基本信息
摘要：1479925 Measuring gas concentration electrically WESTFALISCHE BERGGEWERKSCHAFTSKASSE 24 Aug 1974 37347/74 Heading G1N A method, for determining the concentration of carbon monoxide or methane in a mixture of gases, involves use of a metal oxide semi-conductor (MOS) 2 having a heating coil 7 energized from a current source 8 though a switch 9 actuated by a control 10 so that the temperature of the semiconductor is varied between two given temperatures at predetermined intervals. For example the lower temperature is above -20‹C and the higher temperature is below 800‹C. In a preferred embodiment the lower temperature is ambient temperature. The relay 11 is actuated to be open when the switch 9 is closed and vice-versa. Since the speed of reaction of methane and other hydrocarbons on the surface of the oxide semi-conductor is lower at low temperatures than is that of carbon monoxide, the latter is indicated at temperatures in the normal ambient range whilst at higher temperatures the variation in resistance of the semi-conductor is determined mainly by methane. In an alternative embodiment Fig. 2 (not shown) a permanently heated MOS (16), in parallel with the first (2), is provided for compensation of cross-sensitivity against methane. Alternatively Fig. 3 (not shown), the second permanently-heated MOS may be substituted for the series measuring resistor 3 shown in Fig. 1.
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