Particle counter

Electronic particle (Coulter) counters have been used for counting bacteria and yeasts. Major users are in the wine and beer industries. The problems with this method are that it is non-specific, and there are considerable difficulties in preparing samples which are free of dust and detritus as these may cause erroneous high counts. 

Although rapid and sensitive, ATP detection is very expensive. The cost and level of operator competence required are such that the method cannot be justified unless a large number of samples are envisaged, 

In instrumental particle counters, such as the well-known Coulter counter, the stream containing the particles is forced to pass through a flow 

Principle of operation of a laser diffraction particle counter. 

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Phase Doppler particle analyzers are essentially single-particle counters because they measure one particle at a time within a small sampling volume. This volume must be kept small to minimize the probabiUty of having more than one droplet in the volume at any given instant. This probabiUty increases as the concentration of droplets becomes greater, and there is more risk of measurement errors. 

P. W. HeUeman, The Coulter Electronic Particle Counter. Aspects and Views in Counting and Si ng oJErythroytes,D>Qi Bilt HoUand, the Netherlands, 1972, Chapt. 7-11. 

In order to reduce the influence ol unfavorable stagnation regions and vortex structures with their risk for accumulation of contaminants, tests should be carried out to characterize the functioning of the bench. In connection with these tests, induction tests should also be performed. Here smoke (particles) generated outside the bench and the probe of a particle counter placed inside the bench in the critical regions can give valuable information. 

Efficiency, counting The proportion of particles in a volume or mass flow that are counted as they pass through the sensing element of an optical particle counter. 

Optical particle counter An optical-electronic instrument for measuring the numbei" of airborne particles in different size ranges. 

Particle counters A manual or automatic device used to determine the particulate concentration of a given gas sample. 

Zero count rate The number of counts recorded in unit time by an optical particle counter when a particle-free gas is passed through the measuring chamber. 

Fig. 1.13 Principle of electronic particle counter Coulter counter. 

Optical particle counters provide information on the particles present in different size ranges. A beam of light is collimated and focused onto a measurement cell. Light impinging on a particle is scattered and reaches a photomultiplier tube and converted to an output proportional to particle size. Particle size distributions are computed by appropriate software. 

HHP technique, 14 106-107 HIAC particle counter, IS 150 Hibernia Scholven three-step MIBK process, 16 338 Hibiscus cannabinus, 11 293 Hibiscus sabdariffa, 11 293 Hi-Capacity thickener, 22 66 Hicks and Turner experimental design text versus other texts, S 395t Hidden failure, 15 477 Hide, in paints, 18 57-58, 59 Hide paint, 18 62 Hiding power... 

Optical particle counters, 13 150 Optical properties, See also Light properties... 

Particle contamination, in ion implantation, 14 445-446 Particle counters, 13 466 18 139 Particle counting... 

An acoustical particle counter for counting and sizing fog droplets has been evaluated by Singh and Reist.161 Fog droplets, mostly in the size range of 5-30 pm, were measured by the acoustical particle counter as well as an optical and an electron microscope for comparison. The mean droplet diameters estimated from the acoustical particle counter were in agreement with the microscope values. A Rich 100 condensation nuclei monitor was also operated simultaneously during the fog droplet counting to monitor condensation nuclei counts. 

One of SACHEM s products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. Suspended particles in TMAH solutions could cause severe mechanical damage to the electronic devices manufactured by their customers. The determination of the particle content in such solutions is therefore critical. It is performed with a laser-equipped particle counter, which provides 70% detection efficiency. The counting must take place in a clean room because tiny airborne particles can land in the solutions and give them a false high reading. A class 1000 environment is required in this case, which means that the count of particles in the air that are greater than or equal to 0.5 jrm in diameter must be less than 1000 per cubic foot. Typically, a customer s specification for TMAH solutions is less than 100 particles per milliliter for particles greater than or equal to 0.5 fim in diameter. 

Paul Plumb of SACHEM Inc. counts particles in the ultrapure solutions of TMAH by a laser-equipped particle counter in the clean room. Notice the hair net and special lab coat. 

Allen, J.S. An Improved Electron-Multiplier Particle Counter. Rev. Sci. lustrum. 1947,75, 739-749. 

The basic instrumentation in the present work is a Royco Model 225/518 High Concentration Particle Counter. The location of the air inlet and light sensing unit of the instrument in the card room has been described previously (2). The inlet was fitted with a vertical elutriator preseparator designed to prevent particles >15 vin aerodynamic diameter from entering the light sensor. Thus the collection efficiency of this instrumentation as a function of particle size should be similar to that of the Vertical Elutriator Cotton Dust Sampler. 

A miniaturized version of the conventional flask method with S. capricomutum has been developed by Blaise et al [136]. In this assay the algae are exposed to the toxicant in 96-well microplates for a period of 96 hours, after which the cell density is determined using a hemocytometer or electronic particle counter. ATP content measurements [136] or chlorophyll fluorescence [141,142] have also been proposed as test criteria. Compared to the flask method, the main advantages of the microplate assay are (a) the small sample volumes and reduced... 

The experimental DDO crystallizer was shown in Figures (2-3). A run was made for each set of conditions, e.g. DDO ratio, residence time and recycle ratio. The run was continued until a steady state CSD was obtained. (Size analysis was made using a PDI ELZONE 80 XY Particle Counter). Steady state was ascertained by analyzing particle size in sample intervals of one hour. 

The number distribution of particles having diameters from 0.03-10 urn was measured twice daily on most weekdays with a Thermo Systems electrical aerosol analyzer (EAA) ( ) and a Royco Model 202 Optical Particle Counter (OPC). These measurements were performed at a site three miles southeast of the air... 

The size distribution of the particulate matter in the 0.01-5 ym size range is analyzed on line using an electrical mobility analyzer and an optical particle counter. Samples of particles having aerodynamic diameters between 0.05 and 4 ym are classified according to size using the Caltech low pressure cascade impactor. A number of analytical procedures have been used to determine the composition distribution in these particles. A discrete mode of particles is observed between 0.03 and 0.1 ym. The major components of these particles are volatile elements and soot. The composition of the fine particles varies substantially with combustor operating conditions. 

There are several different approaches that are commonly used to determine particle size distributions in air. One of them, impaction, has been discussed earlier. Multistage impactors with different cut points are used extensively to obtain both mass and chemical composition data as a function of size for particles with diameters > 0.2 /xm. Others, including methods based on optical properties, electrical or aerodynamic mobility, and diffusion speeds, are described briefly in the following section. The condensation particle counter (CPC) is used as a detector in combination with some of these size-sorting methods. 

Calibration of these single-particle counters is usually carried out using monodisperse polystyrene latex or polyvinyl latex spheres, which are available in sizes from 0.1 to 3 /im and have a refractive index of 1.6 alternatively, aerosols with lower refractive indices may be generated from liquids such as dioctyl phthalate (m = 1.49). Whitby and Willeke (1979) discuss the... 

FIGURE 11.61 Theoretical response of a typical single-particle counter (adapted from Whitby and Willeke, f979 data from Cooke and Kerker, f975). 

Potential problems with using single-particle counters in ambient measurements and ways to minimize these are discussed in detail by Whitby and Willeke (1979). 

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