Servomex Or Pato - Dräger Medical Zeus Technical Documentation Manual

Function description
7.4

Servomex or Pato

7.4.1 Servomex
7.4.1.1 Measurement principle
7.4.1.2 Function
44
The patient gas analyzer may be equipped with different oxygen sensors.
The "Servomex" oxygen sensor is used in the GMZ. The "Pato" oxygen sen-
sor is used in the GMZ 2.
Both oxygen sensors measure the patient's O2 concentration at the Y-piece.
The oxygen sensor uses the effect that oxygen molecules are attracted very
much more strongly to a magnetic field (paramagnetism) than the molecules
of other gases, which in some cases are repelled by the magnetic field (dia-
magnetism).
Permanent magnets (7 and 12) in the sensor of the oxygen analyzer provide
a symmetrical magnetic field (11)
nitrogen-filled quartz spheres (9) arranged in the form of dumbbells at the
location of the highest field strength. The dumbbell is suspended rotating
from a taut platinum band. A reel of platinum wire is wound around the dumb-
bell as a feedback coil (10).
When oxygen flows through the measuring cell (1 and 6), the magnetic field
(11) changes based on the paramagnetic effect of the oxygen dependent on
its concentration. This rotates the quartz spheres (9) of the dumbbells out of
the magnetic field.
A mirror attached to the pivot of the dumbbell (8) reflects a light beam (5) onto
a photocell pair (4). The photocells are connected to an amplifier (3) of which
the output signal supplies the feedback coil (10) of the dumbbell. The dumb-
bell is rotated back by the current in the feedback coil (10) until the light beam
(5) is illuminating both photocells (4) equally by means of the mirror (8). Then
the system is at equilibrium. The current flowing through the feedback coil
(10) is proportional to the partial pressure of the oxygen and thus to the oxy-
gen concentration, which is displayed on the display instrument (2).
(Figure 23). The magnet field contains two
Zeus
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