NDIR humidity measurement

Danfoss IXA is developing a multi gas sensor that utilizes NDIR spectroscopy to simultaneously measure various gasses such as CO₂ and humidity. NDIR spectroscopy is vastly ignored in commercial humidity sensing although humidity is absorbing radiation in large parts of the infrared spectrum, seemingly making it an obvious measurand for NDIR spectroscopy. The present work elaborates on the reason for this contradiction and explains why NDIR, despite all, is suitable for humidity measurements and specifically beneficial in aggressive environments where an optical approach allows for non-contact measurement which might enhance the long term stability. It is shown that the performance of the developed NDIR spectroscopy-based prototype can compete with commercially available humidity sensors in the ranges of interest for indoor climate control.