Filter
Top Products
MEASURING PRINCIPLE
2 - 7
ETC00303(1) BINOS E e (2.0) 11/00
Rosemount Analytical
2.3 Oxygen Measurement
Depending on analyzer model different two measuring methods will be used.
2.3.1 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" configu-
ration 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. BINOS E provides a thermostat controlled sensor at
approx. 55 °C. The temperature sensor is used to control the heating system.
OXYGEN MEASUREMENT