joker是什么意思>the mass什么意思毕业设计(论文)英文翻译原文
课题：基于PLC的运料小车控制
院系：机电工程学院
专业：机电一体化
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指导教师单位：桂林航天工业高等专科学校
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职称：副教授
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Programmable Logic Controllers (PLCs)
1 。About Programmable Logic Controllers (PLCs)
PLCs (programmable logic controllers) are the control hubs for a wide variety of automated systems and process. They contain multiple inputs and outputs that u 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 inputs and outputs, ability to expand, and maximum number of channels. Number of points is the sum of the inputs and the outputs. PLCs may be specified by any possible combination of the values. Expandable units may be stacked or linked together to increa 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 memo
vs是什么意思ry is the capacity for control software.
Available inputs for programmable logic controllers include DC, AC, analog, thermocouple, RTD, frequency or pul, transistor, and interrupt
inputs. Outputs for PLCs include DC, AC, relay, analog, frequency or pul, transistor, and triac. Programming options for PLCs include front panel, hand held, and computer.
Programmable logic controllers u a variety of software programming languages for control. The include IEC 61131-3, quential 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 quences, supporting alternative quence lections and parallel quences. FBD us a broad function library to build complex procedures in a graphical format. Standard math and logic functions may be coordinated with customizable communication an
avccd 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 ud for complex mathematical procedures and calculations less well suited to graphical languages. IL is a low-level language similar to asmbly
shining friendcode. It is ud in relatively simple logic instructions. Relay Ladder Logic (RLL), or ladder diagrams, is the primary programming language for programmable logic controllers (PLCs). Ladder logic programming is a graphical reprentation of the program designed to look like relay logic. Flow Chart is a graphical language that describes quential operations in a controller quence or application. It is ud to build modular, reusable function libraries. C is a high level programming language suited to handle the most complex computation, quential, and data logging tasks. It is typically developed and debugged on a PC. BASIC is a high level language ud to handle mathematical, quential, 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
ache什么意思For simple programming the relay model of the PLC is sufficient. As more complex functions are ud the more complex VonNeuman model of the PLC must be ud. A VonNeuman computer process 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 1 Simplified Personal Computer Architecture
Input is obtained from the keyboard and mou, output is nt to the screen, and the disk and memory are ud for both input and output for storage. (Note: the directions of the 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.
工程管理系统Figure 2 An Input-Output Oriented Architecture
In 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 enters the CPU. The CPU outputs data through other circuits. Memory and disks are ud for storage of data that is not destined for output. If we look at a personal computer as a controller, it is controlling the ur by outputting stimuli on the screen, and inputting respons from the mou and the keyboard.
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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
走遍法国下载input -circuits - the rial 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
六级真题听力outputs - a monitor is like a light
storage - memory in PLCs 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 ca of a PLC the inputs and outputs are designed to be more reliable and rugged for harsh production environments.
3 。 OPERATION SEQUENCE
All PLCs have four basic stages of operations that are repeated many times per cond. Initially when turned on the first time it will check it’s own hardware and software for faults. If there are 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 temporary 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 lf check for faults. This process typically repeats 10 to 100 times per cond as is shown in Figure 3.
