hygrostats

A hygrosstat is a humidity-control device that monitors ambient moisture and mediates an environmental system to maintain a specified relative humidity. The term hygrosstat is sometimes used interchangeably with humidistat, though some sources distinguish the two by focusing on sensing versus control functions.

A hygrosstat works by using a humidity-sensing element and a control mechanism. When the current humidity deviates from the set point, the device triggers a humidifier, a dehumidifier, or a ventilation system to restore the target level. In some configurations the hygrosstat directly operates the equipment, while in others it provides a control signal to a building automation system.

Types range from mechanical to electronic. Mechanical hygrostats often employ humidity-sensitive materials such as hair or bimetallic strips to move a switch at a chosen humidity. Electronic hygrostats use capacitive or resistive sensors with a microcontroller to compare the measured humidity against a programmed setpoint, frequently incorporating hysteresis to prevent rapid cycling. Modern versions are available in analog and digital forms and may connect to thermostats or smart home systems.

Typical applications include greenhouses, museums, archives, and electronics manufacturing, where precise humidity control helps protect materials and processes. In residential settings, hygrostats are commonly part of humidifier or dehumidifier systems and are used to maintain comfortable and safe indoor air.

Maintenance and calibration are important for accuracy. Setpoints should be verified periodically, sensors can drift with temperature, dust, or aging, and placement away from direct moisture sources or heat helps ensure reliable operation.