Southwest Research Institute® (SwRI®) News

Thin Film Strain Transducer

San Antonio, TX -- Sept. 27, 1983 -- A novel yet simple strain transducer, used to measure strain in high altitude scientific research balloon skin and other thin film materials, has been chosen as a winner in the 1983 IR-100 Awards competition conducted by Industrial Research and Development Magazine, officials of the publication announced Thursday, Sept. 22, in Chicago.

The awards are presented for developments honored as the 100 most significant technological advances of the year.

The strain transducer was developed at Southwest Research Institute® (SwRI®), a not-for-profit applied research and engineering organization based in San Antonio, as part of a research program conducted for the National Aeronautics and Space Administration (NASA).

Principal developer is Dr. James L. Rand formerly manager for dynamic analysis in the Institute's Division of Engineering and Materials Sciences. He is now president and chief operating officer of Winzen International , a firm concerned with scientific balloon development.

"The instrument," he says, "was developed to measure accurately the strains experienced by scientific balloons during inflation, launch, and ascent."

High altitude scientific balloons, soaring through wide-ranging variations of pressure and temperature to explore far reaches of the atmosphere, have been pressed to the limits of current art in design, analysis, materials, and manufacturing technology. To extend knowledge so that improvements can be made, engineers need to be able to measure the deformations in the film caused by various forces and temperature changes. For many years, accurate measurements have been thwarted by a variety of electrical, mechanical, and optical problems. A principal problem has been that the sending devices used were stiffer than the very fine film (typically 0.0005 inches thick) on which they were applied, causing localized stiffening and distortion of measurement results.

The new strain transducer, while highly sensitive to strain, does not interfere with measurement and can withstand extreme temperature changes without losing calibration.

The instrument's developers foresee its use wherever delicate products are exposed to critical environments, as in the film and packaging industries or in the characterization of materials in medical practice.

The transducer is a ring, 3 inches in diameter, 0.5 inches wide, and only 0.0035 inches thick, constructed from a thin ribbon of beryllium copper. Four foil strain gages, bonded and bridged, produce a signal proportional to strain.

The gage is attached to the thin film surface with tabs designed to cause minimal distortion. Either meridional or circumferential strain may be measured according to the direction o f the tabs.

A small, lightweight amplifier developed by NASA and attached to the load tape close to the transducer sends and amplified signal to a telemetry unit.

"Initial tests of the strain transducer on two balloons launched by the National Scientific Balloon Facility, in Palestine, Texas, proved highly successful," Rand said. Neither the transducers or the balloons suffered any damage. The presence of the gages did not alter film temperatures or distort measurements. Strain signals were successfully measured, amplified, and telemetered.

For more information about the Thin Film Strain Transducer, contact Joe Fohn, Communications Department, Southwest Research Institute, P.O. Drawer 28510, San Antonio, Texas, 78228-0510, Phone (210) 522-4630, Fax (210) 522-3547.

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