Classified by usage scenario:

Laboratory type: focuses on high precision and multifunctionality, with a detection accuracy of ± 0.001Aw. Some also have functions such as data storage, curve analysis, and network transmission, suitable for scientific research institutions and enterprise quality inspection centers to conduct precise analysis and method validation.

Portable: compact in size, lightweight, usually equipped with battery power, short detection time, mostly within 5-10 minutes, suitable for mobile scenarios such as on-site sampling and production line inspection, meeting the needs of fast quality control.

Online type: It can be directly installed in the production line to continuously monitor the moisture activity of materials in real time. The data can be synchronously transmitted to the control system. When the value exceeds the preset range, it will automatically alarm, realizing dynamic control of the production process. It is commonly used in large-scale production fields such as food processing and pharmaceutical preparations.

Classified by working principle:

Cold mirror dew point method: using a mirror condensation dew point sensor to measure the equilibrium water vapor pressure or dew point value between the gaps of the sample, while using a thermometer to measure the temperature of the sample, and then calculating the equilibrium relative humidity and water activity. This method is accurate and rapid, and is recommended for many applications.

Electronic hygrometer method: using resistance or capacitance sensors to measure relative humidity. The sensor converts the electrical signal and humidity signal through changes in capacitance or resistance to obtain an equilibrium relative humidity value, which is numerically equal to the sample water activity.

Electrolytic cell method: also known as Coulomb hygrometer method, uses the sensitive element of the electrolytic cell. When the measured gas passes through the electrolytic cell, all water vapor is continuously absorbed and electrolyzed. The instantaneous electrolysis current can be regarded as the reflection of the instantaneous value of gas moisture content, thus obtaining the water activity of the sample.

Tunable diode laser absorption spectroscopy: a specific wavelength laser is used to measure the relative humidity of the air above the sample. Water vapor has strong absorption at this wavelength, and the sensor can accurately measure the water vapor above the sample and convert it into water activity values.