What is a PLC ?(Programmable Logic Controllers )


PLC stands for programmable logic controller.

A PLC can be defined as an industrialized computer that includes the hardware and software required to automatically control production equipment,machinery, processes and other types of mechanical electrical and electronic devices typically found in industry.It is also includes the flexibility to reprogram its decision making behavior through the software as often as needed.The PLC is the key element behind today’s industrial automation.
Terms related to Programmable logic controller.
Controller - A PLC monitor various conditions and based on these conditions it determines an outcome.In other words it has the ability ‘control’ the outcome based on the status of different input such as sensors switches and numeric values from analog signals etc.
Logic - How the PLC determines an outcome is based on the logical rules it has been taught.
Programmable - The PLC is taught the rules how it should use the input connection to create an outcome through its programming software .being programmable makes it versatile so if needs or conditions change the PLC can be reprogrammed to meet these changes.

Internal Architecture of a PLC
CPU,Memory Communication ports,Input/Output.

CPU - Decision making,control other areas.
Memory - User’s control program stored in nonvolatile section of memory.Also I/O status and data is kept in memory.
Communication ports - load user’s program from PC,also exchange data with external device,including other PLCs.
input/Output - Handles interfaces of signals to real world devices.