Resistazone counter

Resistance furnaces Resistance welding Resistant starch Resistazone counter Resistherm PH-10 Resistivity... 

A general term used to refer to any of the particle or drop-let-sizing techniques that rely on (usually) conductivity or capacitance changes in sample introduced between charged electrodes. Also termed resistazone counter . 

Consider the ideal case of a single smooth sphere present in the center of a cylindrical orifice. It is possible to deduce a simple relationship relating resistance changes in the orifice to the dimensions of the fineparticle and the orifice. Early workers with resistazone counters established that this relationship held for spherical fineparticles provided that the diameter of the fineparticle did not exceed 40 % of the diameter of the orifice. Other experimental studies show that, in general, using the simple orifices available in the early instruments, fineparticles with dimensions of less than 3 % of the diameter of the orifice could not be characterized easily. This lower limit has been reduced by modern techniques such as hydrodynamic focusing and the use of contoured orifice equipped with flow straighteners of the type discussed later in this section [6-8]. 

Figure 6.1. A basic resistazone counter uses the change in resistance of the volume of fluid between the two electrodes to count fineparticlcs as they are drawn through the orifice.

In practice, resistazone counters are calibrated by using standard spherical fmeparticles. Often the assumption that the pulse height is proportional to the volume of the fineparticle is used to extend a one-point calibration by using spheres of known size to calibrate the instrument. Therefore, data from most resistazone characterization studies are not always absolute, and the sizes quoted are often for equivalent spheres. Any report of data from a resistazone counter smdy should clearly state any use of a calibration standard. 

Early workers using resistazone counters anticipated that the behavior of metal fmeparticles in the counter would differ from that of dielectric fineparticles. In practice, it was found that all fineparticles investigated behaved as if they had insulating... 

Figure 6.2. In the IITRl improved resistazone counter, a metal electroformed sieve acts as one electrode and prevents oversize fineparticles from enterii the sensii zone or extremely large fineparticles from blocking the orifice. The hole through the Teflon block between the electrodes acts as a flow straightener.

DeBlois and Wesley used a Nuclepore filter to create a resistazone counter of very small aperture that could be used to measure the size of small objects such as bacteria and viruses [4]. Typical pulses obtained by DeBlois are shown in Figure 6.4. The equipment is available commercially as the Nanopar analyzer [4]. 

Figure 6.4. Using a Nuclepore membrane filter, DeBlois and co-workers made a resistazone counter with an orifice small enough to measure the size of viruses. (Reprinted from [38], John Wiley and Sons.)...

Figure 6.5. High resolution data from the Elzone resistazone counter for a phosphor powder used in the manufacture of television screens, as reported by Kahrun. a) DiflFerential number data for the phosphor powder, b) Differential volume data for the phosphor powder. (Used by permission of R. Kahrun.)...

The way in which the data from a resistazone counter is aflfected by shape of the powders involved is demonstrated by the data shown in Figure 6.6 generated by Allict and Switzer [16]. The powders studied are shown in Figures 6.6(a) and (b). (The shape and surface structure of these powders were discussed in Chapter 2.) In Figures 6.6(c)... 

E. J. Wynn, M. J. Hounslow, Coincidence Correction for Electrical-Zone (Coulter Counter) Particle Size Analyzers , Powder TechnoL, 93 (1997) 163—175 Information on the Coulter Counter is available from Coulter Particle Characterization Electronics Inc., R O. Box 169015, M/C 195-10, Miami, Florida, USA, 33116-9015. Information on Celloscope and Electrozone resistazone counters can be obtained from Particle Data, Inc., P. O. Box 265. Elmhurst, Illinois 60126. 

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