AFS-G2 Room Hygrostat

Brand: KOBOLD Instruments, Inc.

The KOBOLD Room Hygrostat AFS-G2 is a two-position controller for regulating relative humidity. The moisture sensing element in the sensor comprises several strips of plastic fabric each with 90 fibers of 3 µm diameter.

These plastic fibers undergo a special process to acquire hygroscopic properties, this means that they absorb and release moisture. The molecular structure of the fibers changes when they absorb water, giving rise to a measurable change in length.

The length of the plastic fibers is thus a measure of the relative humidity. The swelling effect, acting primarily in longitudinal direction, is transferred over a suitable lever system to a microswitch with an extremely small changeover movement.

The measuring element reacts quickly and accurately to the change in humidity. The setpoint is set with the setpoint button so that the microswitch is actuated by the lever system when the humidity setpoint is reached.

The special treatment of the measuring element ensures that its hygroscopic properties remain stable, that is sensitivity is maintained until destroyed by external influence.

The harp-shaped measuring element is mounted inside the housing and should be protected against coarse dust, dirt and water. The hygrostats are designed for unpressurized systems. The installation position should be chosen so as to prevent condensed water from entering the housing.

The instrument can be installed in any position, but the ventilation slots should be at right angles to the wind direction if possible.



  • ± 3 % Relative Humidity

Ambient Temperature Range

  • 0° to 60° C (32° to 140° F)


  • Air Conditioning Cabinets
  • Building Management Systems
  • Film Industry
  • Glasshouses for Horticultural Businesses
  • Hospitals
  • Office & Computer Rooms
  • Paper Industry & Printing Trade
  • Textile Industry
  • Warehousing of Food Stuffs & Semi-luxury Foods & Tobacco

Differential Pressure

  • 4 % Relative Humidity Approximately (At 50 % Relative Humidity) - Differential Gap (Microswitch)


  • 85 × 55 × 36 mm

Electrical Rating

  • 100 mA - Minimum Contact Rating
  • 20 Vdc/ac - Minimum Contact Rating
  • 5 A at 230 Vac (Service Life 50,000 Cycles) - Resistive Load

Enclosure, Body Material

  • Plastic - Light Grey Plastic Housing

Environmental Protection

  • IP20

Flow Rate

  • 15 m/sec - Allowed Air Speed


  • 30 to 100 % Relative Humidity - Measuring Range


  • Base Mounting

Mounting Position

  • Any Orientation


  • 0.2 A - Inductive Load Cos φ = 0.8
  • 2 A - Maximum
  • 230 Vac - Inductive Load Cos φ = 0.8
  • 5 A - Maximum

RFI/EMI Protection

  • EN 50081-2 - Emitted Interference
  • EN 50082-2 - Noise Immunity

Supply Voltage

  • 250 Vac - Maximum

Temperature Effect

  • -0.2 % Relative Humidity/K (At 20° C & 50 % Relative Humidity) - Average Temperature Coefficient

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