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Because glass is prohibited, they turn to poly carbonate or acrylic for their windows. For gaskets and seals, they use either silicon or nitrile (buna-n). The most common housing material is 316 stainless steel, a highly corrosion-resistant, nonmagnetic metal. The drawback is that the material does not transmit heat as well as aluminum, making thermal management essential. Although a camera can generate 5 W, the biggest concern remains lighting. “We recommend strobing the light source as opposed to having it on continuously,” says McGeary. “That substantially reduces the amount of heat dissipation required.”
A common technique to guard against lens contamination, whether spraying food or flying wood pulp in a paper mill, is the use of an air curtain or an air knife. Like a laminar flow bench, an air curtain uses airflow to prevent particles from passing through, protecting the camera and lens. For a spray that exceeds the power of an air curtain, a range of solutions exist. Technicians can simply clean off the lens periodically, although that can ultimately result in damage to vulnerable optical coatings if too much pressure is applied. A useful alternative, especially for cases involving large amounts of fluid, is an automatic wiper that periodically cleans off the enclosure window. In the case of a application like arc welding, which involves splatter, the most pragmatic solution is to simply include a sacrificial window on the front of the camera that gets replaced on a regular basis.
A problem faced by space systems that is rare for industrial applications is radiation. Like heat, radiation increases dark current. Shielding is an obvious fix, though there’s a tradeoff with weight. Limiting the length of exposure by using a line array versus an area array is another trick. “The amount of time that the individual bucket of charge has been on in the device can be pretty short,” says Ravine. “I can read out a line array in a millisecond. It takes me a hundred times longer to read out an area array, which means I have a hundred times longer to accumulate dark current.”
As with all engineering, imaging system development for harsh environments involves tradeoffs. With careful design using some of the techniques discussed here, integrators and end users can generally come up with a system that meets their needs. AI
Kristin Lewotsky is a freelance technology writer based in Amherst, N.H.