GB900891A - Flame ionization detector - Google Patents

Abstract

900,891. Determining relative quantities of fluid mixture constituents. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. May 5, 1961 [May 6, 1960], No. 16114/60. Class 37. In a flame detector for measuring the conductivity of a flame to determine the concentration of organic material in a gas which may be a hydrogen carrier from a chromatography tube, a third electrode 9 is positioned between a pair of electrodes 6, 2 which are connected in series with a power source 7, whereby a varying voltage from a source 10 applied to the third electrode can temporarily and repeatedly interrupt the current from source 7 so that a variable signal which may be amplified in an A.C. amplifier 11 is developed across a load resistor 8. In a modification described with reference to Fig. 2 (not shown) in which a plurality of load resistors 8 provide for the selection of different ranges, the current across the detector flame is opposed by the current through a reference flame detector burning pure hydrogen, and a further electrode is provided as an electrostatic screen to prevent induction in the measuring circuit from the varying potential source 10. A detector cell having concentric mesh electrodes around the burner is described with reference to Figs. 3 and 4 (not shown). Inaccuracy in the detector due to the current peaks after interruption by a positive voltage peak from source 10 being different from those following a negative peak, which are presumed to be inaccurate due to space charges is overcome in a further embodiment by removing the latter. A switch which is synchronized with the variations in source 10 which may be a vibrator or a transistor switching network is used to eliminate the unwanted half cycles and may only sample the electrode current in the vicinity of its peak, a filter then being provided to eliminate the source frequency and smooth the pulses.