A Coulter counter measures suspended particles by detecting electrical pulses as they cross a constricted conducting path. A particle with different electrical properties from the suspending fluid changes the electric current. Counting pulses in a measured volume gives an estimate of particle abundance, with dilution used to recover the value for the original sample.[ref]
Means for counting particles suspended in a fluid by Wallace H. Coulter. US2656508A, description of Figs.1–4
Wallace H. Coulter's patent, filed in 1949 and granted in 1953, describes two insulating vessels, electrodes and a narrow passage, with detection circuitry registering particle events. It also identifies masking when particles occupy the sensitive region together.[ref]
Means for counting particles suspended in a fluid by Wallace H. Coulter. Publication history; Figs.6–7 and masking discussion
For a synthetic example, 2,500 accepted pulses in of a 100-fold diluted suspension implyThe estimate assumes representative sampling and correctly counted events. A pulse is not automatically a blood cell of a particular type: debris, coincident passage and classification thresholds affect what is counted.
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