programmable logic controller (plc). contents control process what is plc? general architecture of...
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Programmable Logic Programmable Logic ControllerController
(PLC)(PLC)
ContentsContentsControl ProcessWhat is PLC?General Architecture of PLCPLC Operating CyclePLC Hardware TypePLC Architecture EvolutionProgramming of PLC Basic PLC AdvantagesApplications
Control ProcessControl ProcessPhysical Quantity is sensed in the form of
small current/voltage e.g. Temperature, Pressure, Flow, Level etc (Sensor)
This Electrical Signal is amplified to a certain level (Amplifier)
Then amplified analogue output is converted into digital form. (Analogue to Digital Converter i.e. A/D)
This digital output is fed to the controller of the system to control the various physical quantities with the help of different devices. (PLC, Microcontroller, DSP etc…)
Block DiagramBlock Diagram
Physical Quantity(Temperature, Pressure etc..)
Amplifier
Analogue output in mA/mV
A/D
Amplified Analogue output
Controller(PLC, Microcontroller
etc…)
Devices(Motors etc…)
Digital
Control signals Digital
/Analogue
What is PLC?What is PLC?A digitally operating electronic
apparatus which uses a programmable memory for internal storage of instructions
Implement specific functions, such as logic, sequencing, timing, counting and arithmetic
Control various types of machines or process through digital or analogue input/output.
Traditional concept of PLCTraditional concept of PLC
PLC performs relay equivalent functions
PLC performs ON/OFF control
Designed for industrial environment
General Architecture of General Architecture of PLC PLC
PLC Operating CyclePLC Operating Cycle
PLC Signal FlowPLC Signal Flow
Output
PLC Hardware TypePLC Hardware TypeA most basic PLC system is a self contained
PLC which has two terminal blocks, one for the Input and other for the Output, called “Micros”.
Typically they provide front panel LED status indication of I/O and processor status.
2. Modular Chassis Based 2. Modular Chassis Based PLCPLCThe vast majority of PLC’s installed
today are modular chassis based PLC consisting of:
3. Modular Chassis-less PLC 3. Modular Chassis-less PLC SystemsSystemsThe advanced PLC’s are chassis-
lessThese are modular PLC systems.These systems also have: -Processor - Power supply -I/O modules -Communication
card These components mount directly
on a panel to allow easy insertion and removal.
General PLC BlocksGeneral PLC Blocks
Power Supply
CPU
Communicat-ion Module
Analogue Input
Analogue Output
Digital Input
Digital Output
220V, 50/60Hz
AC to DC conversion (12V or 48V)
Personal Computer
RS 232
Contd…Contd…
Contd…Contd…
48V DC
Contd…Contd…
48V DC
Contd…Contd…
Contd…Contd…
Bus system is
PLC Architecture EvolutionPLC Architecture Evolution
PLC Architecture EvolutionPLC Architecture Evolution
PLC Architecture EvolutionPLC Architecture Evolution
PLC Architecture EvolutionPLC Architecture Evolution
PLC Architecture EvolutionPLC Architecture Evolution
PLC Architecture EvolutionPLC Architecture Evolution
Programming of PLCProgramming of PLC The purpose of a PLC program is to
control the state of outputs based on the current condition of the inputs.
Types of programming :Ladder Logic (Analogous to Relay
Technology)Function Block (FB’s based on AND-OR logic)Visual Basic (VB based on C language)
*DOS based programming (Old Technology)
1. Ladder Logic1. Ladder LogicMost popular and most commonly
used PLC language is known as “Ladder Logic” .
Ladder Logic purposely resembles relay logic.
In order to control a process we try to design the logical continuity from input to output of program.
Ladder Logic ConceptsLadder Logic Concepts
Line Neutral
Ladder Logic ConceptsLadder Logic Concepts
Ladder Logic ConceptsLadder Logic Concepts
Read and Write InstructionRead and Write Instruction
Read Instruction
Write Instruction
Some Important Some Important InstructionsInstructionsLatching/Unlatching Instruction:
Latch
UnlatchRetain the output energized until reset
Timer InstructionsTimer Instructions
Timer ON Delay(TON)
Timer OFF Delay(TOF)
Retentive timer-on delay(RTO)
Counter InstructionsCounter Instructions
Counter Up (CTU)
Counter Down (CTD)
Comparison InstructionsComparison Instructions
Equal (EQU)Not Equal (NEQ)Less Than (LES)Less Than or Equal (LEQ)Greater Than (GRT)Greater Than or Equal (GEQ)
Some other instructions are Sequencer Instruction, Shift Register Instruction etc…
Function BlockFunction BlockBased on pre-defined blocks of
various functions
ANDAB
Basic PLC AdvantagesBasic PLC AdvantagesEase of ProgrammingEase of MaintenanceDesigned for Industrial
EnvironmentSuitable for Extreme
Environmental ConditionsQuick InstallationAdaptable to Change
ApplicationsApplications