Oxygen Measurement; Paramagnetic Measurement; Fig. 3-4: Paramagnetic Oxygen Sensor - Assembly Principle - Emerson Rosemount Analytical X-STREAM X2 Series Instruction Manual

Instruction Manual
HASX2E-IM-HS
10/2012

3.2 Oxygen Measurement

Two different principles are used for mea-
suring oxygen concentrations. The currently
used principle is given by the channel code
(sample gas designator) on the nameplate
label ( see figure on page 2-21):
pO2 = paramagnetical sensor
eO2 = electrochemical sensor
3.2.1

Paramagnetic Measurement

Oxygen measurement is based on the para-
magnetical characteristics of oxygen mole-
cules:
Two nitrogen filled quartz spheres (N
paramagnetic) are arranged in a dumbbell
configuration and, hinged to a platinum wire,
placed inside a cell. Fixed to the wire a small
mirror reflects a light beam to a photo detector
(fig. 3-7).
The measuring cell is placed inside an in-
homogeneous magnetical field generated
by a strong permanent magnet of specific
design.
Oxygen molecules within the sample gas now
due to their paramagnetical characteristics
are deflected into the area of highest field
strength. This generates different forces on
both spheres and the resulting torque turns
dumbbell and mirror out of the rest position.
This generates a photodetector signal becau-
se the beam is deflected, too.
Initiated by the photodetector signal a pre-
amplifier drives a compensation current
through a loop surrounding the dumbbell to
turn back the dumbbell into the rest position
by effect of a magnetic field
So the current compensating the torque
affec-ting the dumbbell is a direct measure for
the oxygen concentration within the sample
gas.
Emerson Process Management GmbH & Co. OHG
3.2 Oxygen Measurement
In addition to measuring cell, permanent
magnet, electronics and enclosure the para-
magnetic oxygen detector contains a tempe-
rature sensor and a heating element to hold
the detector at approx. 55 °C.
Several variations are available including
corrosion resistant, solvent resistant and/or
intrinsically safe (for measuring flammable
gases) versions.
is not
2
1 Permanent magnet
2 Platinum wire
3 Mirror
4 Glass ball
5 Loop
Fig. 3-4:
X-STREAM X2
10 11
4 1 5 2 3
6 Photodetector
7 Light source
8 Preamplifier
9 Display
10 Gas inlet
11 Gas outlet
Paramagnetic oxygen sensor -
Assembly principle
7 9
6 8
3-5