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Hygrostat (Hygrometric) (907032)


For easy two-state control of relative air humidity

  • For indoor and duct versions
  • Also available with covered setpoint adjuster
  • Duct version can be used continuously in areas of high humidity
  • Indoor version also suitable for flush-mounted box installation
  • With potential-free changeover contact(s)

Customer benefits

  • Cost-effective solution
  • For wall and channel mounting
  • Mounting holes for flush-mounted boxes
  • Adjustment protection 
  • No mains voltage required
  • Sensing element is mostly maintenance-free


Hygrostats as simple two-state controllers are the preferred choice for controlling relative humidity.
Generally, applications can be found in air-conditioning technology as well as:

  • Climatic chambers and control cabinets
  • Air ducts
  • Humidifiers and dehumidifiers
  • Storerooms and cold-storage rooms
  • Greenhouses
  • And many more


Hygrostats of the 907032 series use the hygroscopic properties of especially prepared plastic fibers to detect relative air humidity. Once prepared, the hair measuring element is capable of absorbing moisture. The changing length is the externally measurable effect that is transmitted to a microswitch with an extremely small changeover path via a lever system. The scale ranges over an area between 30 to 100 % RH.

Values set via the value rotary knob also act as an interference to the lever system in such a way that the microswitch is actuated when the set air humidity is reached. The changeover contact can be operated as N/C or N/O contact (humidification/dehumidification) depending on the application.
Hygrostats in duct version are available as the standard version with microswitch as well as with a double changeover contact. The switching point of the second microswitch is directly coupled to that of the first microswitch; however, it can be precisely set between 0 to 15 % rel. humidity (neutral zone) on the microswitch lever by means of a screwdriver after removing the case lid.

All indoor and duct versions are available with a covered setpoint adjuster (placed beneath the case lid). This can almost fully exclude unwanted adjustment of the switching point. In addition, the highly-developed case of the indoor version not only features a high level of elegance and robustness, it also enables simple mounting on the wall, smooth surfaces, and flush-mounted boxes.

Hygrostats are preferably used as simple two-state controllers to control the relative humidity in conditioning cabinets and air ducts as well as to control air humidifiers and dehumidifiers in the building technology industry. Further application areas are in the storage of food / luxury food, in cold-storage rooms for fruit and vegetables, in greenhouses of market gardens, in the textile/paper/printing industry, and in hospitals.

The great water resistance of the sensing element is also particularly advantageous. As a result, the duct version can be used permanently in high-humidity areas, even up to a complete saturation. Moreover, in normal circulated air the sensing element is almost maintenance free. A further advantage is that device versions with a hygrometric hair measuring element do not require any operating voltage. As a result, an easy installation without any power grid in the vicinity is also possible.