1 EJ 501 PROGRAMMABLE LOGIC CONTROLLER PLC AND

1 EJ 501 PROGRAMMABLE LOGIC CONTROLLER (PLC) AND AUTOMATION

2 UNIT 3 INTRODUCTION TO PLC SYSTEM Objective : 1. Understand basic characteristics of PLC v v v 2. Understand building structure of PLC v 3. CPU, memory unit, interface display and indicator unit, input and output Understand PLC hardware unit v 4. PLC terminologies PLC function/ background Type / advantages of PLC Housing unit, programming unit, power supply unit, printer unit Explain input and output device

3 UNIT 3 INTRODUCTION TO PLC SYSTEM Introduction PLC (Programmable Logic Control) A digital device (microprocessor based controller) that uses a programmable memory to store instructions and to implement functions such as logic, sequencing, timing, counting and arithmetic in order to control machines and processes and has been specifically designed to make programming easy. PLCs are similar to computers but have certain features which are specific to their use as controllers: i. iii. They are rugged and designed to withstand vibrations, temperature, humidity and noise. The interfacing for inputs and outputs is inside the controller. There are easily programmed.

4 UNIT 3 INTRODUCTION TO PLC SYSTEM Definition PLC A digitally operated electronic apparatus 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 digital or analog input/output modules, various types of machines or processes. - National Electrical Manufacturers Association (NEMA)

5 UNIT 3 INTRODUCTION TO PLC SYSTEM Definition PLC An electronic system working digitally for the use in industrial environment with a programmable memory for the internal storage of user-orientated control instructions for the implementation of specific functions, like, for example logic operation control, process control, timer, counting-and arithmetic functions, in order to control various machines and processes through digital or analog input- , and output variables. The logic programmable controls as well as the peripheral installations (PLCsystem) are designed so that they can be easily integrated in an industrial control system and be implemented in all their desired functions. - International Standard IEC 61131 -1

6 UNIT 3 INTRODUCTION TO PLC SYSTEM PLC Background The first Programmable Logic Controller (PLC) was developed by a group of engineers at General Motors in 1968 The company was looking for an alternative to replace complex relay control systems : v Must be programmable (and reprogrammable) v Designed to operate in an industrial environment v Must accept 120 V ac signals from pushbuttons, switches v Outputs must switch and continuously operate loads such as motors and relays of two amps rating Before the 1980’s, programmable controllers were called PCs.

7 UNIT 3 INTRODUCTION TO PLC SYSTEM PLC Functions PLC performs the functions of conventional relays, timers, counters. Capable of storing instructions, such as sequencing, timing, counting, arithmetic, data manipulation, and communication, to control industrial machines and processes.

8 UNIT 3 INTRODUCTION TO PLC SYSTEM Type of PLC - compact TECOMAT TC 600 Omron Mitsubishi Zelio

9 UNIT 3 INTRODUCTION TO PLC SYSTEM Type of PLC - modular Omron Mitsubishi Eaton

10 UNIT 3 INTRODUCTION TO PLC SYSTEM Type of PLC – plug in card

11 UNIT 3 INTRODUCTION TO PLC SYSTEM Advantages and Disadvantages of PLC Advantages Disadvantages Many inputs and outputs, excellent for controlling and monitoring many processes Do not use the full capabilities of the microprocessor Designed for industrial environments, robust and reliable Ladder logic programming style is cumbersome and prone to mistakes Reprogrammable Only good for yes/no decisions Modular Do not handle continuous inputs and outputs, not good for “direct control” Ideally suited to supervisory control Inflexible (compared microprocessors) Easy to set up, good for FMS environment to

12 UNIT 3 INTRODUCTION TO PLC SYSTEM Initial Specifications • 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.

13 UNIT 3 INTRODUCTION TO PLC SYSTEM Recent PLCs • Changes include both hardware (physical components) and software (control program) upgrades • Faster scan times are being achieved using new, advanced microprocessor and electronic technology. • Small, low-cost PLCs (Figure 1), capable of replacing four to ten relays, now have more power than their predecessor, the simple relay replacer.

14 UNIT 3 INTRODUCTION TO PLC SYSTEM • A personal computer (PC) is the most commonly used programming device • The software allows users to create, edit, document, store and troubleshoot programs • The personal computer communications with the PLC processor via a serial or parallel data communications link

15 UNIT 3 INTRODUCTION TO PLC SYSTEM • Hand-held programming devices are sometimes used to program small PLCs • They are compact, inexpensive, and easy to use, but are not able to display as much logic on screen as a computer monitor • It is often used on the factory floor for troubleshooting, modifying programs, and transferring programs to multiple machines

16 UNIT 3 INTRODUCTION TO PLC SYSTEM Basic PLC Structure Basic internal structure of PLC consists essentially of : -processing unit (CPU) -memory -input/output units

17 UNIT 3 INTRODUCTION TO PLC SYSTEM Hardware of the PLC are only consist of several components; such as Power Supply Unit, CPU Unit, Memory Unit and I/O Unit. At the small PLC; Power Supply, CPU, Memory and I/O stay in the same Unit but at the big PLC; Power Supply, CPU, Memory and I/O in the separate Unit.

18 UNIT 3 INTRODUCTION TO PLC SYSTEM Power Supply The Power Supply is used to give power to all the parts. The most PLC works with power 24 VDC or 220 VAC. The big PLC has the separate power supply and the small PLC has power supply which is one. The Power Supply is also provided by the battery back up, when happened the failure of power, automatically battery will replace the power supply to supply the CPU, so that the program of memory user do not lose. Memory Unit The Memory Unit has function to save the data and program will be used by PLC. This Memory is divisible into two type that is ROM and RAM. ROM contains the data like facility of the logic program, facility to edit the program, facility to monitor the program, facility for the communications, etc. The Data will be save permanently and will not lose though the power supply is off. While RAM contains the data of user program, like ladder diagram, memory data, I/O status, etc. The Data can be writed and read. RAM has the character is not permanent, if the power suplply is off the data will lose. To avoid the mentioned, so the power supply is provided by the battery back up to supply if the especial power supply is off.

19 UNIT 3 INTRODUCTION TO PLC SYSTEM CPU Unit (Central Processing Unit) Without seeing to type of PLC ( small, medium, big) processors and memory always in the same unit. This unit is referred as the CPU. The CPU is the brain of a PLC. The CPU is a 8 bit, 16 bit or 32 bit microcontroller. The CPU has function to handle communications with the external apparatus, interconnectivity between the parts of PLC, executes the program, managements the memory, observing or perceiving the input signal and gives the output signal ( as according to the program or process run). The CPU is also provided by the indicator lamp as indicator of the happening of mistake and damage.

20 UNIT 3 INTRODUCTION TO PLC SYSTEM I/O Unit The I/O Unit is the interface unit has function to convert the input signal and output signal so that the CPU can communicate with the external apparatus like the switch, stepping motor, solenoid, sensor, etc. The I/O Unit has two type; Discrete I/O and Analog I/O.

21 UNIT 3 INTRODUCTION TO PLC SYSTEM Omron PLC LG PLC

22 UNIT 3 INTRODUCTION TO PLC SYSTEM Input Devices PLCs can receive input from either automated or manual devices. The PLC could receive data from the user via a pushbutton switch, keyboard, or similar device. Automated input could come from a variety of devices: microswitches, timers, encoders, photosensors, and so on. Some devices, like the Limit Switch shown below, turn ON or OFF when the equipment actually makes contact with it. Other devices, like the Photoelectric Switch and Proximity Switch shown below, use other means, such as light or inductance, in order to get information about the equipment being monitored.

23 UNIT 3 INTRODUCTION TO PLC SYSTEM Output Devices A PLC can output to a myriad of devices for use in automated control. Almost anything that you can think of could be controlled (perhaps indirectly) by a PLC. Some of the most common devices are motors, Solenoids, Servomotors, Stepping Motors, valves, switches, indicator lights, buzzers, and alarms. Some of these output devices; such as the motors, Solenoids, Servomotors, Stepping Motors, and valves; affect the controlled system directly. Others; such as the indicator lights, buzzers, and alarms; provide output to notify personnel.

24 UNIT 3 INTRODUCTION TO PLC SYSTEM