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OVERVIEW OF PROGRAMMABLE LOGIC CONTROLLER PLC
A digital Electronic Device Uses a programmable memory to store instructions & to implement functions as
- Logic
- Sequencing
- Timing
- Counting
- Arithmetic
- In order to control machines & Process
- INPUT devices as switches & o/p devices as motors are connected to PLC.
- Controller monitors the inputs & o/ps according to the program stored in the PLC.
Uses Programmable Logic Controller
- Cost effective for controlling complex systems.
- Ladder logic programming can be applicable for other control system.
- Computational abilities allow more sophisticated control.
- Trouble shooting aids make programming easier and reduce downtime.
- Programming is easier and troubleshooting reduce downtime.
- Reliable components make these likely to operate for years before failure.
- Easy to modify a control system without rewiring the connections to input & o/p devices. Much faster than relay-operated systems
- Widely used for the implementation of logic control functions.
- Easy to use
- Reliability of PLC is greater
- Maintenance is easier
- PLCs take less floor space than do relay control panels.
- Can perform a greater variety of control functions than relay control
- Virtual real-time control becomes feasible
- Used for implementing automatic control of manufacturing systems
- Logical information is rapidly and repeatedly processed and immediately responded to with appropriate actions
- A series of logical decisions have to be made and a variety of actions taken on the basis of input that is obtained from appropriate sensors.
Features of PLC
- PLCs are designed to withstand with vibration, humidity, noise, temperature and any environmental changes.
- The main feature is interfacing for input and output is inside the controller.
- They are easily programmed.
Programmable Logic Control (PLC)
Definition – Dedicated computer for rapid processing of simple logic instructions in a defined time.
Purpose – Send and read signals that can be used to control and monitor devices.
Process – One of scanning all the devices (sensors, timers, etc.) in a cyclical time period.
PLC Control Approaches
Logic Control Method – This closed-loop method uses conditions and events to signal completion of a given step, and then triggers the execution of some other event. This is an asynchronous method of process control, because it does not always proceed in a constant time period.
Sequencing Method – This open-loop method uses timers to trigger the completion of one step and the beginning of the next. This is a synchronous control method.