Electrical particle counters

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. 

Note DMS differential mobility spectrometer, SMPS scanning mobility particle sizer, CPC condensation particle counter, TDMPS twin differential mobility particle sizer, DMPS differential mobility particle sizer, OPC optical particle counter, APS aerodynamic particle sizer, MAS mass aerosol spectrometer, LAS-X optical laser aerosol spectrometer, ELPI electrical low pressure impactor... 

The HVAC controls for critical (validated) areas should be grouped in specified field panels. One may want to label these panels Critical Process Controls Please Follow Change Control Procedures or something similar. This will prevent the necessity of having to validate noncritical controls. Electrical supplies and other utilities must also be evaluated. One may need a UPS (Uninterrupted Power Supply) for critical field panels and PC workstations to continuously moifitor critical equipment such as refrigerators, incubators, and particle counters with the BMS. 

Tuch et. al. [231] ran a Mobile Aerosol Spectrometer (0.1 to 2.5 pm) and an Electrical Aerosol Spectrometer (0.5 to 10 pm) side by side for 6 weeks and found both to be reliable with almost identical results. Total number counts agreed with results from a Condensation Particle Counter. 

ASTM F-662-86 (1992), Measurement of particle count and size distribution in batch samples for filter evaluation using an electrical resistance particle counter, 450... 

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. 

One potential method for measuring the size of aerosol nanoparticles is a scanning mobility particle sizer (SMPS), consisting of a differential mobility analyzer (DMA) and a condensation particle counter (CPC). Aerosol particles enter the DMA where they are charged using a radioactive source and their size is classified based on the electrical mobility, Z, of the particles in the applied electrical field ... 

Figure 6. Basic electrical resistance particle counter (modified from Lieberman, 1996).

Coulter counter Coulter principle Electrical particle detection... 

An optical microscope, a standard set of sieves, an Andreasen Pipette, and any versatile instrumental particle sizer, such as a laser diffraction equipment or an electrical sensing zone particle counter. 

Calibration with known size particles (such as polystyrene latex beads) is used to relate the size of the electrical pulse to the size of the particle. So, the particle counter not only detects that a particle has been detected in the fluid but also the size of the particle. The size threshold determines whether the pulse is large enough to be considered a particle detected or if below the threshold then relegated to just background noise. Liquid chemical particle counters are available for the size range of 0.04—20 pm. 

K. T. Whitby and W. E. Clarke, Electric Aerosol Particle Counters and Size Distribution Measuring System for the Range 0.015 to 1 Micron Size. Tellus 18 (1966), 573—585. Commercial information on the Whitby aerosol analyzer is available from Thermo Systems, Inc., 2500 Cleveland Avenue North, St. Paul, Minnesota, USA 55113. 

Clearly, it is important that any particle counter/ sizer should measure a large number of particles in order to achieve the greatest statistical confidence in the results. In electrical sensing zone models, the concentration should be sufficiently great, but not too great to exceed coincidence limitations. Larger measurement volumes may be preferred, at lower concentrations. Of course, in contamination studies where there are low numbers of particles per unit volume, ideal counting statistics may never be achieved. 

H.G. Merkus, H. Liu and B. Scarlett Improved Resolution and Accuracy in Electrical Sensing Zone Particle Counters through Hydrodynamic Focussing. Part. Part. Syst. Charact. Z (1990) 11-15. 

ASTM F662-86(1992)el Standard Test Mefliod for Measurement of Particle Count and Size Distribution in Batch Samples for Filter Evaluation Using an Electrical Resistance Particle Counter... 

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. 

A Geiger counter monitors radiation by detecting the ionization of a low-pressure gas, as shown in the illustration. The radiation ionizes atoms of the gas inside a cylinder and allows a brief flow of current between the electrodes. The resulting electrical signal can be recorded directly or converted into an audible click. The frequency of the clicks indicates the intensity of the radiation. A limitation of Geiger counters is that they do not respond well to 7 rays. Only about 1% of the 7-ray photons are detected, whereas all the (3 particles incident on the counter are detected. Because the efficiency of a Geiger counter depends on the size of the tube, a counter used to monitor a wide range of activities usually contains two tubes of different sizes. 

Perhaps the most useful method for determining particle distributions is that of electrical conductivity, the most widely used instrument is the Coulter Counter (named after the Inventors), although there are now other similar instruments on the market. Originally, this instrument was designed to measure blood corpuscles which are 2-8 p in size. It has proven to be very... 

Ionic compounds such as halides, carboxylates or polyoxoanions, dissolved in (generally aqueous) solution can generate electrostatic stabilization. The adsorption of these compounds and their related counter ions on the metallic surface will generate an electrical double-layer around the particles (Fig. 1). The result is a coulombic repulsion between the particles. If the electric potential associated with the double layer is high enough, then the electrostatic repulsion will prevent particle aggregation [27,30]. 

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