HCEN12630 Revision 07.2015
Program version 1.xx
AK 98™ Dialysis Machine - Technical description 73
3.3.3.4.2 Conductivity Control System, bicarbonate
The conductivity set point is calculated on basis off the sodium set value, bicarbonate
set value and the information in the concentrate preset.
The bicarbonate mode uses two feedback loops: one for the A-pump (the acid
component) and one for the B-pump (the bicarbonate component). Both pump speeds
are monitored and compared with the calculated speeds to ensure that pump speeds
stay within limits, which are ±10% for the A-pump, and ±20% for the B-pump by
default. If these limits are exceeded there will be a pump speed alarm or attention.
Refer to the AK 98 operator's manual for more information.
The relative pump speed – the deviation between the actual and calculated speed, in
percent, can be logged, of course, and should ideally be zero. On a machine running
with WRO-supply and high quality concentrates, it will normally be very close to zero.
3.3.3.4.3 Composition supervision
The pump speed of each feeding pump is supervised by the protective system. The
control system uses the conductivity values measured from conductivity cells A and B.
The conductivity cell P measures the total conductivity of the fluid.
The dialyzer is bypassed if the conductivity exceeds the alarm limits.
Despite the supervision functions, there is a risk that the dialysis fluid has the correct
conductivity but an incorrect composition.
The composition of the dialysis fluid is supervised during pre-treatment and treatment,
in order to detect if conductivity cell A does not measure correctly. The composition
supervision can detect if the wrong concentrates are used at the same time as the
conductivity is between the alarm limits. This can happen if the powder in the BiCart
cartridge does not dissolve properly.
The composition supervision is monitoring the pump speed ratio. It is the actual pump
speed that is monitored. An alarm or attention will be generated if the pump speed
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