A device for precisely humidifying a process gas is presented, with particular application to document preservation. The machine is designed to minimize the risk of damage from overpressure by incorporating multiple safety mechanisms and a simple user interface. The design theory is presented, discussed, and verified. This device is capable of generating humidified gases with relative humidities between 7% and 96% to high accuracy. At conditions suitable for document preservation, the machine is accurate to within ±3.5%, generating a relative humidity of (40±1.4)%.

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