Types of sensors

The sensors discussed in this book are dealt with according to the classifications based on which the immobilized species is, the type of immobilization used and whether or not an additional separation is included. Thus, sensors have been included in three chapters according to the type of process that takes place in their sensing microzone, namely reaction-detection (Chapter 3), separation-detection (Chapter 4) and separation-reaction-detection (Chapter 5). 

One very useful technical classification of sensors establishes two categories according to the relationship between the recognition element and the transducer. These two essential elements can be connected optically (e.g. 

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Note Locations and type of sensors depend on the type of machine under consideration.)... 

Often, two or more types of sensors may be used in conjunction with each other to give more visibility to what is going on. Monitoring of a turbine generator is a good example. Information may be collected about shaft thrust, eccentricity, rpm, bearing wear, gearbox wear, and othens for maintenance and protection analysis. 

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

This type of sensor typically includes infrared (IR) and ultrasound sensors. TRs detect the heat released from humans, and ultrasound sensors detect the movcnicnt of the human occupant (i.c., the device compares the reflection in different instants if they are different, something is moving in the sensor distance range). 

Special features which characterize the prototypical roof-shaped compound 26 are a rigid molecular skeleton and the type of sensor groups used. They render 26 a potential coordinatoclathrand 50). The capability of 26 in forming inclusion compounds is evident from Table 5. Here, nearly thirty different crystal inclusions of 26 are specified including as guest molecules various alcohols, acids, aprotic dipolar, and rather apolar species. 

The development of on-line sensors is a very costly and time-consuming process. Therefore, if one has available a dynamic model of the reactor which predicts the various polymer (or latex) properties of interest, then this can be used to guide one in the selection and development of sensors. Ideas from the optimal statistical design of experiments together with the present model expressed in the form of a Kalman filter have been successfully used (58) to select those combinations of existing or hypothetical sensors which would maximize the information that could be obtained on the states of the polymerization system. Both the type of sensors and the precisions necessary for them are easily investigated in this way. By changing the choice of the measurement matrix and... 

Optical methods are a perfect tool to characterize interaction processes between a sensitive chemical or bio polymer layer and analytes1. Time-resolved measurements of this interaction process provide kinetic and thermodynamic data. These types of sensors allow the monitoring of production processes, quantification of analytes in mixtures and many applications in the area of diagnostics, biomolecular interaction processes, DNAhybridization studies and evenprotein/protein interactions2,3. 

Enzymes can be used not only for the determination of substrates but also for the analysis of enzyme inhibitors. In this type of sensors the response of the detectable species will decrease in the presence of the analyte. The inhibitor may affect the vmax or KM values. Competitive inhibitors, which bind to the same active site than the substrate, will increase the KM value, reflected by a change on the slope of the Lineweaver-Burke plot but will not change vmax. Non-competitive inhibitors, i.e. those that bind to another site of the protein, do not affect KM but produce a decrease in vmax. For instance, the acetylcholinesterase enzyme is inhibited by carbamate and organophosphate pesticides and has been widely used for the development of optical fiber sensors for these compounds based on different chemical transduction schemes (hydrolysis of a colored substrate, pH changes). 

Using the principles of biological olfaction, electronic nose systems contain arrays of different types of cross-reactive vapor-sensitive sensors. While it is difficult to discriminate analytes entirely by their responses to a single type of sensor, using an array of sensors yields response patterns that can readily distinguish many different vapors. Ideally, the response mechanisms of the sensors are highly varied and encompass both physical and chemical phenomena1. 

This type of sensor often does not have a membrane it instead utilizes the properties of a water-oil interface, a boundary between an aqueous and a non-aqueous (organic) phase. Traditionally, sensors based on non-equilibrium ion-selective transport phenomena were distinguished as a separate group and considered as the electrochemistry of the ion transfer between two immiscible electrolyte solutions (IT1ES). Here, we will not distinguish polymeric membrane electrodes and ITIES-based electrodes due to the similarity in the theoretical consideration. 

Theoretical insight into the interfacial charge transfer at ITIES and detection mechanism of this type of sensor were considered [61-63], In case of ionophore assisted transport for a cation I the formation of ion-ionophore complexes in the organic (membrane) phase is expected, which can be described with the appropriate complex formation constant, /3ILnI. 

Hydrogen delivery infrastructure requires sensors for detecting hydrogen leaks and monitoring pipeline integrity. A brief discussion for each type of sensor technology is given in Sections 10.2.4.1 and 10.2.4.2. 

Another type of sensor was based on the utilization of glucose dehydrogenase enzyme coupling with /ra(2,2 -bipyridylruthenium(II) complex [31]. This sensor can be used in the 10-2500-pmol/L concentration range. Several interferences occur, like NADH, oxalate, proline, and tripropylamine. However, gluconic acid and NAD+ do not interfere. 

More details on appliance markets are given in Chapter 2, together with some data on the sensors in question. There has been some recent research into the markets of modern micromechanical sensors in household appliances, documenting the market potential for various types of sensors in this area, including those for pressure, acceleration and tilt, thermopiles, flow and gas sensors [3]. Examples of future developments will also be given. 

Gas sensors are a new type of sensor for which there is an increasing demand. We include a description of state-of-the-art-gas sensors in Chapter 5.3. 

Appliance Monitored function Type of sensors used today... 

There are also some types of sensors that use the amperometric as well as the potentiometric principle. These seem to have an even higher potential for the application in surveillance and control of small performance combustion systems. With the knowledge of the strength and weakness of either principle, these sensors have been developed specifically for use in small systems. One example of these is given in Fig. 3.20. 

For each type of sensor, a classification framework sets precision tolerance ratings. Platinum temperature sensors have a positive temperature coefficient which is defined as ... 

Appliance Variable measured Type of sensors used... 

The operating principles of the reviewed interferometers are well studied. However, by no means these devices are matured. For example, a mode-selective, wavelength-independent and environmental-resistant 3-dB core-cladding mode coupler is yet to be found to construct an ideal CCMI. As technology advances and research continues, we expect that more device structures will be explored and new methods will be investigated to fabricate these devices. Although the applications of these two types of sensors are yet to be explored, it is almost certain that they will find their way into real-world applications in the future. 

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