Instruction Manual
Model MicroCEM
b.Paramagnetic Oxygen Method
The paramagnetic principle refers to the induction of a weak magnetic field, paral- lel and proportional to the intensity of a stronger magnetizing field.
The paramagnetic method of determina- tion of oxygen concentration utilizes nitro- gen filled quartz spheres arranged at opposite ends of a bar, the center of which is suspended by and free to rotate on a thin platinum wire ribbon in a cell.
Nitrogen (N2) is used because it is dia- magnetic or repelled by a magnet.
A small mirror that reflects a light beam coming from a light source to a photode- tector, is mounted on the platinum ribbon. A strong permanent magnet specifically shaped to produce a strong, highly inho- mogeneous magnetic field inside the analysis cell, is mounted outside the wall of the cell.
When oxygen molecules enter the cell, their paramagnetism will cause them to
be drawn towards the region of greatest magnetic field strength. The oxygen molecules thus exert different forces on the two suspended nitrogen filled quartz spheres, producing a torque which causes the mirror to rotate away from its equilibrium position.
The rotated mirror deflects the incident light onto the photodetector creating an electrical signal which is amplified and fed back to a coil attached to the bar holding the quartz spheres, forcing the suspended spheres back to the equilibrium position.
The current required to generate the restoring torque to return the quartz bar to its equilibrium position is a direct measure of the O2 concentration in the sample gas.
The complete paramagnetic analysis cell consists of an analysis chamber, permanent magnet, processing electronics, and a temperature sensor. The temperature sensor is used to control a heat exchanger to warm the measuring gas to about 55 °C. Refer to Figure
Permanent Magnet
Platinum Wire
Mirror
Quartz Sphere(s)
Wire Loop
Light
Source
Photodetector
Amplifier
Display
Figure
Description and Specifications | Rosemount Analytical Inc. A Division of Emerson Process Management |