12
Operating Instructions BioPAT
®
Xgas
Design and Function
3.1.1
Pressure Measurement
A piezoresistive silicon pressure sensor is used to
measure the pressure.
3.1.2 Humidity Measurement
A capacitive polymer sensor is used to measure
the humidity.
3.1.3
CO₂ Measurement
The CO₂ sensor comprises an IR radiation source, a
detector and the reflection measuring cell (Fig. 2).
The infrared beam is reflected by the gas-filled
measuring adapter. The light, now weakened by
the CO₂, is measured by the detector.
A translucent sapphire disc prevents the optical
components from getting soiled by constituents
of exhaust air.
3.1.4
O₂ Measurement
The BioPAT
®
Xgas oxygen sensor is based on an
oxygen pump cell and runs independently of
reference gases. Applying voltage to the cell
moves the oxygen ions from the cathode to the
anode and generates current. Through a diffu-
sion barrier in front of the cathode, a saturation
current is generated by increasing the supply
voltage, which allows measurement of the
ambient oxygen concentration.
Fig. 2: Measuring setup of the
CO
2
sensor
Fig. 3: Measuring setup of the
O
2
sensor
