:::::::::::::::::::::::::::::Process Control:::::::::::::::::::::::::::::::: Process control is a complex system using statistics and engineering methods in conjunction with architectures, mechanisms, and algorithms to control the output of an industrial automation process. The most common industrial automation control device used for process control is the programmable logic controller (PLC). PLCs read a set of digital and analog inputs, process logic statements, and generate analog and digital outputs to the industrial automation process. For example a logical statement can compare the set point to the input temperature and determine if more or less heating is necessary to keep a temperature constant. A PLC output then opens or closes a hot water valve an incremental amount, depending on the temperature. Large complex systems can be controlled by a Distributed Control System (DCS) or SCADA system. A distributed control system (DCS) is a control system usually a manufacturing system, process or any kind of dynamic system, where the controller elements are not in a central in location but are distributed throughout the process where each sub-system can be controlled by one or more controllers. The entire system of controllers are then connected by a network for communication and monitoring. DCS is a very broad term used in a variety of industries, to monitor and control distributed equipment. SCADA is an acronym for Supervisory Control And Data Acquisition. SCADA systems perform data collection and control at the supervisory level. Some systems labeled as SCADA perform data acquisition only. A SCADA system should not be critical to the controlled process. The SCADA connects to a PLC or real time device, so there is a separate or integrated real-time automated control system that responds quickly enough to compensate for process changes within the time constants of the process. The SCADA controls and monitors the process, but the process must also run independently from the SCADA system in case of failure. In practice, an industrial automation process control system can be characterized as one or more of the following: Discrete – Found in manufacturing, motion and packaging applications. Robotic assembly, commonly found in automotive production, can be characterised as discrete process control. Most discrete manufacturing involves the production of discrete pieces of product, such as metal stamping. Batch – Applications that require specific quantities of raw materials combined in specific ways for particular durations to produce an intermediate or end result. One example is the production of adhesives and glues, which require the mixing of raw materials in a heated vessel for a period of time to form a quantity of end product. Other examples are the production of food, beverages and medicine. Batch processes are used to produce a relatively low to intermediate quantities of product. Continuous – The control of the water temperature in a heating jacket, is an example of continuous process control. Some examples of continuous processes are the production of fuels, chemicals and plastics. Continuous processes used in industrial automation applications produce very large quantities of product.
Posted on: Sun, 01 Sep 2013 10:31:32 +0000
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