Question on dead times

Josep M. Gasol pepgasol at
Thu Aug 6 03:50:33 EST 1998

Dear friends,

Following some recent comments I would like to ask if anybody knows for
sure what's the "true" rate of particles that the electronics of a
FacsCalibur can see without losing events due to them passing in the dead
time zone. My experience counting natural planktonic bacteria suggests that
a flow rate above 500 particles per second underestimates true
concentration (measured with an alternative method). This can certainly be
due to two bacteria coming in the same drop through the laser, but could
also be due to the electronics not being able to handle that many events
per second. By the way, anyone has an idea of a way of checking for two
particles going in the same drop ? Increasing bead concentration and
relating doublets to singlets could be a way. Anyone ever tried ?

A further related question: If I am gating what I see with a "software
gate", (I mean not an electronic gate), I imagine that I should be
concerned with the "total flow rate" (particles in my gate and those
outside the gate) and not with the "acquired data rate". Am I right ?

Thanks for your help !

Josep "Pep" Gasol

Josep M. Gasol
Institut de Ciències del Mar, CSIC
Pg. Joan de Borbó, s/n
E-08039 Barcelona, CATALUNYA
Phone: 34 93 221 6416
Fax: 34 93 221 7340
email address: pepgasol at
Department's web page:   <>

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