Online measurements

In the highest pressure boilers, where online measurement equipment is installed, steam and condensate sampling is taken from the following points, as a minimum ... 

The development of rapid, accurate, and noninvasive online measurement sensors and instraments is a high-priority goal in the commercialization of biotechnology (Figure 3.4). Some of these instraments will build on analytical methods now used in catalysis and other surface sciences, such as... 

The need for a viscosimeter capable of online measurement of the intrinsic viscosity of a polymer sample arose when it was shown that polymer molecules elute in order of decreasing hydrodynamic volume.81 The hydrodynamic volume can be related to the product of intrinsic viscosity and molecular weight. 

Online measurement of myocardial tissue pH. Ann. Thorac. Surg. 72, S2227-S2234 (2001). 

Cobalt (II) has been determined by online measurements on seawater which has been passed through a column containing 8-quinolinol immobilised on silica gel, followed by chemical luminescence detection [244]. 

Over the past 30 years, business automation systems and plant automation systems have developed along different paths, particularly in the way data are acquired, managed, and stored. Process management and control systems normally use the same databases obtained from various online measurements of the state of the plant. Each level in Figure 16.1 may have its own manually entered database, however, some of which are very large, but web-based data interchange will facilitate standard practices in the future. 

Other methods, the signal-model-hased methods, only use the available online measurements. They can detect changes from the normal behavior using... 

S.S. Cherukupalli and A.A. Ogale, Online measurements of crystaUinity using Raman spectroscopy during blown film extrusion of a linear low-density polyethylene, Polym. Eng. Sci, 44, 1484—1490 (2004). 

The rapid determination of BOD enables new possibilities in process control. Online measuring systems for process control have been developed and marketed by Nisshin Electric ( BOD-1100 ) and AUCOTEAM ( BODyline P ) [11]. 

Light absorption at specific wavelengths is another principle often employed for the online measurement of gaseous pollutants. For example, the absorption of 03 in the ultraviolet at 254 nm can be used, though this experiences cross sensitivity to S02 and PAHs, and C02 in the infrared at 4.26 pm (2,350 cm-1), which has little cross sensitivity to other gases. The most common C-H absorption bands are in the range of 3.33-3.57 pm (2,800-3,000 cm-1). 

In contrast to calorimetry, most of the analytical techniques that are applied to the study of kinetics, such as concentration measurements or online measurement of reaction spectra (e.g. UV-vis, near infrared, mid infrared and Raman), can be related to integral kinetic... 

SCISR) during operation is investigated experimentally by online measurement of the... 

Meyerhoff C, Mennel FJ, Bischof F, Sternberg F, Pfeiffer EF. Combination of microdialysis and glucose sensor for continuous online measurement of subcutaneous glucose concentration theory and practical application. Hormone and Metabolic Research 1994, 26, 538-543. 

TABLE 8-8 Online Measurement Options for Process Control... 

Liu, C., J. Qu, J. Jia, L. Qi, and S. Dong. 2005. Online measurement of BOD using a microbial sensor based on organic-inorganic hybrid material. Fenxi Huaxue 33 609-613. 

In order to ensure an adequate quality of products and a safe operation, the monitoring of a batch reactor should include, at least, online measurements of temperature, pressure, and of some composition-related variables. In this context, online measurements may be defined as measurements obtained via instruments strictly connected to the reactor and characterize by response times markedly smaller than the characteristic times of the chemical reaction. In general, this is the case of temperature and pressure, which can be easily measured online by means of reliable, relatively cheap, and poorly intrusive sensors. This allows the introduction of sensor redundancy, a common practice to increase reliability. On the other hand, online... 

It is also interesting to briefly consider online measurements of variables different from temperature [5], Since pressure is defined as the normal force per unit area exerted by a fluid on a surface, the relevant measurements are usually based on the effects deriving from deformation of a proper device. The most common pressure sensors are piezoresistive sensors or strain gages, which exploit the change in electric resistance of a stressed material, and the capacitive sensors, which exploit the deformation of an element of a capacitor. Both these sensors can guarantee an accuracy better than 0.1 percent of the full scale, even if strain gages are temperature sensitive. 

Online measurements of composition would be very appreciated, because composition is the most important variable. Unfortunately, direct measurements of the amount of a single component can be obtained only in a few cases, and typically for gaseous system, an example being the measurement of oxygen based on its paramagnetism. In fact, liquid phase systems are usually made out of components of similar chemical structure, and these must be separated before measuring their quantity. 

Thus, online measurements of composition are usually limited to some overall property. A typical example is pH, defined as the absolute value of the logarithm of the molar concentration (or, more exactly, activity) of hydrogen ion pH can be measured by exploiting the electric potential established between two proper electrodes immersed in the sample fluid, usually a glass membrane electrode and a reference electrode [15], Notwithstanding the temperature dependence and the alkaline error (at high pH, a marked sensitivity to the effect of Na+ and of other monovalent... 

In conclusion, a complete analysis of a complex mixture can require very long times (from a few minutes up to many hours) thus, such a measuring apparatus is not suited for online measurements to be used in reactor control. On the contrary, in the laboratory, chromatography is very often the preferred method of analysis of complex mixtures, since these more accurate data can be used to identify the reaction mechanism and the relevant kinetic parameters. 

To this purpose, a brief overview of the measurable variables in a batch reactor has been included the difference between online measurements, suitable for control purposes, and offline measurements, which can be exploited to obtain experimental data to be used for the identification, has been stressed. 

Bockhom et al. (2002) have introduced an approach, by which a calculated signal course is fitted to the whole experimental signal decay under the variation of different distribution parameters such as the width or the mean primary particle diameter. A major drawback of this method is the relative high computing effort for the evaluation which makes the application for online measurements questionable. Roth and Filippov (1996) have introduced an inversion algorithm that also suffers from a complicated and time-consuming calculation procedure and does not lead to unique solutions. 

As pointed out before when discussing structured models, physiological functions like the single cell growth rate r(m, S), cellular division rate T(m, S), and cell mass partition function p(m, m, S) are difficult to measure and this adds to the complexity of using the model. The mathematical complexity is also a limitation for optimization and control purposes that demand online measurements and calculations. 

The detection limit was 4.8 nM, comparable to that obtained by LC with electrochemical detection combined with an enzyme reactor. In the online measurement of acetylcholine standard solutions, the sensitivity of the biosensor was 43.7 nA/pM at a flow rate of 16 pL/min. 

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