Systematic Solution Finding-Digital Logic Design And Programming-Lecture Slides, Slides of Digital Logic Design and Programming

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Programmable LogicControllersProgramming

Systematic Solution Finding^ ^ Control^ programs^

represent^ an^ importantcomponent of an automation system.

^ Must^ be^ systematically

designed,^ well

structured and fully documented in order tobe error-freelow-maintenancecost effectiveas much as possible.

Phase Model For theGeneration of PLC Software

Phase Model Of PLC SoftwareGeneration (contd.)^ ^ Consist of the following sections^ Specification:^ Description of the task^ Design:^ Description of the solution^ Realization:^ Implementation of the solution^ Integration/commissioning:^ Incorporating into environment andtesting the solution^ ^ Can be applied to basically all technical projects.^ ^ Differences^ occur^ in^ the^

methods^ and^ tools^ used^ in

the individual phases.  The phase model can be applied to control programs of varyingcomplexity; for complex control tasks the use of such a model isabsolutely essential.

Phase 1: Specification^ ^ Following^ are^ available

at^ the^ end^ of

this phase:Verbal description of the control taskStructure/layoutMacrostructuring

of^ the^ system^ or process and thus rough structuringof the solutiondocsity.com

Phase 2: Design (Concreteform of solution concept)^ ^ A solution concept is developed on the basis of the definitionsestablished in phase 1.^ ^ The method used to describe the solution must provide both agraphic and process oriented description of the function andbehavior^ of^ the^ control^ system

and^ be^ independent^ of^ the technical realization.  These requirements are fulfilled by the function chart as definedin IEC 60848.  Starting^ with^ a^ representation

of^ the^ overall^ view^ of^ the controller (rough structure of the solution), the solution can berefined step by step until a level of description is obtained,which contains all the details of the solution (refinement ofrough structure).

Phase 3: Realisation (Programmingof solution concept)^ ^ The translation of the solution concept into a control program iseffected via the programming languages defined in EN 61131-3(IEC 61131-3).^ ^ These are: sequential function chart, function block diagram,ladder diagram, instruction list and structured text.^ ^ Control systems operating in a time/logic process and availablein^ function^ chart^ to^ IEC^

60848,^ can^ be^ clearly^ and^

easily programmed in a sequential function chart.  A sequential function chart, in as far as possible, uses the samecomponents for programming as those used for the descriptionin the function chart to IEC 60848.  Ladder diagram, function block diagram and statement list arethe programming languages suitable for the formulation of basicoperations and for control systems which can be described bysimple operations logic operations or boolean signals.

Phase 3:^ ^ The high-level language structured text ismainly used to create software modules ofmathematical content, such as modules forthe description of control algorithms.^ ^ In so far as PLC programming systemssupport this, the control programs or parts ofa program created should be simulated priorto commissioning.^ ^ This permits the detection and elimination oferrors right at the initial stage.

Documentation^ ^ An essential requirement for the maintenance and expansion ofa system.^ ^ Consists of the document of the individual phases, printouts ofthe control programs and of any possible additional descriptionsconcerning the control program. Individually:Problem descriptionPositional sketch or technology patternCircuit diagramTerminal diagramPrintouts of control programs in SFC, FBD etc..Allocation list of inputs and outputs (this also forms part ofthe control program printouts)Additional documentation

Introduction To The IEC 1131^ ^ The^ International^ Electrotechnical

Commission^ (IEC)^ SC65B- WG7 committee developed the IEC 1131 standard in an effort tostandardize programmable controllers.  One of the committee’s objectives was to create a common setof PLC instructions that could be used in all PLCs.  IEC 1131 standard reached the status of international standardin August 1992.  The effort to create a global PLC standard has been a verydifficult^ task^ to^ accomplish^

due^ to^ the^ diversity^ of^ PLC manufacturers^ and^ the^ problem

of^ program^ incompatibility among PLC brands.  However, the inroads that have been made so far have had atremendous impact on the way PLCs will be programmed in thefuture.

IEC 1131 ProgrammingLanguage Standard^ ^ The^ IEC^1131 programming

language

standard is referred to as the IEC 1131-3 programming standard, since part 3of the standard deals with programminglanguages.

IEC 1131 ProgrammingLanguage Standard^ ^ The IEC 1131-3 standard defines two graphical languages andtwo text based languages for use in PLC programming.^ ^ The^ graphical^ languages^

use^ symbols^ to^ program^ controlinstructions, while the text-based^ languages^ use^ characterstrings to program instructions. ^ Graphical languagesLadder diagrams (LD)Function block diagram (FBD) ^ Text-based languagesInstruction list (IL)Structured text (ST)