GB699641A - Improvements in gas analyzers - Google Patents

Abstract

<PICT:0699641/III/1> <PICT:0699641/III/2> <PICT:0699641/III/3> A gas analyser for continuously determining the content of a paramagnetic gas in a mixture is provided with an elongated temperature sensitive resistor disposed lengthwise in a horizontal tubular gas cell, the axis of the resistor being displaced from the plane defined by the lines of maximum intensity of a magnetic field between pole pieces disposed lengthwise on opposite sides of the cell. The magnetic convection currents assist or oppose the thermal convection currents thus cooling or heating the resistor, the change in temperature of which is proportional to the paramagnetic gas content of the mixture in the cell. In Figs. 1 and 3 identical resistors 16 and 17 are placed in gas cells 14 and 15, the latter being for comparison purposes, on either side of a supply pipe 12. The cell 14 is subjected to an offset magnetic field from magnet 22 with pole pieces 23 (Fig. 3) which set up magnetic convection currents (full lines) to assist thermal convection currents (dotted lines) thus cooling the resistor 16 which with resistor 17 form adjacent arms of a Wheatstone bridge circuit. The unbalance of the bridge consequent upon the cooling and hence decrease in resistance of resistor 16 is proportional to the paramagnetic gas content. Alternatively, as shown in Fig. 7, the magnetic field is applied to both cells, preferably on the same side of the supply pipe, the magnetic convection currents opposing in one and assisting in the other the thermal connection currents, the resistors as before being incorporated in a Wheatstone bridge. Either of the above types of circuits may be used in conjunction with the other the cells in one circuit being filled with a standard gas. The ratio of the unbalance of the two bridges is then measured. Slack diaphragms are provided in the cells containing the standard gas, if other than air, assuming the test cells are worked under atmospheric pressure. In a further modification a single gas cell is provided, the resistor of which forms one arm of a Wheatstone bridge, which is operated isothermally, the unbalance of the bridge being corrected by increasing manually or automatically, the current input to the bridge to restore the temperature of the resistor. An ammeter, voltmeter or wattmeter measuring the current, voltage drop or : input is calibrated to read directly in terms of the paramagnetic gas content. Preferably such a bridge containing instead a cell containing a standard gas is connected, preferably in parallel to a second bridge circuit otherwise similar containing the analysis cell, the first bridge controlling the input to the second. The unbalance of the second cell is measured as before. It is preferable in this case to connect the two four-armed bridges to a six-arm bridge supplied with current from a common source. The isothermal operation of the first circuit, containing the standard gas may also be effected by a separate heater circuit controlled by the unbalance of the first circuit.