GB751568A - Improvements in or relating to apparatus for use in underwater seismic exploration - Google Patents

Abstract

751,568. Geophysical prospecting; depth measuring. NAAMLOOZE VENNOOTSCHAP DE BATAAFSCHE PETROLEUM MAATSCHAPPIJ. Aug. 3, 1954 [Aug. 3, 1953], No. 22480/54. Classes 40(1) and 118(2)) Apparatus for use in underwater seismic exploration comprising a cable adapted to be streamed under water and having a flexible tubular envelope containing at points spaced along its length a plurality of seismic detectors is provided with two or more depth gauges in the form of pressure sensitive elements contained within the flexible cable envelope, which is filled with a liquid, e.g., oil, to increase buoyancy and transmit the hydrostatic pressure from the sea to the said depth gauges. The seismic delectors are preferably piezoelectric microphones and are operated in known manner. Each depth gauge comprises a flexible diaphragm (e.g., rubber) exposed on one side to the liquid within the envelope and mechanically coupled on the other side to an armature of an electromagnet such that magnetic attraction would oppose the hydrostatic pressure. An adjustable back-stop is preset to limit the gap between armature and core to about 0.005 inch. In use the pressure to be measured holds the armature against its stop at the preset separation from the core. At the surface (i.e., on the towing vessel) a battery 63, milliammeter 65, rheostat 67 and primary of a transformer 69 are connected in series with a return lead common to the magnetizing windings 49 of all depth gauges and a selector switch 61 which selects the other lead particular to the depth gauge to be investigated. The rheostat 67 is initially set at a high value and then gradually reduced so as to increase the current in the depth gauge electromagnet 49 until the attractive force on the armature balances the hydrostatic pressure on the flexible diaphragm, whereupon the armature moves into contact with the core and induces a transient electric current in the circuit. This pulse is fed by the transformer 69 to the grid of a thyratron 71 which fires to light an indicator lamp 73. This indicates to the operator that the reading of the milliammeter 65 at this instant corresponds to the pressure to be determined and this pressure may be found from a previously compiled calibration curve, the depth then being obtained from a knowledge of the water density.