Types of measurements

The frequency dependence of the ultrasonic properties of materials can be divided in a number of ways based on pulse-echo, transmission or interferometric measurements. The principal differences between them are the way ultrasonic energy is applied to the sample (Fig. 9.4) and the experimental set-up used to make the measurements. 

The frequency-dependent uitrasonic properties of a materiai can be measured in aimost exactiy the same manner by using this approach and the transmission-based one, except that a singie transducer is used to both generate and receive the uitrasonic puises. 

the velocity and attenuation coefficient are calculated in exactly the same manner as described for the transmission technique, except that the pulse now travels a distance 2d rather than d. 

Laser interferometry employs the principle of optical interference to recover the sought acoustic information from the light reflected from, or scattered by, a surface under ultrasonic vibration. Its non-contact nature makes laser probing a preferred alternative to contact methods in studying surface waves, their diffraction and damping by intrinsically rough surfaces. 

Ultrasound resonance spectroscopic measurements are commonly obtained by applying a broad-pulse and selecting the frequency at which the sample enters into resonance at the frequency concerned. Under these conditions, the velocity, attenuation, impedance and other characteristics of US can be measured and subsequently processed as required. 

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There are two types of measurement errors, systematic and random. The former are due to an inherent bias in the measurement procedure, resulting in a consistent deviation of the experimental measurement from its true value. An experimenter s skill and experience provide the only means of consistently detecting and avoiding systematic errors. By contrast, random or statistical errors are assumed to result from a large number of small disturbances. Such errors tend to have simple distributions subject to statistical characterization. 

Braun and Hauck [3] discovered that the irrotational and solenoidal components of a 2-D vector field can be imaged separately using the transverse and longitudinal measurements, respectively. This result has a clear analogy in a 2-D tensor field. We can distinguish three types of measurements which determine potentials of the symmetric tensor field separately ... 

A second type of measurement that may be made on films, usually in conjunction with force-area measurements is that of the contact or surface potential. One essentially measures the Volta potential between the surface of the liquid and that of a metal probe. 

The points in Fig. V-12 come from three types of experimental measurements. Explain clearly what the data are and what is done with the data, in each case, to get the w-versus- plot. What does the agreement between the three types of measurement confirm Explain whether it confirms that is indeed the correct absolute interfacial (Krtential difference. 

Structural investigations of metal-ion hydration have been carried out by spectroscopic, scadering and diffraction teclmiques, but these teclmiques do not always give identical results since they measure in different timescales. There are tliree distinct types of measurement ... 

These types of measurements, eombined with theoretieal modelling, ean provide a detailed mieroseopie map of the loeal reaetivity of the surfaee as well as eleetron tiumelling rates within the surfaee unit eell. This infomiation is of enieial importanee for the understanding of various impurity-mdueed promotion and... 

In another type of measurement, the parallel between mechanical and electrical networks can be exploited by using variable capacitors and resistors to balance the impedance of the transducer circuit. These electrical measurements readily lend themselves to computer interfacing for data acquisition and analysis. 

Aqueous Solution Viscosity. A special solution preparation method is used for one type of measurement of aqueous solution viscosity (96). The appropriate amount of poly(ethylene oxide) resin is dispersed in 125 mL of anhydrous isopropyl alcohol by vigorous stirring. Because the resin is insoluble in anhydrous isopropyl alcohol, a slurry forms and the alcohol wets the resin particles. An appropriate amount of water is added and stirring is slowed to about 100 rpm to avoid shear degradation of the polymer. In Table 4, the nominal resin concentration reported is based on the amount of water present and ignores the isopropyl alcohol. 

Drape can be measured by placing a circular fabric specimen over a round table or pedestal and viewing from direcdy overhead. A drape coefficient is defined as the ratio of the area of the fabric s actual shadow to the area of the shadow if the fabric were rigid. Drape is closely related to stiffness the drape coefficient for a stiff fabric approaches a value of 1 a limp fabric has a drape coefficient near 0. The Cusick drape tester is an example of this type of measurement. Eor this method, the relative weights of paper rings representing tracings of the fabric s shadows are used to calculate drape coefficient. 

Nature In some types of applications, associated pairs of obseiwa-tions are defined. For example, (1) pairs of samples from two populations are treated in the same way, or (2) two types of measurements are made on the same unit. For applications or tnis type, it is not only more effective but necessary to define the random variable as the difference between the pairs of observations. The difference numbers can then be tested by the standard t distribution. 

Within most companies, the responsibility for cahbrating measurement devices is delegated to a specific department. Often, this department may also be responsible for maintaining the measurement device. The specific cahbration procedures depend on the type of measurement device. The frequency of calibration is normally predetermined, but earlier action may be dic tated if the values from the measurement device become suspect. 

Density and Specific Gravity For binary or pseudobinary mixtures of hquids or gases or a solution of a solid or gas in a solvent, the density is a funcrion of the composition at a given temperature and pressure. Specific gravity is the ratio of the density of a noncompress-ible substance to the density of water at the same physical conditions. For nonideal solutions, empirical calibration will give the relationship between density and composition. Several types of measuring devices are described below. 

Automatic recahbration of the transmitter. Although this is highly desired by users, the capabilities, if any, in this respect depend on the type of measurement. 

A final type of measurement is the detection of localized corrosion, such as pitting or crevice attack. Several corrosion-measuring probes can be used to detec t localized corrosion. Some can detect locahzed corrosion instantaneously and others only its result. These types of corrosion may contribute little to the actual mass loss, but can be devastating to equipment and piping. Detec tion and measurement of localized corrosion is one of the areas with the greatest potential for the use of some of the newest electrochemicaUy Based corrosion monitoring probes. 

The rows represent the type of measurement (e.g., compositions, flows, temperatures, and pressures). The columns represent streams, times, or space position in the unit. For example, compositions, total flows, temperatures, and pressures would be the rows. Streams I, 2, and 3 would be columns of the matrix of measurements. Repeated measurements would be added as additional columns. 

Table 15.5 Recommended limits of voltage and phase displacement errors, applicable for all types of measuring VTs (only electromagnetic and capacitor VTs).

Charts are available to convert from one type of measurement to another as shown in Figure 19-13. Many of these charts also show approximate vibration limits. The charts demonstrate the independence of velocity measurements relative to frequency, except at very low and very high frequencies where the amplitude limits are constant throughout the operating speed range. These limits are approximate—the type of machinery, casing, foundation, and bearings must be considered to determine final vibration limits. 

In the JKR experiments, a macroscopic spherical cap of a soft, elastic material is in contact with a planar surface. In these experiments, the contact radius is measured as a function of the applied load (a versus P) using an optical microscope, and the interfacial adhesion (W) is determined using Eqs. 11 and 16. In their original work, Johnson et al. [6] measured a versus P between a rubber-rubber interface, and the interface between crosslinked silicone rubber sphere and poly(methyl methacrylate) flat. The apparatus used for these measurements was fairly simple. The contact radius was measured using a simple optical microscope. This type of measurement is particularly suitable for soft elastic materials. 

Are statistical studies conducted to analyze the variation present in each type of measurement system and are the results used to effect a reduction in variation ... 

The standard requires appropriate statistical studies to be conducted to anal /ze the variation present in the results of each type of measuring and test equipment system. 

A pressing challenge for epidemiologists interested in occupational health is to derive an accurate picture of disease frequency. This challenge is met by two broad types of measurement prevalence and incidence. These arc briefly described below. 

Once such effects had been noted, it became necessary to interpret the observed results and to classify the solvents. The earliest attempts at this were by Stobbe, who reviewed the effects of solvents on keto-enol tautomers [4]. Since then many attempts have been used to explain solvent effects, some based on observations of chemical reactions, others on physical properties of the solvents, and yet others on spectroscopic probes. All of these have their advantages and disadvantages and no one approach can be thought of as exclusively right . This review is organized by type of measurement, and the available information is then summarized at the end. 

The gamma rays are detected today with sodium iodide crystals scintillation counters. The counters, 6 to 12 in. long (15 to 30 cm) are shock mounted and housed in the drill collars. Several types of measurements can be made total gamma rays, direction-focused gamma rays, spectral gamma rays. 

The graphical plotting technique for computing initial alignment can be performed with any of the three types of measurement fixtures (i.e. reverse dial indicator, rim-and-face, or optical). The following steps should be followed when plotting alignment problems ... 

Cyclic polarisation This type of measurement is similar to potentio-dynamic anodic polarisation with the difference that, following an anodic polarisation plot, the test specimen is subjected to a cathodic stimulus, i.e. a reverse scan. Any hysteresis, i.e. deviation from the anodic plot, can... 

In the combustion reaction as carried out in the calorimeter of Figure 7-2, the volume of the system is kept constant and pressure may change because the reaction chamber is sealed. In the laboratory experiments you have conducted, you kept the pressure constant by leaving the system open to the surroundings. In such an experiment, the volume may change. There is a small difference between these two types of measurements. The difference arises from the energy used when a system expands against the pressure of the atmosphere. In a constant volume calorimeter, there is no such expansion hence, this contribution to the reaction heat is not present. Experiments show that this difference is usually small. However, the symbol AH represents the heat effect that accompanies a chemical reaction carried out at constant pressure—the condition we usually have when the reaction occurs in an open beaker. 

Which liquid should be given Label No. 1, Label No. 2, Label No. 3 Explain how each type of measurement influenced your choices. 

Spectrophotometry. The instrument generally used for this basic type of measurement is the spectrophotometer. The data obtained, usually pictured in the form of a spectrophotometric curve, indicate the ability of the sample to transmit or reflect light of the various wave lengths. Various instruments are available which can be used to determine more or less complete spectrophotometric curves. 

It has been known for nearly eighty years that compressed gases can dissolve solids to give mixtures in which the concentration of the solid component is very large compared to that in the pure saturated vapor. Nevertheless, this effect has not always been appreciated by those working with compressed gases in other fields. Here we discuss briefly two types of measurement in which the enhanced concentration of the second component may have introduced unsuspected errors. 

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