1 April 2002
Detect gas leaks from afar
By Jim Strothman
A mass spectrometer system that detects gas leaks from a safe, remote location may soon become a reality, thanks to a joint
government/industry team at NASA’s Kennedy Space Center (KSC) in Florida that developed the new technology.
Called the Hydrogen Umbilical Mass Spectrometer (HUMS), the leak-detection instrument consists of an integrated sample delivery system, a commercial mass spectrometer–based gas analyzer, and National Institute for Standards and Technology standard gas mixtures for calibration.
Except for the calibration gas mixtures and the remote operator display, the system fits into a standard 24-inch-wide,
6-foot-high, 36-inch-deep (0.61 by 1.83 by 0.91 meters, respectively) equipment rack. The power source is 120 volts AC,
30 amps, and 60 hertz.
HUMS detects leaks and measures cryogenic propellants (oxygen and hydrogen) from a remote location during shuttle launch countdown. It specifically samples the background gas surrounding the 17-inch (0.43-meter) Orbiter-ET disconnect, looking for hydrogen gas leaks.
The instrument was designed by Greg Breznik, Barry Davis, and Frederick Adams of KSC; Guy Naylor, Francisco Lorenzo-Luaces, Charles H. Curley, Richard J. Hritz, Terry D. Greenfield, David P. Floyd, Curtis M. Lampkin, Donald Young, Gary N. McKinney, and Don Greene of Lockheed-Martin; and David R. Wedekind, Larry Lingvay, and Andrew P. Schwalb, formerly of I-NET.
HUMS switches rapidly among background gases (helium, nitrogen, or air) during normal operation. The operator can remotely select one of eight sample lines and switch among any of six calibration gas mixtures.
NASA said it can measure from 0 to 100% hydrogen, helium, or nitrogen; 0 to 25% oxygen; and 0 to 1% argon, in any combination of a helium, nitrogen, or air background. HUMS’ internal cycle mode can cycle among various preset sample and calibration gas lines on a continuous basis, if desired.
Operational features, NASA said, include the ability to update background readings of each gas in the mixture, saving considerable time by eliminating the need to do a complete recalibration during operation.
Selecting calibration gas mixture concentrations was critical to verifying performance remotely.
During the calibration process, linear calibration curves generate for each gas in the mixture (hydrogen, helium, nitrogen, oxygen, argon) based on pure background (helium or nitrogen) and a span gas (1% to 10% of each gas, in each background).
An independent test gas containing mixtures approximating red-line levels, where action must occur, verifies a good calibration to compare directly with an unknown sample and also removes uncertainty reading the unknown mixture.
For more information, click on www.nasatech.com under the Test and Measurement category.IT