Arena Service Manual
water on/off valve. When the magnet is above the sensor, the
condition indicates the air trap is full, closing the incoming water
on/off valve.
In normal operation, as the supply pump draws solution from the
air trap chamber to fill the flow equalizer, the liquid level in the
chamber is lowered along with the float causing the water on/off
valve to open so water again fills the chamber.
When the air trap level rises, the level sensor signal shuts off the
water on/off valve. This cycle is repeated during every fill phase
of the flow equalizer.
4.2.7.4 "A" Conductivity Probe/Thermistor Set
This is one of three conductivity probe sets. The other two are
described in Section 4.2.10.3, "B" Conductivity Probe/Thermistor
Set, and Section 4.2.13.1, Dialysate (Primary) Conductivity
Probe/Thermistor Set.
Figure 4-6. "A" Probe/Thermistor Set
Conductivity is used as a measure of the electrolyte composition of
dialysate. The hardware for measuring conductivity is always a
cell for measuring changing resistance as the amount of dissolved
salt changes and a thermistor for measuring temperature changes.
Electronic circuits are used to equate these changing resistances to
the standard measuring conditions of a 1 cm cell at 25 Celsius.
The information from these devices can be used to give us
conductivity in the units of milliSiemens/cm (mS/cm) @ 25°C.
The “A” conductivity thermistor is not used to control or monitor
the temperature of the dialysate. It is calibrated with the other
thermistors during temperature calibration.
4-8 157-1278-893 Rev A
January 2004
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