HUMIDITY
INDICATORS

Humidity Indicator Cards and Plugs provide external monitoring of humidity levels inside containers.

Humidity Indicator Theory and Characteristics

REVERSIBLE COLOR CHANGE

A color-change element that 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 humidity in excess of 90% for periods of 36 hours or longer, which tends to wash out the element. Such conditions are not uncommon in non-desiccated empty containers during periods of storage. 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 humidity 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 humidity levels. All elements are available in plug-type housings, which are leak-proof and will withstand shock and vibration. The plugs can be installed quickly and easily with common hand tools, and are suitable for almost all applications for Method II packaging of MIL-P-116. RFI/EMI shielding and CARC finish are optional features.

Humidity Indicators should remain in their original packaging until ready for installation. Recommended torque for installation of all Humidity Indicators is 30 in. – lbs. (3.4 N•m).

Maximum Humidity Indicator

A color-stain element warns that certain humidity levels have been exceeded, indicating that the desiccant may need to be recharged or replaced. The element warns of dangerous humidity levels by staining a white disc a brilliant orange (turning later to a dark brown) when it has been exposed to humidity ranging from 55% RH for an eight hour continuous period to 85% RH for two hours. Humidity levels below 55% will not cause the indicator to stain, regardless of duration.

A non-reversible humidity indicator disc is often superior to a reversible humidity indicator disc because it maintains a record of past conditions. For example, a reversible indicator could trip during a cold night when the relative humidity level naturally rises, but then reverse itself during the warmer daytime hours when the indicator is most likely to be checked. In this case, the reversible indicator would give no sign that a dangerous humidity level had occurred overnight. By contrast, after a non-reversible indicator trips, it will always show that its humidity threshold has been exceeded.

Because these elements are irreversible, they should only be installed in a desiccated atmosphere. While it has been common practice to install a humidity indicator plug complete with the irreversible indicating element into a container at the time of container fabrication, this procedure can cause the indicator to trip before the container is put into service. Therefore, it is best to install an empty plug housing into a container during fabrication or refurbishment, and then install the indicating element into the housing at the time that the container is loaded and desiccated. For this reason, you will find these irreversible indicating elements TA378-HC-MHI listed individually. The empty housings are sold as Observation Windows TA456.

The indicator plug is leak-proof and will withstand shock and vibration. It installs quickly and easily with common hand tools, and is suitable for almost all applications for Method II packaging of MIL-P-116. RFI/EMI shielding and CARC finish are optional features.

Recommended torque for installation of all Humidity Indicators is 30 in. – lbs. (3.4 N•m).

Humidity Indicators are often incorporated into plug-type Desiccators for small enclosures. AGM also has custom Humidity Indicators.

Humidity Indicator Cards F.A.Q.

No. The card will turn from pink back to blue once it is exposed to an atmosphere that is dryer than the rating on the card.

Note: Non-reversible Humidity Cards (Maximum Humidity Indicators) will not return to the original color once exposed to moisture.

The time it takes for the card to turn from one color to the other depends on the amount of humidity the card is exposed to and the temperature of exposure. Normally, the cards will change color within minutes of exposure to the ambient conditions.

Note: Non-reversible Humidity Cards (Maximum Humidity Indicators) will not return to the original color once exposed to moisture.

The humidity rating on the cards changes at the rate of 2-1/2% of rated value per 10°F away from 75°F.  That is, for a card that is rated at 30%, when viewing it at a temperature of 35°, the true value becomes 27%.  (2.5 x 4 = 10% rating change, applied to a rating of 30% = 3%, 30% – 3% = 27%.) It works in the opposite direction for higher temperatures.

Yes. AGM’s Engineering Department has designed hundreds of modified and custom versions for previous customers.

Humidity Indicator Plugs F.A.Q.

Yes. AGM’s Engineering Department has designed hundreds of modified and custom versions for previous customers.

This thread is misleading because it actually has a maximum major diameter of 1.027”. Therefore, the recommended mounting hole diameter is 1.050″ (26.7 mm). This thread is commonly used on the small bung of a 55 gallon drum. The reason our humidity indicators have this thread is that they were initially used most commonly on 55 gallon drums.

All of AGM’s plug designs will withstand 10 psig in either direction while our TA284 series is guaranteed to 500 psig outward for high pressure applications.

We recommend 30-40 in-lbs for all humidity indicators we offer that are made of metal except for the TA28X series, which utilize an NPT thread form. For the TA28X series, a higher torque might be required. For the TA380 series (made of SAN plastic), we recommend 5-8 in-lbs, or just finger tight.

Follow these simple steps:

  1. Hold housing by the 1.375” hex flange.
  2. Insert a 1/2” hex wrench (Allen wrench) into the lock screw & turn counter-clockwise to loosen.
  3. Remove lock screw.
  4. Remove Teflon washer.
  5. Remove old humidity indicator card.
  6. Install new humidity indicator card.
  7. Install Teflon washer.
  8. Install lock screw.
  9. Hold housing by the 1.375” hex flange & torque lock screw to 50+/-5 inch-pounds.