| 摘要 |
PROBLEM TO BE SOLVED: To provide a gas detector which reduces the influence due to environment, such as temperature, humidity, wind velocity or the like and which can detect changes in the concentration of a specific gas, and to provide an autoventilation system for a vehicle which uses the gas detector. SOLUTION: In the gas detector 10, using a gas sensor element 11 whose sensor resistance Rs is changed according to the concentration of a gas such as NOx or the like and in the autoventilation system 100 for the vehicle, the output of a sensor-resistance value conversion circuit 14 is A/D-converted, a sensor output value S(n) is acquired, a base value B(n) is calculated using B(n)= B(n-1)+k1 S(n)-B(n-1)}, and a difference value D(n)=S(n)-B(n) is calculated. When the concentration of the gas becomes high and when the difference value becomes higher than a prescribed concentration threshold, a concentration high- signal is generated, a flap 34 is closed, factor k2 which is smaller than k1 is used, and the base value B(n) is calculated using B(n)=B(n-1)+k2 (S(n)-B (n-1)}.
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