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  • 1.
  • 2.
    • A programmable logic controller (PLC) is a solid- state device designed to perform logic functions previously accomplished by electromechanical relays .
    • The PLC is an assembly of solid-state digital logic elements designed to make logical decisions and provide outputs.
      • It used for control and operation of manufacturing process equipment and machinery
  • 3.
      • It has been designed to operate in the industrial environment and is equipped with special input/output interfaces and a control programming language
      • It is capable not only performing relay switching tasks, but also counting, calculating, comparing and the processing the analog signals.
  • 4.
    • It’s eliminated much of the hand wiring associated with conventional relay control circuit.
    • It’s small and inexpensive compared to equivalent relay-based process control systems.
    • Capable of simulating a hundred relay, timers and counters.
    • Easy to program and install
    • Hardware features such as keylocks can restrict the access to PLC, and software features such as passwords.
    • It does can be designed with communications capabilities that allow them to converse with other computer systems or to provide human interfaces.
  • 5. PLC Diagram
  • 6.
    • PLC can be divided into parts:
      • The central processing unit (CPU)
      • The input/out (I/O) section
      • The power supply
      • The programming device .
  • 7.
    • CPU - is the ‘brain’ of the PLC .
      • It consists of a microprocessor for implementing the logic and controlling the communications among the modules.
      • Required memory for storing the results of the logical operation performed by the microprocessor.
      • The CPU is designed so that the user can enter the desired circuit in ladder logic .
    • Power Supply – used to supplies dc power to other modules that plug in rack and other field devices
  • 8.
    • Memory Module – used to control input and output of the process.
    • Programming Device - are used to enter the desired program into the memory of the processor .
      • This program is entered using relay ladder logic. The program determines the sequence of operation and ultimate control of the equipment or machinery .
  • 9. Hand-held with LED display Industrial terminal
  • 10.
    • 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:
      • 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.
      • 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.
  • 11.
    • PLC programming language refers to the method by which user communicates information to the PLC.
    • There are three most common languages:
      • Ladder diagram language
      • The most common used by PLC language.
      • Boolean language
      • The statements refers to the basic AND, OR and NOT logic gate function.
      • Function chart system
      • It is a method of programming a control system that uses a more structured approach.
  • 12.
    • PLCs are divided into three major size categories:
      • 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.
      • 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.
      • 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.
  • 13.
    • There are three major types of PLC applications:
      • 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.
      • 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.
      • 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.
  • 14.
    • Some important characteristics distinguish PLCs from general-purpose computers .
      • The PLC is designed to operate in the industrial environment with the wide range of ambient temperature and humidity .
      • A well designed PLC is not affected by the electrical noise inherent in most industrial locations
    • Hardware and software of PLCs are designed for easy use by plant electricians and technicians
      • Unlike the computer, the PLC is programmed in relay ladder logic or other easily learned languages
      • 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