Rebreather control parameter system and dive resource management system

Abstract

A method and apparatus for automatically controlling partial pressure of oxygen in the breathing loop of a rebreather diving system. A diver may adjustably select a control parameter to maintain partial pressure of oxygen at a setpoint that varies with ambient pressure and is within a range between a maximum safe partial pressure of oxygen at depth and a minimum safe partial pressure of oxygen for the purpose of biasing the performance of the rebreather either towards minimizing gas venting from the rebreather breathing loop or minimizing decompression time. A method and apparatus for managing and monitoring the use of dive resources in comparison with a target dive time specified by the diver, calculating and indicating remaining dive time based on dive resource values and calculating and indicating dive resource values required to meet preselected dive resource end values and dive requirements.

What is claimed is: 
     
         1 . A method for automatically controlling partial pressure of oxygen in a rebreather breathing loop comprising:
 selecting a minimum value of partial pressure of oxygen;   measuring partial pressure of oxygen in the rebreather breathing loop;   adding a portion of a gas supply to the rebreather breathing loop if partial pressure of oxygen in the rebreather breathing loop is less than the minimum value of partial pressure of oxygen;   selecting a value of a first reduction coefficient;   measuring ambient pressure;   calculating a maximum operating value of partial pressure of oxygen as the product of ambient pressure; concentration of oxygen in the gas supply and the first reduction coefficient;   selecting a value of a first control parameter;   calculating a setpoint for partial pressure of oxygen as the sum of the minimum value of partial pressure of oxygen and the product of the first control parameter and the absolute value of the difference between the maximum operating value and minimum value of partial pressure of oxygen; and   adding gas supply to the rebreather breathing loop if partial pressure of oxygen in the rebreather breathing loop is less than the setpoint for partial pressure of oxygen.   
     
     
         2 . The method of  claim 1  wherein the value of the first reduction coefficient is from 0.75 to 0.95. 
     
     
         3 . The method of  claim 1  wherein the value of the first control parameter is from 0% to 100%. 
     
     
         4 . The method of  claim 1  wherein the gas supply is oxygen, further comprising selecting an absolute maximum value of partial pressure of oxygen; and
 limiting the setpoint for partial pressure of oxygen to the absolute maximum value of partial pressure of oxygen. 
 
     
     
         5 . The method of  claim 1  wherein the gas supply is an oxygen-enriched gas mixture, further comprising:
 selecting a gas supply having a concentration of oxygen for which partial pressure of oxygen in the gas supply will not exceed a selected value at a maximum planned dive depth. 
 
     
     
         6 . A method for managing the use of dive resources comprising:
 selecting a target dive time;   measuring an elapsed dive time;   calculating a target remaining dive time;   measuring a dive resource;   measuring a dive resource usage rate;   calculating a dive resource net effect;   measuring a dive variable;   calculating a dive time limitation;   comparing the target remaining dive time and each dive resource net effect; and   identifying a termination time as the lowest value of the target remaining dive time and each dive resource net effect.   
     
     
         7 . The method of  claim 6  further comprising:
 displaying the lowest dive resource net effect if the target remaining dive time is not the termination time and the dive time limitation is less than the termination time. 
 
     
     
         8 . The method of  claim 6  further comprising:
 displaying the absolute value of the difference between the termination time and the lowest dive resource net effect if the target remaining dive time is the termination time and the dive time limitation is less than the termination time. 
 
     
     
         9 . The method of  claim 6  further comprising:
 displaying a first warning indicator if the dive time limitation is equal to or greater than the termination time. 
 
     
     
         10 . The method of  claim 6  further comprising:
 adjusting a setpoint for partial pressure of oxygen in a rebreather breathing loop if the dive time limitation is greater than the termination time so that the termination time will be equal to the target remaining dive time. 
 
     
     
         11 . The method of  claim 6  wherein the dive resource is pressure of a gas supply, scrubber capacity or battery capacity;
 the dive resource usage rate is decrease in pressure of the gas supply over time, number of injections from the gas supply into the rebreather breathing loop overtime or electrical current; 
 the dive resource net effect is gas supply duration, scrubber canister duration or battery duration; 
 the dive variable is depth, elapsed dive time or partial pressure of oxygen in the rebreather breathing loop; and 
 the dive time limitation is no decompression limit, decompression time or central nervous system oxygen toxicity percentage. 
 
     
     
         12 . The method of  claim 11  wherein the dive resource is pressure of a gas supply, the dive resource usage rate is decrease in pressure of the gas supply over time or number of injections from the gas supply into the rebreather breathing loop over time and the dive resource net effect is gas supply duration, further comprising:
 calculating the gas supply duration as a function of the pressure of the gas supply and the decrease in pressure of the gas supply over time or the number of injections from the gas supply into the rebreather breathing loop overtime. 
 
     
     
         13 . The method of  claim 12  further comprising:
 defining a reserve gas supply; 
 displaying a second warning indicator if the termination time corresponds to the gas supply duration, the target remaining dive time is greater than the gas supply duration, the target remaining dive time is less than the sum of the gas supply duration and the reserve gas supply duration, and the dive time limitation is less than the sum of the gas supply duration and the reserve gas supply duration; and 
 displaying a third warning indicator if the termination time corresponds to the gas supply duration, the target remaining dive time is greater than the sum of the gas supply duration and the reserve gas supply duration, and the dive time limitation is less than the sum of the gas supply duration and the reserve gas supply duration. 
 
     
     
         14 . The method of  claim 11  wherein the dive resource is scrubber capacity, the dive resource usage rate is number of injections from the gas supply into the rebreather breathing loop over time, the dive resource net effect is scrubber canister duration and the dive variable is concentration of carbon dioxide in the rebreather breathing loop or temperature of the scrubber canister, further comprising:
 calculating the scrubber canister duration as a function of either the number of injections from the gas supply into the rebreather breathing loop over time, the concentration of carbon dioxide in the rebreather breathing loop or the temperature of the scrubber canister. 
 
     
     
         15 . The method of  claim 11  wherein the dive resource is battery capacity, the dive resource usage rate is electrical current and the dive resource net effect is battery duration, further comprising: calculating the battery duration as a function of the battery capacity and the electrical current. 
     
     
         16 . The method of  claim 11  wherein the dive variables are depth and elapsed dive time and the dive time limitation is no decompression limit or decompression time, farther comprising:
 calculating no decompression limit or decompression time as a function of depth and elapsed dive time 
 
     
     
         17 . The method of  claim 11  wherein the dive variables are elapsed dive time and partial pressure of oxygen in the rebreather breathing loop and the dive time limitation is central nervous system oxygen toxicity percentage, further comprising:
 calculating central nervous system oxygen toxicity percentage as a function of elapsed dive time and partial pressure of oxygen in the rebreather breathing loop. 
 
     
     
         18 . An automatic control system for a rebreather breathing loop comprising:
 a gas supply;   a gas supply pressure regulator;   a scrubber canister;   a counterlung;   a first sensor adapted to measure ambient pressure;   a second sensor adapted to measure partial pressure of oxygen;   a first valve adapted to add the gas supply to the rebreather breathing loop; a power source;   collecting hoses;   check valves adapted to control the direction of flow of gas in the rebreather breathing loop; and   a processor adapted to
 receive data for partial pressure of oxygen in the rebreather breathing loop, ambient pressure, a selected minimum value of partial pressure of oxygen, a selected concentration of oxygen in the gas supply, a selected value of a first reduction coefficient and a selected value of a first control parameter, 
 calculate a maximum operating value of partial pressure of oxygen as a function of ambient pressure, the selected concentration of oxygen in the gas supply and the selected value of the first reduction coefficient, 
 calculate a setpoint for partial pressure of oxygen as a function of the selected value of the first control parameter, the selected value of a first control parameter and the selected minimum value of partial pressure of oxygen, 
 compare data for partial pressure of oxygen in the rebreather breathing loop with the setpoint for partial pressure of oxygen, and 
 send a signal to add a portion of the gas supply to the rebreather breathing loop if the partial pressure of oxygen in the rebreather breathing loop is less than the setpoint for partial pressure of oxygen.