Q: What is an electrochemical cell

A: An electrochemical cell is a device capable of either deriving electrical energy from chemical reactions. In this case the cell reacts with the gas you want to measure. This in turn produces an electical signal proportional to the concentration, where the analyser then translates this signal in to a physical concentration value in for exaple PPM.

Q: What is a infrared measurement

A: The main components are an infrared source (lamp), a sample chamber or light tube, a wavelength sample chamber, and gas concentration is measured electro-optically by its absorption of a specific wavelength in the infrared (IR). The IR light is directed through the sample chamber towards the detector. In parallel there is another chamber with an enclosed reference gas, typically nitrogen. The detector has an optical filter in front of it that eliminates all light except the wavelength that the selected gas molecules can absorb. Ideally other gas molecules do not absorb light at this wavelength, and do not affect the amount of light reaching the detector to compensate for interfering components. For instance, CO2 and H2O often initiate cross sensitivity in the infrared spectrum. As many measurements in the IR area are cross sensitive to H2O it is difficult to analyse for instance SO2 and NO2 in low concentrations using the infrared light principle.

The IR signal from the source is usually chopped or modulated so that thermal background signals can be offset from the desired signal.[