Online measurements sensors

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... 

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. 

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. 

One of the most important sensors needed is one that reliably monitors cell density. An IR fiber-optic cell density probe has been used for this because it can directly monitor cell growth (without dilution) in high-cell-density bacterial fermentations. The ability to do an online sample filtration through the use of hollow fibers or rotating filters has made possible continuous, online measurement of glucose, lactate, and other metabolites. However, glucose, nitrogen substrate, and phosphate sensors that can withstand repeated system sterilization are still needed. 

Weyl, A., Tu, S.W. and Janke, D. (1994) Sensors based on new oxide electrolyte and oxygen reference materials for online measurement in steel melts. Steel Res., 65 (5), 167-72. 

In general, it is difficult to make online measurement of product quality it is often an inferred entity based on experience. The moisture content can be a measured variable if a suitable moisture sensor is used in the process. Analyzers are available for moisture analysis, which can be adapted for automatic, closed-loop dryer control. The most successful of these units rely on infrared, microwave, or capacitance detection [1]. Care must be exercised in the selection to allow for changes in bulk density or for void spaces, which will... 

A turbidostat mode of operation relies on the use of a sensor to measure the biomass concentration in the photobioreactor. Such a sensor can be based on the online measurement of culture turbidity, for example, but any other biomass sensor can be used as well. Based on such a continuous biomass measurement the flow rate through the system then is automatically adjusted such that the biomass concentration is maintained at a preselected value (Fig. 29). 

Nauman, S., Lapeyronnie, P., Cristian, I., et al., 2011b. Online measurement of structural deformations in composites. IEEE Sensors Journal 11 (6), 1329—1336. 

Analytical techniques for organic acid analysis in aqueous matrices are well established especially, if used for routine monitoring purposes. However, as technology advances, methods will also change. New developments include the more frequent use of h)q hen-ated techniques such as ion chromatography coupled to mass spectrometry [84], development of new materials for chromatography columns, e.g., monolithic materials [98], miniaturization of instruments suitable for field monitoring [99], and development of sensors, e.g., online measurements [48]. 

The schematic representation of the self-designed experimental set-up applied for automatic and online measurement of dielectric properties of well conducting liquids in a definite temperature range is shown in Figure 1. It is composed of the following devices and instruments cylindrical sample holder unit, thermostat, peristaltic pump, waveguide, temperature sensor, displaceable piston, stepper motor, magnetron, detectors, control unit, and a PC. 

Figure 4.10 Time gain in accessing transition data for product density, comparing online model application (soft sensor)) versus online measurements (OCS).

Development of sensors for the online measurement of quality characteristics that influence handle and appearance (for example, automatic fabric inspection). More flexible finishing processes for small lots. 

Fig. 5.26 Online measurement of the thermal reaction power q by the sensor during the reaction of methanol and acetic acid anhydride in a tank reactor. The alternating temperature in the reactor...

The use of sensors and biosensors on a continuous real-time measurements (online monitoring systems), at increasingly more and more affordable costs, introduces new possibilities on monitoring that cannot be underestimated. In turn, those new technologies generate new problems, mostly related to the amount of results available and their interpretation. 

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