Patent GB-1276119-A (GB)
Title: Electrical apparatus for controlling environmental conditions, especially suitable for use underwater
IPC: A61M16/10
Filed: 1969-11-21
Abstract: 1,276119 Respiratory apparatus OCEANIC EQUIPMENT CORP 21 Nov 1969 [4 Dec 1968] 57170/69 Heading A5T [Also in Divisions G1 and G3] A closed circuit underwater breathing apparatus comprises three sensor cells 208, 215, 222, located in the closed circuit to provide electrical signals representing the oxygen concentration, with separate amplifiers 225, 226, 227, for amplifying each of the signals. Micro-ammeters 239, 256, 258, respond to each amplified signal to provide data in terms of oxygen partial pressure over a range of zero to one atmosphere. An amplifier 243 combines the amplified signals and delivers an average output proportional to the oxygen concentration to control the input of oxygen through a solenoid operated valve 40. The valve is closed at a predetermined concentration and opens when the concentration falls below the predetermined value. Clipping circuits 247, 252, limit the value of any one of the three signals when they tend to exceed the limits of a predetermined range, the limited signal being included in the average which is within the said range. An alarm 281 sounds when any signal is limited by the clipping circuit. A manual device is adapted to deprive the valve of oxygen and to deliver oxygen to the breathing circuit under manual control. A helium gas supply is connectable into the breathing circuit.  The apparatus comprises tanks for pressurized oxygen and helium, and a carbon dioxide absorbing canister 14, the chamber of which may be made of clear plastics. An expansible breathing bag which may be made of clear plastics material is associated with a mouthpiece connected to conduits 28 and 24. The oxygen content is monitored in chamber 34, and oxygen replenishing takes place in this chamber. The monitoring cells 46 are connected to the electronic system 48 which is housed in a separable chamber 49. The helium supply tank is connected to chamber 38 through line 50 having a manual valve. An oxygen content indicator assembly is connected to lead 62. Oxygen supply may be manually delivered through line 64. A releasable metal band holds together the tanks and canister chamber which have nesting blocks. Harness straps are anchored in the blocks the breathing bag being attached to the harness through twist studs, Fig. 1 (not shown). Each sensor cell comprises inner and outer electrodes 209, 210, which may be respectively of platinum and silver, the latter having a thin coating of silver oxide. A thermistor 207 provides temperature compensation. A liquid electrolyte such as potassium hydroxide is contained between the electrodes. The electrolyte is retained by an oxygen-permeable membrane which may be of polyethylene. The current through the cells is proportional to the concentration of oxygen to which the cells are subjected, Fig. 3 (not shown). The microammeters 239, 256, 258, are set at zero by supplying an oxygen-free gas to the cells and adjusting resistor 237 associated -with operational amplifier 228. The cells are then subjected to gas having known oxygen content, and the gain of amplifier 228 is adjusted by resistor 233 to give a full-scale deflection.