Abacus
4
Service Manual
5
2.1.1. Counting chamber with electrodes and measuring aperture
Impedance method is used for determination of volume and number of cells. In this method a
known volume of dilution is drawn through a small aperture. Constant current is passed through
the aperture from one side to the other. When a cell passes through the aperture, it causes a
change in resistance, which generates a voltage pulse.
The amplitude of the voltage pulse is proportional to the ratio of cell volume per aperture
volume. This is used to determine the volume of cells. The number of cells can be obtained by
counting the pulses.
In the instruments there is one cell-counter probe: the aperture size is 80
µm and has a
reference electrode assembly and U-shaped metal fixing as it is shown in the figure below.
The aperture is made of ruby and it is molded into the measuring tube.
2.1.2. HGB Head
Hemoglobin head is placed around the measuring chamber.
It contains: light source (LED) at 540 nm wavelength and Photo Detector (TSL235). The Photo
Detector converts the light to frequency. The HGB concentration is a logarithmic function of this
frequency measured by the FPGA circuit of the COMB card.
This counter counts up while the LED is on and counts down while the LED is off, the LED and
the
counter directions are switched with a 100 Hz signal. This method provides “real time
backlight correction”, which makes the HGB measurement more precise in changing backlight
environment situations as well.
Connection to the amplifier
LED
TSL235
Assembled Cell-counter Probe
Measuring tube
Measuring tube
Reference electrode
assembly
U-shaped metal fixing
Aperture (80
µm)
O-ring
