Fundamentals And Applications Of Programmable Logic Controllers - Research Paper Example

Fundamentals And Applications Of Programmable Logic ControllersIntroductionIndustrial automation has gone under numerous revolutions from human manual control to electric relays and finally to programmable logic controllers. Programmable logic controller represents a vital factor in industrial automation. The varying industrial processes require flexible adaptations in addition to rapid fault finding and error elimination. Programmable logic controller provides all the three fundamental features that best deal with the varying industrial process thus the most effective in industrial automation.

Programmable logic controller are generally digital computers used in the automation of industrial processes, mostly, electromechanical processes. They are devised for numerous output and input arrangements contrasting to general purpose computers. Apart from the multiple output and input arrangements, PLC are designed to operate at extended temperature ranges, resistance to impact and vibration and has electrical noise immunity unlike the normal computers. (Rehg & Glenn, 2009)The vast number of advantages offered by Programmable logic controllers in industrial automation has ensured their predominance over the last decades and some years to come.

Programmable logic controllers are cost effective for the control of complex systems, flexible and can be easily reapplied to control other systems, simplified programming and reduced downtime given their trouble shooting aid, sophisticated control owing to their computational abilities and long term operation capability without failure given their reliable components. (Evans, 2006)PLC Design There are five key components that constitute a programmable logic controller; Central Processing Unit (CPU), Input module, Memory, Output modules and Power supply.

The central processing unit (CPU) is involved with the performance of logic and arithmetic functions of a PLC. It utilizes the program stored in memory to process the accepted input signal from the input modules into a desired output. It sends the desired output signal to the output modules which converts it into an appropriate actuator signal. In general, the CPU performs the functions of updating the input and output, logic and arithmetic functions and memory communication. The CPU is further divided into three major subsystems; Control Unit (CU), Arithmetic and Logic Unit (ALU) and the Registers.

Instructions are fetched from a specified location and loaded into the registers then decoded by the Control Unit. The arithmetic and logic operations such as the subtraction, addition and basic logic operations such as OR/AND are done by the ALU. Control Unit directs the results into a special memory location for storage. Arithmetic and Logic Unit (ALU) is a logic gate collection with outputs, inputs and control bits for determining operation type. PLC Memory performs the storage functions that allow data and information to be read and written besides the program and code storage for the CPU use.

There are two types of memory used in PLC; RAM and ROM. ROM type of memory is used for the storage of the operating programs used in the PLC while RAM is used to store ladder logic programs. The CPU and memory are always in constant communication. (Evans, 2006)The input and output modules are mainly used to accept and output signals into and out of the CPU. The input module accepts signal from the connected devices and converts the signal into a form that can be processed by the CPU. After the signal is processed by the CPU it is passed to the output modules which converts it actuator signal.

The Power Supply is used to convert the incoming Alternation current into direct current suitable for the operation of the PLC components. About 5v of the DC power is utilized the CPU and memory. Block Diagram Programming: Ladder LogicLadder logic, which has been developed to mimic relay logic, is the main programming method used in programmable logic controllers. PLCs are programmed with a technique similar to the relay logic wiring schematic which do away with the need to teach computer programming to electricians, engineers and technicians.

Apart from ladder logic, mnemonic instructions and state logic can also be used to program programmable logic controllers. Application software on a personal computer is used to program PLC through Ethernet cable connections. Over the years, the functionality of programmable logic controllers has advanced to cater for a variety of other functions such as motion control, distributed control systems, sequential relay control, networking and process control. (Rehg & Glenn, 2009)Work citedRehg, James A.

, and Glenn J. Sartori. Programmable logic controllers. 2nd ed. Upper Saddle River, N.J.: Pearson Prentice Hall, 2009.Evans, William Ted. Programmable logic controllers: fundamentals and applications. Champaign, Ill.: Stipes Pub., 2006.