Calibrating apparatus for isothermally introducing moisture into a stream of dry gas at a very slow rate

A calibrating apparatus for isothermally introducing, into a stream of dry gas, calibrated amounts of moisture, lower than 1000 and even 1 ppb, said apparatus comprising:

• A. a moist gas generating unit, comprising in its turn:
• i) a cylindrical shell, having an inside surface and having too an inlet opening (for said stream of dry gas) and an out let opening (for the corresponding desired stream of moist gas);
• ii) a permeation module, inside said cylindrical shell, containing water and comprising a peripheral membrane, made from a polymeric fluorinated material, which is tangentially lapped by the dry gas to be moistened;
• iii) a thermal conditioner, arranged too inside said cylindrical shell, upstream of said permeation module;
• B. an isothermal heat sink, thermally connected to the outside surface of said cylindrical shell, wherein said heat sink has a cylindrical recess therein, as well as a planar heat conducting surface, and wherein said moist gas generating unit, under item A), is lodged in said recess of said heat sink;
• C) a heat radiator;
• D) a Peltier heater-cooler, thermally arranged between said isothermal heat sink (under item B) and said heat radiator (under item C), wherein said Peltier heater cooler does transfer heat from said isothermal heat sink to said heat radiator or viceversa.