Isaac Newton wrote about his discovery of the phenomenon of air density, or relative humidity, in his 1704 book "Opticks." Ever-increasing and ever-decreasing gas molecules in air volume create a continuously changing relative humidity. Climate control continues to be important in industry and small business alike, as well as in creating a relaxing environment in private residences. Using capacitive or resistive relative humidity sensors is one way to achieve climate control is through the .
Relative Humidity Sensors
Capacitive sensors contain a layer of water absorbent, inorganic or polymetric material coating sprayed over a conductive base. An additional porous conductive layer sits atop the coating. The water on the coating increases as the relative humidity climbs, causing the dialectic constant in water to store an increasing electric charge. The layers of inorganic material or polymer play a smaller part in the process compared to the amount of water molecules that are measured. Resistive sensors use a wafer of water-absorbent polymer with attached interlocking combs of carbon or conductive material. The sensor provides a short positive charge, followed by a negative charge equal in power, and calculates each charge to create a relative humidity value.
Measuring Tools
Measuring relative humidity in a private home or business is possible with a variety of tools. Accuracy and sensitivity are the key elements in choosing the right tool for the job, and relative humidity measuring devises come in many styles and degrees of sophistication. In applications where minute changes in humidity are important, more-sensitive equipment is required. Excessive amounts of relative humidity cause an array of various mold growths. While eliminating all mold spores in the indoor environment is impractical, relative humidity control is the only way to control mold growth.
Considerations
Calibrating capacitive and resistive relative humidity sensors, as well as hygrometers and psychrometers, is the key to getting accurate information. Relative humidity sensors are often unreliable and you must calibrate them at installation and recalibrate them about every six months. You must check at least two relative humidity values to know whether the device is measuring properly. The most common methods to use for recalibrating relative humidity sensors are saturated salt solutions and light and UV sensors. An assortment of portable devices are available for smaller jobs.
Cost
Prices vary widely across a range of available RH sensors. In 2010, simple sensors, such as printed test cards, start at $23.00. More-sensitive equipment can cost as much as $25,000.00. Individuals needing simple information can easily get information from their local weather reporting sources, such as TV or radio newscasts, because cost and maintenance of equipment can be taxing.
Future Sensors
Science and technologists continue to improve methods and tools to measure relative humidity. Health and recreation continue to benefit from the knowledge spanning two centuries. Tools available continue to make easier the task of measuring relative humidity for professionals in industry and private homeowners.
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