How does Testo determine CO2 content in the air?

What method does Testo actually use for CO2 measurement?

The measuring technology used by Testo is based on the NDIR (non-dispersive infrared) absorption principle.
This measuring principle involves the electro-optical measurement of the concentration of the gas being searched for via the extent of absorption of a specific wavelength.

Universal IAQ instrument testo 400

The sequence is as follows:

  •  The light bulb emits radiation.
  • The CO2 absorbs radiation at λ=4.27 μm.
  • High CO2 concentration - high radiation absorption.
  • The filter only lets radiation through with λ=4.27 μm.
  • The radiation on the detector is a measure of the CO2 concentration.

The advantages of this measuring principle:

  • No cross sensitivity with respect to other gases.
  • No wear of the sensor, which means a long service life.
  • If the incidence of gas is too high, this does not lead to contamination of the sensor.