| 摘要 |
PURPOSE:To lower the concn. of the gas in a gaseous mixture to the measuring limit or less of a limiting current type gas sensor, by mixing a standard gas with a gas to be measured in a mixing ratio of a specific value or less. CONSTITUTION:A vacuum pump 21 is started and a valve 17 is closed while a valve 14 is opened and only the standard gas in a tank 10 is guided into an oxygen concn. measuring part 9 and the concn. of oxygen is measured by a limiting current type oxygen sensor 1. Next, both of the valves 14, 17 are opened and a gaseous mixture of a gas to be measured and the standard gas is guided to an oxygen concn. measuring part 19 and the concn. of oxygen is measured by the oxygen sensor 1, and flow rate control valves 13, 16 are adjusted so as to lower the concn. of oxygen to 95% being a measuring limit or less. the measured values of flowmeters 12, 15 are read and the real concn. of oxygen in the gas to be measured is calculated on the basis of the mixing ratio of the gas to be measured and the standard gas, the concn. of oxygen in the standard gas and the measuring result of the oxygen sensor 1 by ratio calculation.
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