Vaisala introduced the world's first thin-film capacitive humidity sensor, the HUMICAP® sensor, in 1973. Since then, Vaisala has become a pioneer in the market for relative humidity measurement, and this type of thin-film capacitive humidity sensor has evolved from a single company's invention to a global standard.
Vaisala's HUMICAP sensor stands for quality and reliability, just as it is renowned for its accuracy, excellent long-term stability, and minimal wet lag.
Working Principle
HUMICAP is a high polymer film capacitor-type sensor, structured with a high polymer film positioned between two conductive electrodes. The sensor surface is covered with a multi-porous upper electrode to prevent contamination and can be exposed to condensation states. The typical material for the lower electrode is glass and ceramic. As the relative humidity of the surrounding air rises or falls, the film-like high polymer absorbs or releases water vapor accordingly. The dielectric constant of the high polymer film, as an insulating material, is related to the amount of absorbed water vapor; hence, when the relative humidity around the sensor changes, the dielectric constant of the high polymer film also changes, resulting in a corresponding change in the sensor's capacitance. The circuit in the instrument measures the sensor's capacitance and converts it into a specific humidity value.
Typical Applications of Humidity Measurement
Vaisala's humidity gauges with HUMICAP sensors are suitable for a wide range of applications, from power and steel to shipping and plastics, as many industrial sectors require humidity measurement – some examples include: humidity measurement and control are essential in many drying processes, such as in the drying of construction materials and papermaking, as well as in fluidized bed dryers. The gas humidity in these processes clearly indicates the progress of the drying process. Cleanrooms and other critical environments also require high-performance environmental measurement instruments to ensure the continuity and controllability of operational processes. Moreover, glove boxes and isolators – materials that are highly sensitive to moisture or gases – will benefit from accurate and reliable humidity measurement. Measuring humidity in critical environments is highly challenging.
In the food industry, dryers and drying ovens in bread baking and cereal manufacturing require precise control of humidity levels to ensure consistent quality and efficiency, while maintaining the unique flavor of the finished products.
In the field of building automation, optimizing both indoor temperature and relative humidity simultaneously is far more effective in enhancing employee comfort than optimizing temperature alone. Careful humidity control is essential in the following areas: museums, archives, warehouses, and environments housing items highly sensitive to humidity.
HUMICAP Sensor Features
▪ A high polymer film capacitive sensor
▪0...1 0 0%RH full-range measurement
Accuracy up to ±1%RH
▪ Traceable humidity measurement
▪Has been in the market for nearly 40 years
Unconventional Advantages of the HUMICAP Sensor
Good long-term stability
▪ Not sensitive to dust and most chemicals
Chemical removal feature options ensure sensor stability in environments with high concentrations of chemical substances.
▪ Even in condensing environments, the sensor's heating function allows for measurement to proceed
Absolutely recoverable from condensation.
Vaisala's INTERCAP Humidity Sensor
The same measurement principle as the HUMICAP sensor
Pre-adjusted at the factory – no additional calibration required.
▪ Sensors can be easily swapped out.
Humidity Gauge for ±3%RH Accuracy
HUMICAP® Humidity Sensor – A Continuously Innovating Product
Prior to the 1970s, wireless radiosondes often employed hair hygrometers, a time when reliable humidity measurement was impossible. To address this challenge, Vaisala began developing a new type of sensor using semiconductor technology and thin-film materials. Two years later, in 1973, the revolutionary HUMICAP humidity sensor was officially introduced at the sixth session of the World Meteorological Organization's Commission for Instruments and Methods of Observation (CIMOVI). The HUMICAP sensor represented a groundbreaking innovation, changing the traditional methods of humidity measurement. Its pioneering aspects included: 1) no moving parts, and 2) compact size, thanks to the early adoption of semiconductor and thin-film technology. The sensor offered rapid response times, good linearity, low hysteresis, and minimal temperature drift. Although the sensor's development was initially for the next generation of wireless radiosondes, it garnered significant interest from other fields. These applications ranged widely, from greenhouses, baking, and storage to construction sites, brick/wood drying kilns, and museums, all sharing a common need for reliable humidity measurement, which was not accurately provided by existing instruments. Since 1980, various products based on the HUMICAP technology—ranging from handheld meters to industrial transmitters, calibrators, and various accessories—have been sold to over sixty countries. Since the inception of HUMICAP, it has become a core part of Vaisala's technology, propelling the company to the forefront of humidity measurement.
