Gas Sensor
Reports the concentration of one or more target gases (CO, CO₂, VOCs, NH₃, NO₂, etc.) as a digital value (ppm) or analog voltage. Crosstalk between gases is the rule, not the exception, on cheaper types.
Metal-oxide (MOX): a heated SnO₂ film changes resistance as reducing/oxidizing gases adsorb. Electrochemical: target gas reacts at a working electrode, producing a proportional current. NDIR (CO₂): IR LED at 4.26 µm; gas absorbs, photodetector reads the dip. PID: UV lamp ionizes the gas, ions are collected as current.
In plain terms
An artificial nose: each technology is a 'nostril' tuned to a class of gas. Some smell flammables (MOX), some smell CO (electrochemical), some smell CO₂ (NDIR).
Why designers use it
- Carbon-monoxide alarms in homes (electrochemical).
- CO₂ sensors in HVAC for demand-controlled ventilation (NDIR).
- Combustible-gas alarms in kitchens and garages (MOX).
- Air-quality monitors and breath-analysis devices.
Best for
- CO alarm
- CO₂ NDIR
- VOC IAQ
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- Sub-ppm trace detection — needs lab-grade FTIR or GC-MS.
- Hot, humid, or oily environments with cheap MOX — readings drift wildly.
Common mistakes
- Forgetting MOX sensors need a long burn-in (24+ hours from new) before stable readings.
- Putting an NDIR sensor downstream of an exhalation point and reading transient peaks instead of average.
Where you will find it
- Senseair / Sensirion / Telaire NDIR CO₂ sensors are standard in HVAC monitors.
- Figaro and Bosch MOX sensors (TGS series, BME688) appear in IAQ products.
- Alphasense electrochemical cells are used in scientific air-quality monitors.
A short history
Figaro's company history describes Naoyoshi Taguchi's work on tin-dioxide gas sensing in the early 1960s, the start of TGS mass production and sales in 1968, and the foundation of Figaro Engineering in 1969. This is the manufacturer's account of its product development, not a claim that all gas-sensing technologies share one inventor or date.