Field sensors types

Special probe geometries and combinations of different types of magnetic field sensors make an important contribution to the further improvement of the eddy-current testing method and results in new applications. 

So, a comparison of different types of magnetic field sensors is possible by using the impulse response function. High amplitude and small width of this bell-formed function represent a high local resolution and a high signal-to-noise-characteristic of a sensor system. On the other hand the impulse response can be used for calculation of an unknown output. In a next step it will be shown a solution of an inverse eddy-current testing problem. 

Lambeck P.V., Hoekstra H.J.W.M., VanLith J., Van Elzakker G., Two novel integrated optical sensor types for measuring chemical concentrations, based on chemically induced changes of modal field profiles, J. Nonlinear Opt Phys. Mat 2004 13 (2) 209-217. 

Buried-line magnetic field sensors detect changes in a local magnetic field that are caused by the movement of metallic objects within that field. This type of sensor can detect ferric metal objects worn or carried by an intruder entering a protected area on foot as well as vehicles being driven into the protected area. 

Fence-associated sensors. Fence-associated sensors are either attached to an existing fence, or are installed in such a way as to create a fence. These sensors detect disturbances to the fence—such as those caused by an intruder attempting to climb the fence, or by an intruder attempting to cut or lift the fence fabric. Exterior fence-associated sensors include fence-disturbance sensors, taut-wire sensor fences, and electric field or capacitance sensors. Details on each of these sensor types are provided below. 

The most important field of application of this sensor type is the determination of cell fluorescence, which depends on the intracellular NADH/NAD+ ratio and is thus a sensitive measure of the cell state (Harris and Kell, 1985). 

Clearly, electrochemical indication prevails over all other methods of transduction. Potentiometric and amperometric enzyme electrodes are at the leading edge of biosensor technology with respect to the body of scientific literature as well as to commercially available devices (Schindler and Schindler, 1983). Only a few conductometric biosensors have been described, but the relevance of this sensor type may increase because of the relative ease of their preparation and use. Furthermore, the development of biochemically sensitized field effect transistors, being at present only at an initial stage, offers new prospects (Pinkerton and Lawson, 1982). 

In the third part of the book (Chapter 7) we present the different sensor types and show the various fields of application, ranging from engine management to safety systems and all the way to comfort systems. 

Magnetic methods can work similarly to the optical shutter method. A magnetic-field sensor is placed opposite a permanent magnet. With metal teeth on an encoded metal disc, it is possible to shield the magnetic field from the magnetic-field sensor. This kind of sensor is less precise than the optical shutter type because of the stray magnetic field, which has to be taken into account. A product... 

In recent years great progress has been made in the development of embedded sensors and remote data acquisition. Some of the sensors are already well proven in the field, others are highly sophisticated research instruments and not (yet) used on a large scale. In this chapter sensor types are described that do not need any reference electrode to be embedded (essentially macrocell and resistivity sensors). 

This chapter has presented a brief review of the main means and methods for the emerging field of SHM of safety-critical composite stmctures. The different physical principles employed by each approach have been detailed for the various sensor types, which may either focus on a specific (small) area or cover large areas of the structure. Examples have also been presented to illustrate the practical interpretation of the sensor-derived data. Considerable further research is needed, however, to mature the development of SHM sensors and methods to achieve viable practical implementation of this promising new technology. 

The sensors employed in wearable body sensor network systems can be divided into active sensors and passive sensors. There is ambiguity in the classification, and many authors are using the other way around. In the biomedical measurement field, however, the definition of sensor type follows the convention of other electronic instrumentation fields the active sensors are those sensors that require an external power source to convert the input into a usable output signal, while passive sensors are those that intrinsically provide their own energy or derive energy from the phenomenon being... 

Field sensors are used to collect information necessary to determine if an emergency situation exists. The purpose of these sensors is to measure process parameters (e.g., temperature, pressure, flow, etc.) or monitor the process condition/status, used to determine if the equipment or process is in a safe state. Sensor types range from simple pneumatic or electrical switches to smart transmitters with on-board diagnostics. These sensors in some applications are dedicated to SIS. Manufacturers approach, in line with lEC 61508 towards the development of sensor, shall include but is not limited to the following ... 

Current source type Here this IS type used because it is the same as the supply and return type IS shown in Fig. X/3.7.3-1B. Blue IS cables are used between field sensor and IS barrier. 

Sensor type and range Principle MAWP (MPa) T(°C) Advantages/I i m itations Fields of application... 

The importance of molecular oxygen sensing is unquestionable, given the role this species plays in nature. According to the required application field, different sensor types have been developed through the years, whether for measurements in the gas-phase or in liquids [82-84]. From the very beginning, silicones have been present in the fabrication of oxygen sensors. The amperometric Clark electrode for waterborne Oj measurements, developed in 1956, was basically formed... 

This chapter is dedicated to the origin, design, calibration, and use of in situ field fluor-ometers. It will serve as a review of considerations to be accounted for during the operation of fluorescence field sensors and call attention to areas of concern when making this type of measurement. Attention is also given to ways in which in-water fluorescence measurements have revolutionized biogeochemical studies of CDOM and how those measurements can be used in conjunction with remotely sensed satellite data to understand better the biogeochemistry of DOM in aquatic environments. 

The selective redection of chiral nematic Hquid crystals has also been used to develop sensors for pressure, radiation (especially infrared), wind shear over surfaces, stmctural fatigue, and foreign chemical vapor (48). Other types of Hquid crystals have been used to make sensors to measure both electric and magnetic fields. 

Fig. 8. Reluctance-type pressure sensor. The E-cote corresponds to the area where the magnetic fields ate produced.

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