Rugged Laser-Diode Oxygen Sensor

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).