How is it made only one cell to pass through an aperture ?

[Garoll]

The question is related to impedance cell counting, determining cell`s size etc.
This method is working like this:
"A small portion of the diluted fluid in each bath is allowed to flow past a small aperture. An electrical current is produced in each aperture by two electrodes, one on the inside and the other on the outside of the aperture. The saline solution is responsible for conducting current between the electrodes. The cells move through the aperture one at a time. When a cell enters the aperture, it displaces a volume of electrolyte equal to its size. The cell acts as an electrical resistor, and impedes the flow of current. This produces a voltage pulse, the magnitude of which is proportional to the size of the cell. Instrument electronics are adjusted to discriminate voltage pulses produced by different cells." - Surgery Encyclopedia

So my question is: How it is guaranteed that only one cell will pass through this aperture?
Maybe two little cells can pass through it and make a resistance as if one big have passed?

 

[Mapes]

Hi Garoll, welcome to PF. This is indeed a source of error in Coulter counting. But if the cell concentration is sufficiently dilute, the chance of getting two adjacent cells will be low. The chances are even lower that the two cells will be relatively small and thus misinterpreted as a single large cell rather than detected as an outlier and ignored.

 

[Garoll]

Thank you for the clarification, it seems reasonable.
By the way, does this Coulter Counter has something in common with the Beckam Coulter company ?

 

[Mapes]

Thank you for the clarification, it seems reasonable.
By the way, does this Coulter Counter has something in common with the Beckam Coulter company ?

http://en.wikipedia.org/wiki/Wallace_H._Coulter" .