88 AK 98™ Dialysis Machine - Technical description
HCEN12630 Revision 07.2015
Program version 1.xx
The heater unit is connected to the relay board, via a cable. The temperature
transducer is connected to a transducer board, via a cable. The transducer board
interfaces directly to the General I/O board, via a board connector.
The temperature maximum deviation from set value is 35°C to 39°C (default) the limit
is wider during priming, low limit is 32.5°C. If the temperature exceeds these limits a
temperature alarm is issued.
Feeding pumps
The water flushes through the ceramic house of each pump to create a water film
which acts as a lubricant. The pumps are ceramic high-precision units, they never
wear out, and never need calibration.
This is how the pump works: The pump piston has a small cut-away on the last 5–6
mm. By combining rotation with an up–and–down movement, the pump volume is
“sucked–lifted–moved–and–pressed” from the pump inlet to the outlet. (What is inlet
and outlet is simply a question of which way the piston rotates).
The piston is rotated by a stepper motor – the up–and–down movement comes from
mounting the pump at an angle to the motor. The small pin on the piston is connected
to the rotating plastic arm through a spheric (ball-shaped) bearing for full freedom of
movement.
Mixing chambers
The mixing chambers are used to mix the fluid and bypass air, if any, to avoid
disturbance in the conductivity measurement.
A mixing chamber consists of a housing and a nipple in the top. The housing is sealed
with an O-ring in the top and welded together in the bottom.
Conductivity cells
The conductivity measuring unit is used to measure the conductivity of dialysis fluid
composition. It consists of a mechanical part, a transducer board, two shielding
carbons and a PT-100. The mechanical part consists of plastic isolators and carbon
electrodes.
The transducer board contains driver and receiver circuitry. The shielding carbons are
used to protect the measurement from noise in the fluid path. The conductivity of the
fluid is dependent on the temperature and the PT-100 is used to measure this.
There are four different conductivity cells in the machine:
● Conductivity cell A
● Conductivity cell B
● Conductivity cell P
●
Conductivity cell C (Diascan
®
) (option)
Conductivity cell P, located right after degassing, is used by the protective system as a
conductivity guard.
BiCart
®
cartridge holder
The BiCart cartridge holder is a device to hold the BiCart cartridge or the CleanCart
cartridge. Bicarbonate concentrate is produced by mixing water with bicarbonate
powder inside the disposable BiCart cartridge.
Citric acid is produced in the similar way using the disposable CleanCart cartridge.
Fluid spillage is prevented by valves. Magnet sensors indicate closed arm position.
Flow pumps
Gear pumps controlled with a duty cycle.
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