Over-specified system

Do not touch the product stream—specifying something here will over specify system... 

Care must be taken not to specify more control objectives than the available remaining degrees of freedom. If this is done then the system becomes over specified and there is no solution to the system, i.e. the system cannot be controlled. For example, it is impossible to design a control system for the distillation column illustrated in Fig. 7.10 which will control not only Xc S, Pc and the two levels—but also (say) the overhead product flowrate D and the bottoms product flowrate W. 

Since the user s company does not have control over the system product to be acquired, the user s company must adequately understand and specify the requirements and capabilities to be provided by the system product. 

Although many excellent commercial systems exist, it is still often necessary to customise these to a particular users needs. It is all too easy for both managers and users to over specify their requirements, making the system more expensive than it needs to be. Consequently a few important considerations taken at the outset of a project can lead to rapid success using the currently available technology. 

Limit of Detection A measurement of the system s ability to detect microorganisms at specified concentration levels over specified periods of time. The lower the number, the better the sensitivity. 

Effective Materials and Spare Parts Description in Procurement Database. Improper stores or procurement descriptions allow inadequate parts, materials or components to enter the plant, increasing the potential for process safety incidents (if under specified) or cost overruns (if over specified). Personnel entering parts descriptions in electronic or paper ordering systems must be trained to ensure the accuracy of their work. See Chapter 2 under Database Discipline. 

In the determination of the bubble-point temperature corresponding to a specified system pressure and liquid-phase composition, the procedure described might appear to lead to a trial determination of both the system temperature and the convergence pressure. However, because of the relatively small dependence of the Ki s on the convergence pressure, the trial-and-error procedure is reduced primarily to the finding of the bubble-point temperature. This characteristic relationship between the K, s and PK permits the use of a single convergence pressure over either the entire column or several plates. 

For both solid phase and soluble polymers metal leaching remains to be solved in some cases and more stable, generally applicable polymeric supports are required. For broad apphcation, however, further development of more flexible, economically attractive, not over-specified catalyst systems is needed. 

This, of course, is not what we want since the pressure (and temperature) must vary to change the heat-transfer rate and the steam flow rate. It is necessary to use Flowsheet Equations in Aspen Dynamics to change the specification to have an exit hot stream with a vapor fraction of zero. Figure 13.5 shows the equation used. It is also necessary to change the pressure of the hot exit stream fxom fixed to free so that the system is not over specified. 

When compared to the disposal systems considered for other types of toxic waste, the HLW repository design presented here appears to be completely over-specified. The rationale for this over-design is primarily socio-political - reflecting the concern of the general public about radioactivity and the extremely high value of the product (electricity) relative to the low volume of waste produced for the case of nuclear power. 

The reliability analysis of nonlinear systems is defined similarly to the linear case as the computation of first excursion probabilities over specified thresholds. While in linear problems these thresholds are specified in terms of... 

In its basic form, the past record of accidents and incidents within a specified system provides the frequency of occurrences over the record period. It is then extrapolated to future years, e.g. by means of linear regression analysis. If the frequency per shipment, per mile or per production unit is desired the corresponding numbers have to be known or estimated not only relating to the present but also with respect to the future. A confidence interval for the inferred probability can also be established. 

A subrule of the Cahn-Ingold-Prelog system specifies that higher mass number takes prece dence over lower when distinguishing between isotopes... 

The assessor should verify that there is a comprehensive formal system that specifies self-audits on a planned frequency. Over time, all areas should be audited. Results should be reported to maiiagemeiit with appropriate follow-up documented. Self-audits should be thorough, addressing all aspects of the area s fuiictioiis. Outsiders riot working in the specific audit area should be iiicluded ill the exercise for objectivity. 

It is neeessary to understand the TDH and it s eomponents in order to make eorreet deeisions when parts of the system are changed, replaced, or modified (valves, heat exchangers, elbows, pipe diameter, probes, filters, strainers, ete.) It s neces.sary to know these TDH values at the moment of specifying the new pump, or to analyze a problem with an existing pump. In order to have proper pump operation with low maintenance over the long haul, the BF P of the pump must be approximately equal to the TDH of the system. 

Standard sampling trains are specified for some tests. One of these standards is the system specified for large, stationary combustion sources (4). This train was designed for sampling combustion sources and should not be selected over a simpler sampling train when sampling noncombustion sources such as low-temperature effluents from cyclones, baghouses, filters, etc. (5). 

The theory that results from the investigation of the dynamics of solute distribution between the two phases of a chromatographic system and which allows the different dispersion processes to be qualitatively and quantitatively specified has been designated the Rate Theory. However, historically, the Rate Theory was never developed as such, but evolved over more than a decade from the work of a number of physical chemists and chemical engineers, such as those mentioned in chapter 1. 

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