On-line measurements

A tube manufacturer wanted to investigate the possibility for on-line measurement, calculation and presentation of eccentricity values on aluminum tubes when drawn at high velocities. Based on our experience from development of tube inspection systems [1, 2] for off-line inspection of precision tubes, a project was formulated. The main specifications for the tube manufacturing are summarized below ... 

Fig. 24. Flow meters for on-line measurement of slurry flow rates (a) magnetic and (b) ultrasonic (6).

Technology has been introduced for on-line estimation of the kappa number based on absorption of ultraviolet light (35). This breakthrough ia optical sensor technology permits closed-loop feedback control of digesters from on-line measurement of the kappa number. 

Continuous emulsion copolymerization processes for vinyl acetate and vinyl acetate—ethylene copolymer have been reported (59—64). CycHc variations in the number of particles, conversion, and particle-size distribution have been studied. Control of these variations based on on-line measurements and the use of preformed latex seed particles has been discussed (61,62). 

Temperature, pH, and feed rate are often measured and controlled. Dissolved oxygen (DO) can be controlled using aeration, agitation, pressure, and/or feed rate. Oxygen consumption and carbon dioxide formation can be measured in the outgoing air to provide insight into the metaboHc status of the microorganism. No rehable on-line measurement exists for biomass, substrate, or products. Most optimization is based on empirical methods simulation of quantitative models may provide more efficient optimization of fermentation. 

An interesting development is the combination of HPLC and on-line measurement of reducing capacity or antioxidative activity. This approach allows both direct identification of antioxidative species in complex foods and quantification of the contribution to the overall antioxidative capacity in the absence of synergistic and antagonistic effects. Major advantages are less sample handling and the ability to rim large series of samples in an automated process. 

The on-line measurement of reducing capacity can be performed with either a single or a series of electrochemical detectors, and linear correlations have been demonstrated between total antioxidative activities determined by the electrochemical detection and those determined by DPPH- reduction or by the ORAC assay (Guo et al, 1997 Peyrat-Maillard et al, 2000). The reducing capacity must also be quantified by post-column reactions, either with DPPH- or by the reduction of phosphomolybdenum complexes followed by UV-VIS-detection (Bandoniene and Murkovic, 2002 Cardenosa et al, 2002). A combination of HPLC and semi-automatic ORAC analysis has also been described (Caldwell, 2001). 

On-line State Estimation. Optimal Sensor Selection and Control. Realistically, it is very difficult to have on-line measurements of all the major polymer or latex properties of interest, but perhaps one could rely upon one or two of the sensors available for the on-line measurement of a few states (e.g. conversion). In order to estimate some of the other states (e.g. particle diameter averages), Kalman filters or Observers should be used. A number of papers have investigated these state estimation schemes (58,6 , 67). 

Wielinga, P., De Waal, E., Westerhoff, H. V., Lankelma, J., In vitro transepithelial drug transport by on-line measurement cellular control of paracellular and transcellular transport,/. Pharm. Sci. 1999, 88, 1340-1347. 

Agents for chemical bleaching rely on different types of peroxides. Potentiometric or amperometric biosensors that detect the highly specific and sensitive reaction of enzymes like katalases with their corresponding substrates can be used for on-line measurement [84]. The sensors can be manufactured with simple technologies at moderate cost, but their stability is not sufficient for integration in household appliances. 

The previous chapters have shown that the classical procedure based on sampling and laboratory analysis is not suitable for the majority of cases, especially in an industrial context, where it is obvious that the efficiency of (treatment) processes must be always guaranteed or at least, most of the time. But there are other reasons for considering on-site (on-line) measurement. Experimental errors related to the numerous steps between sampling and analysis, medium variability with space and time, and sample aging are some good reasons. 

On-site measurement thus seems to be the optimal solution for wastewater quality monitoring. However, as seen previously, wastewater composition is very complex and varyies with time and space. The implementation of on-site measurement must take into account some constraints related to the risk of sampling line clogging or sensor fouling (in the case of on-line measurement). In order to prevent this risk, or at least to space maintenance procedures, on-site measurement must be carried out carefully, depending on the type of system used. 

Relatively far from the present topic and well known, the on-line measurement of the physical and aggregate properties of wastewater does not present any problem. Conductivity, temperature, turbidity and oxido-reduction potential (ORP) are easily measured by well-designed sensors, because these parameters are also used for treatment process control. In practice, turbidity is more used for the treatment of natural water, and ORP for the biological treatment of wastewater. However, conductivity and temperature are often monitored at the same time as the other parameters in this section. 

For non-metallic constituents, several systems exist especially for nutrients monitoring, considering their importance in the eutrophication phenomenon. The on-line measurement of some nitrogen compounds (nitrate and ammo-... 

With the advance of computer techniques, especially implementation of distributed control systems (DCS) to chemical processes, a large set of on-line measurements are available at every sampling period. The rational use of this large volume of data requires the application of suitable techniques to improve their accuracy. This goal has triggered the focus on research and development, during the last ten years, in the area of plant data reconciliation. Complete reviews on the subject can be found in the works of Mah (1990), Madron (1992), and Crowe (1996). 

W. Beyeler, A. Einsele, and A. Fiechter, On-line measurements of culture fluorescence Method and application, Eur. J. Appl. Microbiol. Biotechnol. 13, 10-14 (1981). 

J. H. T. Luong and D. J. Carrier, On-line measurement of culture fluorescence during cultivation of Methylomonas mucosa, Appl. Microbiol. Biotechnol. 24, 65-70(1986). 

H.-P. Meyer, W. Beyeler, and A. Fiechter, Experiences with the on-line measurement of culture fluorescence during cultivation of Bacillus subtilis, Escherichia coli and Sporotrichum thermophile. 

T. Scheper, T. Lorenz, W. Schmidt, and K. Schugerl, On-line measurement of culture fluorescence for process monitoring and control of biotechnology processes, Ann. NY Acad. Sci. 506, 431—445... 

Recommended Practices for On-Line Measurement of Residual Chlorine in Wastewaters... 

Let s start from the beginning of the control loop, at the sensor. Instruments for on-line measurement of many properties have been developed. The most... 

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