In olden days for controlling the manufacturing processes relays were used. Because of excessive consumption of power it is difficult to figure out the linked problems with it, therefore it must be regularly replaced. To solve the problems, Programmable Logic Controller was unveiled. For more information join the electrical automation course to make your career in this field.



For the automation of different electro-mechanical processes in industries a digital computer called Programmable Logic Controller (PLC) is used. For surviving during tough times these controllers are specially used and they are protected from cold, heat, dust, and moisture, etc. Computer Language is used for programming the microprocessor existing in the PLC.

It is a computer written program and is PLC down-loadable via cable. In the nonvolatile memory of PLC these loaded programs are stored. For the user fed program the hard wired logic was exchanged during the change from relay control panels to PLC. For controlling and programming the PLC, Ladder Logic, a visual programing language was created.



CPU, Memory, Input/Output, Power Supply Unit, and Programming device are the hardware components of a PLC system.

CPU– For avoiding the errors the PLC controller is checked. Logic Operations, computer interface, arithmetic operations are some of the performed functions.

Memory– CPU uses fixed data. In the operating system the data is permanently stored in the System (ROM). Status of Input and Output devices, values of timers, counters and other external device information are stored in RAM.

I/O section– Sensors, switches are field devices that are tracked by the input section.

O/P Section- Motors, lights, pumps, and solenoids are some of the devices Output has a a control on. Reduced Instruction Set Computer (RISC) is the basis for I/O ports.

Power Supply– An isolated power supply is available in certain PLC. You can find most of the PLCs working at 220VAC or 24VDC.

Programming device– Inside the memory of the processor, the device is used for feeding the program. First the programming device is fed with the program and the later forwarded to the PLC’s memory.

System Buses: The internal digital signal flows through the buses in the PLCS. The four system buses are:

  • For transferring data among different elements, data bus is used by the CPU.
  • With respect to the action that are controlled internally, control bus transfer signals are used.
  • Location’s address is sent using the Address Bus for accessing the data.
  • The I/O port and I/O unit communicates with each other using system bus.

As PLC has been into existence since 50 years there is a very meager need for improvement and thus if you are planning to work with PLC you can consider it as a mature technology. Any equipment has a competitive counterpart with a never ending need of improvement, providing faster, smaller and cheaper solutions.

In the world of industrial automation, the embedded processor of PLC is providing a real-time proprietary operating system is in demand today.

It is anticipated that there will be a need for improvement in hardware, software, and communication to develop with the adapting technology in the future of PLC. Programmable Automation Controller (PAC) and PLC functionality, will be evolved as a part of the evolution.


In the current electronics industry the circuit boards, components, and processors are shrinking. PLC is in need for stability, reliability, and slow acceptance for the improvements in its technology. For added memory capacity, improved cycle time, and new communication features with the help of fast processors are the current enhancements. Most of the higher end PLCs are converting to lower end PLCs with respect to market demands, functions, and features. For instance it can be considered that small PLCs will improve to have lots of features of PLCs with higher-end and mid and high range PLCs have very less to offer, and the user requirements are met with compact solutions.


Lots of industrial controller suppliers show case the difference between PACs and PLC but the nomenclature is not taken care of by the future of automation engineers targeting on performance and the existing features when their system is specified. PACs and PLCs will keep on growing similar to features and definition of each of them is growing and changing.

There will be lots of demand for low and high-end processors during this transformation period. Who knows, the lower-end processors will make their way with advanced features as there is an advancement in hardware technology with passage of time.

For including more features and options pressure will be put on the suppliers for the above reason. The advanced features of motion control, vision system integration, and similar support for multiple communication controls with steady maintenance of the simplicity thereby making PLCs attractive to their customers.

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