UV sensor

Semiconductor High-power transistors High-power microwave Photovoltaic elements Field-effect transistors UV sensors... 

Application areas for UV sensors in the household environment are introduced and the technological requirements and challenges of UV-sensing discussed. Different detection technologies with their strengths and weaknesses are explained. Finally, reasons that limit the use of UV sensors in household appliances are discussed and way outs are lined out. 

Apart from a few applications, such as UV disinfection and lacquer hardening, the intensity of UV radiation is well below that of visible light in ambient daylight or indoor lighting. A UV sensor must therefore be insensitive to visible light, otherwise the detection signal would easily be drowned out by the visible fraction of the radiation spectrum. Sensors that fulfill this requirement have a selective spectral sensitivity in the UV range. There are two important selectivities, known as visible-blindness and solar-blindness. 

A visible-blind UV sensor detects radiation only below A = 400 nm and thus is sensitive to the UV radiation of sunlight A solar-blind sensor does not react to sunlight and usually detects radiation below A = 300 nm. An outside fire alarm sensor imposes one of the most stringent requirements for solar-blindness. It must be sensitive to 100 pW/cm2 or less between 220 nm and 300 nm but should not react to direct sunlight that gives 100 mW/cm2 between 320 nm and 720 nm. 

Visible- or solar-blind UV sensors can be made from a Si photodiode by additionally using an optical filter that transmits UV radiation only, see below. A more detailed explanation of the physics of UV photodiodes (made from Si as well as from other semiconductor materials) can be found in Ref. [1]. 

A medically reliable UV sensor should have a spectral responsivity that closely follows the erythemal curve between 390 nm and 290 nm. So far, a photodiode with this specific sensitivity has not been available. Modeling the erythema spectrum with the help of filters also delivered only poor results. In fact, most available sunburn detectors vary in their spectral responsivity and may therefore only be used as an indicator for the actual UV charge. 

A popular UV sensor designed for flame monitoring is the SFH 530 sensor by Infinion. It is a UV-enhanced Si photodiode with optical filter, concentrator lens and operational amplifier in a TO-39 package. Flame-sensing in gas ovens is another potential application of the described technique. 

So far, UV sensors have been rarely seen in households although a small proportion of the applications described can be found. Sometimes other sensing methods are used (as in flame controlling) although they are less suitable from the technological point of view or they are simply omitted (as monitoring of sunbeds). Often, the major reason is the high price of the sensor. 

Sufficiently cheap UV photodiodes are available but they are not visible-blind. Filters have to be used, but they raise the costs. Sufficiently selective photodiodes are also available but they are too expensive, mainly due to their only recently established technology. The sensor costs have been a limiting factor in two application fields of UV sensors, namely water disinfection and combustion monitoring, on the industrial as well as on the household scale. 

In power stations or other combustion units above a capacity of, say, 1 MW, UV sensors for flame monitoring are not unusual. Here, even combustion parameters like the air or fuel supply are controlled by sensing the UV emission spectrum of the flames. 

To make a breakthrough in household appliances and other consumer product markets UV sensors have to become significantly cheaper while spectral selectivity as a major key feature must be guaranteed. Most of today s UV photodiodes are made from crystalline semiconductor materials. The cheaper materials (Si) lack spectral selectivity, and the wide band gap materials are very expensive. What they all have in common their top performance regarding sensitivity and speed. Crystalline photodiodes have risetimes of often below 1 s. However, the described processes to be sensed here are not faster than some milliseconds or even much slower. In order to obtain a reasonably-priced SiC or GaN photodiode, the photoactive area is often reduced to below 1 mm2 and barely fills the sensor housing. So far, the top sensitivity offered by the semiconductor has been sacrificed for a competitive... 

Improved UV sensors for tanning appliances as a protection against overexposure to UV radiation... 

Safety and security Temperature Toxic gases like CO, CO2, exhaust gases, smoke,. .. Combustible gases like CH4, C2H6 (gas detection via flame detection (Europe), fire detectors, caravans with gas detectors) UV sensors Radon sensing... 

Fabrication of the prototype is an important step in product development. It demonstrates that the various components can indeed be physically integrated to form the final product with the desired functionalities. Consider a UV sensor. While its functionality depends on the physical response of a certain nanomaterial in the presence of UV light, an electric circuit and a display system are required for a functional consumer product. The availability of a prototype is essential in test marketing, safety tests, reliability tests and so on. However, the development of consumer-oriented products often involves a considerable amount of trial-and-error, which can lead to costly delays in product launching [10]. 

In a closed-loop control circuit, a UV sensor is used to monitor the radiant power of the lamp. In a control unit, the signal is compared with a preset signal or with a signal provided by a tachometer. The resulting difference in the signal is magnified and used to control the lamp current by transductor or thyristor switches. An example of a control system is in Figure 3.11. 

There are shortcomings in this work, however, and we expect to solve these soon. Adsorption is a slower process than most of us realize (25), and at 25°C the adsorption of pyridine onto iron oxide takes about three days to reach equilibrium. The results of Figure 7 with pyridine and those with triethylamine were obtained in about one hour. However Fm was the same for the two temperatures, for the slopes are exactly equal for the two lines. We are now using a flow microcalorimeter to measure the evolution of heat upon adsorption and we are adding a UV sensor to detect concentration changes this combination should give accurate heats of adsorption and desorption. We will then be able to compare these direct measurements of heats of adsorption with those obtained from the temperature coefficients of adsorption isotherms. 

The measurement and control of UV/VIS radiation and/or the quantification of the photon flow (Dp of an industrial lamp is of vital importance to AOP developments. It can also be aciiieved by using radiometers or UV sensors (McCluney, 1994). Moreover, it is essential to determine the UV/VIS absorbance spectrum of the water or air to be treated by UV spectroscopy prior to further research and development efforts. 

I the technology is easily automated by UV monitoring with UV sensors and it is user friendly, safe and rehable to operate ... 

The visible and infrared sensors are fast, but are subject to many false signals from artificial light, sunlight, hot bodies and other heat producing bodies. The ultraviolet (UV) sensor is fast in response and is affected by few extraneous signals which are controllable. The UV sensor must be the type that only responds to a narrow band of UV, from 1850 Angstroms to 2450 Angstroms. 

Let s examine a basic UV system that incorporates this Automatic self-examination feature. UV from an exploding fireball will enter the optical surface of the UV sensor and generate a voltage signal to cause the controller s relay to actuate and... 

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