Datex-Ohmeda S/5 monitors
Document No. 800 1009-1
14
D-fend
TM
The sample is drawn through a sampling line. Then gas enters the monitor through the water trap,
where it is divided into two flows, a main flow and a side flow. The main flow goes into the
analyzers. This flow is separated from the patient side by a hydrophobic filter. The side flow creates
a slight subatmospheric pressure within the D-fend water trap which causes fluid removed by the
hydrophobic filter to collect in the bottle.
Zero valve and absorber
The main flow passes through a magnetic valve before
proceeding to the analyzers. This valve is activated to establish
the zero points for the TPX and OM units. When the valve is
activated, room air is drawn through the absorber into the internal
system and the gas sensors. Paralyme is used as an absorbent.
Figure 5
Absorber
Nafion
TM
A nafion tube is used between the water trap and the zero valve to balance the sample gas
humidity with that of ambient air. The tube will prevent errors caused by the effect of water vapor on
gas partial pressure when humid gases are measured after calibration with dry gases. Another
nafion tube is used between the absorper and the pneumatic unit to prevent humidity caused by
absorb of CO
2
.
Gas analyzers
After the zero valve and nafion tube the gas passes through TPX and OM units. The oxygen sensor
has two inputs. One input accepts the main flow and the other draws in room air for reference. Both
gas flows exit from a single port.
Sample flow differential pressure transducer
The sample flow differential pressure transducer measures pressure drop across OM inlet restrictor
and calculates sample flow from the pressure difference.
Working pressure transducer
The working pressure transducer measures absolute working pressure between the TPX unit and
OM unit. It is used for messages: ‘sample line blocked’, ‘check D-fend’, ‘replace D-fend’ and
‘check sample gas outlet’.
1)
Nafion is a trademark of Perma Pure Inc.