Distributed control systems normal

Distributed Control System (DCS) A system that divides process control functions into specific areas interconnected by communications (normally data highways) to form a single entity. It is characterized by digital controllers, typically administered by central operation interfaces and intermittent scanning of the data highway. 

A distributed control system (DCS) normally uses input and output modules which contain eight, sixteen, or more inputs or outputs. Failure of the module will simultaneously disable a large number of control loops. Attention to the assignment of input/output points to the modules makes the plant more tolerant of a failure of an input or output module (CCPS, 1993a). For a more detailed discussion of process control systems, see the process control part of Section 4.4, and Sections 6.4 and 6.5. 

A number of the basic characteristics of operator stations (OS) are described in Section 7.19.4. Distributed computer control systems normally offer two types of operator station, a stand-alone OS, and a host-dependent OS. Both provide a logical display hierarchy which, if properly configured, improve significantly the... 

The detection and diagnosis tasks can be carried out on the process measurements to obtain critical insights into the performance of not only the process itself but also the automatic control system that is deployed to assure normal operation. Today, the integration of such tasks into the process control software associated with Distributed Control Systems (D-CS) is in progress. The technologies continue to advance, especially in the incorporation of multivariate statistics as well as recent developments in signal processing methods such as wavelets and hidden Markov models. 

ANSI/ISA 84 (3.1.56) Programmable electronics (PE) Electronic component or device forming part of a PE and based on computer technology. The term encompasses both hardware and software and input and output units. Normally these include smart sensors, PE logic solver including PLC, distributed control system (DCS), loop controller, and smart final element. 

An air conditioning system uses an assembly of equipment to treat air. Normally the assembly includes a heating system for modifying winter indoor temperature and humidity a refrigeration system for modifying summer temperature and humidity, a means to maintain indoor air quality (i.e., air filters and fresh air intake) a method of distribution of conditioned air and a control system, such as a thermostat, to maintain desired comfort conditions. 

If the DCCS is required to replace an existing control system (i.e. if the plant is being retrofitted) then the microcontrollers will normally be located in the central control room (CCR). In this case, the distribution features of the DCCS will not be fully utilised and the significance of the digital data highway (DH) will also be reduced. 

The control system must manipulate heat removal from the reactor, but what should be the measured (and controlled) variable Temperature is a good choice because it is easy to measure and it has a close thermodynamic relation to heat. For a CSTR. temperature control is particularly attractive since there is only one temperature to consider and it is directly related to the heat content of the reactor. However, in a spatially distributed system like a plug-flow reactor the choice of measured variable is not so clear. A single temperature is hardly a unique reflection of the excess heat content in the reactor. We may select a temperature where the heat effects have the most impact on the operation. This could be the hot spot or the exit temperature depending upon the design of the reactor and its normal operating-profile. 

The distributions of isoenzymes of aldolase, LD, and CK in the muscles of patients with progressive muscular dystrophy have been found to be similar to those in the earlier stages of development of fetal muscle. The isoenzyme abnormalities in dystrophic muscle have been interpreted as a failure to reach or maintain a normal degree of differentiation. Isoenzyme patterns in regenerating tissues may also show some tendency to approach fetal distributions. This tendency may result from relaxation or modification of control systems in rapidly dividing cells and may account for some of the isoenzyme changes noted (e.g., in muscle in acute polymyositis). 

No matter which of the preceding methods is used to induce hyperthermia, it is essential to monitor the resulting temperature distributions in the normal and neoplastic tissues continually, and to control the power input and position of the heating source so that the temperatures are maintained in the desired range for optimal time. This type of control can be achieved either manually or automatically and is incorporated in most commercial or in-house-built hyperthermia systems used currently. 

Anticipated operational occurrences are off-normal events, usually plant transients, which can be coped with by the plant protection systems and normal plant systems but which could have the potential to damage the reactor if some additional malfunction should happen. Their typical frequency of occurrence may be more than 10 year Some of the anticipated occurrences (PIEs - postulated initiating events) are due to the increase of reactor heat removal (as might occur for an inadvertent opening of a steam relief valve, malfunctions in control systems, etc.). Some are due to the decrease of reactor heat removal (such as for feed-water pumps tripping, loss of condenser vacuum and control systems malfunctions). Some are due to a decrease in reactor coolant system flow rate, as in the case of a trip of one or more coolant pumps. Some are connected with reactivity and power distribution anomalies, such as for an inadvertent control rod withdrawal or unwanted boron dilution due to a malfunction of the volume control system for a PWR. Events entailing the increase or decrease of the reactor coolant inventory may also happen, due to malfunctions of the volume control system or small leaks. Finally, releases of radioactive substances from components may occur. 

The main computer has the task of collecting information from the process control systems, and it communicates with the distributed micro-computers via serial links. The main computer compiles information and generates reports, such as daily weekly operation reports, reports of periodic testing, actual status reports, and disturbance reports. During normal plant operation, the main computer will present occurrences on VDU displays in the control room and in a special "observation room". 

Control systans, in their broadest sense, include sensors, plant status indications, logic systans, alarm systems, and auto-control systems. With process plant digital systans, the control systems are usually referred to as the digital or distributed control systan (DCS). The DCS includes the human-machine interface (HMI) - the computa screens in the main control room - for the normal operation of the plant. The functions of the DCS are self-evidently to control the plant parameters within normal limits, and to advise the operators of plant status, and to raise alarms when normal parameter ranges are exceeded. 

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