Thermometry techniques

Successful soldering is dependent on several factors including suitable, well-maintained, and controlled reflow equipment good-quahty solderable parts a thermally balanced board designed for the reflow process a well-tested and rehable solder paste a proven time-temperature profile and good thermometry techniques. 

Natrajan VK, Christensen KT (2008) A Two-Color Huorescent Thermometry Technique for Microfluidic Devices. AIAA Paper 2008-0689, pp 1-10... 

The construction and use of these thermometers is given in the references. Also of particular interest is the series of books Temperature Its Measurement and Control in Science and Industry," listed as reference 1 at the end of the chapter. It gives many recent discussions of new thermometry techniques. 

We have remarked that a temperature of zero on the absolute temperature scale would correspond to the absence of all motion. The kinetic energy would become zero. Very interesting phenomena occur at temperatures near 0°K (the superconductivity of many metals and the superfluidity of liquid helium are two examples). Hence, scientists are extremely interested in methods of reaching temperatures as close to absolute zero as possible. Two low temperature coolants commonly used are liquid hydrogen (which boils at 20°K) and liquid helium (which boils at 4°K). Helium, under reduced pressure, boils at even lower temperatures and provides a means of reaching temperatures near 1°K. More exotic techniques have been developed to produce still lower temperatures (as low as 0.001°K) but even thermometry becomes a severe problem at such temperatures. 

Temperatures on ITS-90, as on earlier scales, are defined in terms of fixed points, interpolating instruments, and equations that relate the measured property of the instrument to temperature. The report on ITS-90 of the Consultative Committee on Thermometry is published in Metrologia and in the Journal of Research of the National Institute of Standards and Technology The description that follows is extracted from those publications.3 Two additional documents by CCT further describe ITS-90 Supplementary Information for the ITS-90, and Techniques for Approximating the ITS-90.4... 

This comprehensive review of theoretical models and techniques will be invaluable to theorists and experimentalists in the fields of infrared and Raman spectroscopy, nuclear magnetic resonance, electron spin resonance and flame thermometry. It will also be useful to graduate students of molecular dynamics and spectroscopy. 

For the analysis of the chemical structure of flames, laser methods will typically provide temperature measurement and concentration profiles of some readily detectable radicals. The following two examples compare selected LIF and CRDS results. Figure 2.1 presents the temperature profile in a fuel-rich (C/O = 0.6) propene-oxygen-argon flame at 50 mbar [42]. For the LIF measurements, 1% NO was added. OH-LIF thermometry would also be possible, but regarding the rather low OH concentrations in fuel-rich flames, especially at low temperatures, this approach does not capture the temperature rise in the flame front [43]. The sensitivity of the CRDS technique, however, is superior, and the OH mole fraction is sufficient to follow the entire temperature profile. Both measurements are in excellent agreement. For all flames studied here, the temperature profile has been measured by LIF and/or CRDS. 

Our data can be used to estimate the effective temperatures reached in each site through comparative rate thermometry, a technique developed for similar use in shock tube chemistry (32). Using the sonochemical kinetic data in combination with the activation parameters recently determined by high temperature gas phase laser pyrolysis (33), the effective temperature of each site can then be calculated (8),(34) the gas phase reaction zone effective temperature is 5200 650°K, and the liquid phase effective temperature is 1900°K. Using a simple thermal conduction model, the liquid reaction zone is estimated to be 200 nm thick and to have a lifetime of less than 2 usee, as shown in Figure 3. 

In the past, except for the low-temperature range, the uncertainties of noise thermometry were not comparable to those of the gas thermometry due to the non-ideal performance of detection electronics. Up to now, the most successful technique is the switched input digital correlator proposed by Brixy et al. in 1992 [89], In this method, the noise voltage is fed via two separate pairs of leads to two identical amplifiers whose output signals are multiplied together, squared and time averaged (see Fig. 9.10). 

The possibility of using the Brixy technique for low-temperature thermometry is under study (see e.g. ref. [90]). 

As we have seen in Section 9.5.3, in the case of resistance thermometry, the signal produced by a low-temperature thermometer is very low (microvolt range). Low-pass filters are not sufficient to narrow the detection bandwidth in order to get a suitable signal to noise ratio (S/N). Bandpass filters are needed. The most commonly used method is the synchronous demodulation, usually simply called lock-in technique, as shown in the block diagram of Fig. 10.7. 

Above the freezing point of silver, Tgq is defined in terms of a defining fixed point and the Planck radiation law, and optical pyrometers are frequently used as temperature probes. The Comite Consultatif de Thermometrie gives a thorough discussion of the different techniques for approximation of the international temperature scale of 1990 [2, 4],... 

Droplet temperature is of interest in practical spray processes since it influences the associated heat and mass transfer, chemical reactions, and phase changes such as evaporation or solidification. Various forms of Rayleigh, Raman and fluorescence spectroscopies have been developed for measurements of droplet temperature and species concentration in sprays.16471 Rainbow refractometry (thermometry), polarization ratioing thermometry, and exciplex method are some examples of the droplet temperature measurement techniques. 

At the early stages of development, the lack of a convenient and economic excitation modulation scheme has limited the use of such a phase shift technique in fluorescence thermometry. Now with the wide availability of cheap and easily modu-... 

Perhaps the first detailed discussion of such a technique in fluorescent thermometry (shown in Figure 11.10) was given by Zhang et al. in their work(36) based on both mathematical analysis and experimental simulation. Examples of the electronic design of the corresponding system and the application of the technique in a ruby fluorescence-based fiber-optic sensor system are also listed. This shows that there is no difference in the measurement sensitivity between a system using square-wave modulation and one using sinusoidal modulation. However, the former performs a little better in terms of the measurement resolution. 

Schooley, J. F., Ed., 1982, Temperature—Its Measurement and Control in Science und Industry, Vol. 5, American Institute of Physics, New York. An excellent source of state-of-the-art thermometry comprised of papers from the Sixth International Temperature Symposium. Topics which are covered include temperature scales and fixed points, radiation, resistance, thermocouple, and electronic thermometry, temperature control, and calibration techniques. Preceding volumes in the series date back to 1939. 

Two techniques, which appear well suited to the diagnostic probing of practical flames with good spatial and temporal resolution, are coherent anti-Stokes Raman spectroscopy (CARS) and saturated laser fluorescence. The two techniques are complementary in regard to their measurement capabilities. CARS appears most appropriate for thermometry and major species concentration measurements, saturated laser fluorescence to trace radical concentrations. With electronic resonant enhancement (6), CARS may be potentially useful for the latter as well. Fluorescence thermometry is also possible (7, 8) but generally, is more tedious to use than CARS. In this paper, recent research investi-... 

For the case that there are not too many constituents in the gas under investigation the use of the pure rotational CARS technique (Zheng et al., 1984 Alden et al., 1986) may be superior to vibrational CARS thermometry since the spectra are easily resovable (for N2 the adjacent rotational peaks have a spacing of appr. 8 cm ) compared with the... 

The observed temperature dependence of the absorption cross section of 3-pentanone and the corresponding fluorescence intensity offers the possibility for a new type of temperature measurements.This technique gives access to 2D-temperature distributions between 300 and 1000 K relevant for precombustion conditions that could hardly be assessed with other laser spectroscopic techniques developed for combustion thermometry. By calculating temperatures from the ratio of simultaneously acquired intensity distributions, the measurement is independent on local tracer concentrations. Measurements in inhomogeneously mixed environments are therefore feasible. 

Analytical pyrolysis is considered somehow apart from the other thermoanalytical techniques such as thermometry, calorimetry, thermogravimetry, differential thermal analysis, etc. In contrast to analytical pyrolysis, thermoanalytical techniques are not usually concerned with the chemical nature of the reaction products during heating. Certainly, some overlap exists between analytical pyrolysis and other thermoanalytical techniques. The study of the kinetics of the pyrolysis process, for example, was found to provide useful information about the samples and it is part of a series of pyrolytic studies (e.g. [6-8]). Also, during thermoanalytical measurements, analysis of the decomposition products can be done. This does not transform that particular thermoanalysis into analytical pyrolysis (e.g. [9]). A typical example is the analysis of the gases evolved during a chemical reaction as a function of temperature, known as EGA (evolved gas analysis). 

To reliably perform qualitative and quantitative analyses on body fluids and tissue, the clinical laboratorian must understand the basic principles and procedures that affect the analytical process and operation of the clinical laboratory. These include the knowledge of (1) the concept of solute and solvent, (2) units of measurement, (3) chemicals and reference materials, (4) basic techniques, such as volumetric sampling and dispensing, centrifugation, measurement of radioactivity, gravimetry, thermometry, buffer solution, and processing of solutions, and (5) safety. ... 

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