PLCPLCPLCIntroductionFunctional BlocksMechanical DesignInternal Architecture & Memory2PLCScan CycleInput / OutputProgrammingTimersCountersINTRODUCTION Programmable Logic Controller (PLC).3INTRODUCTION PLC is used to replace relay circuits in automated machine control. PLC is optimized for control tasks and industrial environment: 1) 2) 3)4INTRODUCTION5 Comparison between relay logic, solid state logic, PLC:Relay Logic Solid State Logic PLCSlower speed Fast speed Fast speedMoving parts No moving parts No moving partsSparks, less safe No sparks, safer No sparks, saferSlow to design Slow to design Fast, easy to programDifficult to modify Difficult to modify Easy to modifyNeed more space Need less space Need less spaceINTRODUCTION6 Comparison between relay logic, solid state logic, PLC:INTRODUCTION7 Normally Open (NO) Normally Closed (NC) contact:Contact Symbol StateDe-energized EnergizedN.O.OPEN(Switch OFF)CLOSED(Switch ON)N.C.CLOSED(Switch ON)OPEN(Switch OFF) FUNCTIONAL BLOCKS8MECHANICAL DESIGN9Single Box Modular / Rack TypeComplete package complete with power supply, processor, memory and I/O units.Consists of separate modules for power supply, processor, memory and I/O units.Commonly used for smaller PLC. Commonly used for larger PLC.Typically has up to 40 I/O points and can store up from300 to 1000 instructions.Can be used for all sizes of PLC.Various functional modules can be plugged into a base rack to suit particular requirements.Easy to expand the number of I/O and memory by just adding the modules.MECHANICAL DESIGN10PLC ProgrammerHand-held PCLegacy way to program legacy PLC. Current way to program latest PLC.Consists of small keyboard and LCD display.Computer with appropriate PLC software and communication cable.Program is written on paper, before downloaded into the PLC.Program is written directly on PC,before downloaded into the PLC.Program can be saved and transferred easily. INTERNAL ARCHITECTURE11 Data bus, address bus, control bus. Types of memory. SCAN CYCLE12 SCAN CYCLE13Scan CycleInput Scan The current status of every input module is stored in the Input Image Table, bringing it up to date.The input scan is fast, the elapsed time depends on the number of input modules, CPU clock speed and other CPU technical features.ProgramScan Stating from the program first rung till the last rung.The processor continuously keep the Output Image Table up to date.The execution time depends on the program length, complexity of the instructions and CPU technical features.Output Scan Transfer the entire Output Image Table to outputmodules.The output scan is fast, similar to the input scan.INPUT OUTPUT14 Input/Output unit provides the interface between input devices (sensors, switches, push buttons), output devices (motors, solenoids) and CPU. Provides signal conditioning and isolation functions.INPUT OUTPUT15 Optoisolator. Provides electrical isolation from the external world. How it works? Enable a wide range of input voltages 5Vdc, 24Vdc. INPUT OUTPUT16 DC input circuit. Provides electrical isolation from the external world. Converts incoming 5Vdc, 24Vdc to 5Vdc for CPU. How it works? INPUT OUTPUT17 AC input circuit. Provides electrical isolation from the external world. Converts incoming 110Vac, 240Vac to 5Vdc for CPU. How it works?INPUT OUTPUT18Output ModulesRelay Type Transistor Type Triac TypeCan switch large current Can switch small current Can switch small currentSlower switching action Faster switching action Faster switching actionFor DC and AC switching For DC switching only For AC switching onlyProvides mechanical isolationFuse protection for over current and reverse voltage polarityFuse protection for over currentOutput voltages: 24Vdc 100mA, 110Vac 1A, 240Vac 1A, 240Vac 2APROGRAMMING LANGUAGES19Programming LanguagesLAD Ladder DiagramFBD Functional Block DiagramSTL Statement Text Language PROGRAMMING LANGUAGES20Programming LanguagesExample 1 Example 2 Example 3LADFBDSTL LDI40.0OR Q43.1ANII40.1OUTENDPROGRAMMING LANGUAGES21 Latching. A program to hold an output energized, even when the input condition is removed. START I40.0 Q43.0Q43.0 STOP I40.1 TIMERS22 Timers. A program used to control timing operation. Example applications. , , , Types of timers. Pulse timer. On-delay timer. Off-delay timer. How timer operates?TIMERS23 Types of timers: Timer operation: TIMERS24 Application:COUNTERS25 Counters. A counter allows a number of occurrences of input signals to be counted. Example applications. , , , Types of counters. Down-counter. Up-counter. How counter operates?COUNTERS26 COUNTERS27 Application:THANK YOU28