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 Stable environmental conditions are a vital requirement for the preservation of historic buildings and museum collections.
When the humidity is constantly changing, hygroscopic materials will swell and contract, causing internal stress and this continuous cycle of movement will almost certainly result in damage. This problem is exaggerated in composite objects as the different materials may expand and contract at different rates.
Organic objects contain relatively high proportions of water, these materials will respond to humidity changes. When the air is dry, these materials will give off moisture, this could cause the object to become brittle, shrink, or crack. When the surrounding air is damp, these materials will absorb moisture from the air, this could result in swelling, warping, cockling or deformation. Relative humidity levels above 70% will cause mould and fungal growth on organic materials.
Inorganic objects are also affected by changing humidity levels. Materials that contain salts (stone, ceramics) may suffer from efflorescence when the air is dry. The salts are carried to the surface by moisture leaving the object. Metal objects will corrode in a high humidity environment, and archaeological metal in particular needs to be kept at very low humidity levels.
Leaving humidity uncontrolled could lead to irreversible damage.
The ‘ch’ range of conservation humidistats have been specifically designed to provide reliable humidity control in conservation environments. The ch1 is a microprocessor based system with 2 outputs to switch a humidifier, a dehumidifier or both. Used in conjunction with either the HPS-01 or the HPS-03 power supplies the ch1 will control a wide variety of humidifiers, dehumidifiers and heaters (a heater can replace the dehumidifier for conservation heating purposes). Additionally, you can take advantage of the ch2, which has all the features of the ch1, plus comfort mode, a temperature override facility for use in conservation heating schemes, where temperature temporarily becomes the main control and is overridden only at very low RH levels.
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