Datex-Ohmeda CAPNOMAC ULTIMA, Service Manual

Page: 61 / 232

5.3
CAPNOMAC ULTIMA
TM
SERVICE MANUAL
5-13
O
2
measurement
The oxygen measurement is based on the paramagnetic
susceptibility, which is a unique property of oxygen among
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.
CAUTION:
Due to the complicated and sensitive mechanical
construction any service inside the O
2
measuring unit should not
be attempted, and therefore the detailed description of the
circuitry and layout of the transducer is omitted from this
manual.
Reference in
Air gap
Switched
magnetic field