GB588496A - Improvements in or relating to gas analyzers - Google Patents

Abstract

588,496. Magnetic tests and measurements. BAILEY METERS & CONTROLS, Ltd. Feb. 23, 1945, No. 4566. Convention date, Feb. 24, 1944. [Class 37] [Also in Group XXXV] The percentage in a gaseous mixture of a gas having a permeability different from that of the other constituents is determined by introducing the mixture in a gap in a magnetic circuit, varying the reluctance of the gap by periodically inserting and withdrawing a body of substantially unity permeability, and utilising the resulting flux variations to generate a potential which is a function of the permeability of the gaseous mixture. The gaseous mixture to be examined, for example flue gas the percentage of oxygen in which is to be determined, is passed through a closed chamber formed by an axially magnetised Alnico ring 1, Fig. 2, closed at its ends by soft iron plates 2. Each plate 2 has mounted thereon eight coil windings 4 supported by soft iron cores 5 equiangularly spaced about a rotary spindle 20. Pole pieces on opposite plates are aligned and spaced apart about one-eighth of an inch. In the airgap between the pole pieces is a rotatable disc 6 of non-magnetic insulating material such as quartz, glass, or a plastic secured to the spindle 20 and having eight equally spaced radial fingers 7. The spindle 2 is rotated at high speed by a motor 8, Fig. 4, so that the fingers 7 are alternately interposed between the pairs of aligned pole pieces and removed from the air gaps. The disc may alternatively be provided with holes so arranged that alternately pairs of aligned pole pieces are separated by material of the disc and the spaces between the pole pieces are wholly filled with the gas. The permeance of the gaps thus varies by an amount depending on the difference between the permeability of the gas and of the material of the disc. The flux is thus periodically varied and an alternating voltage is induced in the coil windings and is applied to an amplifier 22, the output of which is passed by way of a band filter 23 and power amplifier 24 to current indicating and recording instruments 25, 26 in series with an inductance 27 for rendering the output insensitive to fluctuations in speed. The filter 23 eliminates frequencies produced by vibration. In order to compensate for the permeability of the disc not being exactly unity a compensating, voltage of opposite polarity may be introduced into the output of the amplifier in order to cancel the amplifier output when no oxygen is present. Alternatively a compensating generator operating in a vacuum or inert gas such as nitrogen may be driven by the motor 8. According to another method the disc is made of a section of paramagnetic material bonded with a section of diamagnetic material, for example a celluloid disc may have a lacquered coating of ferric oxide. Static charges induced on the disc may be removed by a brush bearing on a very thin coating of colloidal graphite on the disc, or the disc may be made of a semi-conducting material.