Inaccurate Temperature Measurements

Barium fluoride [7782-32-8] Bap2, is a white crystal or powder. Under the microscope crystals may be clear and colorless. Reported melting points vary from 1290 (1) to 1355°C (2), including values of 1301 (3) and 1353°C (4). Differences may result from impurities, reaction with containers, or inaccurate temperature measurements. The heat of fusion is 28 kj/mol (6.8 kcal/mol) (5), the boiling point 2260°C (6), and the density 4.9 g/cm. The solubiUty in water is about 1.6 g/L at 25°C and 5.6 g/100 g (7) in anhydrous hydrogen fluoride. Several preparations for barium fluoride have been reported (8—10). 

In the use of temperature measurement for control of the separation in a distillation column, repeatability is crucial but accuracy is not. Composition control for the overhead product would be based on a measurement of the temperature on one of the trays in the rectifying section. A target would be provided for this temperature. However, at periodic intervals, a sample of the overhead product is analyzed in the laboratory and the information provided to the process operator. Should this analysis be outside acceptable limits, the operator would adjust the set point for the temperature. This procedure effectively compensates for an inaccurate temperature measurement however, the success of this approach requires good repeatability from the temperature measurement. 

It is in order to ask, whether basically melting occurs in a certain temperature range, or whether the range arises due to inaccurate thermometric measurement. 

The issue is related to a lack of appropriate hardware. Some of the incidents and accidents that have occurred during shutdown clearly show cases such as inaccurate level measurement in reactors inadequate temperature monitoring in the core because the instrumentation was outside the core and instrumentation and controls focused on power operation and not on outages. 

It is important to realize that barrel temperature measurement with a shallow well can be, and most likely will be, inaccurate. With a well depth of 10 mm, the measured temperature will probably be about 10°C below actual temperature. When air drafts occur around the extruder, the measured temperature can be as much as 25°C below the actual temperature. This is shown in Fig. 4.15. 

Mixing to a preset time does not allow for variations in metal temperature at the start of the mix, for cooling rate or for ingredient addition times. This can result in significant batch to batch variation. When mixing to a predetermined temperature the major limitation is the accuracy with which the batch temperature can be measured. The large heat-sink provided by the maclune often makes temperature measurement inaccurate, though there are now available infrared probe thermocouples that are more accurate. 

A temperature measurement of the process fluid at the electrodes is not transmitted (solution tempefatuFe compensation in control room and lab are inaccurate). 

The glass transition temperature is generally measured- by experiments that correspond to a time scale of seconds or minutes. If the experiments are done more rapidly, so that the time scale is shortened, the apparent Tg value is raised. If the time scale is lengthened to hours or days, the apparent Tg value is lowered. Thus, as generally measured, Tg is not a hue constant but shifts with the time scale of the experiment or observation. Moreover, Tg is masked by experimental difficulties, compounded by multiple and often inaccurate definitions of Tg in the literature. The least... 

A disadvantage of 1ST measurements is that the experiments take time (days to weeks). Also, several experiments at different temperatures are necessary to get information with respect to the kinetics of the exothermic decomposition. Finally, it may take several hours to reach equilibrium after inserting a sample due to the time-lag of the system. Thus the recorded heat effect may be inaccurate. This is a particular disadvantage in the case of rapid reactions. 

Figure 7. Using a theoretically determined equilibrium fractionation to interpret measured isotopic fractionations in a hypothetical mineral-solution system. Three sets of data are shown. The theoretical equilibrium fractionation for this system is indicated by the gray arrow. The first set of data, indicated by circles, closely follow the calculated fractionation, suggesting a batch equilibrium fractionation mechanism. The second set of data (stars) is displaced from the theoretical curve. This may either indicate a temperature-independent kinetic fractionation superimposed on an equilibrium-like fractionation, or that the theoretical calculation is somewhat inaccurate. The third set of data (crosses) shows much greater temperature sensitivity than the equilibrium calculation this provides evidence for a dominantly non-equilibrium fractionation mechanism. For the first data set, the theoretical fractionation curve can be used to extrapolate beyond the measured temperature range. The second data set can also be extrapolated along a scaled theoretical curve (Clayton and Kieffer 1991).

Most methods are based on the measurement of physical and chemical changes that occur to a body after death. However, most of these changes are influenced by different variables (e.g., external temperature, physical activity immediately before death, etc.) that make the correlation between a measured variable and postmortem interval (PMI) rather inaccurate. 

These data may be somewhat inaccurate since they were taken (by us) from a graph (Pons, 1980, Fig. 3), and furthermore are evidently preliminary. The predicted room temperature energies are E T (300°K) a 0.71 eV, and Eq (300°K) a 0.68 eV, again, with respect to the conduction band. Thus, Pons s results are in good agreement with those of Martin et al (1980b), except for the temperature dependence of the Cr level. He finds ECr below E0 at room temperature, as we do, but the difference is smaller than that predicted by our electrical measurement data described here [Eqs. (25a) and (25b)]. It seems, therefore, that further investigations of the temperature dependences of the (EL2) and Cr levels will be necessary. 

Evaporation and redissolving. The solvent of the combined upper layer is evaporated under nitrogen flow or low-temperature vacuum distillation. An oily material appears after it is dried. A precisely measured aliquot of mobile phase is normally used to redissolve theextract. These procedures are intended to not only increase the concentration of tocopherols and tocotrienols to the measurable level of the detector, but also to avoid uncertain volume change of organic layer during extraction, which results in inaccurate results. The redissolved sample is transferred to a vial for HPLC analysis. 

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