Light obscuration

Smoke detection depending upon absorption of ionizing radiation by smoke particles light scattering by smoke particles light obscuration. 

It is shown that while solute concentration data can be used to estimate the kinetic growth parameters, information about the CSD is necessary to evaluate the nucleation parameters. The fraction of light obscured by an illuminated sample of crystals provides a measure of the second moment of the CSD. Numerical and experimental studies demonstrate that all of the kinetic parameters can be identified by using the obscuration measurement along with the concentration measurement. It is also shown that characterization of the crystal shape is very important when evaluating CSD information from light scattering instruments. 

Field flow fractionation Light obscuration Microscopy Sedimentation... 

The apparatus is an electronic, liquid-bome particle-counting system that uses a light-obscuration sensor with a suitable sample feeding device. It is the responsibility of those performing the test to ensure that the operating parameters of the instrumentation are appropriate to the required accuracy and precision of the test result. 

Mix one unit by inverting it 20 times. Remove the closure and insert the counter probe into the center of the solution. Gently agitate the contents of the unit by hand-swirling or by mechanical means. Withdraw not less than three aliquot portions, each not less than 5 ml in volume, into the light obscuration counter sensor. Obtain the particle counts and discard the data from the first portion. 

Table 1 Light Obscuration Test Particle Count...

Pharmacopeial count limits for particulates in parenteral solutions is given in Table 39. The limit depends on the method used for the determination and also on the volume of the sample. Two different procedures for the determination are generally proposed light obscuration particle count test (LO) and microscopic particle count test (M), since neither is applicable to all kinds of samples. 

Note The limits are related to the method used for the determination LO = light obscuration particle count test, M = microscopic particle count test, IP = International Pharmacopeia. 

The cone calorimeter,71 which is a dynamic flow-through fire test, can also be used to assess smoke obscuration. The rankings tend to be quite different from those found with the static smoke chamber and are much more realistic. Several empirical parameters have been proposed to make this compensation for incomplete sample consumption, including one called the smoke factor (SmkFct), determined in small-scale RHR calorimeters.188 It combines the two aspects mentioned earlier the light obscuration (as the total smoke released) and the peak RHR. 

This is of fundamental importance in the pulp and paper industry which uses a light obscuration method - the Kajaani FS-200. This instrument is also used in the chemical industry for measuring the length of man-made fibers. 

The USP includes different tests for the detection, sizing, and enumeration of subvisual particles, e.g., 10 and 25 pm. There are two test approaches for particulate matter recognized by the USP. They are automated liquid particle counting either by the light obscuration method or the light (laser) scattering method used mainly for SVPs, and the microscopic method used predominantly for LVPs. 

Primary atomization, the formation of ligaments and drops by an atomizer, has already been a subject of study for over a century. The difficulty in experiments is that the numerous droplets reflect light, obscuring clear views of the atomization process. In addition, the high speed and small size of practical fuel injection means that the experimental images are often not clear. Dense sprays and non-spherical drops also make quantitative data difficult to obtain with laser-based diagnostics. 

The specific, particle sizing method chosen depends on the type of. size information needed and the chemical and physical properties of the sample. In addition to the three techniques discussed here, molecular sieving, electrical conductance, microscopy, capillary hydrodynamic chromatography, light obscuration counting, field-flow fractionation, Doppler anemometry, and ultrasonic spectrometry-are commonly applied. Huch of the particle sizing methods has its advantages and drawbacks for particular samples and analyses. 

The USP lists two recognized techniques for testing for particulate matter in pharmaceutical solutions. Method 1 is based on the principle of light obscuration, in which light from a laser impinging on a photodiode detector is obscured by any particles present in the test medium. Method 2 employs a light microscope, with which particles are visibly counted per unit volume by the analyst. 

Light obscuration is used to obtain the particle size of micron-sized particles. In this technique, a dilute stream of particles in suspension is passed between a laser hght source and a detector. The particles cause blockage of hght at the detector. The reduction of light intensity is related to the particle size. Light obscuration methods are used for particles in the range of 0.5-500 rm. 

Light obscuration by smoke (specific optical density )... 

Table 11.8 ASTM SmaU-Scale Test Apparatuses for the Measurements of Release Rates of Heat and Fire Products and Light Obscuration by Smoke...

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