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Đo nhiệt độ P5
Semiconductor Thermometers Classification of Semiconductor Thermometers Semiconductor thermometers (Sachse, 1975) are made from materials which are neither conductors nor insulators. Research of the thermal properties of semiconductors was first reported by William Faraday in 1834. Their industrial production was started at the Bell Telephone Company and, simultaneously, at Osram in 1930. It is apparent from the work of many authors such as Sze (1969) and van der Ziel (1968), among others, that these materials may have an intrinsic, or pure form, a compound form or a doped form. Compound and doped semiconductors are often called extrinsic semiconductors ....
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Đo nhiệt độ P6
Fibre Optic Thermometers Properties of Optical Fibres Dielectric opticalfibre, which is also referred to as a light guide, is composed of a rod core surrounded by a sheath as shown in Figure 6.1 . The core, which conducts the electromagnetic wave, has a refractive index, nj , while the sheath, which contains the wave within the core, has a refractive index, n2 . To ensure that the wave is contained in the core it is necessary that the condition nj n2 is satisfied. The electromagnetic waves incident on the front part of the optical fibre, within the angle cone, 2a,...
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Đo nhiệt độ P7
Pyrometers Classification and Radiation Laws Classification of Pyrometers The simplest and oldest non-contact way of estimating the temperature of a radiating body is by observing its colour. Table 8 .1 summarises the relationship between temperature and colour . Using this method, experienced practitioners can estimate temperatures over about 700 °C, with a precision sufficient for simpler heat-treatment processes . This is shown in a witty way in Figure 8.1, which is taken from Forsythe's paper (Forsythe, 1941) . It was presented at the historical Symposium on Temperature in November 1939, a symposium that was a milestone in further development of thermometry...
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Đo nhiệt độ P8
Manually Operated Pyrometers Disappearing Filament Pyrometers Principle of operation The first disappearing filament pyrometer was built in 1901 by L. Holborn and F . Kurlbaum (Holborn and Kurlbaum, 1903) . Disappearing filament pyrometers are spectral pyrometers where the brightness of a lamp filament is changed by adjusting the lamp current until the filament disappears against the background of the target, whose temperature is to be measured. In pyrometers of this kind, the eye of the observer is itself the detector . In another seldom applied type of pyrometer the brightness match is achieved by the attenuation ofthe target brightness, using a neutral grey...
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Đo nhiệt độ P9
Optical Systems All of the types of automatic pyrometers, listed in Section 8.1 and shown in Figure 8 .2 are considered in this chapter. To reach a sufficiently high measurement precision, the radiation emitted by the body under measurement is concentrated on the radiation detector by lenses, light-guides or mirrors . Thus, they also reduce the pyrometer viewing angle and consequently the necessary object diameter . It its also essential that the pyrometer optical system should be able to aim properly at the target . ...
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Đo nhiệt độ P10
Practical Applications of Pyrometers When describing different types of pyrometers in Chapters 9 and 10 it was assumed that they operate in ideal conditions . Pyrometer readings, which are measurements of the true target temperature, Tt , are strongly influenced by real, practical, industrial operating conditions as shown in a simplified way in Figure 11 .1 . These measurements, which must account for target emissivity, E (Tt) or E,L (T), in the environment of the surrounding walls of temperature, Tom with emissivity, cw(TW), or, sxw(TW ), are taken in the presence of polluted atmosphere of temperature, Ta , having the equivalent...
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Đo nhiệt độ P11
Conditioning of Temperature Sensor Output Signals Temperature is a physical variable characterising the flow of heat energy. A temperature measurement process attaches real numbers to the degree of hotness of bodies . Although it can only be measured by suitable sensors the output of these components needs to be presented to the human observer by indicators, recorders or other instruments . To accomplish this further task it is necessary to transform the temperature signal, which is in the thermal energy domain, into another more convenient energy form. Transforming to electrical signals is the most convenient for these purposes ....
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Đo nhiệt độ P12
Computerised Temperature Measuring Systems Trends in Process Instrumentation In contemporary industrial processes, the measurement of temperature is one of the most frequently conducted operation among all of the other various physical variables that need to be measured. Current process instrumentation and measurement techniques show an inexorable trend in the use of a wide array of sophisticated procedures, including the capture and advanced algorithmic processing of multi-channel data. This trend is reflected in temperature measurement technology, so that typical temperature measurement circuits are now being replaced by computer-based data acquisition and processing systems ....
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Đo nhiệt độ P13
Imaging of Temperature Fields of Solids Infrared thermal imaging of temperature fields has become an extremely versatile and popular method of real time temperature measurement and thermal condition monitoring in all industrial and research applications. In the near future, the rapid further development of the method is more than guaranteed, as it will replace many existing temperature measuring methods, offering exciting new opportunities with the added most important benefit of a two-dimensional look at problems. The first marketed infrared imagers were based on the use of an opto-mechanical scanning system to sequentially scan the target surface ....
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Đo nhiệt độ P15
Dynamic Temperature Measurement General Information The term dynamic temperature measurement covers all measurements during which thermal transients occur in a sensor irrespective of whether the transient is caused by temperature variations in the medium, whose temperature is to be measured, or in the temperature sensor, itself. Thus, unavoidable dynamic errors occur during the measurement of any temperatures, changing with time. Errors also arise during the temperature measurement of a medium at a constant temperature using a temperature sensor immersed in the medium. Determination of the dynamic errors of a thennometer, requires knowledge of its dynamic properties....
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Đo nhiệt độ Phần 15
Temperature Measurement of Solid Bodies by Contact Method One of the most frequently encountered problems in temperature measurement is measuring the temperature of solid bodies on their surfaces in contact with a surrounding gas or liquid . This may be solved by either contact or non-contact methods. Semi-contact or quasi-contact methods may also be used. Roeser and Mueller (1930) have previously discussed the problem . The non-contact, or pyrometric, methods are described in detail in Chapters 8 to 11 . For a rough estimation of surface temperatures, temperature indicators, described in Section 2.5 are also used. The problem of measuring the...
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Đo nhiệt độ P16
Temperature Measurement of Fluids Low Velocity Gas Contact sensors Assume that a gas, with a temperature, T., flows in a tube with a flow-velocity below about 20 m/s, as shown in Figure 17.1(a) . In the tube there is a sheathed sensor, whose sensitive part, at temperature, TT , is placed in the sheath bottom. This case corresponds to a thermocouple with the measuring junction welded into the sheath bottom . Also let the temperature ofthe internal surface ofthe tube wall be TW , while the length to diameter ratio of the sensor sheath is assumed to be so large that...
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Đo nhiệt độ P17
Temperature Measurement of Transparent Solid Bodies Pyrometric, Contactless Method All solid bodies which partially or totally transmit thermal radiation in the wavelength of visible and infrared radiation, are classified as transparent bodies . The notation used to consider pyrometric methods for measuring the surface temperature of solid bodies has already been introduced in Section 8.2. It will be recalled that solid bodies, which have a transmission factor limited to a = 0, are non-transparent bodies in the whole range of wavelengths used in optical pyrometry . The same notation will be used in this chapter....
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Đo nhiệt độ P18
Temperature Measurement of Moving Bodies The method of measuring the temperature of moving bodies depends upon the character of the movement. For instance, in the flight of rockets, meteorological probes or satellites the only possible way is by wireless signal transmission. Another group of techniques, covering the temperature measurement of bodies in oscillatory or rotational movement will be discussed in detail in this chapter. As the simplest method of temperature measurement of rotating bodies uses pyrometric techniques this possibility should be the starting point ofall analytical considerations ....
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Đo nhiệt độ P19
Temperature Measurement in Industrial Appliances The majority of industrial appliances, and especially industrial heating appliances are equipped not only with temperature measurement and recording installations, but also with temperature control systems. The control systems are necessary for optimal, or at least correct, operation of technological processes such as heat treatment of metals, ceramic firing, sintering, melting, drying etc . For these reasons it has been decided to treat also the problems of temperature measurement for control purposes in this chapter . Such an approach is also justified by the common practice ofusing one temperature sensor, either as a single or double...
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Đo nhiệt độ P20
Temperature Measurement in Medicine Temperature measurement of the human body provides crucial information on its condition in various kinds of illness, on its physiological functions as well as on possible menacing diseases. Already by the time ofHippocrates in Vth and IVth century BC, fever was always connected with an illness . The development of thermometry in the XV111th and XIXth century, which enabled the measurement of human body temperature, was introduced by the German physician Carl Wunderlich as a routine procedure (Daneman, 1992) ...
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Đo nhiệt độ P21
Calibration and Testing of Temperature Measuring Instruments Definitions and Terminology The following main terms are used in the calibration and testing of temperature measuring instruments, necessary for the maintenance and dissemination of ITS-90 . Calibration of a thermometer is the sum of activities concerned with the determination of its thermometric characteristics. These characteristics define the function correlating the chosen property of the thermometer with the temperature. If a thermometer directly indicates the measured temperature, its calibration depends on correlating certain numerical values with the scale graduation . For example, this concerns liquid-in-glass thermometers ...
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Áp dụng DSP lập trình trong truyền thông di động P1
Edgar Auslander and Alan Gatherer This book is about two technologies that have had, and will increasingly have, a significant impact on the way we all live, learn and play: personal wireless communications and signal processing. When it comes to both markets, history has shown that reality has often surprised the most optimistic forecasters. We draw on the experience of experts from MIT, Berkeley, UCLA, Worcester Polytechnic Institute, INRIA, Authentec, Radioscape, Geovector and Texas Instruments, to give a description of some of the important building blocks and implementation choices that combine both technologies, in the past and in the future. ...
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Áp dụng DSP lập trình trong truyền thông di động P2
Programmable Digital Signal Processors (DSPs) are pervasive in the second generation (2G) wireless handset market for digital cellular telephony. This did not come about because everyone agreed up front to use DSPs in handset architectures. Rather, it was a result of a battle between competing designs in the market place. Indeed, the full extent of the use of programmable DSPs today was probably not appreciated, even by those who were proposing DSP use, when the 2G market began to take off. In this chapter we present the argument from a pro-DSP perspective by looking at the history of DSP use...
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Áp dụng DSP lập trình trong truyền thông di động P3
Third generation (3G) mobile radio standards are the result of a massive worldwide effort involving many companies since the mid-1990s. These systems will support a wide range of services, with voice and low rate data to high data rate services up to 144 Kbps in vehicular outdoor environments, 384 Kbps in pedestrian outdoor environments, and 2 Mbps in indoor environments. Both circuit and packet switched services with variable quality of service requirements will be supported.
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Áp dụng DSP lập trình trong truyền thông di động P4
Third generation (3G) cellular systems will be based on Code Division Multiple Access (CDMA) approaches and will provide significant data services as well as increased capacity for voice channels. This results in considerable computational requirements for 3G base stations. This chapter discusses an architecture that provides the needed computation together with significant flexibility. At the same time, this approach is one of the most cost effective known. Based upon a Texas Instruments TMS320C64xe as the core DSP, the architecture utilizes three Flexible Coprocessors (FCPs)...
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Áp dụng DSP lập trình trong truyền thông di động P5
The increasing demand for communications services and the desire for increased data throughput in modern communications systems has fueled research and development into the use of adaptive antenna arrays. Since frequency bandwidth is in short supply and is expensive to acquire, the ability to separate users based on their spatial parameters is very attractive for wireless networks. Adaptive antenna arrays offer the ability to increase the Signal-to-Noise Ratio (SNR) of a wireless communication link while at the same time permit the cancellation and removal of co-channel interference. ...
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Áp dụng DSP lập trình trong truyền thông di động P6
The Challenges of Software-Defined Radio Carl Panasik and Chaitali Sengupta The current move to create and adopt third generation (3G) wireless communications standards has raised tremendous expectations among engineers. To some extent, there is a perception that adopting the new standards will result, almost instantaneously, in being able to design a plethora of multi-purpose wireless Internet appliances with features and capabilities far beyond those found in today’s wireless telephones and palmtop organizers. Recent discussion in the industry has suggested that the coming months will bring a kind of super-communications/entertainment appliance....
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Áp dụng DSP lập trình trong truyền thông di động P7
‘‘DSPs take the RISC’’ From the mid-1980s to the mid-1990s, we were in the ‘‘Personal Computer’’ era and CISC microprocessors fuelled the semiconductor market growth (Figure 7.1). We are now in a new era where people demand high personalized bandwidth, multimedia entertainment and information, anywhere, anytime: Digital Signal Processing (DSP) is the driver of the new era (Figure 7.2).
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Áp dụng DSP lập trình trong truyền thông di động P8
Java offers several benefits that could facilitate the use of wireless Personal Digital Assistants (WPDAs) for the user. First, Java is portable, and that means that it is independent of the hardware platform it runs on, which is very important for reducing the cost of application development. As Java can be run anywhere, the development of applications can be done on a desktop without the need of a real hardware platform.
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Áp dụng DSP lập trình trong truyền thông di động P9
Speech coding is at the heart of digital wireless telephony. It consists of reducing the number of bits needed to represent the speech signal while maintaining acceptable quality. Digital cellular telephony began in the late 1980s at a time when speech coding had matured enough to make it possible. Speech coding has made digital telephony an attractive proposition by compressing the speech signal, thus allowing a capacity increase over analog systems. Speech coding standards are necessary to allow equipment from different manufacturers to successfully interoperate, thereby providing a unified set of wireless services to as many customers as possible. ...
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Áp dụng DSP lập trình trong truyền thông di động P10
Access to wireless data services such as e-mail, news, stock quotes, flight schedules, weather forecasts, etc. is already a reality for cellular phone and pager users. However, the user interface of these services leaves much to be desired. Users still have to navigate menus with scroll buttons or ‘‘type in’’ information using a small keypad. Further, users have to put up with small, hard-to-read phone/pager displays to get the results of their information access. Not only is this inconvenient, but also can be downright hazardous if one has to take their eyes off the road while driving....
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Áp dụng DSP lập trình trong truyền thông di động P11
Increased bandwidth for Third Generation (3G) communication not only expands the capacity to support more users, but also makes it possible for network providers to offer new services with higher bit rates for multimedia applications. With increased bit rates and programmable DSPs, several new types of applications are possible for mobile devices, that include audio and video content. No longer will there be a limited 8–13 kbps, suitable only for compressed speech. At higher bit rates, the same phone’s speakers and DSP with different software can be used as a digital radio....
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Áp dụng DSP lập trình trong truyền thông di động P12
Security Paradigm for Mobile Terminals Edgar Auslander, Jerome Azema, Alain Chateau and Loic Hamon As was highlighted in Chapter 1, the mobile phone has become a personal device that has strong potential to morph into a mobile wallet, or a mobile entertainment device. In both cases, merchants or service providers will want to bill for content or service provision. There lies an opportunity for fraud. When your phone only stores names of people you call, there is not much interest in hacking the device; when it contains your credit card information, however, a lot of energy will be spent trying to steal...
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Áp dụng DSP lập trình trong truyền thông di động P13
Many modern electronic services and systems require a reliable knowledge of the identity of the current user, as an integral part of their security protection [1]. Examples include secure access to automated banking services, access to media services, access to confidential or classified information in the workplace, and security of information within handheld devices. The results of a breach of security can be costly both to the customer and the providers of services or systems. For wireless devices to take on significant roles in these securityconscious applications, the devices must provide the mechanisms needed for reliable user identification. ...
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