Patent GB-1176856-A (GB)
Title: Decompression Monitor.
IPC: B63C11/32
Filed: 1967-12-12
Abstract: 1,176,856. Diver's decompression monitor. GENERAL DYNAMICS CORP. 12 Dec., 1967 [12 Dec., 1966], No. 56400/67. Heading B7U. [Also in Divisions G1 and G3] A decompression monitor for automatically providing a diver with an indication of the maximum permissible rate of ascent comprises at least one body tissue simulator 6, Fig. 2, adapted to develop in a conduit 7 a pressure proportional to the value and length of exposure to the hydrostatic pressure, a detector 8, Fig. 3, for the or each body tissue simulator 6 and operative in response to the pressure developed in the conduit 7 and to the hydrostatic pressure in a chamber 54 to provide an output signal proportional to the difference between the hydrostatic pressure and a critical hydrostatic pressure for the tissue simulated, the output signal thereby affording an indication of the permissible rate of ascent. In the embodiment described three different tissue simulators 6 are used and the output signals from the associated detectors 8 are fed to a permissible ascent indicator which selects for indication the signal representing the smallest rate of ascent or greatest rate of decent. The indicator may be a mechanical device or an electrical device (see Division G1). Each body tissue simulator 6 comprises a bladder 16 filled with silicone fluid and subjected externally to the pressure in a chamber 14. The chamber 14 is pressurized by a piston 38 connected through a lever system to a piston 36 loaded by the hydrostatic pressure. The lever system is adjusted in accordance with the percentage of inert gas in the mixture supplied to the diver and automatically causes the pressure in the chamber 14 to be the correct multiple of the hydrostatic pressure. As pressure builds-up in chamber 14, the silicone fluid in the bladder 16 is forced through a temperature compensated fluid flow barrier 22 (see Division G3H) into a chamber 24 connected to its conduit 7. By selecting the porosity of the barrier and other parameters, the pressure developed in the chamber 24 is made to represent the absorption of gas into a particular body tissue. This pressure in a conduit 7 is fed to bellows 58 in the associated detector 8 to longitudinally load a rod 66. A second rod 64 is loaded in response to the hydrostatic pressure admitted to a second bellows 62. The rods 64, 66 are connected to opposite ends of a balance beam 62 reacting against a fulcrum 74. The fulcrum's position along the beam 62 is adjusted by screws 76, 78 in dependence on the relationship between the pressure of the absorbed gas to the maximum permissible or critical hydrostatic pressure for the tissue simulated. Since this relationship is a function of hydrostatic pressure the position of the screw 78 is automatically changed by a bellows 80 subjected to the hydrostatic pressure. The relative magnitude of the forces acting on the rods 64, 66 is thus representative of the difference between the hydrostatic pressure and the critical hydrostatic pressure and is converted to rotation of the contact 88 of a potentiometer 86 controlling the permissible ascent indicator.