存储器类型166. 基于软件的 PLC 系统167概要178. 实际问题179. 实际问题解答17Programmable Logic Controller (PLC)1. About Programmable Logic Controller (PLC)PLC (programmable l
3、ogic 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 int
4、erfaces and proprietary languages and network options.Programmable logic controllers I/O channel specifications include total number of points, number of inputs 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 speci
5、fied 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 sca
6、n 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 mem
7、ory 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 f
8、or 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), re
9、lay 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 compa
10、tibility 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 functi
11、ons 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 le
12、ss 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 gr
13、aphical 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
14、the most complex computation, sequential, and data logging 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 comp
15、uter interface options, network specifications and features. PLC power options, mounting options and environmental operating conditions are all also important to consider.2. INTRODUCTIONFor simple programming the relay model of the PLC is sufficient. As more complex functions are used the more compl
16、ex VonNeuman model of the PLC must be used. A VonNeuman 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 1Simplified Personal Computer ArchitectureInput is ob
17、tained 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
18、as in Figure 2 to clarify the role of inputs and outputs.Figure 2An Input-Output Oriented ArchitectureIn this figure the data enters the left side through the inputs. (Note: most engineering diagrams have inputs on the left and outputs on the right.) It travels through buffering circuits before it e
19、nters 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
20、 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 switchInput -circuits - the serial input chip is like a 24Vdc input card Computer - the 686 CPU is like a PLC CPU unitOutput - ci
21、rcuits - a graphics card is like a triac output card Outputs - a monitor is like a lightStorage - memory in PLC is similar to memories in personal computersIt 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 out
22、puts are designed to be more reliable and rugged for harsh production environments.3. OPERATION SEQUENCEAll PLCs have four basic stages of operations that are repeated many times per second. Initially when turned on the first time it will check its own hardware and software for faults. If there are
23、no problems it will copy all the input and copy their values into memory, this is called the input scan. Using only the memory copy of the inputs the ladder logic program will be solved once, this is called the logic scan. While solving the ladder logic the output values are only changed in temporar
24、y memory. When the ladder scan is done the outputs will be updated using the temporary values in memory, this is called the output scan. The PLC now restarts the process by starting a self check for faults. This process typically repeats 10 to 100 times per second as is shown in Figure 3.Figure 3PLC
25、 Scan CycleSELF TEST - Checks to see if all cards error free, reset watch-dog timer, etc. (A watchdog timer will cause an error, and shut down the PLC if not reset within a short period of time - this would indicate that the ladder logic is not being scanned normally).INPUT SCAN-Reads input values f
26、rom the chips in the input cards, and copies their values to memory. This makes the PLC operation faster, and avoids cases where an input changes from the start to the end of the program (e.g., an emergency stop). There are special PLC functions that read the inputs directly, and avoid the input tab
27、les.LOGIC SOLVE/SCAN-Based on the input table in memory, the program is executed 1 step at a time, and outputs are updated. This is the focus of the later sections.OUTPUT SCAN-The output table is copied from memory to the output chips.These chips then drive the output devices.The input and output sc
28、ans often confuse the beginner, but they are important. The input scan takes a snapshot of the inputs, and solves the logic. This preventspotential problems that might occur if an input that is used in multiple places in the ladder logic program changed while half ways through a ladder scan. Thus ch
29、anging the behaviors of half of the ladder logic program. This problem could have severe effects on complex programs that are developed later in the book. One side effect of the input scan is that if a change in input is too short in duration, it might fall between input scans and be missed.When the
30、 PLC is initially turned on the normal outputs will be turned off. This does not affect the values of the inputs.3 .1 The Input and Output ScansWhen the inputs to the PLC are scanned the physical input values are copied into memory. When the outputs to a PLC are scanned they are copied from memory t
31、o the physical outputs. When the ladder logic is scanned it uses the values in memory, not the actual input or output values. The primary reason for doing this is so that if a program uses an input value in multiple places, a change in the input value will not invalidate the logic. Also, if output b
32、its were changed as each bit was changed, instead of all at once at the end of the scan the PLC would operate much slower.3.2 The Logic ScanLadder logic programs are modelled after relay logic. In relay logic each element in the ladder will switch as quickly as possible. But in a program elements can only be examines one at a time in a fixed sequence. Consider the ladder logic in Figure 4, the ladder logic will be interpreted left-
