Dew Point Thermometer

Everyone knows the three states of aggregation of water: solid, liquid and gaseous. For the transition from one state to the other, there are the generally used terms freezing, thawing, evaporation, evaporation. The term thawing stands for the transition from the solid to the liquid phase. On the other hand, the water that has become liquid from the gaseous phase is also called dew or condensation. Dew drops are the visible drops of water that can often be seen on the grass in the morning, even when it has not rained. Condensation water, on the other hand, is the water that settles as the liquid on the inner side of tents or on cool glass or metal. Other names for this liquid formed from the humidity in the air are condensate or condensation water. Since warm air can absorb more moisture than cold air, condensation or condensation water is formed when the humid air is cooled down. It is not necessary to cool down the entire air, it is sufficient that the air passes by small cold surfaces. For example, the lenses of the glasses can fog up when you come from the cold into the heated rooms. Also on cold water pipes that lead through warmer areas and on tiles, windows and mirrors in bathrooms, condensation is often visible after showering. Whether the condensation occurs depends on how much water vapor is contained in the air and how far the air is cooled down. If you know the temperature and moisture content of the air, you can determine the minimum temperature of surfaces to prevent the condensation formation on them. The temperature from which the condensation water precipitates is called dew point temperature or dew point.

Uncontrolled moisture ingress can lead to mold growth and other damage to building components, interior decoration and stored materials. The endangered materials often absorb the moisture, so that the moisture on the surface can only be detected when discoloration has already developed. To be able to take remedial action in critical areas at an early stage, dew point meters are used. If you determine with a dew point meter that there is a risk of condensation, you can either raise the temperature above the dew point or lower the humidity. Dew point meters are often used to exclude condensation as a cause of moisture damage in buildings. It is helpful that the dew point meter always measures the air temperature and humidity to determine the dew point temperature. These are the two values that the room user can usually influence by heating and ventilating. In some cases the change of temperature and humidity of the air is not possible or not desired. Then it must be checked whether the endangered areas can be heated or whether it is possible to switch to moisture-insensitive materials.

Measuring ranges of the dew point meter
To determine the dew point, the dew point measuring instrument must be able to register the temperature and humidity content of the air. The dew point is then determined in the device from both values. The dew point meter is therefore a thermohygrometer with a stored algorithm for determining the dew point temperature. The air humidity is usually measured as relative humidity from 0 to 100 percent or from 5 to 95 percent. The range of dew point temperatures that can be determined internally by the dew point meter is usually limited by the measuring range of the temperature and the evaluation function stored in the device. Some devices can only measure air temperatures from 0 °C to 50 °C, the others have a temperature measuring range from -40 °C to 70 °C. When searching for a dew point measuring device, make sure that both the measuring range for the air temperature and the measuring range for the dew point temperature are suitable for your application.

Stationary and mobile dew point meters
With a mobile dew point meter, inspections, for example, in dwellings or office buildings room after room, can be carried out. Some housing companies offer their tenants such a dew point meter with display and mold warning when moving in or in case of moisture damage. With the help of the device data, the tenants can heat and ventilate in accordance with the situation and thus prevent condensation and mold growth. In the offices, such a device with display can also be used to regulate the air humidity by means of the ventilation behavior. Stationary dew point meters are used in industry, for example, to monitor the dew point in operating and storage rooms and in the case of pressurized gases or compressed air systems. One area of application is the monitoring and control of industrial drying plants.

Additional sensors in the dew point meter
Dew point meters can have additional sensors for other parameters, besides the sensors for humidity and temperature. Frequent, for example, is the combination with an additional temperature sensor for surfaces. This is practical if you want to measure the temperature of geometric and material-related thermal bridges to determine whether they are above the determined dew point. These additional sensors are often connected as external temperature sensors to the dew point measuring device via interfaces and can be easily exchanged. Very easy to handle are infrared thermometers as dew point measuring device. With these one can carry out the measurements of the surface temperature also in hard-to-reach locations and in the area of high ceilings easily and fast. Also thermal imaging cameras with sensors for air temperature and humidity can be used as dew point measuring device. These provide an immediate overview of the heat distribution of the targeted surface on the thermal image and make it easier to identify pipelines and other fixtures due to the flat display. Other dew point meters are equipped with the sensors for air pressure and air speed and are suitable for checking ventilation and air conditioning systems, among other things.

Data storage and data transmission in the dew point meter
Some dew point meters allow storing the measured values on SD card or internally in the device. These data loggers, if the display is omitted, can have the size of a USB stick and can be read out on the PC via the USB interface. They can be used as mobile dew point meters, for example to record the indoor climate in apartments and archives, but also to document the climatic conditions during longer transports or storage of sensitive goods. These dew point meters record air temperature and humidity at pre-set intervals over several weeks. If the dew point is not immediately determined and stored, it can be calculated from temperature and humidity later. The measurement data show the rise and fall of the values over the measurement period. For many devices there is evaluation software available, which clearly displays the values as a graphic. For some moisture damages there is no indication of condensation from the measured value curve. Then the cause of moisture could be defective water or heating pipes, penetrating rainwater or an earlier water damage, which is not sufficiently dried up. The values stored in the dew point meter can be transferred to a computer for evaluation, for example via SD cards, RS232 or USB interfaces or Bluetooth. Some dew point meters cannot store values in the device itself, but can transfer measurement data directly via Bluetooth or if connected to a PC or laptop.