Many processes and processes can only succeed when a certain humidity is maintained. Many processes require humidity measurement. For example, in dry paint workshops, and even in indoor air, humidity needs to be detected.
Like temperature, humidity is also an important process variable. For example, the relative humidity of the environment has a significant impact on our physical comfort and health status. In addition, adjusting humidity correctly can help reduce a significant amount of energy consumption. Some applications have high requirements for humidity measurement, and such applications will continue to exist. Continuous monitoring of air humidity becomes crucial when the water vapor content in the air can trigger or affect certain chemical, physical, or biological processes.
Composition of air
In addition to small amounts of neon, helium, krypton, and xenon, clean and dry air also includes the following substances: 78.10% nitrogen, 20.93% oxygen, 0.93% argon, 0.03% carbon dioxide, and 0.01% hydrogen. In addition to these components, the environment and external air also contain a large amount of gaseous and solid substances, as well as a certain amount of water in the form of water vapor. Therefore, air is a mixture of different gases and water vapor.
Relative humidity and the most important derivative variables
relative humidity
The ability of air to absorb humidity increases with the increase of temperature. The humidity level is always determined by measuring relative humidity, which describes the ratio of the current humidity in the air to the possible maximum humidity. All other measurements are taken by measuring probes from relative humidity and temperature.
Dew point temperature
The very low humidity content is represented by the dew point temperature. This is the temperature at which condensation forms in the air.
Absolute humidity
Absolute humidity describes the number of grams of water contained in one cubic meter of air. It is influenced by changes in process pressure.
Mixing ratio
Calculate the mixing ratio during the drying process. It is independent of temperature and pressure and describes the relationship between water vapor mass and dry gas mass. In addition to temperature, humidity measurement probes must also obtain information on process pressure.
measuring method
Capacitive humidity measurement method

Capacitive humidity measurement probe, used to calculate relative humidity and derived variables, using intelligent replaceable probes. In this type of series, the probe is pluggable and replaceable. They are used in various fields, such as climate measurement technology, pharmaceutical industry, greenhouses, as well as clean rooms, storage rooms, and refrigeration rooms.
In most cases, capacitive humidity measurement methods are used to measure humidity levels. This sensor technology mainly includes a capacitor, whose dielectric absorbs or releases according to the humidity of the ambient air. Humidity can affect the dielectric constant of polymer materials, which in turn affects the capacitance of capacitors. Downstream electronic devices use the measured capacitance to calculate relative humidity with high accuracy. This principle applies to most application scenarios. However, special equipment can only be used in high humidity environments. In these devices, the area below the sensor cover is heated, reducing relative humidity and achieving reliable measurements. In contaminated media, use sintered filters to resist the entry of dirt particles and protect sensitive sensor components.
Hygrometer humidity measurement method
The humidity measurement probe of the hygrometer is used to calculate relative humidity. Suitable for humidity measurement in the air conditioning industry and industry. The high resistance of sensing elements to water is a favorable characteristic, allowing devices to be permanently used in high humidity environments until saturation occurs.
In conditions of high humidity or air pollution, measuring humidity with a hygrometer can provide the correct solution. This method belongs to the length variation formula, which means that the fiber components contained can change their length with changes in air humidity. The change in length is transmitted to an indicator or potentiometer through a special transmission system. The system only calculates relative humidity without derived variables. This measurement technology does not require a voltage source and is suitable for cost-effective installation of humidity regulators. The temperature range used is -40~+80 ° C, and the humidity range is 35~100% RH.
Dry wet bulb humidity measurement method
Hygrometer, used to calculate dry bulb temperature and humidity difference. Used for solvent based and corrosive gases; Continuous measurements can also be conducted in the meat processing and cheese industries.
In polluted or corrosive air, humidity can be measured using the wet dry method within the temperature range of 5-95 ° C. In wet dry measurement, the thermometer is directly exposed to the ambient air to measure the dry bulb temperature. Another thermometer is surrounded by a suction core immersed in water, used to measure wet bulb temperature. At the humidity probe, heat is absorbed due to evaporation and a lower equilibrium temperature occurs. The difference between these two temperatures is called humidity difference - the drier the air, the greater the difference. Two RTD temperature probes are connected to an evaluation unit, which calculates relative humidity based on the difference between dry bulb temperature and dry wet measurement. This measurement technique is very robust and can provide good measurement accuracy in the medium to low measurement range. However, in high humidity environments with almost no cooling occurring, it is inaccurate. The installation work is relatively complex and usually requires a fan to generate the corresponding airflow. In addition, the system needs maintenance. For example, it is necessary to monitor the water level and replace the suction core.