Thermal imaging goes digital

Heat can be deadly to products and processes. It can shorten the life of
electronics, indicate the impending failure of electrical or mechanical systems
in buildings or equipment, and predict impending problems or design flaws.

Infrared thermal imaging can help analyze, monitor, and solve such heat problems. With this track record, why isn't industry teeming with IR cameras? Mainly because, in the past, IR cameras were bulky, limited by low-resolution imagery, and had only rudimentary analysis capabilities.

On the other hand, mechanical scanning systems could measure temperatures everywhere, but not very accurately. Even more advanced solid-state cameras measure temperature only at a single point in the center of the screen.

Last year, all those drawbacks went out the window. Attribute the advance to engineers at FLIR Systems Inc., Portland, OR, and the Prism DS-a handheld infrared thermal-imaging camera packed with advanced features.

"An emerging need for bringing very-high-resolution digital data from an IR imaging camera to a PC prompted the design," says Gary Causley, director of industrial engineering and manager of the Prism DS project. "This would allow the user to deal with the data in a more orderly and sophisticated format."

"In our previous camera, we digitized inside, did all sorts of DSP, and then regurgitated the output in analog video," Causley chuckles. "Our customers had no access to the digital data. The biggest thing about the DS is the link to the customer of "true' digital data."

Other project goals: temperature measurement across the entire field of view, instead of at just one point; 12-bit resolution; real-time operation; and light weight. There were also challenges: calibrating 78,080 IR detectors, connecting the detectors to the digitizing electronics, and processing a huge amount of data in real time.

Design of the Prism DS started in March 1994. However, the DS is the third product in the Prism line, so the engineering team didn't start from scratch. Also, FLIR believes in modular designs. Engineers reused or redesigned what components they could from the previous models, designed parts that could be retrofitted into those cameras, and developed others that they could easily integrate into future designs.

The result: the 7-lb Prism DS camera that uses solid-state technology to detect infrared radiation and measure temperature at more than 78,000 points simultaneously. PMCCIA flash-memory cards store the digital images, a 486 microprocessor runs the show, and real-time digital signal processing (DSP) enhances the images. Then, Windows(R)-based AnalyzIR image-analysis and report-generation software let users post-process images and analyze trends on their PCs.

Front to back. Walking through the camera from the lens to the digital output shows how the DS works-and the challenges the designers faced. First, the lens. FLIR developed a family of lenses-25, 50, and 100 mm-for the DS. The IR-transmissive material consists mainly of germanium and silicon.

The company buys the material as blanks, then uses its own diamond-turning optical fabrication facility to build lenses in house. "That gives us tremendous leverage," says Causley. "We can make common parts to keep costs down."

In the process, the engineers developed a new color-correction lens technology

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