Instrumental uncertainties

VanLandingham, M.R., The effect of instrumental uncertainties on AFM indentation measurements. Microsc. Today, 97, 12-15 (1997). 

Finally, a Monte Carlo method coupled with the Latin Hypercube Sampling (LHS) was used to assess the overall model uncertainty. The 2a standard deviation of the model was estimated to be 30-40% for OH and 25-30% for HO2, which is comparable to the instrumental uncertainty. 

Enrico Fermi on his voyage to the new world postulated that a third particle was needed to balance the emission of the electron in 3 decay. However, the existing conservation laws also had to be satisfied, so there were a number of constraints on the properties of this new particle. Focusing on the decay of a neutron as a specific example, the reaction is already balanced with respect to electric charge, so any additional particle must be neutral. The electrons were observed with energies up to the maximum allowed by the decay Q value so the mass of the particle must be smaller that the instrumental uncertainties. Initially, this instrumental... 

The main problem in evaluating the uncertainty of measurements in coulometry lies in identification of important uncertainty sources and estimation of their contribution (Table 2). With very low instrumental uncertainty, other factors become limiting to the achievable uncertainty, mainly those connected to the chemical processes in the cell and the homogeneity of the material. 

Liquid handlers generally face uncertainty when performing transfers. The transferred amount can be a few percent off from the targeted amount, depending on the type of instrument. When serial dilution is used, instrument uncertainty is an accumulating effect. Since the source of the compound in the second point is the first point, the uncertainty of the second point constitutes the uncertainty of the instrument in performing the transfer plus the uncertainty of whatever is already... 

Compound management must take all measures to ensure high process quality by eliminating human error and minimizing instrument uncertainties. 

Usually, from a spectral scan, the wavelength corresponding to the absorption maximum is selected. At max. sensitivity is maximum and, over a narrow region close to the maximum, the absorbance is constant. Therefore, minor wavelength differences do not alter the response, and also the absorbance at >,i ax is less sensitive to instrumental uncertainties. However, if adequate sensitivity exists, measurements can be made at min. if interfering absorbance is negligible at... 

Normally, the laboratories use fixed and inflexible criteria for this control. They define a limit to the percentage difference between the expected and the obtained value, and in low precision techniques they are obliged to increase this value. Assuming the uncertainty associated with the control standard preparation to be negligible when compared to the instrumental uncertainty, the case-to-case interpolation uncertainties can be used as a fit for each case. If the observed confidence interval includes the expected value, there is reason to think that the system is not under control. The instrumental deviation from control can be used as a guide for instrumental checking or as a warning of the inadequacy of the chosen mathematical model for the calibration. 

Figure 26-10 Error curves for various categories of instrumental uncertainties.

In a detailed theoretical and experimental study. Rothman, Crouch, and Ingle have described several sources of instrumental uncertainties andshown their net clfect on the precision of absorbance or transmittance measurements. These uncertainties fall into one of three categories depending on how they are affected by the magnitude of the phoiocurrent and thus T. Tor Case 1 uncertainties, the precision is independent of T that is. Sj Is equal to a constant k,. For Case II uncertainties, the precision is directly proportional to T f T. Finally, C ase III uticeriainiios are directly proportional lo T. Tabic 13-3 summarizes inforniaiion about the sources of these three types of uncertainly and the kinds of instrumeni.s where each is likely to be cncounicred. 

We will pursue the analysis, however, in the sense that it is more important to fit the initial portion of the breakthrough curve than the end (certainly so in design applications). One should also recognize that end-of-breakthrough data can be less reliable because they are more susceptible to influences of extraneous factors such as nonideal flow patterns, the sensitivity of the chemical analysis, and instrumental uncertainty. Continuing then... 

Uncertainty of pitot tube coefficient u(a) Pitot tube as a measuring device, when manufacturing it need to be calibrated. Due to the uncertainty of standard instruments, uncertainty u(a) in the pitot tube coefficient appears. 

Although many van der Waals and cluster species of the utmost chemical interest have been characterized with such jet instruments, uncertainties in the sample density and the degree of cooling attained in an individual jet do not readily lend themselves to reproducible quantitative analysis without careful internal precalibration procedures. 

The purpose of this annex is to provide guidance for establishing instrument setpoints for safety instrumented functions in the process industries. The scope of ANSI/ISA-84.00.01 is requirements for... a safety instrumented system, so that it can be confidently entrusted to place and/or maintain the process in a safe state." This annex provides guidance on instrument uncertainty calculations and setpoint determination for instruments used in an SIS to ensure that each SIF responds to achieve or maintain the safe state of the process within one-half of the process safety time with respect to a specific hazardous event. If measurement uncertainty is not considered in the determination of an SIS setpoint, the SIF may not detect the presence of a valid process demand. 

The bases of the uncertainty calculation (e.g., instrument uncertainties, process effects, calculation methods, data sources, and assumptions) should be stated in the setpoint calculation. 

The minor axis of the ellipse is defined by experimental and instrumental uncertainty. 

Instrumentation uncertainty, the.coarseness of reactor and Brayton speed control actions, other control band allowances, allowances for transients, casualties and age effects all impact the efficiency of the thermal cycle and therefore the sizing of all components. These uncertainties have a significant impact on the SNPP design and the necessary margin to accommodate these uncertainties. Developing an autonomous control scheme that minimizes operating bands and error will be necessary to minimize system mass. 

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