GB896288A - Improvements relating to a galvanic detector cell - Google Patents

Abstract

896,288. Determining relative quantities of fluid mixture constituents. MINE SAFETY APPLIANCES CO. April 8, 1960, No. 12647/60. Class 37. In a galvanic cell 1, Fig. 1, for measuring the concentration of a depolarizing component, e.g. oxygen in a gaseous mixture, a polarizable tubular porous carbon electrode 11 the outside of which is waterproofed at 14 to render it impervious to the electrolyte but pervious to the gaseous mixture, is closed at the end 13 and includes within its bore a tube 6 which leaves a narrow passage 12, the bore of the tube and the passage providing, with hose fittings 5, 8, for the admission and withdrawal of the mixture. Zinc annular electrode 18 is supported by a stainless steel rod 19, and the portions 13 of electrode 11 are coated to limit the effective area. The upper portion of electrode 11 and the clamping head 4 are sealed from the electrolyte by a rubber shield 16. The electrolyte may be acidified ammonium chloride having a pH of 3.0, together with buffering materials. The cell and external resistances are designed to make the meter current proportional to the square root of the oxygen concentration and the meter is provided with a square root scale, this relationship rendering the internal resistance independent of the oxygen concentration. The meter circuit includes a cell 32, Fig. 3, which provides a current in opposition to that of the test cell 30, adjustment of the injected current being achieved by potentiometer R6, a resistor R1 having previously been set by a standard cell. A switch S1 provides a circuit for checking the potential of cell 32, and a resistance R4 is adjustable to give the correct residing when the test cell is exposed to a gas of known oxygen content. A wiper of resistance R14 mechanically coupled to wiper 36 on resistance R4 corrects for deviation from the square root calibration resulting from the adjustment of R4. A potentiometer 34 provides for zero adjustment in an oxygen-free gas. The apparatus may be used for determining the concentration of other oxidizing components of a gaseous mixture such as fluorine, chlorine and some oxides of nitrogen. Calibration of cathodes, i.e. marking with opposing voltage necessary when in use is also described. Specifications 896,289 and 896,290 are referred to.