Humidity sensors are among the most commonly used instruments in environmental monitoring applications. Why? Because they are one of the crucial measurement parameters that must be properly controlled when seeking to create comfortable, safe, and energy-efficient environments. For example, humidity sensors are frequently used in industries such as HVAC, biomedicine, food processing, pharmaceuticals, meteorology, microelectronics, agriculture, and structural condition monitoring. Let's take a quick look at the development of modern humidity sensors and focus on why these instruments are so important—and how Vaisala's HUMICAP® solutions can help you.
The Development of Modern Humidity Sensors in Visala:
Humidity is defined as the amount of water vapor in the air. The commonly used term is "relative humidity" (RH) because this amount of humidity is relative to temperature. Throughout the history of relative humidity measurement, many methods have been available for this task. Early hygrometers measured the physical changes in different materials that absorbed water vapor, examples including animal hair and paper rolls. These methods proved inaccurate, had limited measurement range, and required considerable maintenance.
Other methods for calculating relative humidity were then developed, some of which are still in use today, such as suspended hygrometers and cooled mirror hygrometers. These methods use evaporation and condensation to indirectly measure and calculate humidity levels, but they are not always ideal. With the increasing demand for more accurate and comprehensive relative humidity measurements in weather and research applications, there is a need for more accurate and low-maintenance solutions.
Following the invention of the transistor, electronic humidity sensors were developed. These sensors are based on measuring resistance; the materials they contain absorb water vapor, and their resistance changes accordingly. However, these sensors also have drawbacks, such as poor stability, limited accuracy, and difficulty in responding to decreases in humidity levels (also known as time lag).
To overcome these shortcomings and provide greater reliability for meteorological observation technology, Vaisala developed a capacitive humidity sensor based on thin-film polymers in 1973.
Working principle of humidity sensor:
Modern capacitive humidity sensors consist of a polymer and two electrodes: the polymer reacts with water vapor in the air, and there is one electrode on each side of the polymer. As the air humidity changes, the polymer absorbs and releases water vapor, thus altering the sensor's capacitance. This change in capacitance is measured by the two electrodes, which communicate with a digital device that interprets and transmits the readings. This type of sensor has proven to operate stably and reliably over long periods.
Monitoring humidity using HUMICAP® sensors:
The Vaisala humidity sensor, called HUMICAP, measures a wide range of relative humidity with high stability and a fast response time. This technology enables weather balloons to respond to rapidly changing atmospheric conditions, leading to a better understanding of the weather and improving our ability to make weather forecasts.
Over the years, Vaisala HUMICAP humidity sensors have found increasing applications in industry, life sciences, and other fields where humidity measurement can improve quality and comfort. Combined with temperature sensors, modern hygrometers can calculate many useful humidity-based variables, such as dew point, enthalpy, absolute humidity, and parts per million (ppm).
Combined with transmitters or instruments, Vaisala HUMICAP humidity sensors can deliver their measurement data to personnel and systems that need to make critical decisions using this data. From handheld hygrometers to industrial probes and transmitters, there are few environments that do not use accurate humidity measurements to improve conditions or processes.
Despite the wide variety of products on the market, HUMICAP technology continues to evolve and improve, providing high-quality measurement data.
Different types of humidity meters:
HUMICAP technology has been applied to a variety of instruments. Although it originated from weather balloons, it is now commonly used as an indoor sensor for HVAC applications. These sensors can be mounted on walls, in piping systems, and even in refrigerators. Outdoor sensors are also common, as they are used in weather stations and aircraft to detect icing conditions.
Specialized sensors have also been developed to function in challenging environments, such as ovens, environmental testing chambers, and high-pressure pipelines. Different humidity sensors have also been modified to measure dissolved water in oil, which helps protect our energy infrastructure.
With further modifications, low-humidity dew point measurement devices for pneumatic and breathing air can be developed. The Vaisala DRYCAP® sensor, built on HUMICAP technology, provides measurements for ultra-dry applications.
Few sectors of the global economy do not measure or consider humidity, and Vaisala HUMICAP humidity sensor technology provides reliable and accurate information that we rely on to improve processes and make informed decisions.
