PLC的英文介绍

PLC Introduction

Programmable controller is the first in the late 1960s in the United

States, then called Plc programmable logic controller (Programmable Logic

Controller) is used to replace relays. For the implementation of the

logical judgment, timing, sequence number, and other control functions.

The concept is presented Plc General Motors Corporation. Plc and the basic

design is the computer functional improvements, flexible, generic and

other advantages and relay control system simple and easy to operate, such

as the advantages of cheap prices combined controller hardware is standard

and overall. According to the practical application of target software

in order to control the content of the user procedures memory controller,

the controller and connecting the accused convenient target.

In the mid-1970s, the Plc has been widely used as a central processing

unit microprocessor, import export module and the external circuits are

used, large-scale integrated circuits even when the Plc is no longer the

only logical (IC) judgment functions also have data processing, PID

conditioning and data communications functions. International Electro

technical Commission (IEC) standards promulgated programmable controller

for programmable controller draft made the following definition :

programmable controller is a digital electronic computers operating

system, specifically for applications in the industrial design

environment. It used programmable memory, used to implement logic in their

internal storage operations, sequence control, timing, counting and

arithmetic operations, such as operating instructions, and through

digital and analog input and output, the control of various types of

machinery or production processes. Programmable controller and related

peripherals, and industrial control systems easily linked to form a whole,

to expand its functional design. Programmable controller for the user,

is a non-contact equipment, the procedures can be changed to change

production processes. The programmable controller has become a powerful

tool for factory automation, widely popular replication. Programmable

controller is user-oriented industries dedicated control computer, with

many distinctive features.

First, high reliability, anti-interference capability;

Second，programming visual, simple;

Third, adaptability good;

Fourth functional improvements, strong functional interface

1.Design Theory Development

Today, the primary focus of most design research is based on

mechanical or electrical products. One of the by-products of this proposed

research is to enhance our fundamental understanding of design theory and

methodology by extending it to the field of engineering systems design.

A system design theory for large-scale and complex system is not yet fully

developed. Particularly, the question of how to simplify a complicated

or complex design task has not been tackled in a scientific way.

Furthermore, building a bridge between design theory and the latest

epistemological outcomes of formal representations in computer sciences

and operations research, such as discrete event system modeling, can

advance future development in engineering design.

2.Application in Logical Hardware Design

From a logical perspective, PLC software design is similar to the

hardware design of integrated circuits. Modern VLSI designs are extremely

complex with several million parts and a product development time of 3

years [Whitney, 1996]. The design process is normally separated into a

component design and a system design stage. At component design stage,

single functions are designed and verified. At system design stage,

components are aggregated and the whole system behavior and functionality

is tested through simulation. In general, a complete verification is

impossible. Hence, a systematic approach as exemplified for the PLC

program design may impact the logical hardware design.

Programming languages

Higher level PLC programming languages have been around for some time,

but lately their popularity has been mushrooming. As Raymond Lavelle, vice

president and general manager, Siemens Energy and Automation. Inc,

Programmable Controls Division, points out :”As programmable controls

are being used for more and more sophisticated operations, languages other

than ladder logic become more practical, efficient, and powerful. For

example, it's very difficult to write a trigonometric function using

ladder logic. ”Languages gaining acceptance include Boolean, control

system flowcharting, and such function chart languages as Graphtec and

its variations. And these’s increasing interest in languages like C and