Exploring the Technology of Humidity SensorsMay 2, 2020
Science and processing technology rely on humidity sensors as part of control systems in a variety of applications. Many people are aware of the relative humidity number reported by the local weather reporter on TV. While this helps the average citizen prepare for his day, it is only one very small reason for the existence of sensors to measure humidity. Humidity has impacts on a wide range of industrial and scientific processes and makes a difference in everyone’s daily lives. This short article will examine the technology and uses of humidity measurement.
The basic definition of humidity is the water vapor content in a gas such as air or nitrogen. Notice this refers to water vapor – not water in any form. Water existing as a mist or ice crystal in air is not within the definition of humidity. Also, humidity is discussed in various terms depending on how the measurement is made and used. Within certain ranges it is possible to calculate the equivalent measurement in different terms, such as converting relative humidity measurements to dew point temperatures.
Three often used measurement terms are relative humidity, dew point and absolute humidity. Each of these is measured differently and used differently in process controls or data recording applications. Humidity measurement methods have evolved tremendously over the decades.
Early scientists realized human hair changed when water content in the surrounding air changed. This led to mechanical devices that indicated humidity by the changes in a strand of hair. Both human hair and horse hair were used to power indicators or chart recorders. Materials technology provided nylon and other synthetic fibers that were more predictable and easily calibrated. Today, relative humidity sensors are solid-state electronic devices with lower cost and greater robustness.
Dew point is the combination of temperature and gas pressure at which water vapor begins to condense into liquid. Most people understand this in weather report terms but it is an important factor in many scientific calculations and processes outside of weather. Early dew point measurements used chilled mirror technology which was both expensive and temperature limited. Modern electronic dew point sensors are accurate down to -40degrees F.
Absolute humidity is the precise measurement or calculation of the mass of water vapor in a given volume of air or other gas. (Expressed as grams per cubic meter or grains per cubic foot) This is the most useful measurement for a variety of applications. One interesting application is in drag racing. The grains [of water in the ambient air] number is used by all race teams in setting up their racing engines. Modern electronics can measure absolute humidity at temperatures greater than 200 degrees C in almost any environment.
Sometimes process stability problems are related to humidity changes in the process environment. Monitoring humidity can provide clues why results are not consistent. Painting quality can suffer when humidity changes and the process is not adjusted to compensate. The wide range of sensors on the market today assures coverage for any perceivable application.
Humidity sensor manufacturers can deliver accuracy, robustness, size, and cost to meet just about any scientific or technological requirement. Some online research is sure to reveal a variety of options for any application. This article should provide just enough information to make your research more effective.