Gas sensor

A gas sensor comprising:

• paired first and second thermal conduction type gas detection elements;
• a first storage portion having a first internal space in which the first gas detection element is disposed, and having a first opening establishing communication between the first internal space and an outside space exposed to a detection subject atmosphere;
• a second storage portion having a second internal space in which the second gas detection element is disposed, and having a second opening establishing communication between the second internal space and the outside space;
• a first membrane formed of a material allowing permeation of water vapor and substantially not allowing permeation of a detection target gas, and disposed so as to cover the first opening;
• and
• a calculation unit for calculating a concentration of the detection target gas contained in the detection subject atmosphere introduced into the second internal space, based on outputs from the first gas detection element and the second gas detection element, respectively;
• wherein the gas sensor further comprises a second membrane formed of the same kind of material used to form the first membrane, having a thickness larger than that of the first membrane, and disposed so as to cover the second opening;
• the second membrane having a communication hole extending therethrough in a thickness direction for establishing communication between the outside space and the second internal space;
• and
• the gas sensor having a response time of 3 seconds or less for detecting the concentration of the detection target gas when the concentration of the detection target gas contained in the detection subject atmosphere is suddenly changed from 0 vol % to 2 vol % at a temperature of 25° C. in a state in which the detection subject atmosphere has a water vapor concentration of 2 vol %, and a water vapor concentration difference of 7 vol % or less results between the first internal space and the second internal space when the concentration of water vapor contained in the detection subject atmosphere is suddenly changed from 2 vol % to 18 vol % at a temperature of 60° C. in a state in which the detection subject atmosphere does not contain the detection target gas.