It is designed for use as internal components for portable humidifiers and dehumidifiers, and as wall mounted humidity controls for central systems. The DH55 is a relative humidity control, consisting of a humidity sensing element, adjustable setpoint cam and an electrical switch. The sensing element changes length in response to the exposed RH to move the switch mechanisms at the appropriate switch points. Applications • Ventilation fans for confined spaces. • Space and Product Humidifiers.