Datex-Ohmeda S/5 G-AO, Technical Reference Manual, Page: 23 / 83

S/5 Airway modules
Document No. 800 1005-1
17
Figure 10 CO
2
/N
2
O/AA measurement block diagram
2.2.3 OM measuring unit
The oxygen measurement is based on the paramagnetic susceptibility, which is a unique property
of oxygen among all gases generally present in a breathing gas mixture. The gas to be measured
and the reference gas, which usually is room air, are conducted into a gap in an electromagnet with
a strong magnetic field switched on and off at a frequency of approximately 110 Hz.
An alternating differential pressure is generated between the sample and reference inputs due to
forces acting to the oxygen molecules in a magnetic field gradient.
The pressure is measured with a sensitive differential transducer, rectified with a synchronous
detector and amplified to produce a DC voltage proportional to the oxygen partial pressure
difference of the two gases.