Counter optical

Optical counters Optical crystals Optical data storage Optical device Optical devices... 

Optical counters have been widely used to monitor cleanroom technology and particles in oil. Instmments manufactured by Royco Inc. (Menlo Park, California) are available for studying aerosols and particles in Hquids. The HIAC counter (HIAC Instmments, Monte Claire, California) is a widely used stream counter for particles in fluid. One of the more recently developed optical counters is available from Particle Sizing Systems (Santa Barbara, California). The configuration of one of the widely used counters, the Climet counter, is shown in Figure 16. A general review of photozone counters is available (3). 

The electrical aerosol analyzer and the optical counter are used to measure particle size distributions. Describe the size range and resolution characteristics of each of these instruments. 

Optical methods Optical counters, optical microscopy, and electron microscopy fall under this heading. A review of optical methods is given by Baron et al. (1993). 

Optical counters allow relatively rapid measurements of the size distribution and, unlike some of the other methods of size fractionation, include volatile particles in the measurement. However, some care must be taken in interpreting the detailed shape of the size distribution spectrum because of some anomalies that have been observed for example, around the l-/xm region, interference from light that is reflected or refracted from the front and back of the particle gives a knee in many calibration curves of number of particles versus their diameter (LBL, 1979). 

Single-particle optical counters cannot be easily used for measuring high aerosol concentrations. Whitby and Liu (1967) have shown that if many small particles are in the illuminated sensitive volume of this type of instrument at the same time, significant errors are introduced because the particles are considered by the detector to be fewer in number and greater in size. Thus there is a practical upper limit on the aerosol concentration that can be measured by such an instrument, being on the order of 1000 to 10,000 particles per cubic centimeter. 

On the other hand, optical counters inherently operate on a number basis and therefore are less accurate for larger particles which generally occur in fewer quantities. Any random instrument errors are magnified by the few larger particles but statistically averaged out for smaller par-... 

In summary, particle size distributions measured at similar conditions using optical and sampling probe-impactor methods are vastly different. No conclusions can be drawn concerning the relative accuracy of these two techniques because of experimental differences. All indications are that the optical counter is operating properly and is applicable and advantageous for in situ measurements. Further experiments comparing the two techniques directly on a common engine will be performed soon to substantiate the particulate formation hypotheses. 

Knollenberg and Veal [80] discuss operation, design and performance of optical counters in general and a review of extinction optical particle counters has been presented by Sommer [81] cit. 82). A comprehensive review of laser-based techniques for particle size measurement, covering both stream scanning and field scanning methods, contains 167 references [83]. 

PMS HSLIS liquid optical counter provides continuous real-time monitoring of contamination levels in DI watwer and process chemicals providing size sensitivity down to 0.5 pm in DI water and 0.65 pm in process chemicals. 

Optical counters depend on measuring light scattered from particles as they traverse a defined path. Such instruments can provide rapid, on-line... 

Notice that, although the particle mass concentration emitted in the Test 2 is lower than the Test 4, the total concentration number is higher in Test 2.. Additionally the concentration number measured with the optical counter is higher in Test 2. An efficient combustion, as occurring in Test 2 favours the presence of fine particles as opposed to the poor combustion of Test 4 which produced a high concentration of coarse particles, thus increasing the mass concentration. 

In this section, we briefly review three types of instruments, the optical particle counter, electrical aerosol classifier, and diffusion battery. These system.s are based on very dilTerent physical characteristics of the aerosols. The optical counters respond to signals from individual particles. The electrical analyzers depend on the measurement of a current carried by a slreaJTi of cbrnged aerosol particles. The ditfusion battery also depends on the behavior of particle clouds. The system often used to cover the size range from about 10 nm to 10 /jm is a combination of (a) the electrical analyzer up to about 0.2 jum and (b) the optical particle counter over the rest of the range. 

Difficulties are encountered in using optical counters with aerosols from mixed sources because the refractive Index varies from particle to particle in an unknown way. The usual... 

Figure 6,5 Schematic diagram of the ellipsoidal mirror optical counter (Hu-sar. 1974),...

Figure 6.6 The relative response curves of the ellipsoidal mirror optical counter. The lines wen calculated from Mie theory, and the points were measured experimentally. (Courtesy S. L. HeisEe and R. B. Husar.)...

Figure 10.8 Oscillatory behavior of particle numberdensityfdy, > 0.3 rn) in a flow reactor study of coal gas containing NO at a concenuraiion of 11.6 ppm. Measurements of deposited particles were made with an optical counter. It is likely that many more particles were present in the ultraline range lip < 0.1 //m) and not counted. (After Badger and Drydcn. 1939.)...

More recently, Whitby (1978) has analyzed the results of much more numerous size distribution observations carried out mainly by his group who used a combination of expansion chamber, electrical mobility and optical counter techniques. This analysis clearly shows that the complete size distribution is composed of three separate log-normal distributions as demonstrated in Fig. 26. Whitby speculates that the first distribution, the nuclei mode, is controlled by the condensation of vapour, (predominantly H2S04) formed by chemical reactions. Thus, the concentration of these small particles was found to be very significant in irradiated polluted atmosphere. On the other hand, the so-called accumulation... 

Variations of the size distribution of aerosol particles as a function of relative humidity can be observed in situ in the air. Changes in particle size distributions are detected by optical counters (Laktionov and Bogomolov, 1972), by nephelometers (Charlson et al., 1969) or by diffusion channels (Sinclair et al., 1974). 

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