Industrial Electronic Control EET 425 Industrial Electronic Control Introduction to PLC Syafruddin Hasan

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

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

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

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

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

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

Building 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

Modified Ladder Logic Circuit

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

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

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.

The first Programmable Logic Controllers were designed and History of PLCs 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.

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.

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

Rugged, noise immune equipment 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.

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.

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

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

Execute the Control Instructions contained in the User's 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.

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

Power Supply The power supply provides the voltages necessary to operate the circuitry

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

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

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

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.

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

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

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

PLC I/O module

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

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 1.) Input Scan Detects the state of all input devices that are connected to the PLC 2.) Program Scan Executes the user created program logic

These steps are continually processed in a loop. 3.) Output Scan Energizes or de-energize all output devices that are connected to the PLC. 4.) Housekeeping This step includes communications with programming terminals, internal diagnostics, etc... These steps are continually processed in a loop.

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

The type of delimiter specifies the kind of information that follows: Addressing 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

Address Identifiers

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

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

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

Relationship of Data File Addresses to I/O Modules

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?