Programmable logic controller is a small computer that has in-built operating system. This operating system does multiple tasks that include monitoring inputs and making decisions on stored programs. PLC also controls outputs to get smooth functioning from machines. The term “PLC” was first used by Allen-Bradley in 1970s. Names associated with PLC are Richard Morley and Odo Josef Struger.

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Originally, PLC hardware was used to replace relay circuits. The first programming language that was used in PLC is ladder logic programming. Many PLC programs have their own style for performing their work like any other computer programs. It uses memory to store information and to control the functioning of the machine. PLC hardware has both inputs and outputs that receive information from system and regulate functioning.


Simulation is most useful method for verification of inputs and outputs. This process is time-consuming because it has to verify all possible inputs and outputs. To make the process easier, sometimes, the use of simulation is restricted to the signals of outputs only.


This block diagram is important. It has a block for each function to avoid any kind of complexity between inputs and outputs. For example when input and output signals are more and there is any possibility of a clash, this system works as an alarm.


This function chart performs multiple tasks; it checks inputs and outputs, measures signals and checks alarms. It works as a balance among inputs and outputs and alarms. Whenever the weight is out of the limit it makes the alarm work.

Use of PLC is not that easy. Different programs are loaded in this system and it requires a proper guidance for using this system. So, use ladder diagram to understand the working of this system.

Allen-Bradley name is linked with PLC hardware from its origin. Allen-Bradley’s PLC is more developed and familiar with the needs of common people.


Compact Logix controllers are available in different sizes. Allen-Bradley compact logix controllers deliver high performance within an affordable price. Features of Compact Logix Controllers are as follow:

  • High quality
  • Does not need any extra software and controller for its smooth functioning
  • Gives extra socket for devices like servers and printers
  • Flexible memory options
  • Panel for flexible installation
  • Single controller that handle both safety and motion capabilities
  • It offers affordable price and also simple configuration
  • Developed and advanced connectivity
  • Use of battery is not required as it has an internal storage system

Allen-Bradley PLC and Compact Logix Controllers are more demanding and popular in current market. They deliver world class services within affordable prices without compromising with the quality. Their products are multi-disciplined and provide high performance.

PLC and Compact Logix Controllers are currently considered important as they perform multiple tasks, so, while choosing, one need to choose the best.