Coulter counter

A Coulter counter is an apparatus for counting and sizing particles suspended in electrolytes. The Coulter counter is the commercial term for the technique known as resistive pulse sensing or electrical zone sensing. The apparatus is based on the Coulter principle named after its inventor, Wallace H. Coulter.

A typical Coulter counter has one or more microchannels that separate two chambers containing electrolyte solutions. As fluid that contains particles or cells is drawn through the microchannels, each particle causes a brief change to the electrical resistance of the liquid. The counter detects these changes in the electrical resistance.