Non-Dispersive Infrared (NDIR) Gas Detection

Non-Dispersive Infrared (NDIR) technology utilizes a broadband infrared (IR) emitter, which covers all of the wavelengths of interest for a given set of gases to be measured. Optical Band Pass filters allow that portion of IR wavelengths at which a specific gas absorbs IR energy. For typical gasoline exhaust, the IR spectra are shown below.

Mathematical Model Derived from Actual Spectrographic Data

Each band pass filter is attached to an infrared sensor (detector). The detector produces a signal that is proportional to the amount of IR energy absorbed by the gas of interest. This signal is electronically processed to develop gas concentration information reported in engineering units of interest.

As an OEM only supplier, the focus of our Andros NDIR designs is to address specific measurement needs for the more common measurement applications. This is accomplished by selecting the appropriate Optical Band Pass Filters required for the measurement. Our goal is to develop NDIR technology that can be mass-produced while maintaining high performance, high quality and reliability, all at a reasonable cost to our customers.

Key features of the design:

• High reproducibility between production runs
• Automated pre-inspection, set up, calibration and final verification
• Well-defined communications protocol to facilitate HOST software development
• Minimal customer requirements for field span
• Modular functionality for serviceability
• Conforms to current world wide requirements such as RoHS compliance
• Manufactured in accordance with ISO 9001: 2000 and ISO 13485

The key components in our design are the Infrared (IR) source, optimized optical band pass filters, stable reference filters and well defined response curves for each gas of interest.

Our NDIR designs use single path technology, do not rely on costly mirrors, needs no alignment or focusing or require multi-point field calibration.

Using an automated calibration process provides the capability to fully characterize each gas channel for response curve fit and gas channel interference correction. This process is performed at multiple temperatures to determine each channel's temperature coefficient. At the completion of a successful calibration, the calibration curve data and compensation coefficients are stored in the unit's flash memory.