
Fabius
®
Function Description
2-57
Cop
yr
ight
2000 Dr
aeger
M
edical,
In
c.
sec2_f
uncdescri
p_b
.fm
11
FiO
2
Measurement
The O
2
sensor measures the fraction of inspired O
2
(FiO
2
) in the respiratory gas.
The O
2
sensor contains an alkaline electrolyte, a lead anode, two gold cathodes, and
a plastic membrane. The spatial separation of the two gold cathodes allows to carry
out a voltage comparison.
The O
2
sensor is an electrochemical cell which generates a voltage from the ion
current.
Fig. 40:
O
2
sensor
The O
2
to be measured diffuses through the plastic membrane, reacts at the gold
cathodes (negative polarity) and forms lead oxide and water at the lead anode
(positive polarity). During this chemical process, an electrical voltage is generated
which is proportional to the O
2
partial pressure.
The internal resistance is determined by the surface of the gold cathodes, the O
2
diffusion velocity, and the distance between the gold cathodes and the lead anode.
The resistance is approximately 700 ohms.
This chemical process is temperature-sensitive. Therefore temperature-sensitive
resistors are connected in parallel to the O
2
sensor. These resistors and the internal
resistance of the O
2
sensor correct the measuring voltage. Due to the two gold
cathodes used in the O
2
sensor cell, two different measuring voltages are generated.
These measuring voltages are compared with each other.
If the O
2
sensor fails, the control box will indicate an error on the graphics display.
gold cathode 1
gold cathode 2
lead anode
alkaline electrolyte
plastic housing
O2
–
ϑ
plastic membrane
Содержание Fabius 4116029
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