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  1. Analytical sensors
  2. Air humidity sensor LDH

Advantages and technology of the air humidity sensor

How to ensure the perfect climate for your processes

  • How about making sure that there is no risk of short circuits due to excessive humidity before switching on your electronic controllers?
  • How about always keeping an eye on the climatic ambient conditions, and thus reliably ensure the quality of your product?

The LDH29x air humidity sensor continuously monitors the climatic ambient conditions, thus protecting your process and the electronic controllers from excessive humidity and temperature.

IO-Link benefits

What does the LDH29x offer via IO-Link?

  • 2 process values, humidity and temperature, via one wire only
  • Storage of minimum and maximum values for temperature and humidity
  • Diagnostic data, such as operating hours and switch-on cycles
  • Humidity and temperature histogram
  • Easy sensor replacement – parameters are set automatically when connected to an IO-Link master


This is how the sensor determines air humidity

  • Humidity is measured by means of a capacitive measuring element consisting of two electrodes (capacitor) to which a voltage is applied. Between the two electrodes there is dielectric material which is able to absorb humidity.
  • Constant exchange of substances between the dielectric material and the ambient air ensures an equilibrium between the measuring element and the air to be measured.
  • If the humidity content of the ambient air changes, the humidity content of the dielectric material changes in the same way. This in turn leads to a change in the capacitance of the capacitor, which allows for determination of the current humidity level.
Type Measuring range
Measuring range
Signal Precision


0…100 %

-40…60 °C

• Humidity analogue 4...20 mA
• Temperature analogue 4...20 mA

• 4% humidity
• 1 °C temperature


0…100 %

-40…80 °C

• IO-Link

• 3% humidity
• 0.3 °C temperature


Protection of control cabinets and servers

Electricity and humidity have to be strictly separated from one another– this also applies to control cabinets in automized production systems. However, particularly in processes under hygienic conditions such as in the food industry humidity can enter the control cabinet due to the frequent cleaning processes. Possible causes are PG fittings, air slits, defective sealings or doors which have not been closed properly. If the humidity inside remains undetected this can lead to corrosion.