Programmable Logic Programmable Logic ControllersControllers

Lecture 27Lecture 27

PLC LanguagesPLC Languages

Jesus is a friend who knows all your faults and still loves you anyway.

But God demonstrates his own love for us in this: While we were still sinners, Christ died for us. Romans 5:8

AgendaAgenda

IEC 61131 StandardProgramming ModelsInstruction ListStructured TextLadder DiagramFunction Block DiagramSequential Function Charts

IEC 61131 StandardIEC 61131 Standard

•Common and open framework •Loosely defined•Approved in 1992•Six Main Components

- IEC 61131-1 Overview- IEC 61131-2 Requirements and Test Procedures- IEC 61131-3 Data Types and Programming- IEC 61131-4 User Guidelines- IEC 61131-5 Communications- IEC 61131-7 Fuzzy Control

Programming ModelsProgramming Models

IL (Instruction List)ST (Structured Text)LD (Ladder Diagram)FBD (Function Block Diagram)SFC (Sequential Function Charts)

Instruction ListInstruction List

•Textual PLC Programming Language•Effectively Like Assembly Programming •Best Suited for Small Uncomplicated Programs•Instructions Consist of:

- Operator- Modifier- Operand

Example: AND NOT 00200

Instruction List ExampleInstruction List Example

Instruction List Example 2Instruction List Example 2

Structured TextStructured Text

• Textual PLC programming language• Effectively like BASIC programming • Easiest to troubleshoot and understand• Useful for implementing calculation-intensive functions and other difficult functions• Instructions consist of constructs

•Example: Analog_Out := Error * Gain;

Structured TextStructured Text

* Sample Structured Text Code * (comments)VAR (variables)

temp: INT;error: BOOL;

END_VARtemp := %IW4; (addresses)IF temp > 3200 THEN

error := TRUE;%QW := 200;

ELSE%QW := temp / 16;

END_IF;

Ladder DiagramLadder Diagram

• Primary programming language• Resembles original relay logic documentation• Addressing and memory is different for every manufacturer• Ladder logic scanning (rung order vs. network column)• Not purely parallel processor like relay logic

Ladder DiagramLadder Diagram

Function Block DiagramFunction Block Diagram

• Graphical data-flow programming method• Interconnected blocks• Similar to Ladder Logic

Function Block Diagram ExampleFunction Block Diagram Example

Sequential Function ChartsSequential Function Charts

• Graphical method for structuring programs• Design tool for sequential problems•Consists of:

- Interconnected steps- Actions- Transitions

Sequential Function Chart Sequential Function Chart ExampleExample