DHT21 is kind of a digital relative humidity control device (Higrostat), with alarm output. Relative humidity is measured in 0%RH ~100%RH range by it’s coupled sensor (EHS11) and can be controlled for drying or moistening. In case of humidity value exceed humidity alarm set values, upper, lower or band humidity alarm output can be activated and indicated on the display. These controllers are available in standart compact size 33x75mm, with IP65 protection rating. The user interface consists of a custom display (two line value display and function icons) and three front keys. The device is installed by panel with snap-in brackets.