An instrumentation system monitors rates of leakage of hydrogen from multiple zones on a complexly shaped tank. Each zone is established by bagging a designated exterior portion of the tank. The bag for each zone is purged with a carrier gas (either nitrogen or helium) at a controlled flow rate, then the carrier gas with leaked hydrogen (if any) mixed in is routed to one of two mass spectrometers, which can measure concentrations of hydrogen from 30 parts per million to 4 percent calibrated. Microelectronic sensors are used to measure concentrations from 2.5 to 100 percent, enabling the hydrogen concentration to be determined after the mass spectrometers have reached their saturation point. Inlet valves on each mass spectrometer enable the selection of purge exhaust to be sampled from any of eight zones. The microelectronic sensors are positioned in the exhaust flow from the mass spectrometers. A computer, acting via a programmable-logic controller, monitors and controls valves, flow-control valves, and related instrumentation. Another computer monitors and controls the mass spectrometers. Hydrogen-concentration data acquired by the mass-spectrometer-control computer are fed to the flow-control computer, which computes hydrogen-leak rates from the measured hydrogen concentrations and flow rates. The microelectronic-sensor data are recorded by the facility Data Acquisition System.

This work was done by Glenn Varner of Stennis Space Centerand Phillip Hebert and Lester Langford of Lockheed Martin. SSC-00065


NASA Tech Briefs Magazine

This article first appeared in the September, 1998 issue of NASA Tech Briefs Magazine.

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