In electronically controlled, closed-circuit rebreather diving systems, the partial pressure of oxygen inside the breathing loop is controlled with three oxygen sensors, a microcontroller and a solenoid valve, critical components that may fail. State-of-the-art detection of sensor failure, based on a voting algorithm, may fail under circumstances where two or more sensors show the same but incorrect values. We developed a novel rebreather controller that offers true sensor-signal validation, thus allowing efficient and reliable sensor failure detection. The core components of this validation system are two additional solenoids, which allow an injection of oxygen or diluent gas directly across the sensor membrane.

Figure 1: Schematics of an electronic closed-circuit rebreather (eCCR) 1: mouthpiece, 2: exhale counterlung, 3: overpressure valve, 4: CO2 scrubber, 5: oxygen cylinder, 6: diluent cylinder, 7, 8: pressure regulators, 9: manual diluent valve, 10: solenoid, 11: ppO2 sensors, 12 microprocessor, 13: inhale counterlung, 14: display

Figure 2: The principle schematics of the ppO2 sensor signal validation system; 1: oxygen cylinder, 2: diluent cylinder, 3: sensor support, 4: ppO2 sensor, 5 support for O2 and Diluent inejction, 6, 7: pressure regulators, 8, 9: solenoids, 10, 11: flow restriction orifices, 12 microprocessor

Figure 5: Data from a 100-min open-water test dive to a maximum depth of 40 msw; A: depth profile; B: ppO2 sensor signals from two sensors; C: calculated FO2; D: one validation cycle with 100% oxygen at 10 msw

The developed true sensor signal validation is now commercially exploited in the Poseidon/Cis Lunar  Discovery MK6 rebreather (www.poseidon.com).

References:

Wourld Intellectual Property Organisation - METHOD FOR OPERATING A REBREATHER (WO/2008/080948)

Sieber A, L' Abbate A, Bedini R. Oxygen sensor signal validation for the safety of the rebreather diver. Diving and Hyperbaric Medicine. 2008; 39(1): 38-45.

Sieber A, Jones N, Stone B, Pyle R, Koss B, Sjoblom K. Embedded systems in the Poseidon MK6 rebreather. Proceedings of the Seventh Workshop on Intelligent Solutions in Embedded Systems. 2009: 37-42 (get the paper here).