Arena Service Manual
5.7.4 Bypass System and Flow Sensor
Single Board Computer
Figure 5-22. Bypass System
The Bypass Mode is initiated when a primary dialysate alarm is
detected by the I/O Controller board, when a redundant dialysate
alarm is detected by the UF-Proportioning Controller board, when
the host requests bypass, or when the manual bypass button is
pushed.
The bypass valve is in the bypass position when de-energized. It is
driven from the nominal +24 VDC supply with an on/off transistor
control on the I/O Hydraulics Power board.
To verify that there is not a failure in the bypass system, a flow
sensor just downstream of the predialyzer bypass valve checks for
flow. If flow exists during the bypass mode, a Bypass Fail Alarm
is set and the Instrument is put in the safe, nonfunctional,
Shutdown state. If there is no flow when not in the bypass mode, a
No (dialysate) Flow alarm is generated.
This flow sensor consists of two thermistors. The first is a
reference thermistor used to determine the fluid temperature. The
5-38 157-1278-912 Rev A
November 2003
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