US Patent 7569128 Coulometric water vapor sensor

A sensor for detecting water vapor in a gaseous sample. The sensor comprises (a) an anode, (b) a cathode, (c) an electrolyte intermediate the anode and cathode, and (d) an inlet orifice through a central area of the anode or cathode through which the gaseous sample may be placed into contact with the electrolyte. The electrolyte can be retained on a porous electrical-insulating separator located between the interior-facing major surfaces of the anode and the cathode.