Programmable Logic Controllers (PLC)

A PLC is known as a programmable logic controller and is an industrial computer that connects a number of I/O modules. And are commonly available in various I/O modules such as Micro PLC, Nano PLC, Medium PLC and Large PLC, basically Nano PLC has some 100 I/O modules and Large PLC has more than 5000 I/O modules. Also PLCs are available in compact type and modular type and compact type PLC has fixed size I/O and all the modules included basically compact type PLC does not increase the number of I/O modules but modular PLC has modified these I/O modules as required. A PLC has a separate module and is placed in a rack or box type. Commonly PLC with SMPS and without SMPS. SMPS is a switch mode power supply and is also known as switching or switch mode power supply. Basically SMPS is used in PLC to convert AC supply to DC supply. And it converts 230 volt AC supply to 24 volt DC supply so PLC works on DC as well as AC supply.

And the plc response time is a one tenth of a second. PLC takes digital signals or analog signals from field level components like sensors, actuators, valves and processes them and gives output or task to the system using PLC program. Basically PLC program controls the working of machine and system.

Introduction of the PLC

Programmable Logic Controllers (PLC) are digitally operating electronic devices that use memory to operate Also known as programmable memory. A plc performs functions such as logic, sequencing, timing, counting and arithmetic to control devices connected to various machines or processes through digital or analog I/O modules. A programmable logic controller (PLC) is an industrial computer designed for multiple input and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact.

What is Programmable Logic Controllers (PLC)?

A programmable logic controller (PLC) or programmable controller is an industrial digital computer designed for the control of production processes, such as used in assembly lines, complex systems, robotic equipment, industrial equipment and industrial automation.

History of PLC

PLC was introduced in 1960. The first successful programmable logic controllers designed and developed by Modicon served as relay replacers for common motors.

Major Components of a Common PLC

Power supply

The primary provides the voltage required to operate the PLC components.

Input/Output Modules

Provides single communication and isolation between internal logic level signals and field high level signals in the PLC.

Processor

The entire PLC provides the intelligence to command and control the system's activities.

Programming Device

Used to enter the desired program that will determine the sequence of operation and control of process equipment or driven machines.

Architecture of PLC

A PLC is an industrial microprocessor based controller that stores program instructions for various functions using programmable memory.

Central Processing Unit

A central processing unit (CPU) that interprets inputs, executes control programs stored in memory and sends output signals. CPU memory, called registers, resides in the microprocessor and is used to store information involved in program execution A CPU is a control unit used to control the timing of an operation.

Power Supply

A power supply unit is required to convert the mains AC voltage to a low DC voltage (5 V).

Programming Device

A programming device is used to enter the required program into the processor's memory.

Memory Unit

The memory unit is where the program is stored which is used for the control actions used by the microprocessor and the data stored from the input to the process is used for the output.

Programming languages of PLC

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

Applications

Production and control of robots
Car park control
Train Control Station System
food processing
Materials handling
Machine tools
Conveyor system etc.