POWERPOINT PRESENTATION ON

PROGRAMMABLE LOGIC CONTROLLERS(PLC)

CONTENTSINTRODUCTIONMAJOR COMPONENTS OF COMMON PLC

SYSTEMCOMPARISON B/W PLC & RELAYPLC OPERATION SEQUENCEPLC PROGRAMMING LANGUAGEPLC SIZEADVANTAGESAPPLICATIONS

What is a PLC ?A PLC is a solid state control system that continuously

monitors the status of devices connected as inputs. Based upon a user written program, stored in memory, it controls the status of devices connected as outputs.

INPUT

CPU

OUTPUT

DEFINITION OF PLCA digital electronic device that uses a programmable

memory to store instructions and to implement specific functions such as logic, sequence, timing, counting and arithmetic to control machines and process.

A PLC is a computer designed to work in an industrial environment.

MAJOR COMPONENTS OF COMMON PLC SYSTEM

MAJOR COMPONENTS OF PLC Contd…. POWER SUPPLYIt provides the voltage needed to run the primary PLC components.

INPUT MODULESIt accepts and converts signals from sensors into a logic signal.

OUTPUT MODULESIt converts control signal instructions a signal that can be used by

actuators.

PROGRAMMING DEVICE

The programming terminal is used for programming the PLC and monitoring/sequencing PLCs operation.

Contd…. PROCESSORIt is the brain of PLC and governs the activities of the entire PLC

system.The CPU consists of following blocks: Arithmetic Logic

Unit(ALU), Internal memory of CPU, Internal timers, Counters & Flags.

The various operations performed are: Scanning I/O bus traffic

control, Program execution, Peripheral and External device communication etc.

MEMORYIt is the component that stores information, programs and data

in memory.Types of memories used in PLC are- RAM & ROM.

COMPARISON B/W PLC & RELAY1. It eliminates the hard wiring associated with

conventional relay control circuit.

2. It is small and inexpensive compared to equivalent relay based process control.

3. Capable of simulating a hundred relay, timers and counters.

4. Easy to program and install.

5. It can be designed with communication capabilities that allow them to converse with other computer systems or to provide human interfaces.

PLC OPERATION SEQUENCE

SELF TESTTesting of its own hardware & software for faults.

CHECK INPUT STATUSFirst the PLC takes a look at each I/O to determine if it is on or

off.

EXECUTE PROGRAM

Next the PLC executes the program one instruction at a time.

UPDATE OUTPUT STATUS

Finally the PLC updates the status of the outpts. It updates the outputs based on which inputs were on during first step.

PLC PROGRAMMING LANGUAGEPLC programming languages refers to the method by

which user communicates information to the PLC.LADDER LOGIC is the oldest programming

language for PLC.It is well suited to express Combinational logic.The main ladder logic symbols represent the elements:

LADDER LOGIC FOR BASIC GATES

Contd….

PLC SIZESMALL: It covers up to 128 I/O and memories up to

2Kb. It is capable of providing simple to advanced level of machine control.

MEDIUM: It have up to 2048 I/O and memories up to 32KB. Special I/O modules to make PLCs adaptable to temperature, pressure and any analog function encountered in process control applications.

LARGE: The most sophisticated unit of PLCs family. They have 16000 I/Os and memories up to 2Mb. It has

almost unlimited applications and can control indiviual production process or entire plants.

ADVANTAGES OF PLCRealiabilityFlexibility in programming and reprogramming.Cost effective for controlling complex systems.Small physical size.High speed of operation.Ability to communicate with computer systems in

plant.Ease of maintenance.Reduced space.Energy saving.

APPLICATIONS OF PLC Whenever automation is desired the PLCs are best

suited to meet the task. PLCs were originally used to substitute the switching

relay networks used in industrial applications, but now they can be used to implement other tasks such as timing, delaying counting etc.

Some examples of industries using PLCs are: Food/ Beverage Material Handling Robot manufacturing and control Conveyor System etc.

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