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Metrology

Calibrating a Calibration Tool

NASA invention solves innovators’ problem and manufacturer’s, too.

Published: Tuesday, August 4, 2009 - 03:00

What does an innovator do when existing methods of calibrating a critical environment pressure sensor are cumbersome and produce shoddy results? Richard Deyoe and Stephen Stout, ASRC Aerospace meteorologists based at NASA’s Kennedy Space Center, decided to design and build their own calibration unit. Now, Setra Systems—the company whose pressure sensor Deyoe and Stout were trying to calibrate—is using their invention to improve its own product line.

In the early 1990s, Deyoe and Stout wanted an accurate, cost-effective technique to perform onsite qualification testing of Setra Systems’ Model C264, a new, high-accuracy, low-differential pressure transducer. The basic problem was that new pressure transducer technology and accuracy had exceeded the accuracy of commercially available calibration equipment. For the qualification testing, a portable, lower-cost calibrator was needed that could control the differential pressure to a high degree of resolution without having to be in an environmentally controlled room, and have the capability to transfer the accuracy of the standards laboratory into the qualification testing.

“There was no method and no equipment for qualifying the Setra C264,” Deyoe recalls. “Even the reading of the standards was a problem because the lowest standard we had was a one-pounder. We had a job to do and we needed to find a way to get it done, so we created our own device.”

The researchers decided that to generate the low-differential pressure set points needed for qualification testing, very small gas volume changes could be made against the test article, and a corresponding pressure change would be detected by a pressure standard. The pressure generator utilizes a piston within a cylinder that features both positive and negative pressure generation simultaneously when connected to a two-port differential pressure (DP) sensor. The resulting DP generation is environmentally sealed and immune to outside air disturbances caused by fans, opening and closing of doors, and people walking by. The pressure control, sensitivity, accuracy, and repeatability exceed anything commercially available, then or today. This allowed the researchers to recreate pressure settings as those in a clean room.

In 1993, Deyoe and Stout developed a prototype of the pressure generator, using a pair of PVC tanks, a piston/cylinder volume controller, and a one-psi pressure standard. By 1995, they had perfected the prototype unit that is still used today and known as the Low Differential Pressure Generator. NASA saw the merit of the invention and applied for a patent in 1996. A U.S. patent (No. 5,693,871) was issued for the technology in December 1997.

Ironically, Setra Systems struggled with the same issues as Deyoe and Stout and began searching for a technology for certification testing of its C264. When looking for a possible solution, the company discovered Kennedy’s patented Low Differential Pressure Generator at a NASA booth at the Sensors Expo & Conference.

“At the trade show we learned about an article in NASA Tech Briefs about the technology,” says Terry Troyer, HVAC product marketing manager at Setra. “We had already started down the path of solving the problem and we noticed that they had solved it in a different way. When we saw the NASA patent we thought it would be very advantageous to add this to our IP portfolio. We were happy to tap into it.”

Setra Systems licensed Deyoe and Stout’s technology in March 2005, and then the company advanced it further. Using a product development team of 14 engineers and investing more than $200,000, the company added a computerized micro-control to the NASA generator. They also added Setra Systems on-board standard transducers, battery power, and a nifty pocket PC user interface to complete the calibration package.

Setra Systems now markets the upgraded device, renamed the Micro-Cal 869, worldwide.

Setra manufactures the Micro-Cal 869 in its Boxborough, Massachusetts, facility, with sales in excess of $1 million. Users include the pharmaceutical industry, required by the Federal Drug Administration to certify the accuracy of its air-handling sensors. Other opportunities abound for this device, for calibrating pressure transducers used in clean rooms, hospital isolation rooms, laboratory fume hoods, and nuclear and aerospace laboratories.

setra

“The portable, multi-function 869 Calibrator replaces cumbersome, inaccurate components previously used for in-situ, field calibrations—usually a hand pump, a pressure indicator, and data logger,” Troyer says. “During on-site product demonstrations, we literally observe ‘eye-popping’ responses from calibration technicians when they see the speed, accuracy, repeatability, and convenience of the 869.”

“It is a good feeling to see the device we invented being used by Setra in the private sector,” says Deyoe. “The technology transfer process was a group effort, and the IPP Office [NASA's Innovative Partnerships Program] was a big help with finding a partner and getting the technology out there. I am very proud of what has occurred.”

This article originally appeared in Kennedy Tech Transfer News, published by the Innovative Partnerships Program Office at NASA's Kennedy Space Center (http://technology.ksc.nasa.gov)   

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NASA Kennedy Tech Transfer News

Kennedy Tech Transfer News is a semi-annual newsletter distributed to NASA Kennedy Space Center personnel. Visit http://technology.ksc.nasa.gov.