The abbreviation PLC stands for programmable logic controller. It is used to automate any electromechanical process. The PLC is designed as a compatible input and output device suitable for extended temperature ranges. It is resistant to electrical noise, vibration and impact.
The PLC applications are highly customized systems. The Programs to control machine operations are stored in a battery which is backed by a non-volatile memory expressing the desired sequence of operations. The cost of developing and maintaining any automation system is high. For instance amusement rides, transit busses and metros, lighting fixtures and dishwashers are controlled by electro-mechanical controllers. The machinery in a factory working on assembly lines is also automatically controlled.
Today PLC has been integrated in household devices for reporting power consumption status. The PLC network helps power companies and ordinary users to properly manage power consumption. The complicated process controls as in the chemical industry require algorithms and performance beyond the capability of high-performance PLCs. The programmable controllers are used in motion, positioning and torque control. The high-speed precision controls are also required to customize complicated solutions for aircraft flight controls. Some manufacturers make motion control units integrated with PLCs so that this CNC- computernumerical control machine is used to instruct the process.
In modern CNC systems, the component design is highly automated using computer-aided design (CAD) and computer-aided manufacturing (CAM) programs. These programs are used to extract the commands required to operate a machine via a post processor. It is then loaded into the CNC machines. Recently different machines are used with an external controlling operator that moves the component from one machine to the other.
A proportional–integral–derivative controller (PID controller) is the most commonly used feedback controller. It calculates an "error" value as the difference between a measured process variable and a desired set point. The controller attempts to minimize the error by adjusting the process control inputs via a control element. A PID loop is used to control the temperature of a manufacturing process. The position of a control valve or the power supply of a heating element involves the use of PIP controller.
Some processes require thousands of loops are on a distributed control system (DCS). Today PLCs have become more powerful and similar to Remote Terminal Units –RTU. It usually does not support control algorithm loops. As hardware is becoming more powerful and cheaper in industrial automation, RTUs, PLCs and DCSs are beginning to overlap in function.
Today, Ethernet adapters use PLC as a Power line communication Technology to have easy plug and installation on electrical outlets in any room. This technology becomes perfect when many houses are equipped with multiple digital devices. Here the entertainment centers share the same multimedia files among themselves. Today the Engineers prefer the development of PLC over wireless transmissions. It enables the reception of signals in different rooms. Thus in future we see PLCs engineering services becoming the central nervous system for information integrating electricity, networking and multimedia technology.
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