PLC

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Type of Product : Programmable Logic Controller
Market in Brand :
                           Mitsubishi Electric, Schneider Electric, Fatek, Siemens, Delta, Siemens, Allen-Bradley,Lenze, etc

A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system   continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.

Almost any production line, machine function, or process can be greatly enhanced using this type of control system. However, the biggest benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information.

Another advantage of a PLC system is that it is modular. That is, you can mix and match the types of Input and Output devices to best suit your application.

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.

WHAT IS INSIDE A PLC?

inside-of-plc.gif

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.
  • PLC ACRONYMS

    The following table shows a list of commonly used Acronyms that you see when researching or using your PLC.

    ASCII American Standard Code for Information Interchange
    BCD Binary Coded Decimal
    CSA Canadian Standards Association
    DIO Distributed I/O
    EIA Electronic Industries Association
    EMI ElectroMagnetic Interference
    HMI Human Machine Interface
    IEC International Electrotechnical Commission
    IEEE Institute of Electrical and Electronic Engineers
    I/O Input(s) and/or Output(s)
    ISO International Standards Organization
    LL Ladder Logic
    LSB Least Significant Bit
    MMI Man Machine Interface
    MODICON Modular Digital Controller
    MSB Most Significant Bit
    PID Proportional Integral Derivative (feedback control)
    RF Radio Frequency
    RIO Remote I/O
    RTU Remote Terminal Unit
    SCADA Supervisory Control And Data Acquisition
    TCP/IP Transmission Control Protocol / Internet Protocol
                           

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