Making Measurements

1 Dealing with Multiple Probes (3D Setup). The non-Cartesian velocity components (ui, U2, us) are transformed to Cartesian coordinates (u,v,w) using the transformation matrix C  

Blocking increases calculation speed and reduces the variance of the estimated spectra. 

Filter functions may be applied to smooth noisy spectra (optional). 

skewness, flatness cross-moments (weighted or unweighted). 

Averaging over several blocks reduces variance. 

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The CamuS system consists of a number of components, both hardware and software, as shown in Figure 1. The hub of the system is the data acquisition unit, which collects and stores ultrasonic data in the form of RF waveforms. An accurate probe position monitor provides information on the location and orientation of the probe as it is scanned over the test object. Software tools have been developed to provide assistance to the user with preparing inspection procedures according to the requirements of prEN1714 with visualising the data, in relation to the test object with making measurements of any indications present and with classifying indications. 

A two-dimensional slice may be taken either parallel to one of the principal co-ordinate planes (X-Y, X-Z and Y-Z) selected from a menu, or in any arbitrary orientation defined on screen by the user. Once a slice through the data has been taken, and displayed on the screen, a number of tools are available to assist the operator with making measurements of indications. These tools allow measurement of distance between two points, calculation of 6dB or maximum amplitude length of a flaw, plotting of a 6dB contour, and textual aimotation of the view. Figure 11 shows 6dB sizing and annotation applied to a lack of fusion example. 

One advantage of the photon counting teclmique over the phase-shift method is that any non-exponential decay is readily seen and studied. It is possible to detect non-exponential decay in the phase-shift method too by making measurements as a fiinction of tlie modulation frequency, but it is more cumbersome. 

The way out of this dilemma is to make measurements at several (nonideal) molarities m and extrapolate the results to a hypothetieal value of at m = 0. In so doing we have extrapolated out the nonideality because at m = 0 all solutions are ideal. Rather than ponder the philosophical meaning of a solution in which the solute is not there, it is better to concentrate on the error due to interionic interactions, which becomes smaller and smaller as the ions become more widely separated. At the extrapolated value of m = 0, ions have been moved to an infinite distance where they cannot interact. 

Analytical chemistry is inherently a quantitative science. Whether determining the concentration of a species in a solution, evaluating an equilibrium constant, measuring a reaction rate, or drawing a correlation between a compound s structure and its reactivity, analytical chemists make measurements and perform calculations. In this section we briefly review several important topics involving the use of numbers in analytical chemistry. 

An error due to limitations in the equipment and instruments used to make measurements. 

Sensitivity The sensitivity for a one-point fixed-time integral method of analysis is improved by making measurements under conditions in which the concentration of the monitored species is larger rather than smaller. When the analyte s concentration, or the concentration of any other reactant, is monitored, measurements are best made early in the reaction before its concentration has substantially decreased. On the other hand, when a product is used to monitor the reaction, measurements are more appropriately made at longer times. For a two-point fixed-time integral method, sensitivity is improved by increasing the difference between times t and f2. As discussed earlier, the sensitivity of a rate method improves when using the initial rate. 

In describing the various mechanical properties of polymers in the last chapter, we took the attitude that we could make measurements on any time scale we chose, however long or short, and that such measurements were made in isothermal experiments. Most of the experimental results presented in Chap. 3 are representations of this sort. In that chapter we remarked several times that these figures were actually the result of reductions of data collected at different temperatures. Now let us discuss this technique our perspective, however, will be from the opposite direction taking an isothermal plot apart. 

The concentration dependence of s is eliminated by making measurements at several different concentrations and then extrapolating to zero concentration. The limiting value is given by the symbol s°. This is the sedimentation analog of D°. 

Question. By making measurements ffom Figure 5.3 determine the average separation of rotational transitions in and hence estimate the bond length. 

Make measurements of the transition wavenumbers in the rotational spectrum of silane from Figure 5.10 and hence determine the Si—H bond length. 

Make measurements of band positions in the ultraviolet photoelectron spectmm in Figure 8.7 as accurately as you can and use these to determine cOg and cOgXg (Equations 7.82 and 6.18) for the ground electronic state of Hj. 

The evaluation phase of industrial hygiene is the process of making measurements on some set of samples which permits a conclusion about the degrees of hazard. Before conducting an evaluation, it is necessary to make a number of choices of what and where to sample, when to sample, how long to sample, how many samples to take, what sampling and analytical methods to use, what exposure criteria to use in the analysis of the data, and how to report the results. These choices as a whole constitute the evaluation plan. The object is to find if one or more workers have an unacceptable probabiUty of being exposed in excess of some estabUshed limit. 

K. Kustin, ed.. Fast Reactions, Methods in En mology, Vol. 16, Academic Press, Inc., New York, 1969. Contaias enough detail to allow one to build machines and make measurements. Predates lasers, fast electronics, and computers. 

The abihty to enlarge tiny objects to macroscopic dimensions immediately suggests the need to make measurements and other observations helptiil in documenting what is seen and thus enabling others to confirm that a specimen has been identified with certainty. Many physical and chemical properties of a microscopic substance can be measured, even on particles nearing atomic dimensions. 

Another resonant frequency instmment is the TA Instmments dynamic mechanical analy2er (DMA). A bar-like specimen is clamped between two pivoted arms and sinusoidally oscillated at its resonant frequency with an ampHtude selected by the operator. An amount of energy equal to that dissipated by the specimen is added on each cycle to maintain a constant ampHtude. The flexural modulus, E is calculated from the resonant frequency, and the makeup energy represents a damping function, which can be related to the loss modulus, E". A newer version of this instmment, the TA Instmments 983 DMA, can also make measurements at fixed frequencies as weU as creep and stress—relaxation measurements. 

Water Transport. Two methods of measuring water-vapor transmission rates (WVTR) ate commonly used. The newer method uses a Permatran-W (Modem Controls, Inc.). In this method a film sample is clamped over a saturated salt solution, which generates the desired humidity. Dry air sweeps past the other side of the film and past an infrared detector, which measures the water concentration in the gas. For a caUbrated flow rate of air, the rate of water addition can be calculated from the observed concentration in the sweep gas. From the steady-state rate, the WVTR can be calculated. In principle, the diffusion coefficient could be deterrnined by the method outlined in the previous section. However, only the steady-state region of the response is serviceable. Many different salt solutions can be used to make measurements at selected humidity differences however, in practice,... 

The definition of N as the total length of mobile disloeation per unit volume takes us from the mieroseale (atoms in a erystal lattiee) to the meso-seale (a sealar quantity N. Equation (7.1) then takes us from the mesoseale to the maeroseale in whieh we aetually make measurement of the rate at whieh materials aeeumulate plastie strain. The quantity may also have its own evolutionary law involving yet another mesoseale variable. When the number of evolutionary equations (ealled the material eonstitutive deserip-tion) equals the number of variables, we ean perform a ealeulation of expeeted material response by eombination of the evolutionary law with equations of mass, momentum, and energy eonservation. 

When making measurements in the soil box, it has to be remembered that soil samples can change from their original condition and this will have an effect on the resistivity. Soil resistivity measurements in the soil box only give accurate results with cohesive soils. However, the order of magnitude of the specific resis-... 

In the case of higher protection current densities and protection currents, interference can occur on nearby installations not covered by the protection. The danger of anodic interference must be investigated by making measurements and prevented by taking appropriate measures [7] (see Section 9.2). For the same reasons, anode systems should not be installed near steel-reinforced concrete foundations. 

The check for homogeneous reactions should be done by repeating some experiments with different quantities of catalyst charge. For example, make measurements over 20, 40 and 80 cm of catalyst charges with proportionally increased makeup feed rates. Change the RPM to keep the recycle ratio constant (if possible) or the linear rate u constant. The measured catalytic rate should remain the same if nothing happens in the empty space. 

The following is a brief introduction to making measurements that might be needed in the course of developing an lAQ profile or investigating an lAQ complaint. Emphasis has been placed on the parameters most commonly of interest in nonresearch studies, highlighting the more practical methods and noting some inappropriate tests to avoid. Most of the instruments discussed in this section are relatively inexpensive and readily available from many local safety supply companies. Air contaminants of concern in lAQ can be measured by one or more of the methods described below. 

To make measurements, the working aperture of the cupboard is divided into equal areas by imaginary lines parallel to the sides of the aperture. The air velocity is measured in each of these areas and sometimes its variation with time. If individual velocities are within about 15% of the mean, there should be little cause for con-... 

In industrial ventilation the majority of air velocity measurements are related to different means of controlling indoor conditions, like prediction of thermal comfort contaminant dispersion analysis adjustment of supply airflow patterns, and testing of local exhausts, air curtains, and other devices. In all these applications the nature of the flow is highly turbulent and the velocity has a wide range, from O.l m in the occupied zone to 5-15 m s" in supply jets and up to 30-40 m s in air curtain devices. Furthermore, the flow velocity and direction as well as air temperature often have significant variations in time, which make measurement difficult. 

Secondly, making measurements on atomic and molecular systems generally interferes with the system. If we were to repeatedly make measurements on a single system, we would change the system at each measurement and so would not be dealing necessarily with the same system. The correct interpretation is a statistical one. We would have to prepare a very large number of systems all in the same electronic state, and then do the measurements on all of them. 

There is a nice point as to what we mean by the experimental energy. All the calculations so far have been based on non-relativistic quantum mechanics. A measure of the importance of relativistic effects for a given atom is afforded by its spin-orbit coupling parameter. This parameter can be easily determined from spectroscopic studies, and it is certainly not zero for first-row atoms. We should strictly compare the HF limit to an experimental energy that refers to a non-relativistic molecule. This is a moot point we can neither calculate molecular energies at the HF limit, nor can we easily make measurements that allow for these relativistic effects. 

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