Coulter Device

(also Coulter counter), an instrument for carrying out dispersion analysis of powders and various disperse systems with a liquid conducting dispersion medium. It was developed and first patented by the American W. Coulter in 1953.

The Coulter counter (see Figure 1) measures the voltage pulse arising when a particle passes through an opening in a nonconducting barrier (the ampul wall). The voltage pulse results from an increase in the resistance between the electrodes (4) at the moment in which the particle carried along by the stream of conducting liquid passes through the opening. The pulse amplitude is proportional to the volume of the particle. The system being analyzed, such as a suspension, is sucked into the ampul from the beaker as a result of the fall of the mercury under the influence of gravity in the right-hand column of a manometer (3) when the external vacuum source is turned off. Automatic counting of the pulses and their classification according to amplitude makes it possible to plot curves of particle size distribution (dispersity). Sets of interchangeable ampuls with various aperture sizes make possible the dispersion analysis of suspensions, emulsions, and gas bubbles in liquids with a particle size of 0.3 to 800 microns.

Figure 1. Coulter device: (1) and (2) beaker and ampul with a microscopic aperture, both filled with an aqueous suspension; (3) mercury manometer; (4) electrodes; (5) contact system for (6) counter-recorder

Coulter devices are used in industry, in scientific research, and in medical practice in the analysis of powders (pigments, abrasives, and food products) and the monitoring of dissolution, crystallization, and coagulation processes, as well as to determine pollution levels caused by mechanical impurities in water and other liquids and for carrying out blood counts.