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Good question Ashaad but PLC nowadays can mean many things. For example, in the petrochemical industry, we use PLC's to control the process of operation and to have a safety system in place for emergency situations. However, a PLC can be as little as small remote control car.
Basically, a PLC is a programmable logic controller regardless of its size. it can have thousands of inputs and outputs or it can only take one input and generates one output.
I hope this helps.
A PLC is a device that was invented to replace the necessary sequential relay circuits for machine control. The PLC works by looking at its input and depending upon their state, turning ON / OFF its inputs. The user enters a program, usually through software, that gives the desired result. A PLC can be defined as a solid state device. It is capable of storing instructions to implement control functions such as sequencing, timing, counting, arithmetic, data manipulation and communication to control industrial machines and processes. In industries there will be places where human interaction is dangerous. For examples boilers. A PLC with SCADA system can be used to visualize and control the things carrying out in a boiler plant.
kindly find below the reasons for usage of plc in industries .
1-soft wiring will save the time/effort/cost logic can be updated in minutes.
2-very easy to troubleshoot comparing to relay or electronic controls .
3-can be programmed in many high level languages iec-61131-3
4-it will save a lot of money and components (relys/timers/math logic cards/data logging/interfacing pid,s (pv/sv scaling/calibration etc.
5-system/logic changes/upgrades are always easy and at your fingertips .
i am able to write books of reason to use plc (above is just few hints)
