The figure shows an instrument incorporating an infrared camera for detecting small hydrogen fires. The instrument has been developed as an improved replacement for prior infrared and ultraviolet instruments used to detect hydrogen fires. The need for this or any such instrument arises because hydrogen fires (e.g., those associated with leaks from tanks, valves, and ducts) pose a great danger, yet they emit so little visible light that they are mostly undetectable by the unaided human eye. The main performance advantage offered by the present instrument over prior hydrogen-fire-detecting instruments lies in its greater ability to avoid false alarms by discriminating against reflected infrared light, including that originating in (1) the Sun, (2) welding torches, and (3) deliberately ignited hydrogen flames (e.g., ullage-burn-off flames) that are nearby but outside the field of view intended to be monitored by the instrument.

A Commercial Explosion-Proof Housing contains the electronic circuitry

Like prior such instruments, this instrument is based mostly on the principle of detecting infrared emission above a threshold level. However, in addition, this instrument utilizes information on the spatial distribution of infrared light from a source that it detects. Because the combination of spatial and threshold information about a flame tends to constitute a unique signature that differs from that of reflected infrared light originating in a source not in the field of view, the incidence of false alarms is reduced substantially below that of related prior threshold based instruments.

The camera in the present instrument is a palm-sized commercial one wherein the image sensor is an array of microbolometers that are sensitive in the wave length range from 7.5 to 13.5 ìm. The camera includes circuitry that preprocesses the microbolometer readings to generate digital output. The camera output is coupled to an embedded image-processing computer via a high-speed serial data interface, conforming to standard 1394 of the Institute of Electrical and Electronics Engineers (FireWire). The instrument includes a custom circuit board designed to act as interface between (1) the rest of the instrument and (2) external power supplies and external electronic instrumentation and alarm circuits, such that from the perspective of the external instrumentation and alarm circuits, this instrument exactly mimics an older ultraviolet-based hydrogen-fire-detecting instrument to be replaced.

This work was done by Robert Youngquist and Curtis Ihlefeld of Kennedy Space Center and Christopher Immer, Rebecca Oostdyk, Robert Cox, and John Taylor of ASRC Aerospace Corp. For further information, access the Technical Support Package (TSP) free online at under the Electronics/Computers category. KSC-12845