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  1. 1.
  2. 2. <ul><li>A programmable logic controller (PLC) is a solid- state device designed to perform logic functions previously accomplished by electromechanical relays . </li></ul><ul><li>The PLC is an assembly of solid-state digital logic elements designed to make logical decisions and provide outputs. </li></ul><ul><ul><li>It used for control and operation of manufacturing process equipment and machinery </li></ul></ul>
  3. 3. <ul><ul><li>It has been designed to operate in the industrial environment and is equipped with special input/output interfaces and a control programming language </li></ul></ul><ul><ul><li>It is capable not only performing relay switching tasks, but also counting, calculating, comparing and the processing the analog signals. </li></ul></ul>
  4. 4. <ul><li>It’s eliminated much of the hand wiring associated with conventional relay control circuit. </li></ul><ul><li>It’s small and inexpensive compared to equivalent relay-based process control systems. </li></ul><ul><li>Capable of simulating a hundred relay, timers and counters. </li></ul><ul><li>Easy to program and install </li></ul><ul><li>Hardware features such as keylocks can restrict the access to PLC, and software features such as passwords. </li></ul><ul><li>It does can be designed with communications capabilities that allow them to converse with other computer systems or to provide human interfaces. </li></ul>
  5. 5. PLC Diagram
  6. 6. <ul><li>PLC can be divided into parts: </li></ul><ul><ul><li>The central processing unit (CPU) </li></ul></ul><ul><ul><li>The input/out (I/O) section </li></ul></ul><ul><ul><li>The power supply </li></ul></ul><ul><ul><li>The programming device . </li></ul></ul>
  7. 7. <ul><li>CPU - is the ‘brain’ of the PLC . </li></ul><ul><ul><li>It consists of a microprocessor for implementing the logic and controlling the communications among the modules. </li></ul></ul><ul><ul><li>Required memory for storing the results of the logical operation performed by the microprocessor. </li></ul></ul><ul><ul><li>The CPU is designed so that the user can enter the desired circuit in ladder logic . </li></ul></ul><ul><li>Power Supply – used to supplies dc power to other modules that plug in rack and other field devices </li></ul>
  8. 8. <ul><li>Memory Module – used to control input and output of the process. </li></ul><ul><li>Programming Device - are used to enter the desired program into the memory of the processor . </li></ul><ul><ul><li>This program is entered using relay ladder logic. The program determines the sequence of operation and ultimate control of the equipment or machinery . </li></ul></ul>
  9. 9. Hand-held with LED display Industrial terminal
  10. 10. <ul><li>Software written and run on PC has changed how people work with PLCs. PLC software run on a PLC falls into the following two categories: </li></ul><ul><ul><li>PLC software that allows the user to program and gives the user the tools to write a PLC program using ladder logic or other programming language and document or explain the program is as much detail as is necessary. </li></ul></ul><ul><ul><li>PLC software that allows the user to monitor and control the process is also called man-machine, or operator, interface. It enables the user to view a process or graphical representation of a process on a CRT, determine how the system is running, trend values, and receives alarm conditions. </li></ul></ul>
  11. 11. <ul><li>PLC programming language refers to the method by which user communicates information to the PLC. </li></ul><ul><li>There are three most common languages: </li></ul><ul><ul><li>Ladder diagram language </li></ul></ul><ul><ul><li>The most common used by PLC language. </li></ul></ul><ul><ul><li>Boolean language </li></ul></ul><ul><ul><li>The statements refers to the basic AND, OR and NOT logic gate function. </li></ul></ul><ul><ul><li>Function chart system </li></ul></ul><ul><ul><li>It is a method of programming a control system that uses a more structured approach. </li></ul></ul>
  12. 12. <ul><li>PLCs are divided into three major size categories: </li></ul><ul><ul><li>Small: It covers units up to 128 I/Os and memories up to 2Kb. It capable of providing simple to advanced levels of machine control. </li></ul></ul><ul><ul><li>Medium: It have up to 2048 I/Os and memories up to 32Kb. Special I/Os modules make medium PLCs adaptable to temperature, pressure, flow, weight, position and any type of analog function encountered in process control applications. </li></ul></ul><ul><ul><li>Large: The most sophisticated units of PLCs family. They have up to 16,000 I/Os and memories up to 2Mb. It has almost unlimited applications and can control individual production processes or entire plants. </li></ul></ul>
  13. 13. <ul><li>There are three major types of PLC applications: </li></ul><ul><ul><li>Single-ended: It involves one PLC controlling one process. This would be a stand-alone unit and would not be used for communicating with other computers or PLCs. </li></ul></ul><ul><ul><li>Multitask: It usually calls for a medium size PLC and involves one PLC controlling several processes. It can be a subsystem for larger processes and communicating with a central PLC. </li></ul></ul><ul><ul><li>Control management: It involves one PLC controlling several others. It requires a large PLC processor designed to communicate with other PLCs and possibly with a computer. The control management PLC supervises several PLCs by downloading programs that tell the other PLCs what has to be done. </li></ul></ul>
  14. 14. <ul><li>Some important characteristics distinguish PLCs from general-purpose computers . </li></ul><ul><ul><li>The PLC is designed to operate in the industrial environment with the wide range of ambient temperature and humidity . </li></ul></ul><ul><ul><li>A well designed PLC is not affected by the electrical noise inherent in most industrial locations </li></ul></ul><ul><li>Hardware and software of PLCs are designed for easy use by plant electricians and technicians </li></ul><ul><ul><li>Unlike the computer, the PLC is programmed in relay ladder logic or other easily learned languages </li></ul></ul><ul><ul><li>The PLC comes with its program language built into permanent memory, whereas a personal computer requires a disk operating system (DOS). PLC is limited by the language it comes with, unless it is a modular type </li></ul></ul>