Selectivity of sensor

The use of catalysts and promotors of various reactions applied as a fine dispersion phase to the surface of semiconductor adsorbent became most popular in providing a required selectivity of sensors with respect to a given gas. As it has been established in experiments (see for instance [8] and the reference list therein), apart from obtaining required selectivity application of such additives results in increase of sensitivity of the sensor with respect to a given gas. However, as of today there is no clarity with regard to understanding the mechanism of effect of cata-l)rtic additives on the sensor effect nor in optimization of the choice of catalysts applied. 

Fig. 10.20 (a) Experimental dependence of the coherence spectra on orientation of the linear optical array (Cantor et al., 2008). (b) Enhancement of information content achieved by optimized selection of sensor pairs used in the correlation analysis (Cantor et al., 2008)... 

Different other attractive way to modify the active electrode of amperometric sensors, besides deposition of polymers or electropolymerization, is formation of self-assembled structures, e.g., self-assembled monolayers (SAM) on solid supports 88 89 or bilayer lipid membranes (BLM) on various types of support.90 Both types of theses structures can either induce selectivity of sensor to particular analytes and... 

The specific sensor construction takes into account the space requirements, the possible assembly hole dimension, and the sensor reading types bottom read and side read. Therefore a big selection of sensor versions regarding the housing geometry are available. Fig. 7.9.8 gives an overview of possible versions for passive and active wheel-speed sensors. 

Three odour classes were defined through the selection of sensors pattern parameters for each class. In the simulation dataset one hundred samples for each class were considered and the same sensor is characterized by the same baseline for all the dataset. 

It is important to note that the partition coefficients are strongly temperature dependent with a subsequent decrease in sorption with increasing temperature. Therefore, the solvation parameters determined for polymers used in sensor technology must be determined close to room temperature, that is at normal operating conditions of sensors, otherwise the sensitivity and selectivity of sensors will be underestimated. Table 11 actually indicates a sharp decrease in the acidity (a), basicity (b), and dispersion (/) parameters as a result of increasing temperature in for example FPOL, a fiuoropolyol. 

Selection and installation of sensors According to the specific purpose, objects and environment, selecting the appropriate sensor is the primary problem when measuring a certain value. Effect of the measurement depends largely on whether the selection of sensors is suitable. 

Sensors and AE equipments are already commercially available. In this concern, important aspects are to select proper devices and systems. Depending upon materials and stmctures, selection of sensors, decision of frequency range, techniques to eliminate noises and conditions for system setting may change. Some of standardized procedures and requirements for systems are stated in chapters dealing with applications. 

Thermodynamic stability of the interface with silicon is also important for correct selection of sensor material. According to Hubbard and Schlom (1996), for MgO and ZrO, thermodynamic stability of their interfaces with silicon was predicted. For HfO, AI2O3, CaO, and Y2O3, experimental evidence showed that these oxides also form stable interfaces with silicon. The CeO /Si interface is thermodynamically unstable, in accordance with experimental observations of formation of a Ce203 interlayer at the CeO /Si interface. Present analysis shows that, for the majority of metal oxides used, the interface with Si is stable. However, ZrO or YSZ thin films are permeable for oxygen at elevated temperatures, so that oxygen diffuses to the silicon substrate and a SiO layer is formed at the interface (Jia et al. 1995). It should be noted that this problem exists for all metal oxides used for gas sensor design. 

The huge number of PVC ISEs reported since 1970 means that the selection of sensor topics for this chapter must be restricted. Much of the post-1970 development work with the second class of ISEs has centred on many aspects of PVC calcium electrodes. It is therefore appropriate, in the first instance, to discuss sensor developments in terms of the calcium studies. Indeed, the original electrode model (9) constitutes the basis for the subsequent diverse developments in sensor design wherein the appropriate materials are generally entangled in a polymer matrix (10). 

The highest costs are usually related to development of a selective analyte recognition layer, perhaps the most important part of a complete chemical sensor. Transducer technology is much more highly developed indeed, there seems to be little need here for further improvement without equivalent improvements in the selectivity of sensor elements. 

Meyer, M., J.H. Le Lann, B. Koehret, and M. Enjalbert (1994), Optimal selection of sensor location on a complex plant, using a graph oriented approach. Computers Chem. Eng. 18, Suppl., S535-S540... 

It is needless to argue that measurements affect the safety of a measurement loop. Therefore, it is important to look into the pertinent issues, listed as follows, which influence selection of sensors for various measurements ... 

Sensor Locations. The codes do not specify the exact location of gas sensors inside the feb area they simply state that the gas must be detected. Extremely high air movement rates in the cleanroom play a major role in the selection of sensor location and spacing. 

Wilson, J. 2005. Sensor Technology Handbook. Amsterdam/Boston Elsevier. The purpose of this handbook is to assist engineers and designers in the selection of sensors for their applications. It covers various sensor types, manufacturers, guidelines for selecting and specifying sensors as well as information on MEMS and nanotechnology applications. 

Immobilization techniques with optodes are less multifaceted than those with electrochemical sensors, since the selection of sensor materials is smaller. The most common immobilization procedures are the following ... 

Sumana, C. and Venkateswarlu, Ch. Optimal selection of sensors for state estimation in a reactive distillation process Journal of Process Control 19 (6), 1024-1035 (2009). 

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