Biotek MultiFlo FX, Руководство оператора

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Peri-pump: How it works | 153
Peri-pump: How it works
The Peri-pump component dispenses fluid using a peristaltic pump. It works by
expelling a portion of fluid trapped between advancing rollers. The tubing is
pinched by the rollers to form a full aliquot or
slug
.
Peri-pump drum
The volume of fluid in a single slug depends on the tubing size and linear distance
between rollers. As the rollers spin, the fluid advances and is expelled at the tip in
finite aliquots or slugs. The volume of each slug is the amount of fluid squeezed
between two adjacent rollers.
The stepper motor turns the pump a determined number of steps. The pump drum
can be advanced in smaller increments than the distance between rollers to expel a
fraction of the full aliquot. However, the volume of the fractions is variable,
depending as it does on many factors (exact rotor position, tubing tension, tip
geometry, etc.). The variation between volumes of fractional aliquots is significantly
higher than between dispenses done with full aliquots. Thus,
the best possible
performance and reproducibility from dispense to dispense is done in full
aliquot increments
. That is, specifying a 1 µL dispense volume when using the 1
µL cassette, 5 µL dispense volume when using the 5 µL cassette, and 10 µL
dispense volume when using the 10 µL cassette. The exception is for instruments
that support 0.5 µL dispensing. These late-model instruments apply an offset to the
stepper motor to ensure precise and repeatable dispenses using a 1 µL cassette to
dispense 0.5 µL aliquots, which is the only half increment permitted. Only a 0.5 µL
dispense volume can be requested, not 1.5 or 2.5 µL, for example.
The tubing cassettes are calibrated by stretching the tubing to the size required to
accurately dispense the expected volume per aliquot. BioTek calibrates cassettes to
meet the
specifications
before shipping them. Over time the tubing’s properties
BioTek Instruments, Inc.