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Humidity indicators measure water vapor in the air and are used to establish humidity levels in sensitive areas. They come in chemical, electronic, or dial types and can be simple or complex. Chemical indicators change color when exposed to moisture and are commonly used in shipping containers and packaging. Electronic and dial types provide more accurate readings for applications that require exact control of moisture content.
A humidity indicator is a device that measures the amount of water vapor in the air. These devices range in complexity and functionality from simple boards impregnated with moisture sensitive chemicals to complex systems of sensors and microprocessors. Most are used to establish humidity levels in areas or rooms that are sensitive to excessive humidity in the air or significant fluctuations in humidity levels. These include shipping containers, packaging for perishable or sensitive goods, and housing for electronic equipment. There are three common presentations of humidity indicators: chemical, electronic, or dial.
To varying degrees, humidity is a constant environmental factor even in the driest and coldest climates. Moisture in the air is generally not a serious threat, but excessive or even significant changes in the amount of water in the air can be problematic in certain environments. When keeping track of humidity levels becomes a challenge, a humidity indicator can provide useful information about the amount of water vapor suspended in the air. There are many different examples of moisture indicators in general use which, however, fall into three basic categories. As noted, these are chemical indicators, electronic sensors, and dial hygrometers.
The simplest and most commonly used type of humidity indicator is the chemical humidity indicator. These make use of specific chemicals that tend to change color when exposed to moisture. Cobalt chloride and copper chloride change color when exposed to increasing amounts of moisture in the air; the cobalt chloride changes from blue to pink and the copper variety from yellow to blue. While these types of humidity indicators aren’t as sophisticated or accurate as other types, they can give a good indication of overall humidity levels.
Chemical moisture indicators are often presented in the form of paper strips with several circular areas impregnated with moisture sensitive chemicals. Each chemical “stain” is formulated to change color at a specific humidity level; a single tab can give a pretty good indication of a range of humidity levels. These chemical indicators are often incorporated into small inserts with a plastic window. When installed on the side of a shipping container, electronic equipment enclosure, or any other packaging, they allow for a quick view of the humidity level inside the container. The same type of chemical indicators are also fitted to compressed air lines in applications where control of the water content in the air stream is essential.
Electronic and dial types of moisture indicators can give more accurate moisture readings in applications where exact control of moisture content is required. Electronic types typically consist of a remote sensor and digital readout station and are often used as part of large, centralized environmental control systems. Dial variants usually feature two scales that indicate both humidity levels and temperature.
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