A color-change element turns from blue to lavender to pink as the humidity increases, and turns back to blue when the humidity decreases. This characteristic enables these elements to be reused as long as they have not been exposed to humidities in excess of 90% for periods of 36 hours or longer, which tend to wash out the element. The element has long-term calibration and accuracy to within ±5% when read at 75°F (24°C). At other temperatures a small correction factor of 2-1/2% for each 10°F (5.5°C) higher or lower than 75° must be taken into consideration. For example, at high temperatures the element will indicate a lower humidity than is actually the case, and conversely, a higher humidity will be indicated at low temperatures. As indicated above, these elements are water soluble and should not be placed in direct contact with water or steam or exposed to extremely high humidities for protracted periods of time. Also, ammonia fumes will "set" the elements, causing them to lose color reversibility.
The elements are available in 10% increments from 10% Relative Humidity (RH) to 90% RH, as well as various combinations of these humidities. Both types of elements may be installed in the same plug-type housing, which is leak-proof and will withstand shock and vibration. The plugs are quickly installed with common hand tools, and are suitable for almost all applications for Method II packaging of MIL-P-116. RFI/EMI shielding or CARC finish can be supplied as optional features.
While it has been fairly common practice to install the plugs complete with the color-change indicating elements in containers at the time the containers are fabricated, this procedure can expose the elements to excessive humidities which may affect their characteristics. This is even more true in the case of the Maximum Humidity Indicator. It will be necessary to install the housings without the elements in the containers when they are manufactured or refurbished and install the elements in the housings at the time the container is loaded and desiccated. For this reason, you will find these elements and their housings only listed separately, while the color-change elements are offered both separately and complete with housings. The housings without elements may also be used as Observation Windows.
Humidity Indicators should not be removed from their shipping containers until ready for installation. Recommended torque for installation of all Humidity Indicators is 30 in. - lbs. (3.4 N•m).