The figure depicts selected aspects of a "smart" microelectronic-based hazardous-gas-detection system that simultaneously measures concentrations of hydrogen and oxygen. Unlike conventional gas-leak-detection systems built around mass spectrometers, this system is not restricted to operation in relatively mild and controlled laboratory or shop environments; instead, this system can operate over a range of temperatures and pressures. Also, in comparison with conventional mass-spectrometer-based leak-detection systems, this system is more robust and compact, weighs less, and consumes less power.

The design of this system integrates advanced microelectronic hydrogen and oxygen sensors with microelectronic control, data-processing, and communication circuitry. The system includes multiple sensor modules for measuring concentrations of gases at multiple locations simultaneously. Within each sensor module, the gas sensors are mounted together on a small electronic circuit board. A microcontroller, signal-conditioning circuits, a power-supply circuit, a temperature sensor, and a pressure sensor are also contained within each module. The sensors are thin-film, micromachined silicon devices. Firmware in the microcontroller controls the operation of the gas sensors, collects data from the pressure and temperature sensors, performs real-time compensation for pressure effects and thermal drift, converts sensor readings to engineering units, and effects digital communication between the module and external instrumentation. The use of a digital communication interface minimizes the amount of wiring needed for communication.

ImageAlthough this system was conceived as a prototype of onboard systems for detecting potentially explosive hydrogen/oxygen mixtures aboard reusable launch spacecraft, variants of this system could readily be designed for terrestrial applications (e.g., in hydrogen-fueled vehicles and hydrogen-consuming industrial facilities) in which compact and relatively inexpensive gas-leak detectors are needed. Moreover, sensor modules could be constructed to accommodate interchangeable sensors for measuring gases other than hydrogen and oxygen.

This work was done by Darby B. Makel of Makel Engineering, Inc., for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at under the Physical Sciences category.