Radiation type sensor

In a large obstructed area where there will be turbulence, the only type sensor available is a radiation type sensor because of the increased speed of the flame propagation. 

The detector best suited to meet these conditions is a radiation type sensor. Ultraviolet (UV), infrared and visible radiation are generated when combustion produces a flame and all three types of radiation sensors respond to the radiation from the flame. 

The interaction phenomenon of the analyte with radiation is governed or modifies the principle on which light is transmitted through the waveguide. Depending on that interaction, we can differentiate three basic types of intrinsic optical sensors [82] refractive-index-type sensors, luminescence-based sensors and absorption-type sensors. 

When detecting the interface between two liquids, electrical conductivity, thermal conductivity, opacity, or sonic transmittance of the liquids can be used. Interface-level switches are usually of the sonic, optical, capacitance, displacer, conductivity, thermal, microwave, or radiation types. Differential pressure transmitters can continuously detect the interface, but, if their density differential is small relative to the span, the error will be high. On clean services, float- and displacer-type sensors can also be used as interface-level detectors. In specialized cases, such as the continuous detection of the interface between the ash and coal layers in fluidized bed combustion chambers, the best choice is to use the nuclear radiation sensors. 

Calcium-phosphate-type sensors are essentially unaffected by large doses of Co-gamma radiation (11) and thus the corresponding uranyl phosphate, and possibly neutral carrier types, should be immune to the very modest doses of internally generated uranium radiation. 

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. 

In practice, surface modifications are restricted to sensors of the ATR- or FEWS-type. For other transducer layouts, the sample - radiation interaction is less localised, making a modification difficult to impossible. Depending on the analytes and the environment of the sensor, two basic surface modification strategies can be used to enhance the function of vibrational spectroscopic optical chemical sensors. The functional layers can either be... 

The sensor systems outlined in the present chapter use evanescent electromagnetic radiation to monitor various analytes in aqueous solutions. Therefore, as a beginning, the basic properties of evanescent electromagnetic waves and the so-called TIR phenomena are summarized. Afterwards, two types of waveguide modes will be briefly discussed guided and leaky modes, which both generate evanescent waves at a solid/liquid boundary. 

Type of Interior Sensor Passive infrared (PIR) Presently the most popular and cost-effective interior sensors. PIR detectors monitor infrared radiation (energy in the form of heat) and detect rapid changes in temperature within a protected area. Because infrared radiation is emitted by all living things, these types of sensors can be very effective. 

Fibre optic-based flow-through optical biosensors The dramatic advances in fibre optic development in die last decade have promoted construction of sensors where radiation, whether emitted, transmitted or reflected, is conducted fi-om the sample to the detection system. The wide variety of available optical waveguide types (solid rods, hollow cylinders, micro-planar geometries) has been used with varying success in sensor development. 

This is illustrated in Figure 7.28. Seven different surfaces (red, green, blue, yellow, cyan, magenta, and white) were illuminated by a black-body radiator of different temperatures. A camera that responds only to wavelengths Xr = 450 nm, Xg = 540 nm, and Xb =610 nm is assumed. The temperature of the black-body radiator was varied from 1000 to 10000 K in steps of 20%. We see that the log-chromaticity differences form a line for each surface. The direction of the lines only depends on the type of sensors used in the camera. 

In several renewable energy processes, including the concentrating solar collectors, boilers, and combustion systems, the accurate measurement and control of high temperatures are required. These (over 1,000°C) temperatures are most often detected by thermocouples (types B, C, R, and S) and by optical and IR-radiation pyrometers. These devices are only briefly mentioned here, because they will be discussed in detail later. Here, the emphasis will be on some of the other high-temperature detectors such as sonic and ultrasonic sensors. 

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