A rugged laser-diode oxygen sensor is being developed for detecting leaks of oxygen from diverse systems, including rocket engines, cryogenic systems, and medical equipment. The sensor is required to have a range of 250 to 250,000 parts per million, to be accurate within 5 percent, to be capable of operating at any temperature between -224 °F (-142 °C) to +175 °F (79 °C), and to have a response time -10 seconds. Rugged, low-temperature-capable laser-diode sensors were known previously, but were not sensitive enough. A prototype of the developmental sensor with the measurement range indicated above, having noise less than 5 percent of reading, and response time of 1 second has been demonstrated. The required sensitivity was achieved in the prototype by use of a Herriot cell (a multipass absorption cell) of 20 passes that had a 3-m absorption path length. A conceptual design for an instrument suitable for a rocket-launch site calls for a 4.6-m-path-length Herriot cell, overall package dimensions of 7 by 3 by 12 in. (about 17.8 by 7.6 by 30.5 cm), and a weight <10 lb (mass <4.5 kg).
This work was done by Bruce W. McCaul of Oxigraf, Inc., for Kennedy Space Center.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
Bruce W. McCaul, President
1170 Terra Bella Ave.
Moutain View, CA 94043
Tel. No.: (650) 237-0159 Ext. 221
Refer to KSC-12086.