Measurement techniques instrumentation

F1iy ical quantity (unit) Measuring technique Instruments Advantages Disadvantages Remaiks... 

Thermogravimetric and Sorption Measurement Techniques / Instruments, Proceedings of 6th Int. Symposium on the Characterization of Porous Solids (COPS VI), Alicante, Spain, May 8-11, 2002, Studies in Surface Sciences and Catalysis, Vol. 144, F. Rodriguez-Reinoso et al., Eds., p. 387-394, Elsevier,... 

The X-ray disc centrifuge is a centrifugal version of the gravitational instruments and extends the measuring technique well into the sub- Im-size range. 

Random Measurement Error Third, the measurements contain significant random errors. These errors may be due to samphng technique, instrument calibrations, and/or analysis methods. The error-probability-distribution functions are masked by fluctuations in the plant and cost of the measurements. Consequently, it is difficult to know whether, during reconciliation, 5 percent, 10 percent, or even 20 percent adjustments are acceptable to close the constraints. 

The continuous methods combine sample collection and the measurement technique in one automated process. The measurement methods used for continuous analyzers include conductometric, colorimetric, coulometric, and amperometric techniques for the determination of SO2 collected in a liquid medium (7). Other continuous methods utilize physicochemical techniques for detection of SO2 in a gas stream. These include flame photometric detection (described earlier) and fluorescence spectroscopy (8). Instruments based on all of these principles are available which meet standard performance specifications. 

In addition to their widespread use in research and development in fluid dynamics, laser-based techniques ° are also suited to experiments in industrial ventilation. The use of these advanced experimental methods is reasonable when their advantages in comparison with traditional measurement techniques counterbalance the significantly higher expenses of instrumentation. 

A measurement technique such as titration is employed that provides a single result that, on repetition, scatters somewhat around the expected value. If the difference between expected and observed value is so large that a deviation must be suspected, and no other evidence such as gross operator error or instrument malfunction is available to reject this notion, a statistical test is applied. (Note under GMP, a deviant result may be rejected if and when there is sufficient documented evidence of such an error.)... 

There are several electrical measurements that may be used for analysis of solutions under in situ conditions. Among the properties that may be measured are dielectric constants, electrical conductivity or resistivity, and the redox potential of solutions. These properties are easily measured with instrumentation that is readily adapted to automatic recording operation. However, most of these techniques should be used only after careful calibration and do not give better than 1% accuracy without unusual care in the experimental work. 

In general, optical-based pH measurement techniques require relatively expensive and cumbersome instruments, and their sophisticated method cannot be easily carried out for routine assay. Interfering contact and reactions of the dye molecules, particularly considering in-vivo measurements, cannot be excluded [34], Some other possible factors, such as a weaker signal at shorter response times, complications in microfabrication, and difficulties in attaching the chemical or biological agents to the small fiber tip, are potential limitations for the application of these optical sensors to in-vivo measurements in micro environments [35]. 

Isoperibolic instruments have been developed to estimate enthalpies of reaction and to obtain kinetic data for decomposition by using an isothermal, scanning, or quasi-adiabatic mode with compensation for thermal inertia of the sample vessel. The principles of these measuring techniques are discussed in other sections. 

The development of instrumental measurement techniques during the 1920s and 1930s such as optical emission spectroscopy (OES see Section 3.1) gave... 

Reference materials are homogeneous, stable substances whose properties are sufficiently established as to make them useful for calibrating analytical instruments or validating measurement techniques. High-quality reference materials not only provide essential support for large-scale research studies, but also ensure accuracy of long time-series measure-... 

Traditionally, regulatory and compliance testing requires gravimetric determination of, for example, fuel mass emissions. Instruments utilizing collecting or in situ measurement techniques are used for the analysis of various particle parameters for nonregulatory purposes. 

In practice, the application of x-ray measurement techniques to thin films involves some special problems. Typical films are much thinner than the penetration depth of commonly used x-rays, so the diffracted intensity is much lower than that from bulk materials. Thin films are often strongly textured this, on the other hand, results in improved intensity for suitable experimental conditions but complicates the measurement problem. Measurements at other than ambient temperature, not usually attempted with bulk materials, constitutes additional complexity. Since typical strains are on the order of 1 X 10 , measurements of interplanar spacing with a precision of the order of 1 X 10 are needed for reasonably accurate results hence, potential sources of error must be kept to a low level. In particular, the sample displacement error can be a major source of difficulty with a heated sample. The sample surface must remain accurately on the axis of the instrument during heating. 

Figure 18.2 Experimental facility Measurement Techniques and Instrumentation...

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