Electrochemical sensor for measuring concentrations of species in a fluid mixture, of the type comprising a partial-pressure internal reference electrode

An electrochemical sensor for measuring the concentrations of species contained in a fluid mixture and comprising an electrochemical cell having a flat structure, said cell being constituted by a first partial-pressure internal reference electrode having one face either wholly or partly in contact with a solid electrolyte which is an ionic conductor for one of the species of said fluid mixture or for an ion which is capable of reacting with said species, and by a second electrode which communicates with the fluid mixture to be analyzed, one face of said second electrode being either wholly or partly in contact with said solid electrolyte, all the other faces of said first electrode abutting and being protected by an inert envelope and said envelope being impervious to the species which are present in said fluid mixture;

• wherein said first electrode and said second electrode are both deposited on the same face or on opposite faces of said solid electrolyte and are so arranged with respect to each other such that the first electrode or the projection thereof in the plane of said second electrode is in adjacent relation to said second electrode.