| 摘要 |
776,770. Electric tests. MINE SAFETY APPLIANCES CO. Feb. 11, 1954 [Feb. 26, 1953], No. 4024/54. Class 37. A cell for the electrochemical detection of the percentage oxidizing component (e.g. oxygen) of a gas mixture comprises a zinc electrode, and a carbon electrode whose surface is insulated except for a small window area, the gas being passed through a central bore of the carbon electrode to permeate through the untreated window area and react with a liquid electrolyte, producing an E.M.F. which is indicative of the percentage oxygen content of the gas mixture, and is measured in a circuit giving a substantially linear response characteristic. Cell construction.-The cell container 1 (Fig. 1), of insulating material contains a liquid dielectric, a zinc electrode 3 supported by a stainless steel rod 4, and a carbon electrode 5 whose external surface is coated with enamel 5b except for recessed windows 6, which may be one to four in number depending on the percentage oxygen content to be measured. The gas is passed through a hole 5a running through the middle of the carbon electrode 5, the gas and the liquid electrolyte diffusing through the window 6 of the carbon rod 5 to give an output voltage dependent on the percentage oxygen content. The liquid dielectric is a 2-5 per cent solution of ammonium chloride with hydrochloric or sulphuric acid added to a pH of 3.0. Measuring circuit.-In one embodiment (Fig. 14), the output current of the cell 1 is made proportional to the percentage oxygen content by backing off the current at zero oxygen content with an auxiliary battery 16, which produces a substantially constant P.D. across the tapped-off part of a potentiometer 17 to oppose the zero current, whereupon the current shown in meter 22 is made substantially proportional to the oxygen content of the gas passing through the cell 1 by a predetermined choice of circuit component values. In another method using the same circuit and based on the fact that the percentage oxygen content is proportional to the electrical power developed, the voltage on meter 27 and the current on meter 22 are made constant by adjustment of potentiometers 17 and 21, whereupon the oxygen content is proportional to the current in the auxiliary circuit as indicated by meter 25. The circuit may also include an adjustable shunt resistor 28 (Fig. 11), across the auxiliary battery 16 to simulate the ageing of the cell 1, and a zero adjusting circuit 31 which supplies a small zeroizing current through the meter 22. Specifications 749,147 and 776,771 are referred to. |
