Method and apparatus for measuring gaseous oxygen
First Claim
1. In a system for measuring the percentage content of oxygen gas in an unknown or sample gas by comparison with a reference gas, the combination of a magnetic bridge including means forming a pair of major flux circuits, each having a gap therein, valve means for synchronously and alternately filling said gaps with the reference and sample gases, means interconnected between said major flux circuits for forming a null magnetic bridge arm for deriving a magnetic flux proportional to the difference in circuit reluctance of the major magnetic circuits, sense coil means coupled to said null arm for generating a time varying electrical signal proportional to the magnetic flux in said null arm.
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Abstract
An oxygen detection system including two equal and symmetrically constructed major DC magnetic circuits each having an air gap which is alternatively filled with a sample and a reference gas. A magnetic bridge arm connects the major magnetic circuits in series opposition to derive a null response when the flux carried in the magnetic circuits is equal and a component of varying flux when the sample and reference gases are interchanged to cause an unequal flux to be developed in the circuits caused by a change in the reluctance across the gaps. An encircling inductance coil senses the flux in the null bridge arm which is electronically sampled in sychronism with the sample and reference gas interchange to develop a difference signal directly derived and proportional to the difference in magnetic susceptibility of the sample and reference gases. An active magnetic shield cancels stray fields from affecting the sensor.
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Citations
7 Claims
- 1. In a system for measuring the percentage content of oxygen gas in an unknown or sample gas by comparison with a reference gas, the combination of a magnetic bridge including means forming a pair of major flux circuits, each having a gap therein, valve means for synchronously and alternately filling said gaps with the reference and sample gases, means interconnected between said major flux circuits for forming a null magnetic bridge arm for deriving a magnetic flux proportional to the difference in circuit reluctance of the major magnetic circuits, sense coil means coupled to said null arm for generating a time varying electrical signal proportional to the magnetic flux in said null arm.
- 5. In a magnetic bridge circuit in which a null arm connects primary flux paths and serves as a magnetic bridge to sense differences in said primary paths, an active shield for surpressing stray induced magnetic fields comprising a sense coil surrounding said null bridge arm, a driven null coil surrounding said null arm and closely coupled with said sense coil to form a closely coupled transformer, an amplifier having an input connected to said sense coil and an output connected to drive said driven coil to produce a magnetic field in opposition to a sensed stray EM fields crossing said sense coil.
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