What is a sensor

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Defining the word sensor is far from easy. Because a sensor is currently regarded by many as the magic key to a number of doors, the term is very often used improperly. No doubt, the personal bias of the many authors who have provided a definition for sensor has fostered the wide variety of existing interpretations. Thus, some consider a sensor to be a wavelength at which the absorbance of an analyte or reaction product is measured. Others have an even vaguer idea and call an FIA assembly a sensor, for example. 

There are two complementary definitions of sensor based on its operation-use and composition (structure). Thus, a sensor can be defined as a miniature analytical device (not an instrument or an apparatus) that responds to the presence and/or concentration (activity) of an analyte-species and, according to Fig. 1.4  

Based on its structure, a sensor is an analytical device consisting of two main parts a (bio)chemical microzone (recognition element) that is brought into contact with the sample and closely associated (connected or integrated) 

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In order to show how the properties of the cavity can be used to develop a chemi-cal/biological sensor, the nature of sensor needs to be outlined. What is a sensor In simplistic terms, it is a device that is equipped with proper electronics to quantify changes in a given state of a system. It may be an accelerometer of an automobile, emission gas temperature of a jetliner, environment, bio-metabolism of living bodies, space storms, etc. What is required is a way to detect subtle changes. ... 

Control Engineering [Online], What is a smart sensor Available http //resource.controleng.coin/article/CA6296119. html, accessed 30 June 2009... 

It should be evident from the above arguments that the term quartz crystal microbalance is a misnomer, which could (and indeed has) lead to erroneous interpretation of the results obtained by this useful device. It would be helpful to rename it the quartz crystal sensor (QCS), which describes what it really does—it is a sensor that responds to its nearest environment on the nano-scale. However, it may be too late to change the widely used name. The QCM or its analogue in electrochemistry, the EQCM, can each act as a nano-balance under specific conditions, but not in general. 

It would not be sufficient to see sensors merely as some kind of technical sensing organs. They can be used in many other fields besides just intelligent machines. A modern definition should be comprehensive. Actually, there is still no generally accepted definition of the term. On the other hand, it seems to be rather clear what we mean when we talk about a sensor. We find, however, differences regarding whether the receptor alone is a sensor or whether the term encompasses the complete unit containing receptor plus transducer. 

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. 

Such tight mixture control is beyond the capability of the traditional carburetor. Consequently, after sorting through a number of alternatives, industry has settled on closed-loop-controlled port-fuel injection. Typically, an electronically controlled fuel injector is mounted in the intake port to each cylinder. A sensor in the air intake system tells an onboard computer what the airdow rate is, and the computer tells the fuel injectors how much fuel to inject for a stoichiometric ratio. An oxygen sensor checks the oxygen content in the exliaust stream and tells the computer to make a correction if the air/fuel ratio has drifted outside the desired range. This closed-loop control avoids unnecessary use ot an inefficient rich mixture during vehicle cruise. 

What is novel is the manner in which they are tied together. In IP, new nondestructive evaluation sensors are used to monitor the development of a materials microstructure as it evolves during production in real time. These sensors can indicate whether the microstructure is developing properly. Poor microstructure will lead to defects in materials. In essence, the sensors are inspecting the material on-line before the product is produced. 

In order to evaluate system performance it is useful to plot SR as a function of fo. This may be compared to simulations or model predictions and deviations indicate that there are problems. When this occurs, what are the diagnostics that can be examined There is a great deal of information in the wavefront sensor measurements and provision should be made to store them. Zemike decomposition of the residuals helps to identify if there are problems... 

For what is an apparently straightforward problem, wavefront sensing has produced a large number of apparently quite different solutions (for example the Shack-Hartmann (Lane and Tallon, 1992), curvature (Roddier, 1988) and pyramid (Ragazzoni, 1996) sensors). Underlying this diversity is the problem... 

The key recognitive skill required to carry out the above tasks is the formation of a mental model of the process operations that fits the current facts about the process and enables the operators to correctly assess process behavior and predict the effects of possible control actions. Correct mental models of process operations have allowed operators to overcome the weakness of lost sensors and conflicting trends, even under the pressure of an emergency (Dvorak, 1987), whereas most of the operational mishandlings are due to an erroneous perception as to what is going on in the process (O Shima, 1983). 

This book appears at a moment when one of the major developments of the last century in analytical chemistry, measurement science, is coming to its full maturity. The past hundred years have shown an enormous expansion in measurement activities what is measured, the purpose of the measurements, the use of measured data, and the demands placed upon these data. From the initial, almost exclusive, use of chemical reactions to make measurement the field became wider. Introducing physical and biological reactions and sensors has enormously extended the scope of analytical chemistry. 

As stated above, the beginning of optical pH sensor technology remains hidden. What is nowadays refered to as a sensor layer was formerly mostly refered to as a test strip, a dry reagent chemistry, or an immobilized reagent. 

If the allelochemical is hydrophylic, it cannot enter into the cell and act from outside by binding with chemoreceptors. The compounds from allelopathically active plants may serve as chemosignals and their signalling occurs via alternative pathways (i) Chemoreceptor (sensors) — transducers (G-proteins) —> secondary messengers (Ca2+, cyclic AMP or GMP, inositol triphospate, etc) —> organelles or (ii) Chemoreceptor (sensors) —> ion channels —> action potential organelles, or (iii) Chemoreceptor (sensors) —> ion channels —> cytoskeleton— organelles (Roshchina, 2005 a). What is the effect of acted allelochemical on the pathways, could be analysed to study the effects of substances on separate sites of the transduction chain. 

Unfortunately, most of these applications are designed for their specific tasks only. There is currently no software architecture that integrates them into a network that would enable intelligent interaction between them. This is where the future lies. For example, a sensor could recognize the opening of a window and make the heating control of a radiator shut down. The same information about the window could also be built into a security system that would then check what caused the window to open. An alarm would be set off if the person who opened it is not recognized. 

Kotlikoff Coming back to the context of RyRs coexisting with InsP3 receptors, how do you conceive of this system working in isolation from the RyR Ca2+ sensor In some ways it is easier to do the experiment to exclude the InsP3 receptors because you can use something like heparin and completely block it, and have some confidence. The alternative experiment to block all RyRs is a little dirtier. What are your thoughts on how this system can exist in waves, and what is the wave transmission speed in the arteries ... 

Abstract This is a short review of how neuronal sensors fit in the broader biological context of animal survival. This may help those involved in the development of engineered sensors to put in perspective their task with what the evolutionary process has achieved. Most of the information reported here is available in the educational field of neuroscience, with mention of some recent relevant findings. I have attempted to place these findings in an evolutionary perspective as it clarifies better the intrinsic role of some of the extraordinary particularities of the biological solutions of neuronal sensors. 

Equations (8.32) and (8.33) describe what we call the normal or no failure operation of the system of interest. The problem of failure detection is concerned with the detection of abrupt changes in a system, as modeled in Eqs. (8.32) and (8.33). Changes in (8.33) will be referred to as sensor failures. The main task of failure detection and compensation design is to modify the normal mode configuration to add the capability of detecting abrupt changes and compensating for them. In order to do that, we need to formulate what is called the failure model system ... 

What is the advantage of a time-resolved fluorescence optical sensor ... 

The natural diffusion of those aromatic compounds and essential oils quickly is detected. What is not observed is the diffusion phenomenon of Brownian motion. The ability to be able to determine which brand of cologne or perfume fragrance is in the immediate environment and how widely it is spread is not easy to be achieved. When a device is able to respond to these fundamental events of change, and is able to signa-turize them, the information retrieved is what basically constitutes a sensor response. 

What mechanisms can be used to create a lifetime-based glucose sensor In our opinion, the mechanism should be fluorescence resonance energy transfer (FRET). The phenomenon of FRET results in transfer of the excitation from a donor fluorophore to an acceptor chromophore, which need not itself be fluorescent. FRET is a through-space interactor which occurs over distances of 20-60 A. 

We will consider all the components of this temperature control loop in more detail later in this book. For now we need only appreciate the fact that the automatic control of some variable in a process requires the installation of a sensor, a transmitter, a controller, and a final control element (usually a control valve). Most of this book is aimed at learning how to decide what type of controller should be used and how it should be tuned, i.e., how should the adjustable tuning parameters in the controller be set so that we do a good job of controlling temperature. 

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