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 O$-2$/ using the steady state solution of the differential equation describing oxygen concentrations within the UBA. Consequently, dive transients induce errors in the O$-2$/ 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 O$-2$/ elicits a monoexponential change in the estimated O$-2$/ with a time constant of 5 to 10 minutes. Methods for predicting error and providing a probable error indication to the diver are presented. !2
展开▼
