Particle counter calibration

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 11.62 Experimental calibration curves for a commercial single-particle counter and two types of calibration aerosols dioctyl phthalate (DOP) and coal dust (adapted from Whitby and Willeke, 1979). 

Photon correlators measure scattered light in a sol, equating this with size, and particle counters measure the conductivity or capacitance of dispersed solute calibration is necessary. From particle diameters, volumes can be calculated, assuming a spherical geometry. Sizes and distribution are reported as histograms (Fig. 1). 

Spectrex ILI-1000 Particle Counter combines the Prototron with a Particle Profile Attachment (multichannel analyzer). The instrument has been used [118] for examining volcanic ash. AC Fine Dust was used for calibration in eight 5 pm steps, which indicated that accurate data was obtained for sizes above 2 pm. It has also been shown to correlate well with the more tedious filtration and counting method for large volume parenteral liquids [119]. Although semi-transparent containers or liquids reduce the amount of transmitted light flux, the instrument gives valid data for particulates in oil [120]. 

Only through discrete particle counting can air cleanliness be verified, and the cleanliness class of the sampled environment established. " Periodic in-process monitoring of workstations, buffer rooms, anterooms, production areas, and any other area about which a definitive air cleanliness statement is made or reasonably assumed, should be carried out in accordance with SOPs or industry standards. A discrete particle counter (DPC) with an adequate sampling rate, calibration features, and dynamic range should be used for sample acquisition, based on the specified air cleanliness level. ... 

ISO 11171 specifies calibration parameters for instruments and sensors. Repeatability and reproducibility of particle counters are ensured by a traceable standard such as provided by the National Institute of Standards and Technology (NIST). The medium test dust (MTD) reference fluid SRM-2806A is used to certify that particle counters correctly determine the count and size distribution of particles. The ISO 11171 standard specifies the maximum allowable percent differences in particle counts between test runs. Only counters that are certified as passing the ISO 11171 standard should be used for oil condition monitoring [27]. 

ISO 11171 Hydraulic Fluid Power - Calibration of Automatic Particle Counters for Liquids, www.iso.org... 

Calibration should be traceable to national or international standards through an unbroken chain of comparisons. For instrumentation affecting sterility control in aseptic manufacturing facilities this usually involves comparison of values measured with the item of equipment under test, say a particle counter or a pressure differential gauge, with values measured with a standardized device. In many cases this may mean the use of external contract calibration services, with all that this implies in relation to assuring that the contractor s calibration control systems are themselves under good control. 

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. 

Optical particle counters—single counter useful for only 1 decade of size requires calibration sensitive to shape and refractive index 0.3 (commercial) 0.1 (research) 3-100 >200 possible 20 useful 1 particle/L Light-scattering from single particles... 

Optical particle counter (1) Analyzing particle size from 0.25 to 20 pm (1) Calibration and performance is influenced by particles with very different refractive indices (and shape factors) (2) Requirement of periodical calibration and recalibration... 

The optical particle counter (OPS) uses the principle of light scattering from airborne particles to determine particle size distribution [26]. It is a real time instrument that is typically used to measure particles above 0.05 pm in diameter. Many well established techniques are available for counting air particles. However, the calibration of any two air particle cotmters with the same reproducibility while taking the same air sample has created many challenges. 

Heidenreich and co-workers, have investigated the calibration of an optical stream particle counter using the Aerodynamic Particle Sizer manufactured by TSI Instruments Inc which will be described in the next section [46]. 

S. Heidenreich, H. Buttner, F. Ebert, Investigations in the behaviour of an aerodynamic particle sizer and its applicability to calibrate an optical particle counter . Part. Part. Syst. Charact., 12, 1995, pp. 304—308. 

Figure 4.7. Calibration curves of a combined scattering-extinction optical particle counter [ 10] (by permission of the author).

In this formula, there are two variables, A50 and b. If the response from the mean value of the calibration sample is taken as A50, there is only one parameter (b) to be determined by calibration. After a sample with a known particle size distribution is measured using an optical particle counter and its signal amplitude distribution is recorded, a minimization is carried out by comparing the measured data to theoretical data calculated using different values for b. This procedure should be performed a few times to obtain a representative result. Figure 4.22 shows the OPC result of a 500 nm polymer particle sample with and without correction for inhomogeneous illumination [26]. 

The second type of calibration standard is a batch ofpolydisperse particles with a known size distribution and a carefully determined concentration. For these polydisperse standards, the cumulative concentration at any selected size should not differ from the specified value by more than 10%, except for a certain population of particles that has only a few particles. This type of calibration can be carried out by incorporating data from another particle characterization technology. For example, by comparing the pulse-height distribution from an optical particle counter with the size distribution obtained using an aerod5Uiamic... 

Heidenreich, S., Friehmelt, R., Btittner, H., Ebert, F., Methods to Calibrate Optical Particle Counters, in Preprints of Partec 98, 7 European Symp. Part Charact, Nurnberg, 1998, pp.723-732. 

Peacock, S. L., Accomazzo, M. A., Grant, D. C., Quantitative Count Calibration of Light Scattering Particle Counters, J. Environ. ScL, 1986, 29,23-27. 

ISO/DIS 4548-12 Methods of Test for Full-Flow Lubricating Oil Filters for Internal Combustion Engines - Part 12 Particle Retention Ability and Contaminant Holding Capacity Using Particle Counting ISO/DIS 11171 Hydraulic Fluid Power - Calibration of Liquid Automatic Particle Counters... 

ASTM F328-98 Standard Praetiee for Calibration of an Airborne Particle Counter Using Monodisperse Spherical Particles... 

ASTM F65 8-87(1992) Standard Practice for Defining Size Calibration, Resolution, and Counting Accuracy of a Liquid-Borne Particle Counter Using Near-Monodisperse Spherical Particulate Material... 

ASTM F649-80(1992) Standard Practice for Secondary Calibration of Airborne Particle Counter Using Comparison Procedures... 

FIGURE 16.16 Calculated response curves for six materials and manufacturer s calibration curve for model LAS-X (PMS, Inc., Boulder, CO) optical particle counter. 

BS ISO 11171 1999, Hydraulic fluid power. Calibration of automatic particle counters for liquids... 

The efficiency of the counter measured in this manner will be somewhat in error since the calibration foils are much thicker than the foil discs. This error should be small compared with the error involved in the standard pile flux (10 percent and possibly greater). The selfabsorption of gamma rays in the thick foils will only be about one percent. This is the primary reason for counting gamma rays instead of beta particles. In order to calibrate a counter, a thick foil had to be used to obtain enough activation in the standard pile. If the beta particle s were counted, the self absorption loss would be as high as 20 percent for the gold foil used in the calibration. 

Counter, Gas-flow Proportional (GPC)—P-particles are detected by ionization of the counter gas which results in an electrical impulse at an anode wire. If a sufficient amount of radiostrontium is present and the ionization efficiency is calibrated, the quantity of radiostrontium can be determined. 

The variations in the background, the sensitivity to moisture, the alpha activity of the chamber itself and the influence of recombination were discussed by Hultqvist. The standard deviation due to counting statistics was estimated to be about 3 % (in a few measurements 6 %). The calibration was made by counting each alpha particle by a proportional counter specially designed at the Department for this purpose. The statistical uncertainty of the calibration of the equivalent radon concentration was estimated to be 12 %. 

The rooms without aerosol sources and low ventilation rate (v<0.3 hf1 ) had low aerosol concentrations (2 103 - 104 cm-3) due to the small influence of the higher aerosol concentrations outdoors (aerosols by traffic and combustions) (Table la). In this case the aerosol in the room air was aged by coagulation and plateout and had less condensation nuclei of smaller sizes (d<100 nm). Rooms with a moderate ventilation show higher particle concentrations ((1-5) 10 cm 3) (Table Ila). With aerosol sources in a room (Table III) the aerosol concentrations can increase to 5 105 particles/cm3. The relative error of the measured particle concentration is in the order of 15% primary determined by the uncertainties of the absolute calibrations of the condensation nuclei counter. 

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