Filter
Top Products
MEASURING PRINCIPLE
2 - 6
ETC00781(1) Series 100 e 10/2001
2.2 Oxygen Measurement
Depending on analyzer model different measuring methods will be used.
The installed type of oxygen sensor is to identify at the channel code (see Fig. 1-1).
% O
2
para. = paramagnetic Sensor
% O
2
chem. = electrochemical Sensor
2.2.1 Paramagnetic Measurement
The determination of O
2
concentration is based on the paramagnetic principle (magneto-
mechanic principle).
Two nitrogen filled (N
2
is diamagnetic) quartz spheres are arranged in a "dumbbell" configuration
and suspended free to rotate on a thin platinum ribbon in a cell.
A small mirror that reflects a light beam coming from a light source to a photodetector, is mounted
on this ribbon. A strong permanent magnet especially shaped to produce a strong highly inhomo-
geneous magnetic field inside the analysis cell, is mounted outside the wall.
When oxygen molecules enter the cell, their paramagnetism will cause them to be drawn towards
the region of greatest magnetic field strength. The O
2
molecules thus exert different forces which
produce a torque acting on the sphere arrangement, and the suspended “dumbbell”, along with
the mirror mounted on its suspension ribbon, will be angulary rotated away from the equilibrium
position.
The mirror then will deflect an incident light beam onto the photodetector which itself produces an
electric voltage. The electric signal is amplified and fed back to a conducting coil at the “dumbbell”,
forcing the suspended spheres back to the equilibrium position.
The current required to generate the restoring torque to return the “dumbbell” to its equilibrium
position is a direct measure of the O
2
concentration in the gas mixture.
The complete analysis cell consists of analysis chamber, permanent magnet, processing
electronics, and a temperature sensor. The sensor itself is thermostat controlled up to approx. 55
°C. For warming up the measuring gas is conducted via a heat-exchanger.
Optionally we have built-in a solvent resistant cell or an intrinsic safe cell for potentially explosive
atmosphere.
OXYGEN MEASUREMENT (PO
2
PARAMAGNETIC PRINCIPLE)