10.1 Measuring Principles (continued)
The measured volume drawn through the aperture is 270 µl (Manufacturer
calibrated). Based on the assumption made above, the system will count
270*125 = 33,750 pulses, which is equivalent to 5.0x10
6
cells/µl in the
concentrated blood.
The calculation principle for white blood cells is the same but with a
difference in dilution ratio and cell quantity. An example of this could be as
follows: 5,000 cells/ µl diluted 1:400 =12.5.
10.2 Counting Time RBC & WBC
The counting time is defined as being the time needed for the sample to fill the
metering unit from the start to the stop detector.
The normal counting time limits for the RBC and WBC metering units are
between 13 – 18 seconds and 10 – 13 seconds respectively. If the counting
time is below or exceeds the above mentioned limits, the flag ST, TL or TU
will be displayed.
The ´counting time´ is not related to the actual result. Atmospheric pressure
variations, protein built up within the orifice (aperture) and other secondary
effects that might cause pressure changes will NOT affect the counted
parameters RBC, PLT and WBC.
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