Particle counting instrument

Let us suppose that we have a particle counting instrument which sorts and counts the number of particles at a given particle size. The experimental data that we collect are ... 

Part 7 describes recommended methods for the use of single particle light interaction methods, such as those which are widely used for particle contamination monitoring, in liquids and in gases. This Standard recommends calibration by the use of latex particles the now suspect AC Fine Test Dust method was deliberately not included. This decision was in line with other Standards, such as BS 5540 Part 6 "Evaluating Particulate Contamination of Hydraulic Fluids Method of Calibrating Liquid Automatic Particle-Count Instruments" (now near to final draft). 

Another method is to count particles between a given range and then sum the counts as in 5.9.1. Alternately, one can purcheise an automatic peurticle counting instrument for about 50-60,000. The instrument consists of a microscope, a scanning device (usually a flying-spot sceumer), a television display and a pre-programmed microprocessor. All of the particles within a... 

Air-Classification Measurement Electronic airborne particle monitoring instruments count and size particulate matter in the sampled air with no consideration of whether the particles are viable or nonviable. Air classification is defined as the number of particles per cubic foot of air that are larger than 0.5 pm in diameter. Climet and HIAC-Royco are common instruments for airborne particulate monitoring). 

Time of flight (TOF), 75 660-661 Time-of-flight (ToF) mass analyzers, 24 109 Time of flight diffraction (TOFD), 79 486 Time-of-flight instrumentation, in particle counting, 78 150—151 Time-of-flight-SIMS technique, 24 109 Time-resolved fluorimetry, 74 148-149 Time-resolved spectra, analysis of, 74 613 Time standards, 75 749—750 Time-temperature parameters (TTP), 73 471, 478, 479 creep properties and, 73 480 Time-temperature superposition, 27 746-747... 

Radioactivity of uranium can be measured by alpha counters. The metal is digested in nitric acid. Alpha activity is measured by a counting instrument, such as an alpha scintillation counter or gas-flow proportional counter. Uranium may be separated from the other radioactive substances by radiochemical methods. The metal or its compound(s) is first dissolved. Uranium is coprecipitated with ferric hydroxide. Precipitate is dissolved in an acid and the solution passed through an anion exchange column. Uranium is eluted with dilute hydrochloric acid. The solution is evaporated to near dryness. Uranium is converted to its nitrate and alpha activity is counted. Alternatively, uranium is separated and electrodeposited onto a stainless steel disk and alpha particles counted by alpha pulse height analysis using a silicon surface barrier detector, a semiconductor particle-type detector. 

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. 

Spherical particles of known diameter (e.g., 5% to 20% of the diameter of the aperture in the glass tube) are used to calibrate the electrical pulse counting instrument. The particles are suspended to an appropriate concentration in electrolyte solution (see recipe). Monodisperse latex particles are commercially available, which can be used for this purpose. Particle size calibration standards can be obtained from a number of chemical suppliers or from the National Institute of Standards and Technology (e.g., NBS 1003b). Lines (1996) lists a number of standards that are appropriate for this purpose. 

Laser diffraction is most suitable for analyzing dilute emulsions that are fluid, and therefore competes directly with electrical pulse counting methods, which are applicable to similar systems (see Alternate Protocol). Most laser diffraction instruments can cover a wider range of particle sizes (i.e., 0.01 to 1000 pm) than electrical pulse counting instruments (i.e., 0.4 to 1000 pm using a number of different aperture sizes), and do not require the presence of electrolyte in the aqueous phase, which could destabilize some electrostatically stabilized emulsions. Nevertheless, electrical pulse counting techniques are considered to have greater resolution. 

The major disadvantage of the laser diffraction and electrical pulse counting techniques is that they are only directly applicable to dilute emulsions or emulsions that can be diluted without disturbing the particle size distribution. However, many food emulsions are not dilute and cannot be diluted, either because dilution alters the particle size distribution or because the original sample is partially solid. For concentrated systems it is belter to use particle-sizing instruments based on alternative technologies, such as ultrasonic spectrometry or NMR (Dickinson and McClements, 1996). 

ISO 14644 describes methodology and instrumentation for particle counting in the clean room. The tests described there are the basis for assigning a cleanliness rating... 

Climet manufacture the following range of instruments for liquid-borne and air-borne particle counting. 

The instrument has also been used for size analysis of sugar crystals from 40 pm to several mm in size. By means of a vibratory feeder, the sugar is fed in free fall, past a vision camera and sized every 5s. The final result of the measurement is available after 100-300 frames and documented via an interface with a database and printer. Measured data includes particle count and size or projected area. 

Spectrex SPC-510 (Figure 9.14) uses both diffuse vertical illumination for visual identification of large particles and a scanning laser for detection of small particles. The instrument is widely used for quantitative particle counts in bottles [116] including in situ examination of bottled beer [117]. 

KRATEL Instruments GmbH and Ci)KG, KRATEL PARTOSCOPE F Particle Counting System, Operators Manual, Stuttgart (1982). 

There are many accounts of alpha particle detection instruments for the measurement of Rn (Sedlet, 1966). Lucas (1957) was one of the first to develop a very low background counting system. Higgins et al. (1961) adapted the method for well-water Rn and Ra surveys. Peacock and Williamson (1962) developed a shallow-borehole probe using ZnS(Ag) that could make in-situ Rn determinations without the use of a pump, but required a 5 cm diameter light-proof hole into which the ZnS(Ag)-coated Incite rod and photomultiplier assembly was inserted. Rushing et al. (1964) used a similar technique for the determination of Rn in effluents and environmental samples. For U prospecting, Dyck (1969) and Allen (1976) applied a Lucas-type cell to determine Rn in soil, lake waters and stream waters. 

A pressure gauge at the diffuser Inlet monitored the gas pressure Into the diffuser while the gas was Injected from a cylinder. The vessel was maintained at atmospheric pressure or slightly higher. Particles of known diameter were Injected Into the vessel using the PMS particle generator. Particle counts were obtained with and without particles Introduced In the vessel surrounding the diffuser. The gas pressure at the diffuser Inlet was Increased until no statistically significant differences were observed In the proper Instrument channels In the two modes of operation. 

The tests utilized to measure these contaminants and degradation by-products include infrared (IR) spectroscopy, electronic particle counting (PC), Karl Fischer titration (KFT), atomic emission spectroscopy (AES) and X-ray fluorescence (XRF) spectroscopy. These methods are available in the form of off-line or at-line benchtop instruments and online/in-line sensors. Most off-line instruments are automated to provide several hundred analyses per day by a single technician. At-line instruments and sensors permit immediate results and diagnostic capabilities. Online sensors can be integrated into machinery control systems to provide real-time monitoring capability. 

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]. 

The AeroSizer, manufactured by Amherst Process Instmments Inc. (Hadley, Massachusetts), is equipped with a special device called the AeroDisperser for ensuring efficient dispersal of the powders to be inspected. The disperser and the measurement instrument are shown schematically in Figure 13. The aerosol particles to be characterized are sucked into the inspection zone which operates at a partial vacuum. As the air leaves the nozzle at near sonic velocities, the particles in the stream are accelerated across an inspection zone where they cross two laser beams. The time of flight between the two laser beams is used to deduce the size of the particles. The instrument is calibrated with latex particles of known size. A stream of clean air confines the aerosol stream to the measurement zone. This technique is known as hydrodynamic focusing. A computer correlation establishes which peak in the second laser inspection matches the initiation of action from the first laser beam. The equipment can measure particles at a rate of 10,000/s. The output from the AeroSizer can either be displayed as a number count or a volume percentage count. 

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