Reliable measurement of high air humidity - It's a question of the principle

A correct climatic detection is the only way to control correctly. No algorithm or actuator can help if sensors are not measuring the real value and providing reliable signals.

The challenge

Various process and storage conditions require a high ambient humidity >80%RH, often combined with low temperatures. Production & storage of vegetables, fruits, drugs as well as ripening processes have also to comply with close tolerances. Inaccurate humidity control can lead to unwanted condensation or product drying, which have a negative impact on quality. Especially for quality relevant processes it is recommended to compare the different measurement principles and characteristics.

The influence of the measurement principle

The most popular air humidity measurement principle is the capacitive technology, based on a solid polymer, which changes its capacitance according to the humidity. This principle is quite inertial and variations, especially at high humidity are detected slowly or not at all. The polymer incorporates the moisture and releases it very slowly. Also the outgassing of volatiles, e.g. ammonia in a cheese ripening cellar lead to a significant measurement drift.

The best choice

What works better for high humidity is the resistive-electrolytic measurement, where an electrolytic substance changes its resistance according to the humidity. This detection allows a stable and accurate measurement over the whole range up to the saturation point without any hysteresis effect and with linear response, even during frequent humidity changes at high humidity levels. This technology reduces also the cross-sensitivity caused by volatiles such as ammonia or CO2, which normally lead to measurement drift with other detection principles.

The solution - nSens-HT for humidity & temp. measurement

Based on above mentioned technology, Novasina has created a probe, which excels in robustness and accuracy and can be used for applications over the whole humidity range, even in rough environments. Relevant data such as serial no. and calibration points are stored on the probe. This allows to replace it quickly without measurement interruptions. The replaced probe can be calibrated in the lab and used again as replacement. The probe can be integrated in measurement and control systems using either analogue output or digital Bus signals. For room mapping, the nSens-HT can also be connected to a data logger. Other solutions with data transfer over Ethernet are also available.