CELL-DYN
3000 System Operator’s Manual
3-19
9140240E — May 1995
Chapter 3 Principles of Operation
The count portion of the cycle is initiated when the meniscus reaches the
upper detector. The count cycle stops when the meniscus reaches the
lower detector. The amount of time required for the meniscus to travel
from the upper to the lower detector is called the RBC count time. The
computer also monitors the time it takes the meniscus to reach the upper
detector once the RBC/PLT cycle is initiated. This is called the RBC
upper metering time. (For convenience, these times are referred to as
“RBC” times. Both times actually monitor the RBC/PLT metering
process.)
The RBC count time (CNT) and the RBC upper metering time (UMT)
are automatically monitored to detect variation from the expected values.
Variation may be caused by debris in the aperture, vacuum fluctuation or
air bubbles in the metering tube. If significant variation is detected, the
bulletin line on the
METERING FAULT-CLOG or FLOW ERROR and the RBC and PLT
data are suppressed.
At the end of each cycle, the RBC count time is displayed on the
to the right of the MPV result. If an RBC metering
fault was detected, one of two messages is displayed and printed: the
message if either time is too slow or the
message if either time is too fast. Both the RBC upper metering
time (UMT) and the RBC count time (CNT) are displayed and printed
when an RBC metering fault occurs.
RBC/PLT Measurement
The 1:12,501 RBC/PLT dilution is delivered to the mixing chamber in
the RBC/PLT transducer assembly where it is bubble mixed. A 100 µL
metered volume of the dilution is drawn through the 60 x 72 µm aperture
by vacuum. The RBCs and PLTs are counted by impedance. If the pulse
generated is above the PLT lower threshold (1 fL), it is counted as a PLT.
If the pulse generated is above the RBC lower threshold (35 fL), it is
counted as an RBC. There are 256 size channels for each of the
parameters, each RBC size channel being equivalent to 1 fL and each
PLT size channel being equivalent to 0.137 fL.
The von Behrens Plate located in the RBC/PLT transducer counting
chamber minimizes the effect of recirculating cells. As cells exit from the
aperture, they tend to swirl around and may re-enter the sensing zone and
be counted a second time, causing the counts to be falsely elevated.
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