Accuracy, of measurement

Comparison of the measurements with the microdensitometers and the algorithms of calculation inclusive the filter function and the accuracy of measurement of all project partners. 

Calibration of an arc or spark source is linear over three orders of magnitude, and detection limits are good, often within the region of a few micrograms per gram for elements such as vanadium, aluminum, silicon, and phosphorus. Furthermore, the nature of the matrix material composing the bulk of the sample appears to have little effect on the accuracy of measurement. 

For a second series of measurements, the precision is much better than for the series shown in Figure 48.7. Neither Figure 48.8 nor Figure 48.7 reveal any information on the accuracy of measurement. 

Molecules such as 3,4 and 5 in Figure 2.6, which have a zero velocity component away from the source, behave uniquely in that they absorb radiation of the same frequency Vj-es whether the radiation is travelling towards or away from R, and this may result in saturation (see Section 2.3.4). If saturation occurs for the set of molecules 3, 4 and 5 while the radiation is travelling towards R, no further absorption takes place as it travels back from R. The result is that a dip in the absorbance curve is observed at Vj-es, as indicated in Figure 2.5. This is known as a Lamb dip, an effect which was predicted by Lamb in 1964. The width of the dip is the natural line width, and observation of the dip results in much greater accuracy of measurement of v es. 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

Calibration unsuitable for current process/step. Some processes require greater accuracy of measurements. 

There are two systems used for maintaining the accuracy and integrity of measuring devices a calibration system and a verification system. The calibration system determines the accuracy of measurement and the verification system determines the integrity of the device. If accuracy is important then the device should be included in the calibration system. If accuracy is not an issue but the device s form, properties, or function is important then it should be included in the verification system. You need to decide the system in which your devices are to be placed under control and identify them accordingly. 

Electronic instrumentation is available for the measurement of D.C. and A.C. voltage, current and power as well as impedance. Such instruments usually have higher sensitivities, operating frequencies and input impedance than is normally found in the electromechanical instrumentation described above. However, they may need to incorporate amplifiers and they invariably need power to operate the final display. Hence, an independent power source is needed. Both mains and battery units are available. The accuracy of measurement is very dependent on the amplifier, and bandwidth and adequate gain are important qualities. 

How does yield stress depend on a filler concentration It is shown in Fig. 9 that appreciable values of Y appear beginning from a certain critical concentration cp and then increase rather sharply. Though the existence of cp seems to be quite obvious from the view point of the possibility of contacts of the filler, i.e. the beginning of a netformation in the system, practically the problem turns on the accuracy of measuring small stresses in high-viscosity media. It is quite possible to represent the Y(cp) dependence by exponential law, as follows from Fig. 10, for example, leaving aside the problem of the behavior of this function at very low concentrations of the filler, all the more the small values of are measured with a significant part of uncertainty. 

In this investigation (Table VIII), it was found that Kw values for CO hydrogenation depend on the 0.9 power of the reciprocal of particle diameter. In view of this and the literature, a linear (first power) dependence on the reciprocal of particle diameter was used in the Kw expression. Accuracy of measurement is certainly insufficient to distinguish between a 0.9 and a 1.0 power dependence. 

Loops are not calibrated accurately and a loop of nominally 20 p.l is unlikely to have this exact volume. This will not affect either the precision of measurement and, as long as the same loop is used for obtaining the quantitative calibration and for determining the unknowns , the accuracy of measurement. 

Definition and Uses of Standards. In the context of this paper, the term "standard" denotes a well-characterized material for which a physical parameter or concentration of chemical constituent has been determined with a known precision and accuracy. These standards can be used to check or determine (a) instrumental parameters such as wavelength accuracy, detection-system spectral responsivity, and stability (b) the instrument response to specific fluorescent species and (c) the accuracy of measurements made by specific Instruments or measurement procedures (assess whether the analytical measurement process is in statistical control and whether it exhibits bias). Once the luminescence instrumentation has been calibrated, it can be used to measure the luminescence characteristics of chemical systems, including corrected excitation and emission spectra, quantum yields, decay times, emission anisotropies, energy transfer, and, with appropriate standards, the concentrations of chemical constituents in complex S2unples. 

Functions of Standards. Fluorescent standards can be used for three basic functions calibration, standardization, and measurement method assessment. In calibration, the standard is used to check or calibrate Instrument characteristics and perturbations on true spectra. For standardization, standards are used to determine the function that relates chemical concentration to Instrument response. This latter use has been expanded from pure materials to quite complex standards that are carried through the total chemical measurement process (10). These more complex standards are now used to assess the precision and accuracy of measurement procedures. 

Our goals in designing the immersion testing system were (i) to emulate or improve upon operations as specified in the manual immersion test method, (ii) to increase sample throughput, (iii) to improve the precision and accuracy of measurements, (iv) to establish procedures for testing materials in hazardous liquids, and (v) to provide sufficient flexibility to handle different types of specimens and enable future expansion of operations. 

At the design stage, factors we considered to be paramount were heating and cooling demands, accuracy of measurement and the control equipment, and data logging. 

In terms of the accuracy of measurement, it appears from Tables III - V that detection of a narrow distribution particle mixture at 350 or 280 nm is just as advantageous as detection at 25U nm. However for a broad particle size distribution sample, detection at 25U nm or lower where particles absorb, provides a distinct improvement in small particle detection (T.) ... 

In terms of accuracy of measurement, for a narrow distribution sample, there appears to be no preferred wavelength for signal detection in the UV range. 

The issue of data reproducibility had been the previous focus of the AOAC Official Methods Program. The TDRM will assist AOAC in responding to an expanded scope of it mission to include statements of accuracy with AOAC methods. This extra step requires independent verification of the accuracy of measurements generated by the method. Accuracy of an analytical method must be verified at three separate points ... 

Gham, J. Instruments for Stereometric Analysis with the Microscope -Their Application and Accuracy of Measurement , in ADVANCES IN OPTICAL AND ELECTRON MICROSCOPY, Barer, R. and Cosslett, V.G., Ed.. 1973, 5, 115-162, Academic Press, New Tork. 

High resolution mass spectrometry becomes indispensable for the analysis of biomolecules with ESI (see Chapter 2, Section 2.1.15) and MALDI (see Section 2.1.22) techniques. In these cases very high resolving power and accuracy of measurements are required to measure reliably the real masses of the sample molecules. 

It is not true that an increase in the resolving power always simultaneously leads to an increase in the accuracy of mass measurement. As soon as the resolving power allows peaks separation it is useless to increase it more as the signal intensity will decrease with subsequent decrease in accuracy of measurements. 

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