Process controls system reliability

Reactivity with ubiquitous contaminants (oil, rust, air, water, etc.) Training and experience of operational personnel Reliability of metering, agitation and heat transfer systems Integrity of basic process control system Reliability of safety instrumented systems... 

Design and implement a reliable and fault-tolerant basic process control system to ensure the design limitations of the primary containment system are not exceeded. 

There is no standard or specification within the industry which specifies the dual redundancy for PLCs used for process control functions. The requirement for control system redundancy is primarily a function of the desired availability or demand of the process control system. Most control sytem availability percentages are in the range of 99 to 99.9%. Depending on the type of PLC system configuration defined, availability generally improves in relation to the amount of redundancy added to the various system components, but does not necessarily improve system reliability. 

Automatization of all stages of the analytical process is a trend that can be discerned in the development of modern analytical methods for chemical manufacture, to various extents depending on reliability and cost-benefit considerations. Among the elements of reliability one counts conformity of the accuracy and precision of the method to the specifications of the manufacturing process, stability of the analytical system and closeness to real-time analysis. The latter is a requirement for feedback into automatic process-control systems. Since the investment in equipment for automatic online analysis may be high, this is frequently replaced by monitoring a property that is easy and inexpensive to measure and correlating that property with the analyte of interest. Such compromise is usually accompanied by a collection of samples that are sent to the analytical laboratory for determination, possibly at a lower cost. 

Instrumentation is the critical link between the manufacturing process and the control system. Instruments are the eyes (i.e., transmitters, sensors) and limbs (i.e., actuators, positioners) of a process control system and enable it to perform the actions that were once performed by operators and laboratory technicians. If an instrament should malfunction, data integrity and the predefined control actions will be affected. Indeed unsatisfactory instrumentation can cause significant operational problems. It is essential that an instrument is carefully chosen to be fit for purpose (i.e., correct type, size, materials, accuracy, repeatability, reliability, documentation, etc.) to enable confidence to be gained in its ability to perform its intended function. ... 

Cell number and viability determination is not only an excellent direct process parameter, but also the basis for all specific and calculated parameters (growth rate, specific consumption and production rates). Therefore, the apphcation of a sophisticated process control system is largely dependent on a reliable cell number measurement. Most laboratories determine the cell number within the reactor by sampling and off-line analysis. This is not satisfactory because of the necessity of frequent handling, overnight attendance and problems with reproducibility. On the other hand, automatic devices are either very complicated (hke sampling photometers or sampling cell counters) or are relatively new and not validated. 

Up to the present time it has not been possible to demonstrate the ultimate reliability of characterizations based on random disturbances. However, the use of random disturbances offers great potential advantage in studying existing process control systems where upsets like step disturbances cannot be tolerated. Because of the extensive calculation required to reduce the random operating records to statistical-correlation functions, high speed digital computation is essential in this treatment. 

Several of FM s Loss Prevention Data Publications (1, 17B, 17C) discuss the concept of triply-redundant, fault-tolerant, high-reliability hardware/software systems for manufacturing operations. Risk analysis and systems reliability research is currently underway to develop better guidelines for the design and application of reliable process control systems. 

Mahood, R.F. and Martin, J.E. Improve Automatic Control System Reliability. Hydrocarbon Processing, May 1979, p. 215. 

The Dynasafe SDC2000 has also demonstrated the ability to process the types of munitions associated with Requirement BG-2. DEs are high enough, although they have not been demonstrated with the proposed new air pollution control system. Reliability has been good during the operations in Germany. The system is not transportable. 

The committee reviewed the process control systems at the TOCDF and ANCDF in detail to assess their capability and capacity to handle current and forecast workloads. In addition, maintenance procedures, spares supportability, reliability, and availability were evaluated. The control systems at these sites are typical of those at the other two incineration sites. 

Process-control systems wiU become more integrated with condition-based monitoring systems that in turn link to CMMS/EAM systems or even back to the condition-based equipment suppliers for real-time troubleshooting. Condition-based monitoring systems wUl eventuaUy link data coUection directly back to suppliers such as CSI, ENTER, SKF, and others via the Internet or RF. Reliability data analysis by off-site reliability experts providing contract services wUl be as close as e-mail. 

The measurement "reliability" requires that a system be successful for an interval of time. While this probability is a valuable estimate for situations in which a system cannot be repaired during a mission, something different is needed for an industrial process control system where repairs can be made, often with the process operating. 

Process Control Systems Software Engineering Soetware Reliability... 

HAZOP is used to identify the design, operating, and quality problems related to planned process. Operational problems generally come from human error, operating procedural error, or from equipment/control system reliability issues. HAZOP is well suited for such applications. 

A process control system must primarily ensure that the production process is safeguarded and maintained. In addition, it must reliably provide the means of operator/process communication and make possible the connection of higher-order system components for optimization duties. 

The components and subsystems described in the foregoing sections co-operate within the overall framework of a process control system. An important condition for reliable combined action and economical operation is to have properly interadjusted elements which are readily combinable with one another — also for subsequent extensions of the control system. Uniform interfacial structure and consistent signal language are especially important aspects to consider. 

While these are useful aids to operation, neither the systems themselves nor the human interface with them are designed or managed in accordance with BS EN 61511. Therefore the credit to be taken for them should be limited. As they also typically rely on the same operator who has to bring the transfer to a stop, it is not appropriate for them to be considered as a protection layer. Instead they may be considered as a contributing factor to the reliability claimed for the operator, for example in relation to error recovery, in carrying out the basic process control function, and are therefore part of the basic process control system. 

The operation of complex industrial plants would be difficult, if not impossible, without the measurement and control of critical process variables. Large plants typically have hundreds or thousands of process variables that are repetitively measured on-line every few seconds or minutes. In addition, important product properties are measured in quality control labs less frequently—e.g., once per hour, once an eight-hour shift, or daily. Consequently, the design and maintenance of accurate, reliable measurement systems is a critical aspect of process control. The lack of a rehable, cost-effective on-line sensor can be a key limitation on the effectiveness of a process control system. 

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