Types of Sensing Systems

we may class sensors according to the activity required of the sensing system. Hence a system may be passive, active, or semiactive. Passive sensors 

Trace Chemical Sensing of Explosives, Edited by Ronald L. Woodfin Copyright 2007 John Wiley Sons, Inc. 

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Abstract Cataluminescence (CTL) is chemiluminescence emitted in a course of catalytic oxidation. Since 1990, the present authors and coworkers have observed CTL during the catalytic oxidation of various organic vapors in air. This phenomenon has been applied to the CTL-based sensors for detecting combustible vapors. THE CTL response is fast, reproductible and proportional to the concentration of the combustible vapors of ppm orders in air. Based on two types of models of the CTL, the relationship between the CTL intensity and the rate of catalytic oxidation have been investigated analytically. In this article, the effects of catalyst temperature, gas flow-rate and gas concentration on the CTL intensity are demonstrated. Finally, various types of sensing system using the CTL-based sensor are proposed. The results of discrimination and determination of more than ten types of vapors of various concentrations are shown. 

The next factor to be evaluated is what kind of pressure sensitivity may be expected of this type of sensing system in order to actuate a pressure switch-type mechanism. If a filling pressure of 100 psia at 300 K is assumed for the system shown, then the curve of P vs. V is, of course, a straight line With a sensitivity of. 3 psi/°K. If a 10°K rise is set as the requirement for actuation of the switch, we will have a pres sure change of 3.3 psi or Z,3% of the total pressure with which to perform this actuation. 

From a physiological point of view, uptake systems make sense to a cell only when their substrates are both available in the medium and useful to the cell. As a matter of fact, the expression of the permease structural genes and the activity of the corresponding permeases are controlled and modulated by different types of regulatory systems. 

No doubt, one of the most intuitive classifications of sensors is that based on the type of transducer used to reveal the physico-chemical changes that occur in the sensing microzone in the presence of the analyte. Figure 1.6 shows the principal types of transducing systems eire connected to or... 

Yang, Z., S. Matsumoto, and R. Maeda. 2002. Comparison of dynamic transient- and steady state measuring methods in a batch type BOD sensing system. Sens. Actuat. A 95 274—280. 

The simplest type of vision system is one that senses only along a line. These one-dimensional sensors function best when used to simply detect the presence or absence of an object, and generally make no further attempt at interpretation. Typically, these are used in applications such as automated assembly line counters, where perhaps the number of bottles passing by a particular point needs to be monitored. The light passing from one side of a conveyer belt to a detector on the other side is occluded when a bottle passes by. This break in the light signal is then recorded electronically and another unit is added to the total count. 

While in most applications heat pipes operate in a passive manner, adjusting the heat flow rate to compensate for the temperature difference between the evaporator and condenser [37], several active control schemes have been developed [38]. Most notable among these are (1) gas-loaded heat pipes with some type of feedback system, (2) excess-liquid heat pipes, (3) vapor-flow-modulated heat pipes, and (4) liquid-flow-modulated heat pipes [9], In one such pipe, a temperature-sensing device at the evaporator provides a signal to the reservoir heater, which when activated can heat the gas contained in the reservoir, causing it to expand and thereby reducing the condenser area. 

We can conceptualize this control system as a loop (Figure 4.4.4). The input level is sensed, the control system acts on the input level, and this, in turn, changes the input level. This type of control system is caWedfeedback control, because information about the output of the system is fed back to the input in order to maintain stability. 

In a chemical sense, what relates molecular subunits with their assembly product To answer this question precisely is to define self-assembly. From a qualitative standpoint, we can state that the two sets of molecules are related by a complex series of intertwining equilibria some of them dead-ends, some of them leading as directly to the assembly product as possible. As a step toward analyzing this type of complex system, we recently described a general, semiquantitative analysis of self-assemblies. This probabilistic approach" focuses on the options available to each molecular subunit as the assembly occurs and engenders a common frame of reference by which the efficiency of all assemblies leading to discrete species can be compared. 

The effects of experimental conditions e.g., temperature, H2 pressure, type of experimental system, contact time, type of catalyst, origin of feed, etc.) on catalyst performance can be quantified by kinetic measurements. For a series of catalysts varying widely in composition and structure, kinetie parameters determined under identical conditions are of partieular importance. Such a database is suitable for a direet comparison of the eatalyst performance. Otherwise, this is prevented when the parameters were obtained under conditions different from what is usually the case of many studies published in the scientific literature. Then, kinetie parameters refleet speeifie eonditions applied in a particular study. Therefore, eaution is required when using such information in a more general sense. 

That the method can reveal hardness anisotropy in nonmetallic materials, even if neither example might be considered to be a ceramic in the accepted sense, is shown in Figure 3.18. In order to achieve these results the temperature had to be elevated so that untorn grooves were produced. The two materials used, LiF and Cap2, are examples of the two types of slip system mainly encountered in cubic ceramics, as Table 3.1 shows, and clearly they are the converse of each other, as Fig. 3.18 clearly shows. This method is worthy of development. 

There are two ways by which OP/FT-IR spectra can be measured bistatic and monostatic. For bistatic OP/FT-IR measurements, the source is located at one end of the optical path and the detector is located at the other end. Two types of bistatic systems can be distinguished. In the first (shown in Figure 22.3a), the radiation from the source is modulated by the interferometer before being expanded by a telescope and passed over the path of interest. The beam is collected by a second telescope and focused onto the detector. This design has the advantage that the electronics only sense the signal that has been modulated by the interferometer any stray radiation reaching the detector is unmodulated and hence is not sensed (see below). This very real benefit is offset in practice by the fact that the detector... 

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