FBM214 FOXBORO
develop hardware components for users to choose from,and configure them into PLCs of varying scales.Moreover,the openness of this hardware configuration brings a lot of convenience to manufacturers,distributors(agents),system integrators,and end users,and greatly facilitates the sales supply chain.This is a great success experience.
In addition to general DI/DO,AD/DA templates,I/O templates within PLC have also developed a series of special functional I/O templates,which have opened up a way for PLC to be used in various industries,such as ASCII/BASIC
templates for barcode recognition,PID templates for feedback control,high-speed counting templates for operation control and mechanical processing,single axis position control templates,dual axis position control templates,cam locator templates,radio frequency identification interface templates,etc,This will have great development in the future.In addition,related components for input and output,as well as input and output electrical isolation and ground isolation in strong interference situations,will also be improved.
The CPU and memory in the PLC cooperate to complete control functions.It is different from the DCS system that processes parameters such as temperature,pressure,and flow rate.It adopts a fast scanning cycle,generally ranging from 0.1 to 0.2 seconds,while faster ones use a scanning cycle of 50ms or less.It is a digital sampling control system.
3.3 PLC software
In order to complete control strategies and replace relays,a set of control algorithm functional blocks(or subroutines),called instruction systems,have been developed for users to complete ladder diagrams of control systems similar to relay circuits.These blocks are fixed in the memory ROM and can be called by
users when programming applications.Instruction systems can be roughly divided into two categories,namely basic instructions and extended instructions.The instruction system of general PLC is divided into basic instructions,timer/counter instructions,shift instructions,transfer instructions,comparison instructions,conversion instructions,BCD operation instructions,binary operation instructions,increment/decrement instructions,logical operation instructions,special operation instructions,etc.These instructions are mostly similar to assembly language.In addition,PLC has increased sufficient internal resources such as timers,counters,internal relays,registers,and storage areas,bringing great convenience to programming.
programming language
IEC61131-3
Due to the differences in instruction systems and different user requirements for programming methods among PLC manufacturers,IEC has developed the Windows based programming language standard IEC61131-3(International Standard IEC1131 for Programmable Controllers issued by IEC in 1993),which specifies five programming languages:Instruction List(IL),Ladder Diagram(LD),Sequential Function Diagram(SFC),Function Block Diagram(FBD),and Structured Text(ST).This includes both textual programming(IL,ST)and graphical programming(LD,FBD),while SFC can be used in both programming languages.IEC Technical Committee(TC65)has come to carry out
