Hygrostate

Our reliable and versatile HYGRASREG® hygrostats regulate and monitor the relative humidity and/or temperature of a room and control downstream humidification/dehumidification equipment or cooling or heating systems. The surface-mounted and duct hygrostats are IP65-compliant, room hygrostats achieve protection class IP30.

Go to the Guide to Humidity Controllers
14 products
  • Raumhygrostat mit Drehregler für die relative Luftfeuchtigkeit
    %RH

    Room humidistat

    HYGRASREG® RH-2

    1202-40C0-0010-000

    $103.49

  • Raumhygrostat mit geschlossenem Gehäuse
    %RH

    Room humidistat

    HYGRASREG® RH-2 U

    1202-40C0-0020-000

    $106.64

  • Aufputzhygrostat mit geschlossenem Gehäuse und Display
    %RH

    Surface-mounted hygrostat

    HYGRASREG® AH-40W LCD

    1202-1065-0221-000

    $226.17

  • Raum-Hygrothermostat mit geschlossenem Gehäuse
    °C %RH

    Room hygrothermostat

    HYGRASREG® RHT-30W U

    1202-4077-1021-200

    $226.97

  • Kanalhygrostat mit Schutzrohr und Display
    %RH

    Duct hygrostat

    HYGRASREG® KH-40W LCD

    1202-3065-0221-000

    $227.67

  • Raum-Hygrothermostat mit geschlossenem Gehäuse und Einstellrad
    °C %RH

    Room hygrothermostat

    HYGRASREG® RHT-30W

    1202-4077-1011-200

    $230.31

  • Raum-Hygrothermostat mit Display im geschlossenen Gehäuse
    °C %RH

    Room hygrothermostat

    HYGRASREG® RHT-30W LCD

    1202-4077-1211-200

    $246.86

  • Raum-Hygrothermostat in Frontalansicht mit zwei Einstellreglern
    °C %RH

    Room hygrothermostat

    HYGRASREG® RHT-1

    1202-4010-0000-000

    $279.34

  • Kanalhygrostat mit geschlossenem Gehäuse und Schutzrohr
    %RH

    Duct hygrostat

    HYGRASREG® KH-10 U

    1202-3012-0020-000

    $282.93

  • Kanalhygrostat mit Einstellrad und Schutzrohr
    %RH

    Duct hygrostat

    HYGRASREG® KH-10

    1202-3012-0010-000

    $285.96

  • Aufputz-Hygrothermostat in Frontalansicht mit Display
    °C %RH

    Surface-mounted hygrothermostat

    HYGRASREG® AHT-30W-U LCD

    1202-7127-1421-000

    $294.01

  • Kanal-Hygrothermostat in Frontalansicht mit Display
    °C %RH

    Duct hygrothermostat

    HYGRASREG® KHT-30W-U LCD

    1202-8127-1421-000

    $294.01

  • Aufputz-Hygrothermostat mit Display und Schutzrohr
    °C + % RH

    Surface-mounted Hygrothermostat

    HYGRASREG® AHT-30W-A-LCD

    1202-7127-E421-000

    $294.01

  • Kanal-Hygrothermostat in Frontalansicht mit Display
    °C + % RH
    AOS signal

    Channel Humidistat-Thermostat

    HYGRASREG® KHT-30-AW LCD

    1202-8127-E421-000

    $294.01

Humidity Controllers for Automatic Humidity Control

A hygrostat monitors relative humidity and activates an electrical contact when the humidity exceeds or falls below a preset setpoint. This allows dehumidifiers, humidifiers, ventilation systems, or other building automation components to be controlled as needed.

HYGRASREG® hygrostats are available for a variety of installation locations and control tasks. The product line includes room, surface-mounted, and duct-mounted units, as well as hygrothermostats that additionally measure and output or switch the temperature. Key factors in selecting the right model include the installation location, protection class, setting range, setpoint access, and the output required by the downstream control system.

Contents

Hygrostat, hygrometer, or hygrothermostat—what's the difference? Which hygrostat is right for your application? What should you look for when choosing a hygrostat? Installation and Setpoint Adjustment Choose the Right Humidity Controller for Your Project

How does a hygrostat work?

A hygrostat measures relative humidity using a humidity-sensitive sensing element or an electronic sensor. The current reading is compared to a preset setpoint. If the humidity exceeds or falls below the defined threshold, the switch contact changes state. This allows the connected control system to, for example, turn a humidifier, dehumidifier, fan, or an activation signal on or off.

Mechanical HYGRASREG® models use hygroscopic plastic fibers. Other versions combine humidity sensing with electronics, a display, an analog signal, and additional relays. The specific switching function depends on the wiring, device model, and selected setpoint.

A hygrostat is typically a two-point controller: it switches between two states. To prevent the output from switching constantly in response to the slightest fluctuations, the device operates with a switching differential or hysteresis. The adjustment range, switching differential, contact rating, and permissible environmental conditions are specified in the respective product data sheet.

Hygrostat, hygrometer, or hygrothermostat—what's the difference?

These terms refer to different functions. When selecting a product, the key consideration is whether the device is intended merely to display a measured value, to trigger a humidity threshold, or to also control the temperature.

Hygrometer

A hygrometer measures humidity and displays the reading or makes it available for analysis. It does not necessarily have to automatically control a connected device. For integration into a building management system, humidity sensors or transducers with a suitable output are often used.

Humidity Controller

A hygrostat monitors relative humidity against a preset setpoint. When the switching threshold is reached, it activates a contact. It is therefore suitable for simple and robust switching tasks, such as enabling or disabling a dehumidification or humidification process.

Hygrothermostat

A hygrothermostat combines humidity and temperature functions in a single device. Depending on the model, it offers separate switching stages, analog measurement signals, or both. This allows two relevant parameters to be measured using a single housing and transmitted to the downstream control system.

In short: A hygrometer measures humidity, a hygrostat switches based on humidity, and a hygrothermostat also takes temperature into account.

Which hygrostat is suitable for your application?

  • For Rooms

    Suitable version: HYGRASREG® RH-2 or RH-2 U
    Suitable for: Room air monitoring and simple humidity switching in indoor areas
    Features: Setting range 25–95% RH, mechanical measuring element, potential-free changeover contact for 24 V, external or internal adjustment, protection class IP30

    View room humidistats

  • For robust surface-mounted applications

    Suitable version: HYGRASREG® AH-40W LCD
    Suitable for: Surface mounting in areas with higher enclosure requirements
    Features: Adjustment range 5–95% RH, changeover contact for 24 V, internal adjustment, display and protection class IP65

    View surface-mounted humidistats

  • For ventilation and air conditioning ducts

    Suitable version: HYGRASREG® KH-40W LCD, KH-10 or KH-10 U
    Suitable for: humidity monitoring directly in the air duct
    Features: depending on the model, electronic or mechanical detection, internal or external setting, changeover contact and IP65 protection

    View duct humidistats

  • For room humidity and room temperature

    Suitable for: HYGRASREG® RHT product series
    Ideal for: combined humidity and temperature applications in rooms
    Features: depending on the variant 0–10 V, two separately adjustable changeover contacts, display and internal or external setting; IP30 protection

    View room devices with humidity and temperature function

  • For robust humidity and temperature control

    Suitable design: HYGRASREG® AHT-30W product series
    Suitable for: Surface-mount applications with combined humidity and temperature detection
    Features: IP65 protection, display, analogue signal and two separately adjustable changeover contacts; depending on the version, 0–10 V or automatic 0–10 V / 4–20 mA

    View surface-mounted devices with humidity and temperature function

  • For humidity and temperature in the duct

    Suitable version: HYGRASREG® KHT-30W product series
    Suitable for: combined humidity and temperature applications in ventilation and air conditioning ducts
    Features: IP65 protection, display, analog signal and two changeover contacts; depending on the version 0–10 V or automatically 0–10 V / 4–20 mA

    View Duct Units with Humidity and Temperature Function

What should you pay attention to when choosing a humidistat?

  1. Determine the location of use: Different housings and mounting styles are required for normal interiors, robust surface-mounted applications and air ducts.
  2. Determine the measuring or switching task: Should only a limit value be switched or does the building management system also need a continuous humidity or temperature value?
  3. Check protection type: Room devices in the RH and RHT families are designed for IP30, depending on the version. Surface-mounted and duct versions are available with IP65. The relevant data sheet is always relevant.
  4. Adjust the setting range: The ranges offered differ depending on the model. The planned setpoint must be within the specified setting range.
  5. Choose indoor or outdoor setting: An outdoor setting makes on-site adjustment easier. An internal setting better protects the setpoint from unintentional adjustment.
  6. Set output: A changeover switch can be suitable for a simple switching task. Depending on the hygrothermostat, 0-10 V or 4-20 mA are available for integrating continuous measured values.
  7. Check switching capacity and supply: Voltage, current, load type and contact load must match the downstream component. A potential-free contact does not replace the electrical testing of the entire circuit.
  8. Consider temperature function: When humidity and temperature are needed together, a hygrothermostat can avoid two separate devices and additional installation effort.

What does potential-free changer mean?

A potential-free changeover contact transmits a switching state without providing its own output voltage. Depending on the wiring, the common contact can switch between normally closed and normally open. The permissible switching voltage, current and load type must match the data sheet and the connected controller.

Installation and Setpoint Adjustment

A room hygrostat should be installed in a location where the humidity is representative of the relevant area of the room. Immediate proximity to doors, windows, heating surfaces, humidifiers, dehumidifiers, or strong air currents can affect the measured conditions. Duct hygrostats are positioned according to installation specifications so that the sensor element is exposed to the relevant airflow.

During commissioning, the switching function and setpoint must be tested together. Depending on whether the unit is intended to humidify or dehumidify, the downstream system must respond when the threshold is exceeded or not reached. An existing switching differential prevents frequent cycling on and off near the setpoint.

Electrical installation and commissioning must be performed only in accordance with the device-specific wiring diagram and the applicable electrical requirements. After installation, the measurement conditions, switching point, and response of the connected system should be verified in practice.

Choose the Right Humidity Controller for Your Project

Do you need a simple room hygrostat, a rugged IP65 enclosure, a duct-mounted model, or a combined humidity and temperature control system? Compare the HYGRASREG® models based on installation location, setpoint range, setpoint access, output, and protection rating. For special requirements, S+S Regeltechnik provides technical advice and custom solutions.

Compare Humidity Controllers

Frequently Asked Questions About Humidity Sensors

What is the difference between a hygrostat and a hygrometer?

A hygrometer measures and displays the humidity or provides the measured value. A hygrostat also performs a switching function: It responds to a preset humidity setpoint and changes the state of its output contact when the switching threshold is reached. The terms therefore describe different functions.

What is the difference between a hygrostat and a hygrothermostat?

A hygrostat responds to relative humidity. A hygrothermostat combines humidity and temperature functions in a single device. Depending on the model, both parameters can be controlled separately or output as analog signals. A hygrothermostat is useful when the control system requires both parameters.

When should a room humidistat be used, and when should a duct humidistat be used?

A room hygrostat measures the relative humidity of the indoor air and is installed in a representative location. A duct hygrostat monitors the humidity in the airflow of a ventilation or air conditioning duct. The design, protection rating, and sensor position must therefore be suitable for the actual installation location.

Can a hygrostat control both a humidifier and a dehumidifier?

In general, a suitable hygrostat can be used to activate a dehumidifier or humidifier. Whether the connected device can be switched on directly or whether a relay or an input on the building automation system must be activated depends on the switching voltage, contact rating, and load type. The relevant circuit diagrams are decisive.

Does a hygrostat need a separate sensor?

Every hygrostat requires a humidity-sensitive measuring element or sensor. In many room, surface-mounted, and duct-mounted units, this is already integrated into the respective design. A separate external sensor is only required if the measuring point is to be located separately from the controller and the specific model supports such a connection.

We also manufacture individually

Do you have special requirements? As a manufacturer with our own production facilities in Germany, we are also able to produce products outside of the standard range at any time.

 Contact us

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