Oxygen monitor for semi-closed rebreathers: design and use for estimating metabolic oxygen consumption

John R. Clarke; David Southerland

doi:10.1117/12.354647

23 July 1999 Oxygen monitor for semi-closed rebreathers: design and use for estimating metabolic oxygen consumption

John R. Clarke, David Southerland

Proceedings Volume 3711, Information Systems for Navy Divers and Autonomous Underwater Vehicles Operating in Very Shallow Water and Surf Zone Regions; (1999) https://doi.org/10.1117/12.354647
Event: AeroSense '99, 1999, Orlando, FL, United States

Abstract

Semi-closed circuit underwater breathing apparatus (UBA) provide a constant flow of mixed gas containing oxygen and nitrogen or helium to a diver. However, as a diver's work rate and metabolic oxygen consumption varies, the oxygen percentages within the UBA can change dramatically. Hence, even a resting diver can become hypoxic and become at risk for oxygen induced seizures. Conversely, a hard working diver can become hypoxic and lose consciousness. Unfortunately, current semi-closed UBA do not contain oxygen monitors. We describe a simple oxygen monitoring system designed and prototyped at the Navy Experimental Diving Unit. The main monitor components include a PIC microcontroller, analog-to-digital converter, bicolor LED, and oxygen sensor. The LED, affixed to the diver's mask is steady green if the oxygen partial pressure is within pre- defined acceptable limits. A more advanced monitor with a depth senor and additional computational circuitry could be used to estimate metabolic oxygen consumption. The computational algorithm uses the oxygen partial pressure and the diver's depth to compute O₂ using the steady state solution of the differential equation describing oxygen concentrations within the UBA. Consequently, dive transients induce errors in the O₂ estimation. To evalute these errors, we used a computer simulation of semi-closed circuit UBA dives to generate transient rich data as input to the estimation algorithm. A step change in simulated O₂ elicits a monoexponential change in the estimated O₂ with a time constant of 5 to 10 minutes. Methods for predicting error and providing a probable error indication to the diver are presented.

Citation Download Citation

John R. Clarke and David Southerland "Oxygen monitor for semi-closed rebreathers: design and use for estimating metabolic oxygen consumption", Proc. SPIE 3711, Information Systems for Navy Divers and Autonomous Underwater Vehicles Operating in Very Shallow Water and Surf Zone Regions, (23 July 1999); https://doi.org/10.1117/12.354647

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