Introduction to Programmable Logic Controller(PLC) Akram Hossain, Professor, Purdue University Calumet Hammond, IN 46323 A Hossain/August 24 2010 1 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. A Hossain/August 24 2010 2 Major Manufacturer of PLC Allen-Bradley (A-B) General Electric Gould-Madicon Texas Instruments Square-D Reliance Electric Siemens A Hossain/August 24 2010 3 Areas of PLC Applications Annunciators Auto Insertion Bagging Baking Blending Boring Brewing Calendaring Casting Chemical Drilling Color Mixing Compressors Conveyors Injection Molding Assembly Motor Winding Oil Fields Painting Palletizers Pipelines Polishing Reactors Robots Rolling Security Systems Stretch Wrap Cranes Crushing Cutting Digesters Drilling Electronic Testing Elevators Engine Test Stands Extrusion Forging Generators Gluing Grinding Heat Treating A Hossain/August 24 2010 Slitting Sorting Stackers Stitching Stack Precipitators Threading Tire Building Traffic Control Textile Machine Turbines Turning Weaving Web Handling Welding 4 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 (1) survive in an industrial environment, (2) 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. A Hossain/August 24 2010 5 PLC and Computer A PLC and a computer both are electronic processor unit. The architecture of a PLC’s 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. A Hossain/August 24 2010 6 Why PLCs ? Soft Manufacturing Process Flexible Manufacturing Process Retrofit Existing Process Less Maintenance Easy to Debug A Hossain/August 24 2010 7 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. A Hossain/August 24 2010 8 Advantages of PLC A. B. C. Flexibility Universal Controller - can replace various independent/ standalone controller. Implementing Changes and Correcting Errors Do not have to rewiring relay panel. Change program using keyboard. Large Quantity of Contact Large number of' Soft Contact' available. D. Lower Cost Advancement in technology and open architecture of PLC will reduce the market price. E. Pilot Running (Simulation Capability) A program can be simulated or run without actual input connection. A Hossain/August 24 2010 9 Advantages of PLC F. G. 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. H. Ladder or Boolean Programming Method. Easy for 'Electrician , I. Reliability In general -very reliable J. Simplicity of Ordering Control Sys. Components One package with Relay, Timers, Control Block, etc. A Hossain/August 24 2010 10 Advantages of PLC K. Documentation L. Printout of ladder logic can be printed easily Security M. Software lock on a program (Password) Ease of Changes by Programming Ability to program and reprogram, loading and down loading A Hossain/August 24 2010 11 Disadvantages of PLC A. New Technology Change from ladder and relay to PLC concept B. Fixed program Application Not cost effective for single- function application C. Environment Consideration Not adapted for very high temperature, high humidity level, high vibration, etc. D. Fail-safe operation Does not start automatically when power failure ( can be programmed into ) Not "Fail-safe" -Fail-shorted rather than OPEN E. Fixed-circuit operation Fixed control system -less costly A Hossain/August 24 2010 12 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 A Hossain/August 24 2010 13 PLC Series 5 Input/Output Chassis A Hossain/August 24 2010 14 Allen-Bradley PLC Series 5 Processor Module A Hossain/August 24 2010 15 PLC 5/25 Processor Mode of Operation A Hossain/August 24 2010 16 A-B Series 5 Power Supply A Hossain/August 24 2010 17 120 VAC Input Module Connection A Hossain/August 24 2010 18 120 VAC Output Module Connection A Hossain/August 24 2010 19 Two Slot Addressing A Hossain/August 24 2010 20 PLC Scan and Update Sequence A Hossain/August 24 2010 21 How PLC Works? Input Map 00 0 Output Map 00 I:001 01 1 I:001 O:001 01 0 00 1 01 0 02 0 03 0 04 01 00 03 04 0 02 1 03 0 01 01 03 O:001/01 04 O:001 O:001 03 01 120 VAC Input Module La dder Log ic in Pr oces sor Mem ory A Hossain/August 24 2010 120 VAC Output Module 22 PLC Input & Output Mapping M START SW STOP SW RELAY COIL M SELF HOLDING FOR "M" L1 CONTROL POWER I: INPUT START STOP N ON LIGHT 00 00 01 01 02 02 03 03 MOTOR RELAY COIL O: OUTPUT I:001 0 RACK 0 RACK I:001 01 SLOT 01 SLOT / / 03 ADDRESS 03 ADDRESS O:001 00 L1 04 04 MOTOR N ON LIGHT 01 01 O:001/01 O:001 01 A Hossain/August 24 2010 O:001 03 23 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. A Hossain/August 24 2010 24 Input/Output Addressing A Hossain/August 24 2010 25 Memory Organization for Data Files A Hossain/August 24 2010 26 Memory Map of File Types A Hossain/August 24 2010 27 A-B PLC Series-5 Data Organization A Hossain/August 24 2010 28 Floating Point Files A Hossain/August 24 2010 29 Timer and Counter Data Files A Hossain/August 24 2010 30 Control Data File A Hossain/August 24 2010 31 PLC Logical Addressing A Hossain/August 24 2010 32 General Instruction Format A Hossain/August 24 2010 33 General Instruction Format A Hossain/August 24 2010 34 Status File A Hossain/August 24 2010 35 TIME ON DELAY (TON) A Hossain/August 24 2010 36