Patent GB-606521-A (GB)
Title: Improvements in measuring apparatus, relays and other similar instruments
Filed: 1945-09-19
Abstract: 606,521. Galvanometers; magnetic measurements. SOC. DE PROSPECTION ELECTRIQUE PROCEDES SCHLUMBERGER. Sept. 19, 1945, No. 24262. Convention date, Aug. 13, 1941. [Class 37] A measuring device comprises a movable element adapted to rotate inside a casing filled with a liquid, the element having an average density substantially equal to the density of the liquid and its centre of gravity coinciding with the centre of gravity of the displaced liquid. The moving element comprises a cylindrical float 1, Fig. 1, of plastic material supported by wires 4, 5. The wire 4 is directly fastened to a casing 17, 171 at the point 6, whilst the wire 5 is fastened to a piston 21 forced upwards by a spring 22. The float 1 carries the moving coil 7 and also a mirror 8. The coil 7 moves in the gap between an iron core 9 and polepieces 11, 12. The casing 17, 17<1>, with the moving system 1, 7, is immersed in a liquid contained in a vessel formed by the polepieces 11, 12, which are welded to non-magnetic members 13, 14, Fig. 2, and hoods 15, 16. The liquid is of high density and low viscosity, for example carbon tetrachloride. The movable element is so formed that its mean density is the same as that of the liquid and its centre of gravity coincides with that of the liquid it displaces. The piston 21 and attachment for the wire 5 are so formed that the whole is of the same average density as that of the liquid, so that the tension on the wires 4, 5 is always equal to the tension of the spring 22 and is unaffected by accelerations due to vibrations or shocks. A pipe 23 enters the bottom of the hood 16 and communicates with an expansion vessel 24 soldered to the hood 15 and closed, at the top by a plate 26. The lower part of the casing 17 is provided with a protecting baffle tube 27. If the apparatus is subjected to a downward acceleration the liquid tends to flow towards the top, but since the upper hood 15 is hermetically closed, the only result is increased pressure on the walls of the hood. If the acceleration reaches such a point that the pressure on the bottom of the hood 16 becomes less than the maximum vapour pressure of the liquid, part of the liquid is vaporized and a flow of liquid is caused in the pipe 23 and dilates the membrane 25. If the acceleration decreases sufficiently, the vapour condenses and the liquid is returned owing to the elasticity of the membrane 25. The baffle 27 prevents damage to the suspension 4 by vortexes. Fig. 4 shows an instrument with a horizontal suspension, the temperature being maintained constant by immersing the instrument in a thermostat using melting ice. Both suspension wires 4, 5 are attached to pistons 22, 22<1> provided with springs 21, 21<1>. The movable element is provided with trunnions 31, 32 which pivot on bearings 33, 34 leaving a certain amount of play. When the thermostat is in operation and therefore the instrument is at the desired temperature, the trunnions 31, 32 are free inside their bearings, the movable element rotating only on the suspension wires 4, 5. When the thermostat is no longer working, the trunnions rest on the bearings and maintain the movable element to prevent risk of breakage of the suspension wires 4, 5. In the case of an instrument designed to operate vertically, the bearings and trunnions may be replaced by conical pivots and corresponding stops. The invention may be applied to geophysical measuring instruments such as magnetic balances, torsion balances, &c.