Real time computer control

The external devices and processes to which the process control computer is connected all behave with respect to their own particular time-scales. When the actions of the computer are related to the time-scales of these external systems (often termed the external world) the computer is said to operate in real lime 141. Process control computers are normally concerned with real-time operations and ClVERA et al.(52) have divided the latter into  

Type 1. systems which are required to have a mean execution time measured over a defined time interval which is lower than a specified maximum, and Type 2. systems in which the cycle of computations must be completed within a specified maximum time on each and every occasion. 

Real-time operations may be clock based, sensor based, or interactive and may involve combinations of these. 

These are actions of the computer which are initiated by events, e.g. switching off a pump when a tank has been filled to a certain level. They form the basis of the response of computer-controlled plant to alarm conditions, e.g. if the temperature in the reactor described in Fig. 7.102 exceeds a specified value then action must be taken by the computer, such as rapidly increasing the flow of coolant or reducing the feed to the reactor. Generally, sensor-initiated operations must be performed within a specified maximum time interval and are often in the form of alarm interrupts (Section 7.18.3). Smaller systems will regularly scan a set of specific process variables via a multiplexer to see if any action is necessary. The latter arrangement is called polling. 

These are generally of Type 1, i.e. the real time requirement is that the mean response time is not greater than some predetermined value. Such systems are similar to the sensor based type, but the response of the computer control system depends upon the number of operations that are being performed at any given time. 

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AstrOm K. J. and Wittenmark, B. Adaptive Control (Addison-Wesley, Wokingham, U.K., 1989). Bennett, S. Real-Time Computer Control An Introduction (Prentice-Hall, Hemel Hempstead, U.K., 1988). 

Bennett, S. Real-Time Computer Control An Introduction (Prentice-Hall, Hemel Hempstead, U.K., 1988). 

I worked on this problem for six years. Control experts devised advanced, real-time, computer control programs. Meetings were held to resolve the issue. Finally, I observed that the control valve on the liquid propane flow to the vaporizer would stick in a closed position and suddenly jerk open to 60 percent, where it would stick. It took six years for me to identify and two hours to correct the cause of the unstable fuel gas pressure. Of course, this erratic valve position was not seen on the control center panel. 

Haeder, D.-P. and Lebert, N., Real time computer-controlled tracking of motile microorganisms, Photochem. Photobiol., 42, 509, 1985. 

Time Systems, McGraw-HiU, New York, 1985 Hawryszldewycs, Database Analysis and Design, Science Research Associates Inc., Chicago, 1984 Kham-hata, Microprocessois/Microcomputers Architecture, Software, and Systems, 2d ed.. Whey, New York, 1987 Liptak, Instrument Engineers Handbook, Chilton Book Company, Philadelphia, 1995 Melhchamp (ed.), Real-Time Computing with Applications to Data Acquisition and Control, Van Nostrand Reinhold, New York, 1983. 

Smith, C. L., "Control-Oriented Languages (Table-Driven Software)", pg. 448, "Real-Time Computing", Duncan Mellichamp, ed., Van Nostrand Reinhold (1983),... 

The computer systems that can directly impact the quality attributes of pharmaceutical drug products and associated production records include a wide range of applications. Typically candidate systems can include real-time process control/... 

It is also important that the extent of the FAT is maximized. This will reduce the risk of problems arising during the final acceptance tests carried out on site and during system qualification. At this stage any dynamic testing considered for real-time computer process control systems will need to be undertaken utilizing simulation software, which in itself may need to be validated. 

Cook, 1992] Cook, P. R. (1992). A meta-wind-instrument physical model, and a meta-controller for real time performance control. In Proc. 1992 Int. Computer Music Conf, San Jose, pages 273-276. Computer Music Association. 

Future advances in precursor purity and manufacturing technology, real-time monitoring of chemical reactions, MOCVD reactor chamber design, computer-controlled epitaxial growth systems, detailed chemical process models, and real-time process control will lead to improved process efficiencies, reduced hazardous waste, and enhanced device reproducibility, yield, and performance. The future of MOCVD is certainly bright. We are on the frontier of a great expansion of the abilities of MOCVD to provide materials for products that improve and expand the human experience on earth, under the oceans, and in space. 

Although dynamic responses of microbial systems are poorly understood, models with some basic features and some empirical features have been found to correlate with actual data fairly well. Real fermentations take days to run, but many variables can be tried in a few minutes using computer simulation. Optimization of fermentation with models and real-time dynamic control is in its early infancy however, bases for such work are advancing steadily. The foundations for all such studies are accurate material balances. 

Groth T, Moden H. Related articles. A knowledge-based system for real-time quality control and fault diagnosis of multitest analyzers. Comput Methods Programs Biomed 1991 Feb-Mar 34(2-3) 175-190. 

Dynamic simulation may be used for off-line or on-line applications. An offline dynamic model runs independent of the plant. This is a predictive mode in which a column or an entire process is simulated to predict transient behavior with no input from the plant. Such a model is typically used for the design of equipment and control strategies and as a training simulator. An on-line dynamic model may be used to monitor the column performance and to provide vital information for the control system. It reads current plant conditions and, in real time, computes properties that are not measured on-line, such as product compositions. This makes it possible to control such properties directly. The on-line dynamic simulator can also predict future column trends, thereby allowing the control system to take corrective action in advance. 

Advances in computation greatly contributed to the above-mentioned burst in efficiency in reading the genome. While many thanks are due to the fully automatic capillary sequencers, micro-electrophoresis chips, and their flat-out efforts, sequencing 24 hours a day, 7 days a week, much more is due to improvements in downstream processing power, real-time process control, databases with 6 terabytes of storage, as well as, in the laboratory, automated quality control with data-driven process control. 

Implementation of an on-site computer control unit eliminates the need for mechanical systems, and enables real-time computation of bottomhole pressures. Monitoring techniques and pressure calculation methods vary extensively throughout the service industry. However, the measurable parameters such as surface treating pressure, liquid and gas injection rates, proppant concentration, and slurry temperature are the parameters that must be used to determine the bottomhole pressures. 

Real-Time Computing (with Applications to Data Acquisition and Control), Van Nostrand Reinhold Co. 

Perry Cook, A Meta-Wind Instrument Physical Model, and a Meta-Controller for Real-Time Performance Control. Proceedings of the International Computer Music Conference 273-276 (1992). 

Linked to each external controlled object is an entity within the real-time computer system that shadows its behavior. The real-time state variable (RTSV) must always be sufficiently up to date for the control functions of the system to be discharged. This applies to output as well as input activities. Having computed the required valve setting, for example, there is a temporal constraint on the time that can be taken before the actual physical valve has taken up that position. The use of COs and RTSVs in the event-triggered model is identical to that in the time-triggered approach (Kopetz, 1998). 

Hepburn Engineering Inc. is a pioneer in the development and application of computerized systems for mine hoists, having commissioned its first real time, computer-based operator control station in 1997. Further application and development includes ... 

Various neural network-based adaptive control techniques were discussed in this study. A major problem in implementing neural network-based MRACs is the translation of the output error between the plant and the reference model so as to train the neural controller. A technique called iterative inversion, which inverts the neural identification model of the plant for calculating neural controller gains, has been used. Due to the real-time computer hardware limitations, the performance of neural network-based adaptive control systems is verified using simulation studies only. These results show that neural-network based MRACs can be designed and implemented on smart structures. 

The fault tolerant design discussed here mainly pertains to computing systems and intelligent systems for real-time computer systems such as DCS/PLC and/or associated intelligent devices. Here, the discussion is on the basics of hardware and software fault tolerant principles in computing systems, whereas that applicable to control systems is covered in Clause 1.2. Two ways in which fault tolerant designs can be developed are hardware technique and software technique. 

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