Measurement inaccuracies

Due to its nature, random error cannot be eliminated by calibration. Hence, the only way to deal with it is to assess its probable value and present this measurement inaccuracy with the measurement result. This requires a basic statistical manipulation of the normal distribution, as the random error is normally close to the normal distribution. Figure 12.10 shows a frequency histogram of a repeated measurement and the normal distribution f(x) based on the sample mean and variance. The total area under the curve represents the probability of all possible measured results and thus has the value of unity. 

The measuring inaccuracy is given as a percentage of the corresponding measured value plus the corresponding temperature coefficients. This is the most important characteristic of every pressure sensor. 

The inherent difficulty in the measurement of the complex dynamic moduli of viscoelastic materials is emphasized by the results of this paper. The agreement among the shifted modulus data as measured by different systems is limited by several difficulties (1) measurement inaccuracies of the instruments, (2) differences in the data reduction techniques used to apply the time-temperature superposition principle and propagation of shift curve errors and, (3) nonuniformity of the test samples. 

As a variation we discuss in the present paper an even simpler procedure where we make use of only two measured points (2PM). In our paper we compare both methods and we assess the accompanied increase of measurement inaccuracy. Though the following approach is based on gravimetric measurements it is valid likewise for any other measuring method e.g. the volumetric one. 

Already with Jantti s 3PM a timesaving of the stepwise measurement of nitrogen isotherms up to 70 percent was possible 2PM is even faster. For both methods we show that the gain of the shortening of the measurement time is accompanied by a drawback, i.e. the increase of measurement inaccuracy, which is shown to be inversely proportional to the square of the measurement time. In case the molecular adsorption mechanism is not a given factor before the start of the measurement, the application of the time saving measurement will involve extra uncertainties. 

To summarize, process models can be incorrect from the beginning—where correct is defined in terms of consistency with the current process state and with the models being used by other controllers—or they can become incorrect due to erroneous or missing feedback or measurement inaccuracies. They may also be incorrect only for short periods of time due to time lags in the process loop. 

The measurement problems in the areas of MW or MWD are similar to those for composition measurement. Dead times and measurement inaccuracies may be greater than for composition measurement. Adding to the difficulty is the fact that it is uncommon that a single simple relationship between a manipulated process input and MW can be identified. More commonly, a change in polymer MW is effected by the simultaneous adjustment of several process variables. 

Intrinsic imprecision is also called repeatability and is usually determined included in total repeatability. Intrinsic measurement inaccuracy is checked by calibration. 

Nondestructive determination of coating thicknesses can also be made by magnetic interference (like ASTM B 499 and ASTM E 376) or X-ray spectrometry (like ASTM B 568), provided that the measured surface is first cleaned to remove corrosion products that would otherwise result in measurement inaccuracies. 

Motivation of the management Often managers and supervisors have a critical look towards more advanced control systems and advanced control strategies it should be clear from the operational resirlts that improvements have been achieved. But in practice this is sometimes hard to prove, since savings are usirally small, perhaps 5% in energy consumption, smoother process operation, etc. These small improvements are often hard to monitor owing to process noise and measurement inaccuracies. 

What is the accuracy of the method Accuracy refers to how close the average of a large number of measurements comes to the true value. Even if an analytical method is precise, it does not mean that the measured concentration is accurate. There are several sources of measurement inaccuracy, one of which is chemical interference. Chemical interference occurs when (i) responses obtained during... 

An alternative flowsheet, which is more costly but easier to control, uses two distillation columns. As illustrated in Figure 1.5, the first is a reactive distillation column into which an excess of one of the reactants is fed (component B), along with the second flesh feed of component A. The total B fed to the reactive column is 10-20% in excess of the stoichiometric amount needed to react with the moles of A being fed. The amount of this excess is determined by the variability in the compositions of the two fresh feeds and by flie flow measurement inaccuracies. Reactant A is the limiting reactant in this column and its conversion is high. The conversion of reactant B is not high in the reactive column. Because not all of the B is consumed by the reaction, the excess comes out of the bottom of the column with product component D. This binary mixture is fed to the second distillation column, the recovery column, which produces component D out the bottom and component B out the... 

On the basis of Fig. 4, it is possible to explain a fundamental correlation between tensile and compressive curves. This Figure shows the relationship between technical compressive stress and technical tensile stress as a function of the deformation. Apart from the result that considerably higher stresses can be achieved under compressive load than under tensile load, it can also be said that the quotients established display virtually no dependence on the temperature within the scope of the measuring inaccuracy and the error due to the approximation. Further investigations showed that the influence of the strain rate can be neglected by way of an initial approximation [16]. 

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