What is a Programmable Logic Controller (PLC) ?
Download
1 / 24

What is a Programmable Logic Controller PLC - PowerPoint PPT Presentation


  • 180 Views
  • Updated On :

What is a Programmable Logic Controller (PLC) ?. Agenda. History PLC Overview Hardware Inputs/Outputs Operation Programming Software Communication What you need to know when specifying a PLC Glossary. History of the PLC.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'What is a Programmable Logic Controller PLC ' - Anita


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Agenda

  • History

  • PLC Overview

  • Hardware

  • Inputs/Outputs

  • Operation

  • Programming Software

  • Communication

  • What you need to know when specifying a PLC

  • Glossary


History of the PLC

  • First Programmable Logic Controllers were designed and developed by Modicon as a relay replacer for GM and Landis.

    • These controllers eliminated the need for rewiring and adding additional hardware for each new configuration of logic.

    • The new system drastically increased the functionality of the controls while reducing the cabinet space that housed the logic.

  • The first PLC, model 084, was invented by Dick Morley in 1969.

  • The first commercial successful PLC, the 184, was introduced in 1973 which was designed by Michael Greenberg.


Inputs

Outputs

What is a PLC?

The Basic Block

CPU

A PROGRAMMABLE LOGIC CONTROLLER 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.


Inputs

Outputs

Remote

Outputs

Inputs

What is a PLC with Distributed I/O?

Getting Complex

CPU


CPU

CPU

Outputs

Inputs

Inputs

Outputs

Outputs

Inputs

What is a PLC with Distributed Control?

Getting Really Complex

Remote


MEMORY

data

program

Inside a PLC

Communications

Port

Circuits

Circuits

Central

Processor

Unit

(CPU)

Input

Output

CR

High

Voltage

High

Voltage

Isolation

Barrier

Isolation

Barrier

Low Voltage

or

DC Power Supply

AC Power Supply


Inside a PLC

  • The CPU contains an “Executive” program that tells the PLC how to:

    • Execute the control Instructions

      • User’s Program

    • Communicate with other devices

      • Other PLCs, Programming devices, I/O devices, etc.

    • Perform Housekeeping activities

      • Diagnostics, etc

  • This program is stored in “nonvolatile” memory

    • Meaning that the program will not be lost if power is removed


What are Inputs?

  • Switches and Pushbuttons

  • Sensing Devices

    • Limit Switches

    • Photoelectric Sensors

    • Proximity Sensors

  • Condition Sensors

    • Pressure Switches

    • Level Switches

    • Temperature Switches

    • Vacuum Switches

    • Float Switches

  • Encoders


What are Outputs?

  • Valves

  • Motor Starters

  • Solenoids

  • Actuators

  • Control Relays

  • Horns & Alarms

  • Stack Lights

  • Fans

  • Counter/Totalizer

  • Pumps

  • Printers


START

Housekeeping

Input

Scan

Output

Scan

Program

Scan

PLC Operating Cycle

  • Four Steps in the PLC Operations

    • Input Scan

      • Scan the state of the Inputs

    • Program Scan

      • Processes the program logic

    • Output Scan

      • Energize/de-energize the outputs

    • Housekeeping

      • This step includes communications, Internal Diagnostics, etc.

  • The steps are continually repeated - processed in a loop


Programming the PLC

Types of Programming Software Languages

  • Ladder Logic (LL)

  • IEC Format

    • Function Block Diagram (FBD)

    • Structured Text (ST)

    • Instruction List (IL)

    • Ladder Diagram (LD)

    • Sequential Function Chart (SFC) - also known as “Grafcet”


Ladder Logic

Inputs

Outputs

Read / Conditional

Instructions

Write / Control

Instructions

( )

| |

Start (Rung #1)

( )

| |

|/|

| |

( )

| |

|/|

( )

| |

|/|

End (Rung #4)

| |








Communication Basics

  • Protocols

    • A set of rules for data exchange (format and timing of data) in a communications system

    • Stack / profile = selected set of protocols for a communication application

  • Communication Relationships

    • Master / Slave - request / response & response only

    • Peer-to-Peer - client / server, publisher / subscriber

  • Communication Architectures

    • Star (point-to-point)

    • Bus, Ring, LAN (multidrop)


Communication Protocols

  • Ethernet

  • Modbus Plus

  • Modbus

  • S908

  • LonWorks

  • Interbus

  • Profi-bus

  • DeviceNet

  • Uni-Telway

  • CAN-Open

  • ASi

  • Seriplex

  • FIPIO/FIPway

  • RIO

  • HART

  • DIO

  • ControlNet

  • ASCII

Protocols are similar to languages -

Devices must support the same protocol to understand each other


What you need to know when specifying a PLC

  • Quantity, Type and Location of I/O

    • Number of Inputs and output points

    • AC or DC voltage

    • Analog or Discrete

    • Concentrated or spread out (distributed)

  • Communication Requirements

    • Protocol/Network used

    • Devices to communicate with (HMI, other PLCs, etc)

  • Speed of Application

    • Response time required (throughput) of the system

    • How fast does the process change


What you need to know when specifying a PLC

  • Control Architecture Philosophy

    • Centralized Control, Distributed Control or combination

    • Redundancy - CPUs, Power Supplies, etc

  • Programming Software

    • IEC vs. 984

    • Installed base / what is currently being used

  • User Logic

    • Size and complexity of Program

    • Feedback control used

    • etc.


Alphabet Soup

HMI / MMIHuman Machine Interface / Man Machine Interface

I/O Input(s) and/or Output(s)

LSB / MSB Least Significant Bit / Most Significant Bit

MODICONMOdular DIgital CONtoller

PID Proportional Integral Derivative (feedback control)

RF Radio Frequency

RTU Remote Terminal Unit

SCADA Supervisory Control And Data Acquisition

TCP/IP Transmission Control Protocol / Internet Protocol


ad