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The electrical resistance measurementv(ERM) method of measuring the particle size and particle counting utilizes the effect which nonconducting particles have on the electrical resistance of a suspension of such particles in conductive fluid. This effect can be enhanced by limiting the flow to a narrow aperture with the cross section comparable in size to that of the particles. A particle passing through such aperture causes a momentary change (pulse) of the aperture resistance (see also ERM method detects particle charge. The amplitude of that rise is proportional to the particle volume, hence this method yields the ESD as the particle size. This phenomenon has been employed in the Coulter counter, developed by Wallace H. Coulter (Coulter WH 1949, Coulter WH 1957) and introduced in mid 1950s as an automated blood cell analyzer.
Although aimed at the clinical market, the Coulter counter was quickly adopted in other fields. Sea water is a conducting fluid naturally suitable for use as a suspension medium with the Coulter counter. Hence, applications in marine sciences soon followed (for example, Sheldon and Parsons 1967, Sheldon RW et al 1972, Kranck K and Milligan 1979).
Commercially available particle counters based on the electrical resistance principle include:
The low end of the particle size range characteristic of the electroresistive particle counters is on the order of few tenths of 1 µm (for example, Longhurst AR et al 1992, see also Electrical resistance nanoparticle counter on microchip). The upper end reaches about 600 µm. The particle size range accessible with a single aperture is about 2% to 50-60% of the aperture diameter, i.e. 2 to ~50 µm for a 100 µm aperture. Hence, measurements of the PSD in a wider particle size range require using a series of apertures with a suitable range of diameters. Such multi-aperture measurements present a nontrivial problem of splicing the PSDs obtained each with a different-diameter aperture (for example, Milligan TG and Kranck 1991).
The ERM method is also referred to as the Coulter method, the aperture impedance technique (Jackson GA et al 1995), the electrozone or electrical sensing zone method (for example, Xu R and Di Guida 2003), and the electroresistance method (for example, Milligan TG and Kranck 1991).
| CITATION: Jonasz M. 2006. Electrical resistance (Coulter) method: Principle and instruments (www.tpdsci.com/Tpc/ERM.php). In: Top. Part. Disp. Sci. (www.tpdsci.com). |
HISTORY: Published: 22-Feb-2006 Modified: 22-Aug-2011 Peer-reviewed: PENDING |
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