Gas sensor


This is a thermal conductivity gas sensor that uses a highly sensitive thin-film thermistor, and detects gas concentration by detecting differences in the thermal conductivity of the tested gas.
Thermal conductivity gas sensors exhibit output changes when the thermal conductivity of the ambient atmosphere differs from that of air. The output signal shows excellent linearity with respect to the concentration of the measured gas, for example, carbon dioxide can be measured from 0.5% to 20%.
Thermal conductivity sensors using thermistors are temperature- and humidity-dependent, so the actual circuit design must take these characteristics into account when making temperature and humidity corrections.

Appearance of thermal conductivity gas sensor (reference shape)


Uses highly sensitive and responsive thin-film thermistors (1005M t=0.1mm) (High precision achieved by high-precision pairing of thin-film thermistors)
– Low power consumption is achieved by keeping the heating temperature at or below 100℃
– Continuous measurement is possible, enabling constant monitoring of gas concentration

Detectable Gases

Gases with a difference of ±30% or more relative to the thermal conductivity of air can be detected.
– Inert gases such as hydrogen, helium, krypton, xenon, etc.
– Toxic gases such as sulfurous acid gas
– Refrigerant gases such as CFC substitutes with high global warming potential

Gas name Chemical formula Thermal conductivity [W/m K]
Air (calculated with standard atmosphere) 0.0238
Carbon dioxide CO2 0.0145
CFC substitute HFC-134a CH2FCF3 0.0120
Sulfurous acid gas SO2 0.0084
Xenon Xe 0.0056
Krypton Kr 0.0087
Helium He 0.1442
Hydrogen H2 0.1675

Measurement circuit

Example of gas sensor and carbon dioxide detection characteristics

– The output of the carbon dioxide sensor is temperature dependent.
– Carbon dioxide concentrations between 0% and 5% tend to be less temperature dependent.