NAP-21A is a thermal-conductive type gas sensor to detect gases making use of the variation of the thermal conductivity of a target gas. This sensor is suitable for detection of highly concentrated gases more than percent order or inert gases that are not chemically reacted.

This sensor detects the changes of outputs when the thermal conductivity of the ambient atmosphere becomes different from the conductivity of the air. More specifically, the output shifts towards (+) side when the target gas has a larger molecular weight than the air, and shifts towards (-) side in case of a smaller molecular weight. The output characteristic of this sensor shows excellent linearity to the gas concentrations that is good enough to measure concentrations up to 100%. However, this sensor is humidity-dependent (As “humidity is “steam” which makes the output shift towards (-) side.), a compensation circuit would be needed upon designing circuits. Because of these characteristics, this sensor is suitable for CO2 gas measurement & CO2 gas monitoring in containers for vegetables & fruits etc.


NAP-21A's Structure

Gas sensitivity characteristics

Gas Concentration & Output Voltage
 Carbon dioxide CO2 0.2 mV / % CO2


Items Ratings
Supply voltage DC 1.8±0.1V
Current (1.8V supplied) DC 120 - 130mA
Ambient Temperature In operation -10 - +50°C
In storage -20 - +60°C
Ambient humidity In operation 95%RH or less
In storage 99%RH or less(No dew condensation)