How Does a PLC (Programmable Logic Controller) Work? Factory Example & Operation Principle

HOW FUNCTION PLC (programmable logic controller).
CAN EXPLAIN ANYWONE  ONE EXAMPLE (WITH FACTORY) WHEN USED PLC.
PRINCIPLE OF OPERATION?

Ken, this is a HUGE subject.  In the old days you would use relays in a switchboard to control things in factories and buildings.  You'd also use timers, thermostats, limit switches, position sensors etc to control the relays which would then switch things (motors, machinery, etc) on and off.Then someone invented PLCs.  A PLC does the same as the relays did, but using digital logic and (these days) microcontrollers.  PLCs can use Ladder Logic, which is a system of representing inputs and outputs in the same way we used to use sensors and relays.The advantage of a PLC is that if you want to change the operation of a complicated machine, you don't need to rewire a switchboard, which is time-consuming and costly.  You just change the program of the PLC, which is quicker and easier.I could write a whole series of columns on PLCs so it is better to direct you to a good website that has more detail than I can put here.  The best one I have found is http://www.plcs.net/contents.shtml
I am sure you will find there answers to all the questions you have, this is a really good site.If you are interested in going further, many technical colleges do courses on PLCs, or you can buy one yourself and program it with your PC, small PLCs cost only a couple of hundred dollars.  Make sure you get one with Ladder programming - most these days connect to a PC and have a downloadable programming software, but some have an LCD display and small keyboard so they are self-contained.Good luck with this, it is a very interesting subject.

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The functionality of the PLC has evolved over the years to include
sequential relay control, motion control, process
control, distributed control systems, and networking. The
data handling, storage, processing power, and communication
capabilities of some modern PLCs are approximately equivalent
to desktop computers. PLC-like programming combined with remote
I/O hardware, allow a general-purpose desktop computer to overlap
some PLCs in certain applications. Desktop computer controllers have
not been generally accepted in heavy industry because the desktop
computers run on less stable operating systems than do PLCs, and
because the desktop computer hardware is typically not designed to
the same levels of tolerance to temperature, humidity, vibration, and
longevity as the processors used in PLCs.Operating systems such as
Windows do not lend themselves to deterministic logic execution, with
the result that the controller may not always respond to changes of
input status with the consistency in timing expected from PLCs.
Desktop logic applications find use in less critical situations, such
as laboratory automation and use in small facilities where the
application is less demanding and critical.

The most basic function of a programmable controller is to emulate the functions of electro-mechanical relays. Discrete inputs are given a unique address, and a PLC instruction can test if the input state is on or off mybkexperience.