Analytical redundancy

In view of the conflict between the reliability and the cost of adding more hardware, it is sensible to attempt to use the dissimilar measured values together to cross check each other, rather than replicating each hardware individually. This is the concept of analytical i.e. functional) redundancy which uses redundant analytical (or functional) relationships between various measured variables of the monitored process e.g., inputs/outputs, out-puts/outputs and inputs/inputs). Figure 3 illustrates the hardware and analytical redundancy concepts. 

In many ground-water investigations, more data are collected than the minimum required to describe the carbonate system. Measurements of dissolved CO2 concentrations are often made as part of the suite of analyses for all dissolved gases or by base titrations in the field. Measurements of total dissolved carbonate concentrations made by precipitation of solid carbonate or evolution of CO2 following acidification may also be available. With such redundant analytical data, the internal consistency of all the carbonate data can be tested. 

Fathi, Z., W.F. Ramirez, and J. Korhicz, Analytical and Knowledge-Based Redundancy for Fault Diagnosis in Process Plants, AlChE Journal, 39(1), 1993, 42-56. (Fault diagnosis)... 

In analytical redundancy schemes, the resulting difference generated from the consistency checking of different variables is called a residual signal. The residual should be by convention zero-valued when the system is normal and should diverge from zero when a fault occurs. This zero and non-zero property of the residual is used to determine whether or not a fault has occurred. Analytical redundancy makes use of a quantitative model of the monitored process and is therefore often referred to as the model-based approach to fault diagnosis. 

P.M. Prank. Pault diagnosis in dynamic systems using analytical and knowledge-based redundancy A survey and some new results. Automatica, 26(3) 459-474, 1990. 

Performance trials and evaluation tests on the technique indicate that it is both rehable and accurate, and, in addition, that the specificity is sufficient to cope with most chnical requirements. An evaluation was made by Haeckel et al. [19]. If this approach is successful, the dispensers and tubes in laboratories will become redundant. It may well become possible for a clinical test to be undertaken close to the patient rather than in the laboratory. Whilst the techniques have as yet been used only for clinical analyses, there are many other potential applications, for example in the water industry. However, the very nature of the technique necessitates development by Eastman Kodak. Very few users will be able to influence the choice of analytical problems to be tackled by this unique approach. 

The development of a plethora of HPLC CSPs in the 1980s and 1990s has, to a large extent, made the use of chiral mobile-phase additives (CMPAs) redundant in most modem pharmaceutical analytical laboratories [23]. Before this period, chiral selectors were used routinely as additives in HPLC, but are now only used for a small number of specific applications [23]. CMPAs are used to form... 

Not rarely, analytical signals are composed of hundreds or thousands of variables. Many of them are uniquely or predominantly associated with noise, while contiguous informative variables are often very intercorre-lated, so that they carry redundant information. For these reasons, chemometric tools to perform the selection of a limited number of informative predictors and to realize data compression are enormously profitable. 

A number of different approaches have been suggested for systematic reduction of detailed reaction mechanisms [160,313], The most common approach involves a two-stage procedure. First, a skeletal mechanism is established by removing all redundant species and reactions. Second, the skeletal mechanism is further reduced by order-of-magnitude approximations, resulting in the analytically reduced mechanism. 

In the last two decades, the researchers interest has been focused mainly on quantitative model-based methods, based on the concept of analytical or functional redundancy, which use a mathematical model of the process to obtain the estimates of a set of variables characterizing the behavior of the monitored system. The inconsistencies between estimated and measured variables provide a set of residuals,... 

In this chapter, an FD framework for batch chemical processes is developed, where diagnosis of sensor, actuator, and process faults can be achieved via an integrated approach. The proposed approach is based on physical redundancy for detection of sensor faults [38], while an analytical redundancy method, based on a bank of diagnostic observers, is adopted to perform process/actuator fault detection, isolation, and identification [4],... 

J. Gertler. Analytical redundancy methods in fault detection and diagnosis. In Proceedings of IFAC SAFEPROCESS Symposium, pages 9-21,1991. 

In the fifth chapter, a general overview of temperature control for batch reactors is presented the focus is on model-based control approaches, with a special emphasis on adaptive control techniques. Finally, the sixth chapter provides the reader with an overview of the fundamental problems of fault diagnosis for dynamical systems, with a special emphasis on model-based techniques (i.e., based on the so-called analytical redundancy approach) for nonlinear systems then, a model-based approach to fault diagnosis for chemical batch reactors is derived in detail, where both sensors and actuators failures are taken into account. 

Other advantages of microfabricated devices include faster response times, and the fabrication of multiple test sites for simultaneous replicate assays in one microfabricated device. This analytical redundancy provides a safeguard that is not easily attained in a conventional macroscale analyzer, where duplicate assays represent the usual extent of repetitive assay of a sample. Encapsulation technology used in the microelectronics industry may also be applicable to microscale devices and could be extended to operations over a wide range of environmental conditions of humidity, and temperature. 

The analytical data (spectra) for each chemical available in the OCAD for each technique varies from single to multiple entries. It is quite common to find at least three MS spectra for particular widely known scheduled compounds. This has several advantages, for instance, if on-site data is requested, there is a range of choice of data to choose from. Spectra acquired from different instruments or conditions can be selected to suit the scenario of an inspection. As the database grows, however, analytical data determined to be redundant or of low quality maybe replaced. 

A comparison between different encoding techniques was never attempted using the same library and building it with two, or more, different codes. While many authors reported or claimed specific advantages for a particular technique, a detailed examination of the available methods reveals a fundamental complementarity, rather than redundancy, of the approaches, such that different libraries may better benefit from different encoding methods. Moreover, variables such as the availability of analytical or synthetic instrumentation, resources, which may be devoted to the assessment for a chosen encoding technique and the expertise of the chemist(s) involved in the project, will also strongly influence the final choice of a particular method. 

Some thirty years ago the perfumery profession was shaken by the commercialization of the gas chromatograph. In lectures, roundtable discussions, and private conversation hot debates centered around the question whether this analytical tool, by greatly simplifying the separation of complex mixtures of volatile materials, would make the perfumer redundant. 

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