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NDIR Sensor Types

Non-Dispersive Infrared (NDIR) CO2 Sensor

  • Example: NDIR CO2 sensor
    • Infrared absorption of CO2 molecules at a specific wavelength of 4.26 μm
    • Sensor consists of IR source, light path, active detector and reference detector
    • Concentration of CO2 determines intensity of light striking active detector
    • Reference detector provides a real-time signal to compensate the variation of light intensity due to ambient or sensor itself/

Single wavelength NDIR sensors

Single wavelength NDIR sensors
  • Affected by:
    • Humidity
    • Temperature
    • Pressure
    • Aging of detector
    • Dust
    • Aging of IR-emitter

Double wavelength NDIR sensors

  • Affected by:
    • Humidity
    • Temperature
    • Pressure
    • Aging of detector
  • Not affected by:
    • Dust
    • Aging of IR-emitter
Double wavelength NDIR sensors
  • Commonly used in many portable instruments
Non-dispersive infrared

GfG IR sensor (Note longer pathlength)

Non-dispersive infrared

"4 Series" sized format used by City Tech, Dynament and E2V infrared sensors (Note shorter pathlength)

Double wavelength NDIR sensors
Double wavelength NDIR sensors

Three wavelength NDIR sensors

  • Simultaneous measurement CO2 and combustible gas
    • LEL: 3.3 μm
    • CO2: 4.3μm
    • Ref: 4.0μm
Three wavelength
Three wavelength

Light path through two wavelength NDIR sensor

  • Affected by:
    • Humidity
    • Temperature
    • Pressure
    • Ageing of detector
  • Not affected by:
    • Dust
    • Ageing of IRemitter
Light path through two wavelength NDIR sensor

Catalytic pellistor combustible gas response curves

Catalytic pellistor combustible gas response curvesr

Two wavelength NDIR combustible gas response curves

Catalytic pellistor combustible gas response curvesr

Next on the horizon: Four wavelength NDIR combustible gas sensors

  • Measure at two wavelengths for combustible gas
  • Measure at one reference wavelength
  • Measure water vapor at another wavelength and deduct interfering effect from combustible gas reading
Four wavelength NDIR combustible gas sensors
Four wavelength NDIR combustible gas sensors
Four wavelength NDIR combustible gas sensors
Four wavelength NDIR combustible gas sensors

Four wavelength NDIR combustible gas response curves

Four wavelength NDIR combustible gas sensors

Side by side comparison

Side by side comparison
Side by side comparison
Side by side comparison