The cell contains a ceramic strip with printed platinum electrodes. They are coated with a hygroscopic layer made of Phosphorus Pentoxide (P2O5) which attracts the water. In electrolytic cells the electric current is strictly proportional to the number of dissociated water molecules per time unit. This is an absolute measurement and requires no calibration.
While a sample gas streams through the cell at a typical rate of 100 ml/min, the current is measured with the acquisition box. This sensing technique is able to find single water molecules among a million gas molecules (ppm range). A water content of 1 ppmV (parts per million of the volume) corresponds to 13.2 µA.