Process control systems example

To allow flexibility, the database manager must also perform point addition or deletion. However, the abihty to create a point type or to add or delete attributes of a point type is not normally required because, unlike other data processing systems, a process control system normally involves a fixed number of point types and related attributes. For example, analog and binary input and output types are required for process I/O points. Related attributes for these point types include tag names, values, and hardware addresses. Different system manufacturers may define different point types using different data structures. We will discuss other commonly used point types and attributes as they appear. 

Example 4.5 (Liquid-Level Process Control System)... 

For uniform and stable extrusion it is important to check periodically the drive system, the take-up device, and other equipment, and compare it to its original performance. If variations are excessive, all kinds of problems will develop in the extruded product. An elaborate process-control system can help, but it is best to improve stability in all facets of the extrusion line. Some examples of instabilities and problem areas include... 

Examples of multi-disciplinary innovation can also be found in the field of environmental catalysis such as a newly developed catalyst system for exhaust emission control in lean burn automobiles. Japanese workers [17] have successfully merged the disciplines of catalysis, adsorption and process control to develop a so-called NOx-Storage-Reduction (NSR) lean burn emission control system. This NSR catalyst employs barium oxide as an adsorbent which stores NOx as a nitrate under lean burn conditions. The adsorbent is regenerated in a very short fuel rich cycle during which the released NOx is reduced to nitrogen over a conventional three-way catalyst. A process control system ensures for the correct cycle times and minimizes the effect on motor performance. 

LOPA is a semi-quantitative tool for analyzing and assessing risk. This method includes simplified methods to characterize the consequences and estimate the frequencies. Various layers of protection are added to a process, for example, to lower the frequency of the undesired consequences. The protection layers may include inherently safer concepts the basic process control system safety instrumented functions passive devices, such as dikes or blast walls active devices, such as relief valves and human intervention. This concept of layers of protection is illustrated in Figure 11-16. The combined effects of the protection layers and the consequences are then compared against some risk tolerance criteria. 

Some guidelines and recommendations are discussed below, together with a few examples of their application. The books by Buckley (Techniques of Process Control, Wiley, 1964) and Shinskey (Process-Control Systems, McGraw-Hill, 1967) arc highly recommended for additional coverage of this important topic. 

At Merck KGaA in Darmstadt (Germany), in-line UV spectroscopy has been used for monitoring a distillation setup for solvent purification." A transmission probe was implemented at the top of the column. Solarization-resistant UV fibers guided the light to a diode array spectrometer. From the spectra, a quality parameter was extracted and fed to the process control system (PCS). As an example, the quality parameter would exhibit a transient behavior upon column startup. Below a defined threshold value of the parameter, the PCS would assume sufficient product quality and switch the exit stream from waste to product collection. The operation of the spectrometer does not take place in a direct manner, but rather via the PCS. 

MEMS technology also allows embedding of actuators and sensors in single reactor channels. Despite problems with temperature robustness, a solution must be found to transport the signals from the micro channels to the central process control system. To avoid a confusing cable set-up ( spaghetti conditions ), it is desirable to process the sensor data on-site, for example in an A/D converter, and to feed the digital data in a common bus system [13]. 

To prevent material loss due to excursions such as the previous example, robust process control systems are required throughout the supply chain from the raw materials manufacturer to the pad manufacturer and the CMP module. Invariably, incident reviews of such excursions reveal that the excursion could have been prevented or limited to only a small amount of material lost if the proper statistical process control systems had been in place. Invariably, the excursion could have been detected by careful scrutiny of an in-process parameter that was either monitored or should have been monitored by the subsupplier, pad manufacturer, and/or the CMP operation. 

Process safety interlocks can be used to prevent ttnd/or mitigate tin upset condition. Salety interlocks consist of outputs from process control systems, such as programmable logic controllers or distributed control systems, which trigger tut action designed to compensate I ot an upset condition and thus avoid an accident even in the e em of human or computer error. An example of a salety interlock would be the introduction of full cooling if the temperature of a reaction exceeded a safe level. 

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