EET 425 Industrial Electronic Control

1. EET 425 Industrial Electronic Control Introduction to PLC INDRA NISJA

2. Industrial Motor Control Circuits • Complex industrial machines require sophisticated control systems • These control systems schematics are referred to as motor control circuits even though other types of systems may actually be controlled, such as hydraulic, pneumatic or mechanical systems

3. Relay Ladder Logic Circuits • Electrical control circuits are referred to as relay ladder logic diagrams • Ladder refers to the manner in which the diagrams are constructed • Logic refers to the decision-making function of the circuit

4. Elements of a Wiring Diagram • The ladder circuit consists of four elements: • A power source • An input control device • A load device • Interconnecting wires

5. Components Used as Input Devices • Manual switches • Momentary switches • Normally open push buttons • Normally-closed push buttons • Multiple-pole push button • Palm operated • Foot switches • Maintained Switches • Selector Switches • Mechanical limit switches • Proximity limit switches • Pressure switches • Flow switches • Level switches • Temperature switches

6. Components Used as Output Devices • Direct Devices • Motors • Pilot lights • Indirect Devices • Relays • Time delay relay • Contactor • solenoid

7. Relay ladder Logic Circuits • Relay ladder logic circuits perform several logical functions • AND • OR • NOT • NAND • NOR

8. Develop a Ladder Diagram • Using the water pumping system as a guide, the following diagram illustrates how various elements are constructed to build a ladder diagram

9. Modified Ladder Logic Circuit

10. Labeling Components in a Ladder Circuit • Labeling is important for troubleshooting, diagnosis, and analysis purposes • The example below is a properly labeled circuit

11. Motor Control Starter Circuits • Three-phase motor control circuits are common in industrial applications

12. Definition A Programmable Logic Controller (PLC) is defined by Capiel (1982) as: (based on National Electrical Manufacturers Association (NEMA) standard ICS3-1978 Part ICS3-304): “A digitally operating electronic system designed for use in an industrial environment, which uses a programmable memory for the internal storage of instructions for implementing specific functions such as logic, sequencing, timing, counting and arithmetic to control through analog or digital input/output modules, various types of machines or processes”. What Is A PLC? A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.

14. The first Programmable Logic Controllers were designed and • developed by Modicon as a relay re-placer 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 and was designed by Michael Greenberg.

15. Initial specification was provided: The controller must be: • Easily programmed and reprogrammed, preferably in-plant, to alter its sequence of operations. • Easily maintained and repaired—preferably using plug-in modules. • More reliable in a plant environment. • Smaller than its relay equivalent. • Cost competitive, with solid-state and relay panels then in use.

16. Basic Stop/Start Circuit • The most basic of all industrial control circuits • Demonstrates two important functions of a ladder diagram: stopping and interlocking

17. Although PLCs are similar to ‘conventional‘ computers in terms of hardware technology, they have specific features suited to industrial control: • Rugged, noise immune equipment • Modular plug-in construction, allowing easy • replacement/addition of units • (e.g. input/output). • Standard input/output connections and signal • levels. • Easily understood programming language (e.g. • ladder diagram or function chart) • Ease of programming and reprogramming in- • plant.

18. PLC Advantages: Flexibility. Security. Implementing Changes and Correcting Errors. Large Quantities of Contacts. Ease of Changes by Reprogramming. Lower Cost Pilot Running. Visual Observation. Speed of Operation. Ladder or Boolean Programming Method. Reliability and Maintainability. Simplicity of Ordering Control System Components. Documentation.

19. PLC Disadvantages: Newer Technology. Fixed Program Applications. Environmental Considerations. Fail-Save Operation. Fixed-Circuit Operation.

20. Introduction to PLC Components • All PLC systems are comprised of the same basic building blocks • Rack assembly • Power supply • Programming unit • Input/Output Section • Processor unit

21. What Is Inside A PLC? • The Central Processing Unit, the CPU, contains an internal program that tells the PLC how to perform the following functions: • Execute the Control Instructions contained in the User's • Programs. This program is stored in "nonvolatile" memory, • meaning that the program will not be lost if power is removed • Communicate with other devices, which can include I/O • Devices, Programming Devices, Networks, and even other PLCs. • Perform Housekeeping activities such as Communications, • Internal Diagnostics, etc.

23. The rack assembly contains the power supply, I/O modules, processor unit and is built upon a back plane which provides the various connections

24. The power supply provides the voltages necessary to operate the circuitry

25. PLC Programming Units • Several types of programming units are available for PLCs • Handheld programmers • Dedicated terminals • Microcomputers

26. Input/Output Sections • The purpose of the I/O section is to provide an interface for the internal circuitry to the outside world • Input/Output modules serve four functions: • Termination • Signal conditioning • Isolation • Indication

27. Input Modules • Input modules receive signals from switching devices • The input module provides the necessary conversion to logic voltages • Three common types of input signals are: • 120 VAC • Low-level DC • High-level DC

28. The input module performs 4 tasks electronically: • It senses the presence or absence of an input signal at each of its input terminal. • The input signal tells what switch, sensor, or other signal is on or off in the process • being controlled • It converts the input signal for on, or high, to a dc level usable by the module’s • electronic circuit. For a low, or off, input signal, no signal is converted, indicating off. . • The input module carries out electronic isolation by electronically isolating the • input module output from its input. • Its electronic circuit must produce an output to be sensed by the PLC CPU.

29. A typical input module has 4, 6, 8, 12, 16 or 32 terminals plus common and safety ground terminals

30. Output Modules • Outgoing discrete signals are transmitted to field devices using output modules • Typical output modules are: • 120 VAC • Low-level DC • High-level DC

31. The output module operates in the opposite manner from the input module.

32. PLC I/O module

33. Processor Unit • The processor unit coordinates and controls the operation of the PLC • The PLC processor is composed of three main sections • The central processing unit • The arithmetic logic unit • Memory

35. How Does A PLC Operate? There are four basic steps in the operation of all PLCs; Input Scan, Program Scan, Output Scan, and Housekeeping. These steps continually take place in a repeating loop. Four Steps in the PLC Operations

36. These steps are continually processed in a loop.

37. Processor Files • The processor contains several types of files to support the program and logic being used • In an Allen-Bradley system there are four types of program files and 11 types of data files

38. To address data files, alphanumeric characters separated by delimiters are used • The type of delimiter specifies the kind of information that follows: • A number that follows a colon represents which element will be used • A number that follows a slash represents the bit is used in a file • A number that follows a period represents which bit is used within a word

39. Address Identifiers

40. Word Address File Number File Type Word T4:7.ACC Word delimiter Element Delimiter

41. Element Address File Number File Type Element N7:12 Element Delimiter

42. Input Output Address • Input addresses are formatted as: I:e/b I = identifier as Input : = slot delimiter e = slot number of module / = bit or terminal delimiter b = terminal number of the module • Output addresses are formatted as: O:e/b O = identifier as Input : = slot delimiter e = slot number of module / = bit or terminal delimiter b = terminal number of the module

43. Relationship of Data File Addresses to I/O Modules

44. What Do I Need To Consider When Choosing A PLC? • There are many PLC systems on the market today. Other than cost, you must consider the following when deciding which one will best suit the needs of your application. • Will the system be powered by AC or DC voltage? • Does the PLC have enough memory to run my user program? • Does the system run fast enough to meet my application’s • requirements? • What type of software is used to program the PLC? • Will the PLC be able to manage the number of inputs and outputs • that my application requires? • If required by your application, can the PLC handle analog inputs • and outputs, or maybe a combination of both analog and discrete • inputs and outputs? • How am I going to communicate with my PLC? • Do I need network connectivity and can it be added to my PLC? • Will the system be located in one place or spread out over a large • area?