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Glossary /­ FAQ /­ LexiconTHERMACERN(R): The new method for precipitation analysis

THERMACERN(R): A new method!

THERMACERN(R) is the name of a new technology for analyzing solid-liquid precipitation whose scope of analysis goes far beyond that of conventional ice detectors. The technology enables the differentiation and quantification of precipitation events in the transition area between the solid and liquid phases, such as supercooled precipitation, sleet, freezing rain and black ice. The novelty lies in the systematic evaluation of the heat flows associated with the phase transitions. Conventional ice detectors (only) use the different dielectric properties of water and ice or the change in mass due to adhering ice as a measuring principle.

THERMACERN(R), an integral component of numerous Thies CLIMA measuring instruments The basic component of THERMACERN(R) is contained in numerous Thies products and is easily recognizable due to its blue glass surface. We have brought the full functionality of THERMACERN(R) to life in the Precipitation Analyzer (5.4107.xx.xxx), and selected functions have been implemented in the WSC Advanced,the WSC11, the ClimaSensor US and Rain Monitor. Devices

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A blue glass surface makes THERMACERN(R) easily recognizable, from left: WSC11 , Clima Sensor US , WSC Advanced, WSC Agrar (new, coming soon), Precipitation Analyzer

Physical principles

Temperature and frequency measurement:
The sensor surface consists of a thermally conductive ceramic material with temperature sensors on the back. In addition, the sensor is designed as an electrical oscillating circuit, whereby the sensor surface forms a capacitance dependent on wetting.

The following measuring principles are used:
  • Detection of characteristic temperature peaks that occur when water freezes due to the heat of crystallization released.

  • Change in the dielectric properties of water and ice: these properties are used to differentiate between solid and liquid wetting of the surface.‎

  • Measurement of the sensor capacity: the sensor capacity depends on both the wetting of the sensor surface and the wetting water and ice content.‎
    With THERMACERN(R), solid and liquid wetting can be reliably distinguished.

List of detectable precipitation types

THERMACERN(R) can be used to detect a wide range of precipitation events and their intensity:
  • Supercooled fog (FZFG)‎
  • Subcooled drizzle (FZDZ)


  • Supercooled rain (FZRA)
  • Supercooled spray (freezing spray)
  • Black Ice
  • Drizzle, rain, sleet, sleet, dew, hoarfrost

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    Behavior of supercooled droplets on THERMACERN(R)

    Behaviour of supercooled droplets on THERMACERN(R) during crystallization (figure on the left)
    Schematic representation of the thermal state shortly after the impact of a (large) supercooled droplet on the THERMACERN(R) sensor plate. At the moment of impact, the drop temperature rises abruptly to freezing point due to crystallization. A dendritic crystal structure forms in the drop, which quadruples the thermal conductivity of the drop. Due to the high thermal conductivity, the temperature gradient within the drop is low. The temperature gradient between the 0° warm droplet and the colder sensor surface therefore forms directly at the sensor surface, which is why the heat flow into the substrate is high. Steep, clearly recognizable temperature peaks can therefore be detected. As a crystallizing drop forms a local heat point, the temperature rise is detected by the temperature sensors with a time delay depending on the distance between the drop and the temperature sensors. In contrast, a temperature rise due to solar radiation affects all sensors simultaneously (not shown here).

    Behaviour of supercooled droplets on THERMACERN(R) without crystallization (figure on the right)
    Schematic representation of the thermal state when a small supercooled droplet hits the sensor plate. In the case of freezing drizzle (FZDZ) or freezing fog (FZFG), crystallization does not occur if the kinetic energy of the droplet is too low when it hits the surface. The droplets remain supercooled on the sensor surface. As no crystallization heat is released, there is no heat flow into the substrate and no temperature peaks occur. Since crystallization can occur at any time, the danger posed by (initially) non-crystallizing supercooled liquids is just as great as that posed by immediately crystallizing precipitates. THERMACERN(R) can also be used to detect non-crystallized supercooled water. This is because the dielectric property in this case does not correspond to that of ice, but remains the same as that of water, even though the temperature is below the freezing point.‎


    Behaviour of supercooled drops on THERMACERN(R), with (Fig. left) and without crystallization (Fig. right).

    THERMACERN(R): Applicative

    The application areas of THERMACERN(R) are diverse and include:
    • Building management systems‎

    • Airports, enables full automatic METAR coding through the detection of supercooled precipitation (FZFG, FZDZ, FZRA) and other dangerous phase changes, important data for the calculation of holdover time at airports

    • Shipping, detection of freezing spray in saltwater and freshwater situations at sea


    • Energy: Timely icing warnings enable the protection of wind turbines and power lines from structural damage.

    • Road traffic: Safe traffic routes - THERMACERN(R) enables timely warning of icing hazards on roads and bridges, especially in the event of black ice.

    • Meteorological networks

    • Industry: Process machines and systems, for example in the chemical and process industry or agricultural equipment


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    Much more than an ice detector

    In contrast to conventional ice detectors
    THERMACERN(R) offers a more precise analysis and differentiation of precipitation events, including supercooled precipitation. By accurately detecting wetting phases and phase changes, THERMACERN(R) offers a completely new analysis tool for evaluating weather phenomena.‎

    THERMACERN(R), integrated in Thies products as well as an industrial component

    As a Thies product as well as an industrial component with design-in support

    THERMACERN(R) is an innovative technology that is available both in our own products and as a component in third-party industrial products. By integrating THERMACERN(R) into our in-house products, we offer our customers a compact precipitation analysis function that delivers comprehensive and reliable results with minimal power consumption. We also offer THERMACERN(R) as a component with design-in support for industrial applications. THERMACERN(R) can be used in process machines and systems, for example in the chemical and process industry or agricultural equipment. This gives users the opportunity to quickly upgrade devices with comprehensive functionality for wetting conditions, phase conditions and phase transitions.

    Products with THERMACERN(R): Thies CLIMA precipitation gauges, combination devices and weather stations:
    WSC 11
    Clima Sensor US
    Precipitation Analyzer
    NEW: WSC Advanced & WSC Agrar

    Graph: Evaluation of temperature peaks (spikes)

    as a characteristic of supercooled precipitation
    K3T1 = Temperature measuring point 1 under ceramic 3.
    K3T2 = Temperature measuring point 2 under ceramic 3.
    T_ext = outside temperature or air temperature
    Freq 3 = Frequency of ceramic 3

    Spikes can be seen in the ceramic at temperature measuring points 3 and 2 (yellow and orange curve).