Industrial process control

The most common applications of methods for handling sequential series in chemistry arise in chromatography and spectroscopy and will be emphasized in this chapter. An important aim is to smooth a chromatogram. A number of methods have been developed here such as the Savitsky-Golay filter (Section 3.3.1.2). A problem is that if a chromatogram is smoothed too much the peaks become blurred and lose resolution, negating the benefits, so optimal filters have been developed that remove noise without broadening peaks excessively. 

Another common need is to increase resolution, and sometimes spectra are routinely displayed in the derivative mode (e.g. electron spin resonance spectroscopy) there are a number of rapid computational methods for such calculations that do not emphasize noise too much (Section 3.3.2). Other approaches based on curve fitting and Fourier filters are also very common. 

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C. Puebla, Industrial process control of chemical reactions using spectroscopic data and neural networks. Chemom. Intell. Lab. Syst., 26 (1994) 27-35. 

Many materials are complex mixtures of multiple molecular species and components and each component can be in multiple chemical or physical states. Realtime determination of the components and their properties is important for the understanding and control of the manufacturing processes. This paper reviews a recently developed technique of 2D NMR of diffusion and relaxation and its application to identify components of materials. This technique may have further applications for the study of biological systems and in industrial process control and quality assurance. 

Industrial process control, when the interrelation of process vari-... 

Solid samples can also be measured in transmission, although reflection or transflection measurements are more common. Open arrangements with the source on one side of the sample and the spectral analyser on the other side are prevalently used, e.g. in industrial process control. For absolute quantitative analysis the thickness of the object must either be constant or be measured. 

A few ATR probes are commercially available. In the near-IR ATR probes are mostly used as easy-to-use sticking probes for liquids and solids. As the aim is primarily to identify a material, not to measure low concentrations, probes with typically one or two reflections (Figure 5-d) are used. In the mid-IR, similar layouts can be found, using e.g. zinc selenide, germanium or silicon crystals as sensing elements. More sensitive and generally better suited for industrial process control DiComp -type probes (Figure 5-e). The actual ATR element is in this case a thin diamond disc supported by a suitably shaped ZnSe crystal. ATR probes of that type are available off the shelf with between one and nine reflections. If more... 

Temperature is one of the four or five most important parameters in industrial process control and in the chemical industry. Almost all chemical processes and reactions are temperature dependent, and not infrequently in the chemical plant temperature is the only indication of the progress of the process. Where the temperature is critical to the reaction, a considerable loss of product or efficiency may result from operation at incorrect temperatures. In some cases, loss of control of temperature can result in catastrophic plant failure with attendant damage and possible loss of life. 

Riekkola, M. L., and Wiedmer, S. K. (1997). Potential of capillary electrophoresis with micelles or chiral additives as a purity control method in pharmaceutical industry. Process Control Qual. 10, 169-180. 

P. Kotidis, R. Crocrombe and W. Atia, Optical, tunable filter-based micro-instrumentation for industrial process control. Abstracts of Papers, Federation of Analytical Chemistry and Spectroscopy Societies (FACSS), Orlando, EL, USA, October 19-23, 2003, Federation of Analytical Chemistry and Spectroscopy Societies, Santa Fe, NM USA, 2002. 

A review on instrumental methods of analysis) (313 refs) 3) L.A. McColl, Fundamental Theory of Servomechanisms, Van Nostrand, NY (1945) 4) D.P. Eckman, Principles of Industrial Process Control, J Wiley, NY (1945)... 

In flow injection analysis, a sample is injected into a moving liquid stream to which various reagents can be added. After a suitable time, the reacted sample reaches a detector, which is usually a spectrophotometric cell. Flow injection is widely used in medical and pharmaceutical analysis, water analysis, and industrial process control. 

This instrument has evolved from ihe laboratory spectrophotometer to satisfy the specific needs of industrial process control. While dispersive instruments continue to be used in some applications, the workhorse infrared analyzers in process control are predominantly nondispersive infrared (NDIR) analyzers. The NDIR analyzer ean be used for either gas or liquid analysis. For simplicity, the following discussion addresses the NDIR gas analyzer, hut it should be recognized that the same measurement principle applies to liquids. The use of infrared as a gas analysis technique is certainly aided by the fact that molecules, such as nitrogen (N ) and oxygen tO , which consist of two like elements, do not absorb in the infrared spectrum. Since nitrogen and oxygen are the primary constituents of air. it is frequently possible to use air as a zero gas. 

Applications of fiber-optic pH sensors in environmental analysis, biomedical research, medical monitoring, and industrial process control have been reviewed by Lin [67]. A multitude of luminescent systems for pH monitoring are commercially available, mostly under special trademarks. Pyrene [68-70], coumarin, bromothymol blue [71] and fluorescein [72-74] derivatives are typical examples that have been used in research in the past two decades. Carboxyfluorescein derivatives have been directly applied to skin tissue samples for the lifetime imaging of pH gradients in the extracellular matrix of the epidermis [75]. Two-photon excitation microscopy became an estab-... 

IEC 534-8-3 1995 Industrial process control valves Part 8 Noise Considerations... 

Initially, these systems were designed to address the needs of clinical laboratories, but at present they are used in such diverse areas as industrial process control (process analyzers) or routine determinations of various substances in the air, water, and soil (environmental monitoring). Automatic analyzers can be classified according to the way in which samples are transported and manipulated ... 

Potentiometric microelectrodes are very suitable for in vivo real-time clinical monitoring of blood electrolytes, intracellular studies, in situ environmental surveillance, or industrial process control. For example, Simon s group... 

Downs, J. J. and Vogel, E. F. (1993). A plant-wide industrial process control problem. Comput. Chem. Eng., 17, 245-255. 

Sequential signals are surprisingly widespread in chemistry, and require a large number of methods for analysis. Most data are obtained via computerised instruments such as those for NIR, HPLC or NMR, and raw information such as peak integrals, peak shifts and positions is often dependent on how the information from the computer is first processed. An appreciation of this step is essential prior to applying further multivariate methods such as pattern recognition or classification. Spectra and chromatograms are examples of series that are sequential in time or frequency. However, time series also occur very widely in other areas of chemistry, for example in the area of industrial process control and natural processes. 

Such methods are applicable not only to coupled chromatography but also in areas such as pH dependence of equilibria, whereby the spectra of a mixture of chemical species can be followed with change of pH. It would be possible to record 20 spectra and then treat each independently. Sometimes this can lead to good quantification, but including the information that each component will be unimodal or monotonic over the course of a pH titration results in further insight. Another important application is in industrial process control where concentrations of compounds or levels of various factors may have a specific evolution over time. 

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