Infrared light emitting diodes (LEDS) can replace the thermal source, bandpass filters and rotating chopper wheel of conventional infrared gas monitors. Their long-term stability, high modulation rate and compact size also provide design advantages. The performance of a family of mid-infrared monitors for measuring carbon dioxide and hydrocarbons is described. Various schemes are outlined for compensating temperature drift, output/gain fluctuations, changes in cell transparency and mismatch between components.
