Electric sensing zone testing
woman doing electric sensing zone testing

Electric Sensing Zone

Electric Sensing Zone, also referred to as the Coulter Technique or Coulter Counter, is a true high-resolution, high-speed particle counter and particle size distribution analyzer. It covers a nominal span of about 1.0 µm to 260 µm. Being a true particle counter, the instrument can also be used to determine the concentration of Particles/mL of Fluid vs. Size.

During this process, particles suspended in a conductive fluid (aqueous or organic) are drawn through a precision sapphire aperture, on either side of which are two platinum electrodes. A current is impressed upon the electrodes, resulting in a constant voltage across the aperture. Upon the passage of a particle through the aperture, a voltage pulse is generated due to the change in electrolyte resistance. The change is proportional to the volume of the particle, determining the envelope volume of a particle in three dimensions. The signal is counted as one event (i.e. particle count) while, simultaneously, the volume is directly determined.

Because there are no optical theories of light involved in the measurement principle, data presented on the basis of Equivalent Spherical Diameter is enhanced.

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  • Not sensitive to color, refractive index, density, conductivity or particle opacity
  • Suitable for analyzing samples of mixed optical properties, densities, and shapes
  • Suitable for irregularly shaped (e.g. elongated or needle like) particles
  • Low quantities of sample are analyzed
  • Conforms to ISO 13319:2021 Determination of particle size distributions – Electrical sensing zone methods


  • Heterogenous material cannot be distinguished
  • Allows blending of data from multiple orifice tubes to cover the entire detection range
  • Concentration (particles per mL) requires additional (optional) analysis

Sample Requirements

If the samples have a lot of particulate, approximately 100 mL is required. If the sample is mostly clear, closer to 500 mL is needed.

For dry materials a minimum of 200 mg is needed, though 1 to 2 grams is recommended.

Detection Range

Covers a nominal span of about 1.0 µm to 260 µm.

Data Reported

A comprehensive summary including the general graphical particle size distribution on both a volume-weighted and number-weighted basis will be provided, as well as the most commonly requested parameters (10th, 50th and 90th percentiles, etc.). Information on specific sizes can be reported on request.


Particle Technology Labs uses the Micromeritics Elzone II 5390 which is a 300-channel analyzer with high resolution.

Micromeritics Elzone II 5390

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