Introduction to Programmable Logic Controller(PLC)

1
Introduction to Programmable Logic
Controller(PLC)

• Akram Hossain, Professor,
• Purdue University Calumet
• Hammond, IN 46323

2
Definition of PLC

• Programmable Logic Controllers are solid state
  devices that can be programmed to performed
  sequential and discrete state operation on
  external equipment
• They are designed to perform the logic functions
  previously accomplished by electromechanical
  relays, drum switches, mechanical and electronic
  timers and counters, standalone digital PID
  controllers etc.

3
Major Manufacturer of PLC

• Reliance Electric
• Siemens

• Allen-Bradley (A-B)
• General Electric
• Gould-Madicon
• Texas Instruments
• Square-D

4
Areas of PLC Applications

• Annunciators Injection Molding
• Auto Insertion Assembly
• Bagging Motor Winding
• Baking Oil Fields
• Blending Painting
• Boring Palletizers
• Brewing Pipelines
• Calendaring Polishing
• Casting Reactors
• Chemical Drilling Robots
• Color Mixing Rolling
• Compressors Security Systems
• Conveyors Stretch Wrap

Cranes Slitting Crushing Sorting Cutting
Stackers Digesters Stitching Drilling Stack
Precipitators Electronic Testing
Threading Elevators Tire Building Engine Test
Stands Traffic Control Extrusion Textile
Machine Forging Turbines Generators
Turning Gluing Weaving Grinding Web
Handling Heat Treating Welding
5
History of PLC

• The Hydramatic Division of the General Motors
  Corporation specified the design criteria for the
  first
• programmable controller in 1968. Their primary
  goal was to eliminate the high costs associated
  with inflexible, relay-controlled systems. The
  specifications required a solid-state system with
  computer flexibility able to
• survive in an industrial environment,
• Be easily programmed and maintained by plant
  engineers and technicians, and
• (3) Be reusable. Such a control system would
  reduce machine downtime and
• provide expandability for the future. Some of
  the initial specifications
• included the following
• The new control system had to be price
  competitive with the use of relay systems.
• The system had to be capable of sustaining an
  industrial environment.
• The input and output interfaces had to be easily
  replaceable.
• The controller had to be designed in modular
  form, so that subassemblies could be removed
  easily for replacement or repair.
• The control system needed the capability to pass
  data collection to a central system.
• The system had to be reusable.
• The method used to program the controller had to
  be simple, so that it could be easily understood
  by plant personnel.

6
PLC and Computer

• A PLC and a computer both are electronic
  processor unit. The architecture of a PLCs CPU
  is basically same as that of a general purpose
  computer however, some important characteristics
  set them apart.
• Unlike computer, PLCs are specifically designed
  to survive the harsh conditions of the industrial
  environment. A well-designed PLC can be placed in
  an area with substantial amounts of electrical
  noise, electromagnetic interference, mechanical
  vibration, and noncondensing humidity.
• Distinction of PLCs is that their hardware and
  software are designed for easy use by plant
  electricians and technicians. The hardware
  interfaces for connecting field devices are
  actually part of the PLC itself and are easily
  connected.
• The modular and self-diagnosing interface
  circuits are able to pin point malfunctions and
  moreover, are easily removed and replaced.
• Software programming uses conventional relay
  ladder symbols, or other easily learned
  languages, which are familiar to plant personnel.
• A computer can execute a complex programming task
  and also multitasking. An standard PLC is
  designed to executes a single program in an
  orderly fashion. As PLCs are rapidly changing,
  modern PLCs have multitasking capabilities.

7
Why PLCs ?

• Soft Manufacturing Process
• Flexible Manufacturing Process
• Retrofit Existing Process
• Less Maintenance
• Easy to Debug

8
Why PLCs are so Popular?

• Programmable logic controller have made it
  possible to precisely control large process
  machines and driven equipment with less physical
  wiring and wiring time than it requires with
  standard electro-mechanical relays, pneumatic
  system, timers, drum switches, and so on.
• The programmability allows for fast and easy
  changes in the relay ladder logic to meet the
  changing needs of the process or driven equipment
  without the need for expensive and time consuming
  rewiring process.
• Modem PLCs are "electrician friendly", PLC can be
  programmed and used by plant engineers and
  maintenance electricians without much electronic
  and computer programming background. They can
  programmed by using the existing ladder
  diagrams.

9
Advantages of PLC

•  
• A.     Flexibility
• v     Universal Controller - can replace various
  independent/ standalone controller.
•  B.     Implementing Changes and Correcting
  Errors
• v     Do not have to rewiring relay panel.
• v     Change program using keyboard.
•  
• C.     Large Quantity of Contact
• v     Large number of' Soft Contact' available.
•  
• D.    Lower Cost
• v     Advancement in technology and open
  architecture of PLC will reduce the market price.
•  
• E.     Pilot Running (Simulation Capability)
• v     A program can be simulated or run without
  actual input connection.

10
Advantages of PLC

• Visual Observation.
• Can observe the opening and closing of contact
  switch on CRT .
• Operator message can be programmed for each
  possible malfunction.
• Speed of Operation
• Depends on scan time -millisecond.
• Asynchronous operation.
•  
• Ladder or Boolean Programming Method.
• Easy for 'Electrician ,
•  
• Reliability
• In general -very reliable
•  
• Simplicity of Ordering Control Sys. Components
• One package with Relay, Timers, Control Block,
  etc.
•  

11
Advantages of PLC

• Documentation
• Printout of ladder logic can be printed easily
•  
• Security
• Software lock on a program (Password)
•  
• Ease of Changes by Programming
• Ability to program and reprogram, loading and
  down loading

12
Disadvantages of PLC

• New Technology
• Change from ladder and relay to PLC concept
• Fixed program Application
• Not cost effective for single- function
  application
• Environment Consideration
• Not adapted for very high temperature, high
  humidity level, high vibration, etc.
• Fail-safe operation
• Does not start automatically when power failure (
  can be programmed into )
• Not "Fail-safe" -Fail-shorted rather than OPEN
• Fixed-circuit operation
• Fixed control system -less costly

13
What is a Ladder Diagram?

• A complete control scheme normally drawn as a
  series of contacts and coils arranged between two
  vertical control supply lines so that the
  horizontal lines of contacts appear similar to
  rungs of a ladder. The control contacts (input
  devices) are to left and coils (output devices)
  on the right.
• Ladder diagrams are an industrial standard for
  representing relay-logic control system

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PLC Series 5 Input/Output Chassis
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Allen-Bradley PLC Series 5 Processor Module

16
PLC 5/25 Processor Mode of Operation
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A-B Series 5 Power Supply
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120 VAC Input Module Connection

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120 VAC Output Module Connection
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Two Slot Addressing
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PLC Scan and Update Sequence
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How PLC Works?
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PLC Input Output Mapping
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PLC Program and Data Files
Program Files -Reserved Files (File 0) -SFC
file (File 1 ) -Ladder file (File 2- 999)
-File 2 Main Ladder File -Subroutine file (File
3 -999) -Selectable Interrupt file (File 3
-999) -Fault Routine File (File 3 -999)
Data Files -Files which store data of the I/0
module. -Can be integer data, floating point
(real) data, timer data, counter data, discrete
input data, discrete output data, etc.
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Input/Output Addressing
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Memory Organization for Data Files
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Memory Map of File Types
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A-B PLC Series-5 Data Organization
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Floating Point Files
30
Timer and Counter Data Files
31
Control Data File
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PLC Logical Addressing
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General Instruction Format
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General Instruction Format
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Status File
36
TIME ON DELAY (TON)