BY Jim McCorry
Moisture has long been the enemy of aerospace and defense electronics and electro-optics in systems, such as missiles, munitions, avionics, imaging systems and optical guidance systems. Sensitive electro-optical equipment can be damaged by moisture—not only from corrosion of wiring and metal parts, but also from condensation and fog on lenses and mirrors.
To prevent moisture from contaminating equipment during transport and storage, aerospace and defense engineers historically have designed air-tight shipping containers able to withstand large pressure, temperature, and altitude differences. These heavy, bulky, steel containers, however, are costly to build and ship. A better solution involves controlled breathing systems that allow for lighter, less bulky containers.
The key elements of a controlled breathing system include a breather valve, which controls pressure, vacuum, and moisture entry; a desiccator, which removes moisture; and a humidity indicator, which indicates when to replace a desiccator when it’s saturated and humidity levels begin to rise. The breather valve basically allows a sealed enclosure to “burp” a little air in and out, to equalize internal and external air pressure.
While the moisture problem in shipping containers has long been solved with the use of these controlled breathing systems, the field of battle is evolving again. For mission-critical functionality, reliability, and longevity, the leading edge of moisture control is moving from inside the container to inside the equipment.
The continual pressure to improve the functionality, reliability, and longevity of mission-critical, electro-optical devices is now resulting in controlled breathing systems being used for moisture control directly in the equipment. After all, what is a camera housing or missile casing other than a container for the sensitive components inside?
“Reducing moisture in the presence of electronics and optical imaging systems is critical for performance and longevity,” says James Weaver, a mechanical engineering manager at thermal imaging specialist FLIR Systems in Wilsonville, Ore. “With superior moisture control in the shipping container and even the equipment enclosure itself, you can operate longer and more reliably in harsher and harsher environments. Everything is demanding higher definition, more functionality, and more processing capability in a smaller, more rugged package.”
While a traditional shipping container has plenty of room for a separate breathing valve, desiccant, and humidity indicator, space was at a premium for FLIR’s Star Safire HD system, which features megapixel thermal, daylight, and low-light cameras with high-magnification optics, laser payloads, and a fully integrated inertial measurement unit to locate targets precisely.
“For us, every inch and every ounce must provide functionality,” Weaver says. “We didn’t have the luxury of using a large panel to put three separate, controlled breathing system modules in our device. To free up space for enhanced capabilities on the Star Safire HD system, we sought to combine the moisture control modules.”
AGM Container Controls in Tucson, Ariz., teamed with FLIR to develop a controlled breathing system, called the TA340, with a combined breather valve, desiccator, and humidity indicator for space-efficient moisture control.
Incorporating a humidity indicator and two-way breather valve all in the same aluminum housing not only saved space, but also helped to avoid drilling an additional hole in the case. With only one mounting hole in the equipment, potential leak paths in the equipment were reduced, which makes its moisture control capabilities even more reliable.
Since the TA340’s desiccant cartridge is mounted on the back end of the valve, when it breathes air in, the air goes directly over the desiccant bed to efficiently capture moisture on entry. For ease of desiccant replacement, the system is also designed to accept an externally accessible replacement desiccant cartridge.
“It’s critical for anyone servicing a controlled breathing system to have an externally accessible replacement desiccant cartridge,” Weaver says. “Besides being easier and quicker, it minimizes moisture entry from outside air since the entire enclosure does not have to open. I’m glad we were able to include this in its compact design.
“Since the TA340’s 3-in-1 controlled breathing system reduced its ‘footprint’ by two-thirds compared to separate moisture control systems, we had more space to enhance our thermal imaging, visible imaging, and laser elimination capabilities,” Weaver says.
On a more recent project, AGM again teamed with FLIR and added RFI/EMI shielding to the compact, controlled breathing system. “RFI/EMI shielding enables an electronically tighter enclosure, with even less susceptibility,” Weaver says. “It should allow its use on installations with higher emissions, and should shield customers from noise made on more sensitive equipment.”
As the aerospace and defense arena demands ever more functionality and ruggedness in a smaller package, the leading edge of moisture control will increasingly move from inside the container to inside the equipment for mission-critical functionality, reliability, and longevity. The aerospace and defense engineers who keep pace with this trend will be ready to deliver.
Jim McCorry is the director of business development at AGM Container Controls Inc. in Tucson, Ariz. Contact the company online at www.agmcontainer.com.