7. Dialysate Preparation
proportional to the negative peak of the AC stimulation voltage.
The other is proportional to the negative peak of the probe's AC
current.
The ratio of the voltages is proportional to the resistance of the
respective probe. The resistance of the probes has been modeled
as a function of temperature and conductivity. Since each of the
conductivity probes contains a thermistor, the temperature at each
probe is known. The conductivity is calculated using the
temperature and resistance readings measured at the probes. The
UF–Proportioning system generates alarms from the measured
conductivities at the “A” and “B” probes. Since these conductivity
alarms are used to verify the proportioning ratios, the alarms are
generated by testing the “A” conductivity and the “B” portion of
the total conductivity (“B” portion = “B” conductivity – “A”
conductivity). The alarm limits are determined from the
concentrate treatment mode and are stored in the UF–
Proportioning controller by the SBC. Therefore, only during a
bicarbonate treatment would the SBC store a non-zero expected
“B” conductivity portion.
The UF–Proportioning microcontroller directly deactivates the
bypass valve (removing flow through the dialyzer) during a backup
conductivity alarm when in the Dialyze Mode.
The UF–Proportioning microcontroller indirectly (via the 8040
microprocessor) triggers an audible and visual alarm.
7.7 CENTRAL CONCENTRATE SUPPLY SYSTEMS
The optional internal concentrate line regulators permit the
Instrument to be used with central concentrate delivery systems.
Figure 7-2 shows the position of these regulators in the fluid path.
The concentrate surface height of the gravity-feed system must be
between 2 feet and 60 feet (0.6 to 18 m) above the Instrument floor
level. Pump-driven concentrate supply systems must provide
concentrate to the Instrument at 1 to 30 psi (52 to +1560 mmHg).
To provide the optimum performance, the preferred range for
gravity-feed systems is 2 to 20 feet (0.6 to 6 m) and for pump-
driven systems is 1 to 10 psi (52 to 520 mmHg). In addition, the
concentrate flow rate to each Instrument for a dialysate flow rate of
500 mL/min must be at least 35 mL/min for acid and 60 mL/min
for bicarbonate. For a dialysate flow rate of 1000 mL/min the
concentrate flow rate must be at least 70 mL/min for acid and 120
mL/min for bicarbonate.
157-1278-914 Rev A 7-17
January 2004
To Next Page
Loading...
