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| Typical Number in Hospital: 5 | Cost Bands: 4 | References: 6 |
Oxygen is unique among gases in that it is strongly paramagnetic. Thus it will move towards a stronger part of a magnetic field, whereas other gases are diamagnetic and move away. The device consists of a small glass dumbell with the bulbs filled with nitrogen (diamagnetic). These are placed between magnetic poles shaped to provide a gradient of magnetic field so that they tend to move in the direction of decreasing field strength. The dumbell is suspended at its centre on a torsion wire such that rotation occurs in proportion to the difference in magnetic properties between the nitrogen in the bulbs and the surrounding gas. The test gas is fed into the space between the magnetic poles such that the rotating force depends on the concentration of oxygen in the test gas.
A direct reading instrument can be constructed by fitting a small reflecting mirror on the dumbell, but more accurate and linear types employ electrostatic or magnetic feedback such that the rotating force is measured with only minimal movement. Such devices provide accurate, fast acting and robust oxygen analysers suitable for measuring oxygen in a wide range of gas mixtures.
Content and Design Copyright 2000 Dr. Malcolm C Brown. See Title Page for more details