Dry cabinets come in various shapes and sizes and there are different technollogies available, such as dehumidifying cabinet, electronic dry cabinet, dry nitrogen cabinet, baking dry cabinet, etc. As opposed to it's name, a dry cabinet's purpose is not to provide an environment devoid of any humidiy, as this might actually be detrimental to the equipment encased within. Much like a cigar humidor, the dry cabinet’s job is to maintain an optimal relative humidity. Most dry boxes are equipped with a hygrometer to allow you to check the humidity level inside.
http://www.gms-industrial.com/dry-cabinet/